Important Questions Class 10 Science Chapter 2

Important Questions Class 10 Science Chapter 2 – Acids Bases And Salts

Science is an essential subject which helps you to comprehend changes in the natural and physical world. Chapter 2 of Class 10 Science is about ‘Acids, Bases, And Salts’. The chapter covers all the important topics that are related to the understanding of chemical reactions and how these chemical substances work with each other.

Going through the important questions will help you analyse your weak points, and you can overcome them to score well in your exams. It’s important to read NCERT books, which are an important resource for enhancing your learning abilities by offering a deeper conceptual understanding of each subject matter. It will help engineering and medical aspirants as well. Students are advised to refer to the Extramarks question bank of Important Questions for Class 10 Science Chapter 2 to help them score well in the examinations.

Extramarks is one of the best online learning platforms for lakhs of students across the country for all classes from Class 1 to Class 12. Students rely on our comprehensive study materials such as NCERT chapter-wise solutions, CBSE revisions, past years’ solved question papers, etc. to prepare for their exams.

Extramarks experts have curated important questions Class 10 Science Chapter 2 is a useful resource for students preparing for science. CBSE Class 10 is a vital stage in career-making as it helps you to make important decisions about your future career prospects. To help students excel in science subjects, we are providing the CBSE Class 10 important questions for science subjects. These questions will help students understand the types of questions asked on exams. It will give students good practise, and they will be able to face the board exam with full preparation.

These questions are available for all the chapters and cover the entire CBSE Class 10 Science syllabus. The questions are aligned with the CBSE exam pattern after analysing the previous year’s question paper pattern and the types of questions asked and by referring to the latest NCERT textbooks and exemplar books.

Our question Chapter 2 Class 10 Science Important Questions plays a vital role in scoring excellent marks in the board exams. Our subject experts have provided detailed answers with step-by-step instructions for students to understand the different concepts used in each of these questions.

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CBSE Class 10 Science Important Questions 2022-23

CBSE Class 10 Science Important Questions are also available for the following chapters:

Important Questions Class 10 Science Chapter 2 – With Solutions

The question bank of Class 10 Science Chapter 2 Important Questions covers different topics from the chapters. The questions are carefully picked from the exam point of view and cover MCQs, fill in the blanks, short answer questions, and long answer questions. By solving these questions from our Important Questions for Class 10 Science Chapter 2, students will be able to fully revise the chapter Acids, Bases, and Salts.

Given below are a set of a few questions and answers from our question bank Important Questions in Class 10 Science Chapter 2: Acids, Bases, and Salts

Question 1: Which of the following gives CO2 on heating?

• Slaked
• Quick lime
• Limestone
• Soda ash.

Answer1: The correct answer is (c) Limestone

Explanation: Slaked lime Ca(OH)2 on heating gives calcium oxide and water. Limestone CaCO3 on heating gives calcium oxide and carbon dioxide.

CaCO3 + heat   CaO + CO2

Ca(OH)2 + heat CaO + H2O

Question 2: Chemical formula of baking soda is

•  MgSO4

•  Na2CO3

•  NaHCO3

• MgCO3

Answer 2: The correct answer is (c) NaHCO3

Explanation:  Chemical formula for baking soda is sodium bicarbonate or sodium hydrogen carbonate  NaHCO3.

Question3: The odour of acetic acid resembles that of

• Rose

• Burning Plastic

• Vinegar

• Kerosene 

Answer 3: The correct answer is (c) Vinegar

Explanation: Acetic acid is also known as ethanoic acid, and the formula is CH3COOH. Vinegar is a dilute solution of acetic acid (ethanoic acid) in water. So,  the odour of acetic acid resembles vinegar.

Question 4: A drop of the liquid sample was put on the pH paper, and the pH paper turns  blue. The liquid sample must be of

• Lemon Juice

• HCl

• Sodium bicarbonate

• Ethanoic acid

Answer 4: The correct answer is (c) Sodium bicarbonate

Explanations: Bases change red litmus paper solution to blue. The liquid sample could be sodium bicarbonate. Another option is that all are acidic.

Question 5: Farmers neutralise the effect of acidity on the soil by adding

(A) Slaked Lime

(B) Gypsum

(C) Caustic Soda

(D) Baking Soda

 Answer 5: Correct Option is (A) Slaked lime

Explanations: Option A is correct. A few quantities of quicklime or slaked lime are used. If the solution is acidic, it decreases the solubility of minerals and affects the availability of nutrients. Thus, a small quantity of slaked lime solution is added to convert the acidic soil. Lime is alkaline, which neutralises the soil. While iron sulphate, aluminium sulphate is acidic and can be used to reduce the alkalinity of the soil.

Question 6:  CuSO4.5H2O In this Compound, the water molecule is called –

(A) Pure Water

(B) Water of Crystallisation

(C) Soda Water

(D) None of these

Answer 6: Correct option is (B)

Explanations: The exact number of water molecules chemically bonded to a salt molecule within the hydrated crystalline compounds is called water of crystallisation. It is  essential for the maintenance of a particular crystal. Blue crystals copper sulphate contains five molecules of water CuSO4.5H2O and is also known as blue vitriol. 

Question 7: Two solutions, A and B, have pH values of 5 and 8, respectively. Which solution will be basic?

Answer7: Solution B will be basic as its pH value is 8.

Explanations: Solutions having a pH greater than 7 are basic. So, solution B is basic(pH value 7 to 14). Solution A pH value is 5, so it is acidic (1 to 7).

Question 8: The setting of the plaster of Paris takes place due to

• Oxidation

• Reduction

• Dehydration

• Hydration 

Answer 8: The correct answer is (d) Hydration

Explanation: The setting of the plaster of Paris takes place by hydration due to the formation of a solid crystalline hydrate, and the hardening of the plaster of Paris is a hydration reaction, which is the reverse of the dehydration of gypsum. Plaster of Paris quickly sets to shard mass when made into a thin paste with a water solution. A slight expansion takes place in this process, and heat evolves. This process is exothermic. Students can refer to important questions from Class 10 Science Chapter 2.

Question 9: Which salt is Neutral salt?

(A) NH4Cl

(B) CH3COONH4

(C) CH3COONa

(D) Na2CO3

Answer 9: Correct Option is (B) ammonium acetate

Explanations: Option B is correct. Ammonium acetate is a WAWB type of salt. It has ammonium and acetate ions from acetic acid.

It will have neutral pH. The remaining option is acidic or basic salt behaviour.

Question 10: If the pH of the solution is 13, it means that it is

• Weakly acidic

• Weakly basic

• Strongly acidic

• Strongly Basic

Answer 10: The correct answer is (d) Strongly Basic

Explanations: A solution with pH 13 is a strong base as the basicity increases from 7 to 14. At pH 7, it is less basic and moving to 14, it increases.

Question 11: Name the acid-base indicator extracted from Lichen.

Answer 11: Litmus

Explanation:  Litmus is a natural indicator extracted from Lichen. A purple dye indicator is extracted from a plant termed Lichen. This natural dye is called a litmus solution and is generally used as an indicator.

Question 12: Complete & balance the following chemical equations :

(i) NaOH(aq) + Zn(s) →

(ii) CaCO3(s) + H2O(l) + CO2(g) →

(iii) HCl(aq) + H2O(l) →

Answer 12:

(i) 2NaOH(aq) + Zn(s) → Na2ZnO2(aq) + H2(g)

(ii) CaCO3(s) + CO2(g) + H2O(l) → Ca(HCO3)2(aq)

(iii) HCl(aq)+H2O(l)→H3O+(aq)+Cl−(aq)

Explanations:

1. i) Zinc reacts with sodium hydroxide to produce zincate sodium and hydrogen. This reaction takes place at a temperature near 550°C.
2. ii) Calcium carbonate reacts with carbon dioxide and water to produce calcium hydrogen carbonate. The reaction proceeds at room temperature.

iii)Hydrochloric acid, HCl, is strong, so right from the start, you should expect it to ionise completely in an aqueous solution. In other words, every molecule of hydrochloric acid added to water will donate its proton H+ to the water molecule to form a hydronium ion, H3O+. Hydrochloric acid’s ionisation will also produce chloride anions, Cl-.

Question 13: Sodium carbonate reacts with hydrochloric acid to produce

(A) NaCl

(B) CO2

(C) H2O

(D) All of the above

Answer 13: Correct Option is (D)

Explanations: Sodium carbonate is a base that reacts with an acid, like, hydrochloric acid, to give salt along with carbon dioxide and water. Brisk effervescence is observed by indicating the presence of carbon dioxide CO2 gas. The reaction is shown as follows,

Na2CO3 + 2HCl 2NaCl + CO2 + H2O

Students can refer to important questions Class 10 Science Chapter 2.

Question 14: Which of the following medicines is used for treating indigestion?

• Antibiotics

• Analgesic

• Antacid

• Antiseptic 

Answer 14: The correct answer is (c) Antacid

Explanations: Antacid is used for treating indigestion. Indigestion causes acidity in the stomach. We add antacids to neutralise it.

Antacids are basic and hence neutralise the acids.

Question 15: Bleaching powder forms a milky solution in water. Explain.

Answer 15:  Bleaching powder reacts with water to form Ca(OH)2, which has a milky appearance. The reaction is given by,

CaOCl2 +  2H2O  → Ca(OH)2 + 2HCl

Explanations: When bleaching powder (CaOCl2) gets dissolved in water, the solution turns milky due to the formation of Ca (OH)2

Question 16: Why should curd and sour substance not be kept in brass and copper vessels?

Answer 16: Brass is an alloy of copper Cu and zinc Zn metals. Both metals react with acids present in curd and sour substances to form poisonous soluble salts. Hence, storing curd and acidic substances in brass or copper vessels makes them unfit for consumption.

Explanations: Curd and sour substances contain acids. Acids interact with metals to develop salt and hydrogen gas. Hence, if such substances are kept in a copper container, the acid will interact, and the container will be corroded. Therefore it may spoil the food.

Metal + Acid → Salts + Hydrogen

Lactic acid is an organic acid that consists of the -COOH group. Hence, it is a weak acid because of the presence of this alkali group.

• Lactic acid(C3H6O3) forms in cow milk because of the breaking down of bacteria.
• Fresh milk does not contain lactic acid. Dairy products such as yoghurt, cheese and condensed milk have high levels of lactic acid.
• The acidic taste of substances contains acids such as vinegar containing acetic acid, tamarind, grapes containing tartaric acid, and lemons and oranges containing citric acid.

Question 17: Why does distilled water not conduct electricity, whereas rainwater does?

Answer 17: The presence of little amounts of acid in rainwater aids the conduction of electricity. Distilled water is pure water & lacks ions. Therefore, it cannot conduct electricity.

Explanations: Electricity needs ” ions” to move in electrolytes. Distilled water contains no ions and does not conduct electricity.

Question 18: What is the exact chemical formula of POP (Plaster of Paris)?

(A) CaSO4.2H2O

(B) CaSO4.3H2O

(C) CaSO4.1/2H2O

(D) CaCO3.1/2H2O

Answer 18: Correct Option is C

Explanations: On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate (CaSO4.½ H2O). It is called Plaster of Paris.

Question 19: While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Answer 19: Adding water to acid produces a highly exothermic chemical reaction. The intensity of the heat formed can break the glass container or cause severe burns to the person diluting   it. On the other hand, adding acid to water with constant stirring aids the absorption of the heat produced by water, and any harm/damage is avoided during the process.

Explanations: While diluting an acid, it is recommended that the acid should be added to water and not water to the acid because if water is added to a concentrated acid, it releases a huge amount of heat which may result in an explosion and can cause acid burns on the face, clothes and body parts. Thus it is safe to add acid to water rather than water to acid.

Question 20: Which gas is generally liberated when an acid reacts with a  metal? Illustrate with a suitable ex. How will you identify and test for the presence of this gas?

Answer 20: Hydrogen gas is liberated when an acid reacts with a metal. For example: Take some pieces of zinc granules in a test tube and add H2SO4 to it. Shake it and pass the gas evolved into a soap solution. Bubbles are formed in the soap solution. These soap bubbles contain hydrogen gas. The chemical equation of the reaction is:

H2SO4+ Zn → ZnSO4 + H2↑

Identification test- Hydrogen gas is identified by bringing a burning candle near the soapy bubbles. The candle will burn with a pop sound.

Explanations: When an acid reacts with metal, salt and hydrogen gas are formed.

Metal + acid → Salt + Hydrogen gas↑

When a burning candle or matchstick is brought near hydrogen gas, it burns with a popup sound.

Question 21: Name the sodium compound used to soften hard water.

Answer 21: Sodium carbonate is used for softening hard water.

Explanation: Washing soda(Na2CO3.10H2O) is the sodium compound used to soften hard water.

Question 22: Fresh milk has a pH value of 6. How do you suppose the pH will change as it converts into curd? Explain your answer.

Answer 22: Fresh milk is turned to curd due to the formation of lactic acid. Lactic acid reduces the pH value of the milk.

Explanations: The pH of milk is 6. The pH will reduce as it changes to curd because it is acidic. The acids present in it reduce the pH.

Question 23: Why does an aqueous solution of acid conduct electricity?

Answer 23: Charged particles are directly responsible for the conductance of electricity in an acid. These charged particles, called ions(cations/anions), are the reason behind the conductance of electricity in acid.

Explanations: Acids tend to dissociate into hydronium ions (H3O+) or hydrogen ions(H+) in an aqueous solution. Because of the movement of these ions, the solution can conduct electricity. Hence, an aqueous solution of acid can conduct electricity.

Question 24: 10 ml of a solution of sodium hydroxide NaOH is neutralised by 8 ml of a given solution of hydrochloric acid HCl. When we take 20 ml of the same solution of sodium hydroxide NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be

(a) 4 ml (b) 8 ml (c) 12 ml (d) 16 ml

Answer 24: Since 10 ml of NaOH requires 8 ml of HCl, 20 ml of NaOH requires 8 x 2 = 16ml of HCl. Hence the answer is an option (d) 16ml.

Explanations: It is given that

10ml of NaOH neutralises 8ml Solution of HCl

So 1 ml of NaOH neutralises = 8/10 = 4/5ml Solution of HCl

Therefore, 20 ml of NaOH will neutralise = 4/5x 20= 16 ml solution of HCl.

Hence, 16 ml of HCl solution will be required to neutralise the 20 ml NaOH.The correct answer is (d)

Question 25: Write word equations and then balanced chemical equations for the reaction taking place when

(a) Dilute sulphuric acid interacts with zinc granules.

(b) Dilute hydrochloric acid interacts with magnesium ribbon.

(c) Dilute sulphuric acid interacts with aluminium powder.

(d) Dilute hydrochloric acid interacts with iron filings.

Answer 25: Solutions are

1. dilute sulphuric acid interacts with zinc granules-

Dilute Sulphuric acid(aq) + Zinc → Zinc sulphate + Hydrogen gas

H2SO4(aqueous) + Zn(s) → ZnSO4(aq) + H2(g)

1. b) dilute hydrochloric acid interacts with magnesium ribbon-

Dilute Hydrochloric acid + Magnesium → Magnesium Chloride + Hydrogen Gas

2HCl(aq) + Mg(s) → MgCl2(aqueous) + H2(g)

1. c) dilute sulphuric acid interacts with aluminium powder-

Dilute Sulphuric Acid + Aluminium(s) → Aluminium Sulphate + Hydrogen Gas

3H2SO4(aq) + 2Al(s) → Al2(SO4)3(aqueous) + 3H2(g)

1. d) dilute hydrochloric acid reacts with iron filings-

Dilute Hydrochloric Acid + Iron(s) → Ferrous Chloride + Hydrogen Gas

6HCl(aq) + 3Fe(s) → 3FeCl2(aqueous) + 3H2(g)↑

Question 26: A milkman adds a very less amount of baking soda to fresh milk-

1. a) Why does he shift the pH value of the fresh milk from 6 to slightly alkaline? 
2. b) Why does this milk take as much time to set as curd?

Answer 26: a) In alkaline conditions, milk does not set as curd easily due to the formation of lactic acid as in the acidic condition.

1. b) Since this milk is slightly more basic than normal milk, acids produced to set the curd are neutralised by the base mix to the milk. Hence, it takes a longer time for the curd to set.

Explanations: a) He shifted the pH of the fresh milk from 6 to slightly alkaline to prevent milk from getting sour due to the production of lactic acid.

1. b) This milk takes a long time to set into curd because the lactic acid produced here first neutralises the pH then the pH is reduced to turn the milk into curd.

Question 27: Give two main important uses of Washing Soda and Baking Soda.

Answer 27:  Uses of Washing Soda are:

1. a) It is used to remove the permanent hardness of the water.
2. b) It is utilised in glass, soap, paper industries and factories.

Uses of Baking Soda are-

1. a) It is used as baking powder. Baking powder is a combination of baking soda and tartaric acid. Baking powder makes bread or cake and pastries fluffy.
2. b) It is mainly used in soda-acid fire extinguishers.

Explanations: Uses of washing soda: As cleansing agent and removing permanent hardness of the water.

They are used in the glass, soap and paper industries.

Uses of baking soda: For making baking powder as an antacid ingredient.

Question 28:  Explain why Plaster of Paris should be stored in a moisture-proof container. Give reasons.

Answer 28: Plaster of Paris should be stored in a moisture-proof container because moisture can affect the plaster of Paris by slowing down the setting of the dressing application because of hydration. It will turn the plaster useless.

Explanations: Plaster of Paris (POP) should be stored in a moisture-proof container because it is a powdery mass that can absorb water or moisture to form a hard solid mass known as gypsum. The reaction takes place as follows:

CaSO4.½ H2O  +     1½ H2O           → CaSO4.2H2O

Plaster Of Paris     water               gypsum(hard solid)

Question 29: What is a neutralisation reaction? Give two examples.

Answer 29: A reaction in which an acid and base react with each other to give salt and water is termed a neutralisation reaction. In this reaction, energy is evolved in the form of heat.

For example:- NaOH + HCl ⟶ NaCl + H2O

Base    +   Acid ⟶ Salt + water

(ii) During indigestion (caused due to the production of excess hydrochloric acid in the stomach), we administer an antacid (generally milk of magnesia, Mg(OH)2, which is basic). The antacid neutralises the excess acids and thus gives relief from indigestion.

Mg(OH)2 + 2HCl → MgCl2+2H2O

Explanations: The reaction of the acid + base gives a product of salt + water, which is considered a neutralisation reaction.

Examples:

NaOH + HCl → NaCl + H2O

Mg(OH)2 + H2CO3 → MgCO3 + 2H2O

Question 30: Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are equal. In which test tubes A and B will the fizzing occur intensely and vigorously. Give reasons. 

Answer 30: HCl is a stronger acid than CH3COOH. Therefore, the H+ ions concentration in test tube A will be higher than in test tube B. Hence, the reaction will occur faster in test tube A than in test tube B. So, fizzing will occur more vigorously in test tube B.

Explanations: When an acid reacts with magnesium metal, hydrogen gas is produced, which causes fizzing. Stronger acids have more hydrogen ions (H+ )in them. Thus, fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added. It is because HCl is a stronger acid than CH3COOH, and therefore, during the chemical reaction with magnesium metal, HCl will produce more hydrogen gas, due to which fizzing will be more vigorous in test-tube A.

Question 31: Five solutions, A, B, C, D and E, tested with a universal indicator, showed pH of 4,1,11,7 and 9, respectively. Which solution is

(a) neutral?

(b) strongly alkaline?

(c) strongly acidic?

(d) weakly acidic?

(e) weakly alkaline?

Arrange the pH value in increasing order of hydrogen-ion concentration

Answer 31 :

(a) D

(b) C

(c) B

(d) A

(e) E

Explanation: a) Neutral = Solution D with pH=7

1. b) Strongly Alkaline= Solution C with pH=11
2. c) Strongly Acidic= Solution B with pH=1
3. d) Weakly Acidic= Solution A with pH=4
4. e) Weakly Alkaline= Solution E with pH=9

Arrange the pH value in increasing order of Hydrogen-ion Concentration.

The pH value can be arranged in the increasing order of the concentration of hydrogen ions as follows:

11<9<7<4<1

Student can refer to important questions Class 10 Science Chapter 2.

Question 32: You are given three test tubes. These three test tubes contain distilled water, acidic and basic solutions, respectively. Only red litmus paper is available to identify what is there in each test tube. How will you separate what is in each of the three test tubes?

Answer 32: We can identify the content in each test tube using red litmus paper. It can be done by noticing the colour change of the red litmus paper.

• The three solutions in the test tubes are poured separately onto litmus paper.
• The solution that changes red litmus to blue contains a basic solution.
• Divide the formed blue litmus paper into two parts.
• The solution from the test tube, which turns blue litmus paper red, will be the acidic solution.
• The solution of the test tube, which does not change either red or blue litmus paper, contains water.

Explanations: Red litmus paper is a base indicator that turns blue in the presence of a base.

Let us consider the three test tubes, A, B, and C. Put the given red litmus paper in every solution. If the colour of red litmus paper turns to blue (as in test tube A), then it is a base, and if there is no change in colour, it is either acidic or neutral.

Now, a drop of the solutions from test tube A is put on the red litmus paper. The same process is repeated with solutions B and C. If either of them changes colour to blue, it is basic (let’s suppose B). Hence, out of three, one is removed as a base.

Out of the remaining two test tubes (A and C), any solution can be acidic or neutral. If we test them for acidic or neutral, a few drops of basic solution are added with a drop of each of the remaining two solutions separately, and then the nature of the drops of the mixtures is checked. If the colour of red litmus changes to blue, then the second solution is neutral (C), and if there is no change in colour, the second solution is acidic (A). It is because acidic and basic solutions neutralise each other. This way, each test tube’s contents can be checked and identified.

Question 33: A student was asked to collect apparatus from the lab store to experiment on the sample’s pH. Identify the article that he is not supposed to pick. 

• pH paper

• Petri dish

• Litmus paper

• Dropper

Answer 33 : (B) petri dish

Explanations: In the above-given options, all options are used for experimenting on the pH process, except Petri dish.

Question 34:  An aqueous solution turns the red litmus solution to blue. Excess addition of which of the following given solutions would reverse the change?

(a) Baking powder

(b) Lime

(c) Ammonium hydroxide solution

(d) Hydrochloric acid

Answer 34:The correct option is (d) Hydrochloric acid

Explanation: When the solution turns red litmus to blue, the solution should be basic. Adding acid can neutralise its effect; thus, (d) Hydrochloric acid is the correct answer.

Question 35: What happens when a solution of an acid is added with a solution of a base in a test tube?

(i) The temperature of the solution increases

(ii) The temperature of the solution reduces

(iii) The temperature of the solutions remains the same

(iv) Salt formation takes place

(a) (i) option only

(b) (i) and (iii)

(c) (ii) and (iii)

(d) (i) and (iv)

Answer 35: The correct option is (d) (i) and (iv)

Explanations: When an aqueous solution of an acid is mixed with a base solution, salt and water are formed. This chemical reaction is known as a neutralisation reaction. Heat is evolved in this reaction. Therefore, it is an exothermic reaction and increases the temperature of the solution. Hence, the correct answer is option d.

Question 36: Which of the following salts does not contain water of crystallisation?

(a) Blue vitriol

(b) Baking soda

(c) Washing soda

(d) Gypsum

Answer 36: The correct option is (b) Baking soda

Explanation: Baking sodas are white amorphous powder, whereas other salts given in the question are crystalline.

Blue vitriol is CuSO4.5H2O

Baking soda is NaHCO3

Washing soda is Na2CO3.10H2O

Gypsum is CaSO4.2H2O

Hence, the correct answer is option b.

Question 37: During the preparation of hydrogen chloride gas on a humid day, the gas is generally passed through the guard tube containing calcium chloride salt. The role of calcium chloride salt taken in the guard tube is to-

(a) absorb the released gas

(b) moisten the gas

(c) absorb moisture from the gas

(d) absorb chloride Cl– ions from the evolved gas

Answer 37: The correct option is (c) to absorb moisture from the gas

Explanation: Calcium is a good dehydrating agent. It has the characteristic property of absorbing moisture. Thus it is used as a desiccant to dry gases and Hydrocarbons in industries and labs. Calcium chloride taken in the guard tube behaves as a dehydrating agent. It absorbs moisture from the hydrogen chloride(HCl) gas that flows through it to obtain dry hydrogen chloride gas. Thus option c is correct.

Question 38: Calcium phosphate is present in tooth enamel. Its nature is

(a) basic nature

(b) acidic

(c) neutral

(d) amphoteric

Answer 38: The correct option is (a) basic nature

Explanation: The phosphate ion present in calcium phosphate is a strong base, and it forms a strong salt. Hence, calcium phosphate is basic.

Calcium phosphate is a basic salt formed by the reaction of a strong base, calcium hydroxide and a weak acid, phosphoric acid.

2H3PO4    +     3Ca(OH)2            →      Ca3(PO4) 2      +      6H2O

(Phosphoric acid)     (Calcium hydroxide)      (Calcium phosphate)

Hence, the correct answer is option a.

Question 39: Sodium carbonate is a basic salt because it is a salt of

(a) strong acid and strong base

(b) weak acid and weak base

(c) strong acid and weak base

(d) weak acid and strong base

Answer 39: The answer is (d) weak acid and strong base

Explanation: Salt is formed by weak acid and a strong base from strong salt. Here, sodium is a strong base, & carbonate is a weak acid. If sodium hydroxide, a strong base, reacts with carbonic acid, a weak acid, sodium carbonate salt and water are produced.

2NaOH + H2CO3 → Na2CO3 + 2H2O

Hence, the correct answer is option d.

Question 40: A soil sample is mixed with water & allowed to settle. The clear supernatant solution changes the pH paper to yellowish-orange. Which of the following options would change the colour of this pH paper to greenish-blue?

(a) Lemon juice

(b) Vinegar

(c) Common salt

(d) An antacid

Answer 40: The correct answer is (d) An antacid

Explanation: The sample solution turns pH paper yellowish-orange, confirming the sample’s acidic nature. To make the colour greenish-blue, we must add an antacid because it is basic. Hence the correct answer is d.

Question 41: Which of the following gives the correct increasing order of acidic strength

• Water < Acetic acid < Hydrochloric acid

• Water < Hydrochloric acid< Acetic acid

• Acetic acid< water < Hydrochloric acid

• Hydrochloric acid< water <Acetic acid

Answer 41: The correct option is (a) Water < Acetic acid < Hydrochloric acid.

Explanation- Water is neutral in its pure form, Acetic acid is a weak organic acid, and Hydrochloric acid is a mineral acid. So it is a strong acid. Hence, the correct answer is option a.

Question 42: Sodium hydrogen carbonate, when mixed with acetic acid, evolves a gas. Which of the following given statements are true about how the gas evolved?

(i) It changes lime water milky

(ii) It extinguishes a burning splinter

(iii) It dissolves in a solution of (NaOH) sodium hydroxide

(iv) It has a pungent smell

(a) (i) & (ii)

(b) (i), (ii) and (iii)

(c) (ii), (iii) and (iv)

(d) (i) and (iv)

Answer 42: The correct option is (b) (i) (ii)and (iii)

Explanation- Reaction between Sodium hydrogen carbonate and acetic acid leads to the evolution of carbon-dioxide gas. CO2 turns the lime water milky and extinguishes a burning splinter.

When sodium hydrogen carbonate is combined with acetic acid, the following reaction takes place-

NaHCO3 + CH3COOH → CH3COONa + CO2↑ + H2O

Evolved gas is carbon dioxide, a fire extinguisher and, hence, extinguishes a burning splinter.

On transfer, the carbon dioxide gas evolved through lime water, turning lime water milky due to forming a white precipitate of calcium carbonate.

Ca(OH)2 + CO2 → CaCO3 + H2O

The carbon dioxide gas, a non-metallic oxide, dissolves in a sodium hydroxide solution to form sodium carbonate and water.

CO2 + 2NaOH → Na2CO3 + H2O

Hence, the correct answer is option b.

Question 43: What should be done if a few drops of concentrated acid accidentally spill over a student’s hand?

(a) Wash the hand with saline solution

(b) Wash the hand immediately with sufficient water & apply a paste of sodium hydrogen carbonate  

(c) After washing hands with plenty of water, apply a solution of sodium hydroxide on the hand

(d) Neutralise the acids with a strong alkali

Answer 43: The correct option is (b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate. If a few drops of concentrated acid accidentally spill over the hand, it should be washed immediately with plenty of water to remove the acid from the hand. After this, a paste of sodium hydrogen carbonate should be applied to neutralise the remaining acid on hand. Sodium hydroxide or strong alkali is highly corrosive and will burn the hand.

Explanation: Washing the affected hand with plenty of water will reduce the concentration of the acid. The remaining traces of the acid can be neutralised by applying a paste of Hydrogen carbonate, which is basic. NaOH is also a base; it is corrosive and is not used to neutralise the acid. Hence, the correct answer is option b.

Question 44: Common salt, besides being used in the kitchen, can also be utilised as the raw material for making–

(i) Washing soda

(ii) slaked lime

(iii) baking soda

(iv) bleaching powder

(a) (i) & (ii)

(b) (i), (ii) and (iii)

(c) (i) and (iii)

(d) (i), (iii) and (iv)

Answer 44: The correct option is (c) (i) and (iii)

Explanation: Baking soda is sodium hydrogen carbonate (NaHCO3) prepared by the Solvay process, which is the reaction of sodium chloride, ammonia and carbon dioxide in water. Calcium carbonate is used in the reaction to get carbon dioxide gas. Washing soda is sodium carbonate (Na2CO3.10H2O) prepared from sodium chloride. As only washing soda and baking soda has a compound of sodium so the correct option is c.

Question 45: One of the constituents of baking powder is sodium hydrogen carbonate; the other constituent is

(a) hydrochloric acid

(b) tartaric acid

(c) acetic acid

(d) sulphuric acid

Answer 45: The correct option is (b) tartaric acid

Explanation: A mild edible acid and Sodium Hydrogen Carbonate are used to form baking powder. Here, acetic or citric acid can also be used in place of tartaric acid. Baking powder combines baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. Hence, the correct answer is option b.

Question 46: The pH of the gastric juices released during digestion is

(a) less than 7

(b) more than 7

(c) equal to 7

(d) equal to 0

Answer 46: The correct option is (a) less than 7

Explanation: The pH value is acidic to below 7 to ensure an easy breakdown of food particles. The pH of stomach juices is between  1 to 4 range. Our stomach produces hydrochloric acid (HCl) that helps in the digestion of food. Hydrochloric acid(HCl) is one of the components of gastric juice. The pH of gastric juice is about 1-2. Hence, the correct answer is option a.

Question 47: Which one of the following can be used as an acid-base indicator by a visually impaired student?

(a) Litmus

(b) Turmeric

(c) Vanilla essence

(d) Petunia leaves

Answer 47: The correct option is (c) Vanilla essence

Explanation: Vanilla essence can be utilised as an olfactory indicator. Therefore it can be used as an acid-base indicator by visually impaired students. So option c is correct.

Question 48:  Which of the following is acidic?

(a) Lime juice

(b) Human blood

(c) Lime water

(d) Antacid

Answer 48: The correct option is (a) Lime juice

Explanation– Lime juice has citric acid in it. Thus it is acidic. Human blood is slightly basic (pH value is 7.4). Lime water Ca(OH)2 & antacids are basic. Lime juice is sour, and it contains citric acid. Hence, the correct answer is option a.

Question 49: Which of the following is used to dissolve gold?

(a) Hydrochloric acid

(b) Sulphuric acid

(c) Nitric acid

(d) Aqua regia

Answer 49: The correct answer is (d) Aqua regia

Explanation: Gold is a noble metal that will not react even with strong acids, hence aqua regia, a mixture of concentrated Nitric acid & conc. Hydrochloric acid(HCl) in the ratio of 1:3 is used to dissolve gold, refer to important questions in Class 10 Science Chapter 2.

Question 50: Match the following chemical compounds given in Column (A) with their appropriate application given in Column (B)-

(a) A—(iii), B—(i), C—(iv),and  D—(ii)

(b) A—(iii), B—(iv), C—(i), and D—(ii)

(c) A—(iii), B—(iv), C—(i), and D—(ii)

(d) A—(iii), B—(iv), C—(i), and D—(ii)

Answer 50: The correct option is (c) A—(iii), B—(iv), C—(i), D—(ii)

Explanation: Bleaching powder is utilised for bleaching (decolourising) purposes. Baking

soda is an antacid because it neutralises the excess acid in our stomach to eliminate the pain. It is a mild non-corrosive basic salt. Washing soda is mainly used in the glass industry. Aqueous sodium chloride (NaCl)on electrolysis yields hydrogen and chlorine gases. Hence, the correct answer is option c.

Question 51:  Identify the correct representation of the reaction occurring during the chlor-alkali process–

(i) 2NaCl(l) + 2H2O(l) → 2NaOH(l) + Cl2 (g) + H2 (g)

(ii) 2NaCl(aq) + 2H2O(aq) → 2NaOH(aq) + Cl2 (g) + H2 (g)

(iii) 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2 (aq) + H2 (aq)

(iv) 2NaCl (aq) + 2H2O (l) → 2NaOH (aq) + Cl2 (g) + H2 (g)

Answer 51: The correct answer is (iv) 2NaCl (aq) + 2H2O (l) → 2NaOH (aq) + Cl2 (g) + H2 (g)

Explanation: When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide near the cathode. This process is called the chlor-alkali process because of the products formed-chlor for chlorine and alkali for sodium hydroxide(NaOH). Chlorine gas(Cl2) is given off at the anode, & hydrogen gas at the cathode.

2NaCl(aq) + 2H2O(l) → 2NaOH(aqueous) + Cl2(g) + H2(g)

So the correct answer is option iv.

Question 52: Name the acid in ant sting and give its chemical formula. Also, provide a common method to relieve the discomfort caused by the ant sting.

Answer 52: Ant sting releases formic acid. The chemical formula of this methanoic acid is HCOOH. Rubbing baking soda on the affected area can relieve the discomfort caused by the ant sting.

Explanation: The acid present in the ant’s sting is methanoic. Its chemical formula is HCOOH, and its common name is formic acid. The mild base, as baking soda on the stung area, gives relief.

Question 53: What happens when nitric acid is added to an eggshell?

Answer 53: Nitric acid dissolved eggshell, made up of Calcium carbonate. Calcium carbonate reacting with nitric acid yields Calcium Nitrate and carbon-di-oxide gas.

Explanation: Eggshell is composed of calcium carbonate, which dissolves in nitric acid and produces carbon dioxide gas.

CaCO3 + 2HNO3→ Ca(NO3)2 +H2O +CO2

Question 54: For making a cake, baking powder is taken. If at home, your mother picks baking soda instead of baking powder in the cake,

(a) how will it affect the taste of the cake & why?

(b) how can baking soda be turned into baking powder?

(c) what is the role of tartaric acid mixed with baking soda?

Answer 54: a) If we use baking soda instead of baking powder, the cake will taste bitter. After baking soda, sodium carbonate will be formed, making the cake taste bitter.

so 2NaHCO3 +heat→ Na2CO3+CO2+H2O

1. b) Baking soda can be turned into baking powder by mixing an edible weak acid like tartaric acid.
2. c) If tartaric acid is dissolved in water, it releases hydrogen ions. Hydrogen ions interact with Sodium Carbonate to produce carbon dioxide, making the cake fluffy.

Explanation: The chemical name of baking soda is sodium hydrogen carbonate (NaHCO3). It is a mild basic non-corrosive salt.

1. a) When your mother uses baking soda instead of baking powder in a cake, the taste of the cake will be bitter because of the formation of sodium carbonate.

b)Baking soda can be changed into baking powder by mixing a mild edible acid such as tartaric acid.

1. c) Tartaric acid is combined with baking soda to neutralise the sodium carbonate; hence, the cake will not taste bitter.

Question 55: A metal carbonate X reacting with acid gives a gas which, when passed through a solution Y, gives the carbonate back. On the other hand, a gas G obtained at the anode during electrolysis of brine is passed on dry Y, and it gives a compound Z, used for disinfecting drinking water. Identity X, Y, G and Z.

Answer 55: X is showing calcium. When calcium carbonate interacts with HCl, it gives out CO2 gas.

CaCO3 + 2HCl→ CaCl2+CO2+H2O

When carbon dioxide CO2 is passed into lime water, it turns milky due to the formation of Calcium carbonate.

CO2 + Ca(OH)2 → CaCO3 + H2O white ppt calcium carbonate

Thus, solution Y shows lime water

If chlorine gas is passed on dry lime water, it gives bleaching powder used to disinfect water.

2NaCl + 2H2O→ 2NaOH + H2 + Cl2

Ca(OH)2 + Cl2 → CaOCl2 + H2O

Hence, the metal carbonate X is CaCO3, and Solution Y is lime water [Ca(OH)2], gas G is chlorine (Cl2), Y is dry slaked lime [Ca(OH)2], Z is bleaching powder (CaOCl2).

Question 56: A sulphate salt of the Group 2 element of the Periodic Table is a white, soft substance that can be moulded into different shapes by making dough. If this compound is left in the open for some time, it becomes a solid mass & cannot be used for moulding purposes. Identify the sulphate salt & why does it show such behaviour? Give the reaction involved.

Answer 56: The sulphate salt should be calcium sulphate, a white and soft substance. Calcium sulphate is popularly known as the plaster of paris.

The Plaster of Paris has half a molecule of water of crystallisation. When we leave the plaster of paris open for some time, it absorbs moisture to gain several molecules of crystallisation. This newly formed compound is known as gypsum, which is hard to make moulds.

Explanation: Calcium sulphate is a salt of group 2 element (calcium), a white, soft substance that can be moulded into different shapes by making dough. It is commonly known as the Plaster of Paris. When this compound is left open for some time, it changes to gypsum, giving a hard solid mass.

CaSO4.½ H2O + 1 ½  H2O  → CaSO4.2H2O

(Plaster of Paris)                   (Gypsum)

Question 57: What are strong & weak acids? In this following list of acids, separate strong acids from weak acids-

Hydrochloric acid(HCl), Acetic acid, Citric acid,  Nitric acid, formic acid, and sulphuric acid.

Answer 57: The strength of acids depends on the number of hydrogen ions (H+ ions) produced. Acids that give rise to maximum hydrogen ions are said to be strong acids, and acids that give fewer hydrogen ions are said to be weak.

Hydrochloric acid, nitric acid & sulphuric acid get ionised completely, so they are strong acids.

Citric acid, acetic acid, and formic acid get ionised partially, so they are weak acids.

Explanations: Strong acids are those that get completely ionised, and weak acids are those that get partially ionised.

Hydrochloric acid is Strong Acid

citric acid- Weak Acid

acetic acid- Weak Acid

nitric acid – Strong Acid

formic acid- Weak Acid

sulphuric acid- Strong Acid

Question 58: What will be the action of the following substances on litmus paper? Dry hydrochloric acid HCl gas, Moistened NH3 gas, Lemon juice, Carbonated soft drink, curd, and Soap solution.

Answer 58: Dry HCl gas- No effect

Moistened NH3 gas- Turns litmus paper into blue colour

Lemon juice- Turns litmus paper into red colour

Carbonated soft drink- Turns litmus paper into blue colour

Curd- Turns litmus paper into red colour

Soap solution- Turns litmus paper into blue colour

Explanation: Dry HCl gas will not affect litmus paper.

Moistened NH3 gas will convert red litmus to blue.

Lemon juice will change blue litmus to red.

Carbonated soft drinks will turn blue litmus to red.

The curd will change from blue litmus to red.

Soap solution will change red litmus to blue.

Question 59: A student prepared solutions of (i) an acid & (ii) a base in two separate beakers. She forgot to label the solutions, & litmus paper was unavailable in the laboratory. As both the solutions are colourless, how will she distinguish between the two?

Answer 59: Students can use the Phenolphthalein indicator to check the nature of the solution.

Explanation: Students can distinguish acid and base by using other indicators like phenolphthalein (pink colour in acidic medium), methyl orange (red colour in acidic medium), turmeric (red colour in basic medium) etc.

Benefits of Solving Important Questions Class 10 Science Chapter 2

Science demands a lot of practice with conceptual clarity. Classes 8, 9 and 10 are very important for students to develop a strong fundamental knowledge. We recommend students access Extramarks comprehensive set of Important Questions Class 10 Science Chapter 2. By solving questions and going through  the solutions daily, students will gain confidence to solve various problems from the acid-base reactions and equations Chapter 2.

Below are some benefits of frequently solving questions from our Important Questions Class 10 Science Chapter 2:

• By referring to the detailed step-by-step solutions given in our solutions, students will better learn about all the balanced chemical equations and the chemical reactions topics covered in Chapter 2 of the Class 10 Science syllabus.
• The questions & answers are based on the latest CBSE syllabus and as per NCERT exam guidelines. So students can rely on them fully.
• The questions covered in our set of Important Questions Class 10 Science Chapter 2 are based on various topics covered in the Acid-base reactions and equations chapter. So while solving these questions, students can revise the chapter and clarify any doubts.
• Practising questions similar to exam questions would help students perform better in their exams and score good marks.

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