Class X Science / Acids, Bases and Salts

Class X Science
Notes For Acids, Bases and Salts

SYLLABUS

Their definitions in term of furnishing of H+ and OH- ions, General properties, examples and uses, Concept of pH scale (Definition relating to logarithm not required), Importance of pH in everyday life; Preparation and uses of Sodium hydroxide, Bleaching powder, Washing soda and Plaster of Paris.

Facts that Matter

Acids : Acids are sour in taste, turn blue litmus to red, dissolve in water to release H+ ions.

E.g., vinegar, hydrochloric acid and sulphuric acid.

• Reaction with Metal

Acid + Metal → Salt + Hydrogen gas

e.g., 2HCl + Zn → ZnCl2 + H2

• Reaction with Metal carbonate

Acid + Metal carbonate → Salt + CO2 + H2O

e.g., 2HCl + Na2CO3 → 2NaCl + CO2 + H2O

• Reaction with Metal hydrogen carbonate

Acid + Metal hydrogen carbonate Salt + CO2 + H2O

e.g. HCl + NaHCO3 → NaCl + H2O + CO2

• Reaction with Metallic oxide

Acid + Metal oxide → Salt + Water

e.g. 2HCl + CuO → CuCl2 + H2O

• Acids in water:

Acids produce H+ ions when dissolved in water. H+ ions cannot exist alone. They combine with water molecule (H2O) to form H3O+ (hydronium ions). It conducts electricity.

• Decrease in H30+ ions concentration per unit volume results in formation of dilute acids.

• It is a highly exothermic reaction.

Acids when dissolved in water release large amount of heat. If water is added to concentrated acid then the heat generated may cause the mixture to splash out and cause bums. Hence to avoid burns acid must be added drop wise into water with constant stirring. So that the heat generated spreads over in water.

strong acids → release more H+ ions → HCl

weak acids → releases less number of H+ ions → acetic acid

strong base → give more OH– ions → NaOH

weak base → gives less OH– ions → CH3COOH

Bases: Bases are bitter in taste, turns red litmus to blue and when dissolved in water releases OH– ions;

e.g., NaOH and KOH.

• Reaction with metal

Base + Metal → Salt + H2 gas

e.g., 2NaOH + Zn → Na2ZnO2 + H2

This reaction is possible only with reactive metals like sodium and potassium.

• Reaction with non-metallic oxide

Base + Non-metallic oxide → Salt + H2O

Bases in water → Bases produce OH– ions when dissolved in water. Bases soluble in water are called alkalis. It conducts electricity.

• Decrease in OH– ions single concentration per unit volume results in formation of dilute bases.

• It is a exothermic reaction.

To make basic solution, base must be added drop wise into water with constant stirring, so that the heat generated spreads over in water.

Indicators: Indicators are those substances which tell us whether a substance is acidic or basic by change in colour. For e.g., litmus solution.

• Olfactory indicators: Those substances whose odour changes in acidic or basic media are called lfactory indicators. For e.g., clove, vanilla, onion.

• Natural indicators: Turmeric, litmus (obtained from lichen)

• Synthetic indicators: Methyl orange, phenolphthalein.

Indicator	Acids	Bases
1. Red litmus	remains red	turns blue
2. Blue litmus	turns red	remains blue
3. Phenolphthalein	colourless	pink
4. Methyl orange	red	yellow

Class X Science
NCERT Solutions For Acids, Bases and Salts

NCERT IN–TEXT QUESTIONS SOLVED

Q1. You have been provided with three test tubes, one of them contains distilled water and the other two contain an acidic solution and a basic solution respectively. If you are given only red litmus paper; how will you identify the contents of each test tube?

Ans. Add few drops of solution from all three test tubes on the red litmus paper separately. The solution which turns red litmus to blue contains basic solution. Use this blue litmus paper to test the solutions in other two test tubes. The solution from the test tube which turns blue litmus paper to red will be the acidic solution and solution of the test tube which do not change either red or blue litmus paper contain water.

Q2. Why should curd and sour substances not be kept in brass and copper vessels?

Ans. Curd and sour substances contain acids which can react with copper vessels and brass to form toxic compounds.

Q3. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

Ans. When an acid react with a metal it liberates hydrogen gas.

E.g., Zn(s) + 2HCl(aq) → ZnCl2 (aq) + H2(g)

To test the presence of H2 gas, bring a burning splinter near the mouth of the test tube where H2 gas is released, the match stick bums with a pop sound.

Q4. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Ans. Metal compound A is CaCO3

Gas evolved is CO2

Balanced equation:

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)

Q5. Why do HCl, HNO3 etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

Ans. Solutions like HCl, HNO3 etc. get ionised in aqueous solutions and due to the presence of H+ ions they show acidic characters. While solutions of compounds like alcohol and glucose do not form any such ions so they do not show acidic characters.

Q6. Why does an aqueous solution of an acid conduct electricity?

Ans. Acid when forms a solution in water gets ionised, due to the presence of these ions electricity is conducted through it.

Q7. Why does dry HCl gas not change the colour of the dry litmus paper?

Ans. Dry HCl gas does not release H+ ions and hence, the acidic property of gas is not imparted.

Q8. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Ans. When acid and water mix, the reaction is highly exothermic, the acid may splash, cause burns and even the bottle/container can break. To avoid this and allow the heat evolved to be absorbed by water slowly, acid is added to water for diluting it.

Q9. How is the concentration of hydronium ions (H30+) affected when a solution of an acid is diluted?

Ans. When the solution of acid is diluted the H+ ions are released from the acid to combine with H2O and H3O+ ions is increased.

Q10. How is the concentration of hydroxide ions (OH– ) affected when excess base is dissolved in a solution of sodium hydroxide?

Ans. When base is mixed with water there is decrease in the concentration of OH– ions per unit volume.

Q11. You have two solutions A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?

Ans. A with pH = 6 is acidic B with pH = 8 is basic ‘A’ has more hydrogen ion concentration.

Q12. What effect does the concentration of H+ (aq) ions, have on the nature of the solution?

Ans. If a solution has higher concentration of H+ ions it is more acidic in nature.

Q13. Do basic solutions also have H+ (aq) ions? If yes, then why are these basic?

Ans. Yes basic solutions also have H+ ions, but they are basic in nature due to more number of OH– ions.

Q14. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

Ans. When the soil is acidic in nature, the farmer would add quick lime (CaO) or slaked lime (Ca(OH)2) or chalk (CaCO3)to make it neutral.

Q15. What is the common name of the compound CaOCl2?

Ans. The common name of CaOCl2 is bleaching powder and chemical name is calcium oxychloride.

Q16. Name the substance which on treatment with chlorine yields bleaching powder.

Ans. Calcium hydroxide (Ca(OH)2) when treated with chlorine yields bleaching powder.

Ca(OH)2 + Cl2 → CaOCl2 + H2O

Q17. Name the sodium compound which is used for softening hard water.

Ans. Sodium carbonate.

Q18. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

Ans. When sodium hydrocarbonate is heated, sodium carbonate, water, and carbon dioxide gas is obtained.

Q19. Write an equation to show the reaction between Plaster of Paris and water.

QUESTIONS FROM NCERT TEXTBOOK

Q1. A solution turns red litmus blue, its pH is likely to be

(a) 1 (b) 4

Ans. (d) 10

Q2. A solution reacts with crushed egg-shells to give a gas that turns lime water milky. The solution contains:

(a) NaCl (b) HCl

Ans. (b) HCl

Q3. 10 ml of a solution of NaOH is found to be completely neutralised by 8 ml of a given solution of HCl. If we take 20 ml of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be

(a) 4 ml (b) 8 ml

Ans. (d) 16 ml

Q4. Which one of the following types of medicines is used for treating indigestion?

(a) Antibiotic (b) Analgesic (c) Antacid (d) Antiseptic

Ans. (c) Antacid.

Q5. Write word equations and then balance equations for the reaction taking place when:

(a) dilute sulphuric acid reacts with zinc granules.

(b) dilute hydrochloric acid reacts with magnesium ribbon.

(d) dilute hydrochloric acid reacts with ions filings.

Ans. (a) Step I Zinc granule + dil. Hydrochloric acid → Zinc chloride + Hydrogen gas

Step II Zn(s) + 2HC1 (aq) → ZnCl2(aq) + H2(g)

(b) Step I Magnesium+dil. Hydrochloric acid → Magnesium chloride + Hydrogen gas

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

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

(d) Step I Iron + dil. Hydrochloric acid → Iron chloride + Hydrogen

Step II 2Fe(s) + 3HCl(aq) → Fe2Cl3(aq) + 3H2(g)

Q6. Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.

Ans. • Take a cork with two nails fixed on it.

• Keep this cork inside the beaker.

• Connect the nails to the battery, bulb and key as shown in the figure.

• Now add ethanol in it and record your observation repeat the same set up for glucose and record your observations.

Conclusion: The experiment shows that glucose and ethanol do not ionise, H+ ions are not released therefore, they are not categorised as acids. Observation: The bulb will not glow because charge is not flowing through it.

Q7. Why does distilled water not conduct electricity, whereas rain water does?

Ans. Distilled water is pure water and it does not form ions. Whereas rain water contains impurities in it like acid which contains ions and release them when dissolved in water. Hence no ions in distilled water, so electricity is not conducted but ions are there is rain water so electricity is conducted.

Q8. Why do acids not show acidic behaviour in the absence of water?

Ans. Acids cannot release H+ ions in absence of water, only on dissolving in water acids release H+ ions. Acids show acidic behaviour only due to H+ ions released in presence of water.

Q9. Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is

(a) neutral? (b) strongly alkaline?

(e) weakly alkaline?

Arrange the pH in increasing order of hydrogen ion concentration.

Ans. (i) A with pH = 4 is weakly acidic

B with pH = 1 is strongly acidic

C with pH = 11 is strongly alkaline

D with pH = 7 is neutral

E with pH = 9 is weakly alkaline

(ii) (a) ‘D’ with pH = 7 is neutral

(b) lC with pH = 11 is strongly alkaline

(d) A’ with pH = 4 is weakly acidic

(e) ‘E’ with pH = 9 is weakly alkaline

(iii) pH in increasing order of hydrogen ion concentration

Q10. 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 same. In which test tube will the fizzing occur more vigorously and why?

Ans. In test tube A hydrochloric acid is present which is a strong acid as compared to acetic acid present in test tube B.

The fizzing occurs more vigorously in test tube A as HCl is strong and dissociates completely into H+ and Cl ions for the reaction.

Q11. Fresh milk has pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

Ans. pH of milk will decrease when it turns into curd due to the formation of lactic acid.

Q12. A milkman adds a very small amount of baking soda to fresh milk.

(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?

(b) Why does this milk take a long time to set as curd?

Ans. (a) pH is shifted to alkaline so that milk does not spoil by becoming sour by releasing lactic acid.

(b) Milk is made alkaline by adding baking soda and the lactic acid formed, will get neutralised and therefore will take a little more time to set become acidic.

Q13. Plaster of Paris should be stored in a moisture-proof container. Explain why?

Ans. Plaster of Paris reacts with moisture/water to form gypsum.

Q14. What is a neutralisation reaction? Give two examples.

Ans. The reaction in which acid reacts with base (loses their property) to form salt and water is called neutralisation reaction.

Q15. Give two important uses of washing soda and baking soda.

Ans. Washing soda

(i) It is used in glass, soap and paper industries.

(ii) It is used to remove permanent hardness of water.

Baking Soda

(i) It is used as an antacid.

(ii) It is used in soda, acid fire extinguisher.

MULTIPLE CHOICE QUESTIONS
ACIDS, BASES AND SALTS

1. Which one of the following is acidic?

(a) Lemon juice (b) Tomatoes (c) Milk (d) All

2. Which one of the following will turn red litmus blue?

(a) Vinegar (b) Baking soda solution (c) Lemon juice (d) Soft drinks

3. Which one of the following will turn blue litmus red?

(a) Vinegar (b) Lime water (c) Baking soda solution (d) Washing soda solution

4. Methyl orange is

(a) Pink in acidic medium, yellow in basic medium

(b) Yellow in acidic medium, pink in basic medium

(d) Pink in acidic medium, colourless in basic medium.

5. Lime water is

(a) CaO (b) Ca(OH)2 (c) CaCO3 (d) CaCI2

6. The nature of calcium phosphate is present in tooth enamel is

(a) Basic (b) Amphoteric (c) Acidic (d) Neutral

7. Which of the following salts has no water of crystallization?

(a) Blue vitriol (b) Washing soda (c) Baking soda (d) Gypsum

8. The function of quick lime in soda lime mixture is to

(a) Absorb moisture present in soda lime

(b) Increase the efficiency of soda lime

(d) Take part in reaction with NaOH

9. The Ph of a solution of HCL is 4. This shows that the molarity of the solution is

(a) 4.0M (b) 0.4M (c) 0.0001M (d) 0.001M

10. The difference of molecules of water in gypsum and PoP is

(a)5/2 (b) 2b (c) 3/2 (d) ½

11. Which of the following does not form an acidic salt?

(a) Phosphoric acid (b) Carbonic acid (c) Hydrochloric acid (d) Sulphuric acid

12. The chemical formula of caustic potash is

(a) NaOH (b) Ca(OH)2 (c) NH4OH (D) KOH

ANSWERS

1. (d)

2. (b)

3. (a)

4. (a)

5. (b)

6. (a)

7. (c)

8. (a)

9. (a)

10. (c)

11. (b)

12. (d)

Sample Paper
Acids, Bases and Salts

1. How will you test for a gas which is liberated when HCL reacts with an active metal? (CBSE 2008)

2. What is baking powder? How does it make the cake soft and spongy? (CBSE 2008)

3. When fresh milk is changed into curd will its pH value increase or decrease? Why?

4. Give Arrhenius definition of an acid and a base. (CBSE 2009)

5. What happens chemically when quick lime is added to water? (CBSE 2008)

6. Name the gas evolved when dilute HCL reacts with Sodium hydrogen carbonate. How is it recognized? (CBSE 2008)

7. How does the flow of acid rain water into a river make the survival of aquatic life in the river difficult? (CBSE 2008)

8. How is the pH of a solution of an acid influenced when it is diluted? (CBSE 2008 F)

9. How does the pH of the solution change when a solution of base is diluted? (CBSE 2008 F)

10. Arrange these in increasing order of their pH values- NaOH, blood, lemon juice. (CBSE 2008 F)

11. Two solutions of A and B have pH values of 5 and 8. Which solution will be basic in nature? (CBSE 2008 C)

12. Why does tooth decay start when pH of mouth is lower than 5.5? (CBSE 2009)

13. What would be the colour of litmus in a solution of sodium carbonate? (CBSE 2009)

14. Name the products obtained when sodium hydrogen carbonate is heated. Write the chemical equation for the same. (AI CBSE 2009)

15. Write the chemical formula of washing soda and baking soda. Which one of these two is an ingredient of antacids? How does it provide relief in stomachache? (CBSE 2008 F)

16. What do you mean by ï¿½water of crystallizationï¿½ of a substance? Describe an activity to show that blue copper sulphate crystals contain water of crystallization. (CBSE 2009 F)

17. How can washing soda be obtained from baking soda? Name an industrial use of washing soda other than washing clothes. (AI CBSE 2008)

18. Why does 1 M HCL solutions have a higher concentration of H+ ions than 1M CH3COOH solution? (AI CBSE 2009)

HIGH ORDER THINKING SKILLS
ACIDS, BASES AND SALTS

1. Why is Plaster of Paris stored in a moisture proof container?

2. What do you mean by neutralization reaction? Give two examples.

3. Mention two uses of baking soda and washing soda.

4. Why does a milkman add a small amount of baking soda to fresh milk to shift the pH of fresh milk from 6 to slightly alkaline?

5. Why do acids not show acidic behavior in the absence of water?

6. Rain water conducts electricity but distilled water does not. Why?

7. Why don’t we keep sour substances in brass and copper vessels?

8. What is the common name of CaOCl2?

9. Name the compound used for softening hard water.

10. What happens when baking soda is heated?

11. Give the properties and uses of bleaching powder.

12. Give a few uses of acids, bases and salts respectively.

ACIDS, BASES AND SALTS TEST

MM: 20

Time: 25 mins

1. Name two constituents of baking power. (1 mark)

2. What is universal indicator? (1 mark)

3. Name the chemicals that can be made of common salt (1 mark)

4. Why does cake become fluffy after adding baking soda? (1 mark)

5. Write the pH value, after which teeth start decaying? (1 mark)

6. State some uses of baking soda? (2 marks)

7. How is the concentration of hydroxide ions (OH-) affected when excess base is dissolved in a solution of sodium hydroxide? (2 mark)

8. Name the gas evolved when dilute sulphuric acid acts on sodium carbonate.Write the chemical equation for the reaction involved. (2 mark)

9. What are the properties and uses of bleaching powder?(3 marks)

10. Write a chemical formula to represent the action of atmospheric CO2 gas on bleaching powder when left exposed in open. (2 marks)

11. What happens when quick lime is added to water? (2 marks)

12. Write any two properties of acids. (2 marks)

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