Class 10 › Science Acids, Bases and Salts Class 10 Science · Chapter 2
Practice all → Summary Questions & answers Practise this chapter → View all Page 1 free about 8 min read , Full kit about 55 min read Page 1 free about 8 min read , Full kit about 55 min read View all 12 amazing Marks Booster kits → Acids release hydrogen ions (H⁺) in water, while bases release hydroxide ions (OH⁻); alkalis are water-soluble bases. We identify them using indicators such as litmus, phenolphthalein and methyl orange, and we measure their strength on the pH scale from 0 to 14, where 7 is neutral. When an acid reacts with a base, neutralisation occurs, producing a salt and water. Acids and bases also react with metals, metal carbonates and metal oxides in predictable ways. The chapter studies several important salts — common salt, sodium hydroxide, bleaching powder, baking soda, washing soda and plaster of Paris — explaining how each is made and used. It also introduces the idea of water of crystallisation, the fixed number of water molecules in a salt’s crystal structure, as in hydrated copper sulphate.
pH scale
A 0–14 scale measuring acidity (low) or basicity (high); 7 is neutral.
Neutralisation
Reaction of an acid with a base to give salt and water.
Indicator
A substance that changes colour to show acidic or basic nature.
Water of crystallisation
Fixed water molecules present in a crystalline salt.
Q1 What happens to the pH when an acid is diluted with water? Answer Q2 Why does dry HCl gas not turn blue litmus red? Answer Q3 How do acids and bases behave in water? Answer Q4 What are indicators? Name a few. Answer Q5 What is the pH scale, and why is it important? Answer Q6 How do acids react with metals and with metal carbonates? Answer Q7 What is neutralisation? Give the general reaction. Answer Q8 How are baking soda and washing soda made and used? Answer Q9 What is bleaching powder, and how is it prepared? Answer Q10 What is water of crystallisation? Give an example. Answer Q1 1. 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? Answer Q1 1. Why should curd and sour substances not be kept in brass and copper vessels? Answer Q2 2. 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? Answer Q3 3. 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. Answer Q1 1. Why do \(\mathrm{HCl}\), \(\mathrm{HNO_3}\), etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character? Answer Q2 2. Why does an aqueous solution of an acid conduct electricity? Answer Q3 3. Why does dry \(\mathrm{HCl}\) gas not change the colour of the dry litmus paper? Answer Q4 4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid? Answer Q5 5. How is the concentration of hydronium ions \(\mathrm{(H_3O^+)}\) affected when a solution of an acid is diluted? Answer Q6 6. How is the concentration of hydroxide ions \(\mathrm{(OH^-)}\) affected when excess base is dissolved in a solution of sodium hydroxide? Answer Q1 1. 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? Answer Q2 2. What effect does the concentration of \(\mathrm{H^+(aq)}\) ions have on the nature of the solution? Answer Q3 3. Do basic solutions also have \(\mathrm{H^+(aq)}\) ions? If yes, then why are these basic? Answer Q4 4. 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)? Answer Q1 1. What is the common name of the compound \(\mathrm{Ca(ClO)_2}\)? Answer Q2 2. Name the substance which on treatment with chlorine yields bleaching powder. Answer Q3 3. Name the sodium compound which is used for softening hard water. Answer Q4 4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved. Answer Q5 5. Write an equation to show the reaction between Plaster of Paris and water. Answer Q1 1. A solution turns red litmus blue, its pH is likely to be
(a) \(1\) (b) \(4\) (c) \(5\) (d) \(10\) Answer Q2 2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
(a) \(\mathrm{NaCl}\) (b) \(\mathrm{HCl}\) (c) \(\mathrm{LiCl}\) (d) \(\mathrm{KCl}\) Answer Q3 3. \(10\ \mathrm{mL}\) of a solution of \(\mathrm{NaOH}\) is found to be completely neutralised by \(8\ \mathrm{mL}\) of a given solution of \(\mathrm{HCl}\). If we take \(20\ \mathrm{mL}\) of the same solution of \(\mathrm{NaOH}\), the amount \(\mathrm{HCl}\) solution (the same solution as before) required to neutralise it will be
(a) \(4\ \mathrm{mL}\) (b) \(8\ \mathrm{mL}\) (c) \(12\ \mathrm{mL}\) (d) \(16\ \mathrm{mL}\) Answer Q4 4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic Answer Q5 5. Write word equations and then balanced equations for the reaction taking place when –
(a) dilute sulphuric acid reacts with zinc granules. Answer Q6 (b) dilute hydrochloric acid reacts with magnesium ribbon. Answer Q7 (c) dilute sulphuric acid reacts with aluminium powder. Answer Q8 (d) dilute hydrochloric acid reacts with iron filings. Answer Q9 6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it. Answer Q10 7. Why does distilled water not conduct electricity, whereas rain water does? Answer Q11 8. Why does dry \(\mathrm{HCl}\) gas not show acidic behaviour in the absence of water? Answer Q12 9. 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? Answer Q13 (b) strongly alkaline? Answer Q14 (c) strongly acidic? Answer Q15 (d) weakly acidic? Answer Q16 (e) weakly alkaline? Answer Q17 Arrange the pH in increasing order of hydrogen-ion concentration. Answer Q18 10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid \(\mathrm{(HCl)}\) is added to test tube A, while acetic acid \(\mathrm{(CH_3COOH)}\) 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? Answer Q19 11. Fresh milk has a pH of \(6\). How do you think the pH will change as it turns into curd? Explain your answer. Answer Q20 12. 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? Answer Q21 (b) Why does this milk take a long time to set as curd? Answer Q22 13. Plaster of Paris should be stored in a moisture-proof container. Explain why? Answer Q23 14. What is a neutralisation reaction? Give two examples. Answer Q24 15. Give two important uses of washing soda and baking soda. Answer Q1 (I) Prepare your own indicator
Crush beetroot in a mortar.
Add sufficient water to obtain the extract.
Filter the extract by the procedure learnt by you in earlier classes.
Collect the filtrate to test the substances you may have tasted earlier.
Arrange four test tubes in a test tube stand and label them as A,B,C and D. Pour \(2\ \mathrm{mL}\) each of lemon juice solution, soda-water, vinegar and baking soda solution in them respectively.
Put \(2\)-\(3\) drops of the beetroot extract in each test tube and note the colour change if any. Write your observation in a Table.
You can prepare indicators by using other natural materials like extracts of red cabbage leaves, coloured petals of some flowers such as Petunia, Hydrangea and Geranium. Answer Q2 (II) Preparing a soda-acid fire extinguisher
The reaction of acids with metal hydrogencarbonates is used in the fire extinguishers which produce carbon dioxide.
Take \(20\ \mathrm{mL}\) of sodium hydrogencarbonate \(\mathrm{(NaHCO_3)}\) solution in a wash-bottle.
Suspend an ignition tube containing dilute sulphuric acid in the wash-bottle (Fig. \(2.10\)).
Close the mouth of the wash-bottle.
Tilt the wash-bottle so that the acid from the ignition tube mixes with the sodium hydrogencarbonate solution below.
You will notice discharge coming out of the nozzle.
Direct this discharge on a burning candle. What happens? Answer
Acids release which ion when dissolved in water?
A Hydroxide ion (OH⁻) B Hydrogen ion (H⁺) C Sodium ion (Na⁺) D Chloride ion (Cl⁻)
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