Extra Questions for Class 10th: Ch 2 Acids, Bases and Salts (Science) Important Questions Answer Included
Very Short Answer Questions (VSAQs): 1 Mark
Q1. Which gas is usually liberated when an acid reacts with a metal?
Answer
Hydrogen gas.
Q2. Name a salt which does not contain water of crystallisation.
Answer
Baking soda.
Q3. Write an equation to show the reaction between Plaster of Paris and water.
Answer
CaSO4. ½H2O +1½ H2O → CaSO4.2H2O
Plaster of Paris: CaSO4. ½H2O
Gypsum: CaSO4.2H2O
Q4. What would be the colour of litmus in a solution of sodium carbonate?
Answer
The colour of litmus in a solution of sodium carbonate is blue.
Q5. Name the sodium compound which is used for softening hard water.
Answer
Sodium carbonate.
Short Answer Questions-I (SAQs-I): 2 Marks
Q1. Classify the following into acidic oxides anc basic oxides : Na2O, SO2, MgO, CO2
Answer
Acidic oxides — SO2, CO2
Basic oxides — Na2O, MgO2
Q2. What is the change in pH values of milk when it changes into curd? Explain.
Answer
pH decrease by the presence of lactic acid in curd because acids generally have a low pH value. Hence, pH will decrease when milk changes into curd.
Q3.What is cause of decay of tooth? What is the pH of mouth required.
Answer
The enamel of our tooth started getting damaged when pH of tooth is less than 5.5. Tooth decay starts when the pH of the mouth is lower than 5.5 . Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. Toothpaste is basic in nature is used to neutralize the acid.
Q4. A white powder is added while baking breads and cakes to make them soft and fluffy. What is the name of the powder? What are the main ingredients in it? What are the functions of each ingredient?
Answer
Baking powder.
Baking soda and an edible acid like tartaric acid. Baking soda (NaHCO3) is used to release CO2 gas when heated. Tartaric acid is used to avoid the bitter taste by reacting with the Na2CO3 formed.
Short Answer Questions-II (SAQs-II): 3 Marks
Q1. (a) What is the action of litmus on:
(i) dry ammonia gas
(ii) solution of ammonia gas in water
(b) State the observations you would make on adding sodium hydroxide to aqueous solution of
(i) ferrous sulphate
(ii) aluminium chloride. Give balanced chemical equations.
Answer
(a) (i) No change in colour
(ii) Red litmus turns blue
(b) (i) 2NaOH(aq) + FeSO4(aq) → Fe(OH)2(s) + Na2SO4(aq)
Sodium hydroxide + Ferrous sulphate → Ferrous hydroxide + Sodium Sulphate
(ii) 3NaOH(aq) + AlCl3(aq) → Al(OH)3(s) + NaCl(aq)
Sodium hydroxide + Aluminium chloride → Aluminium hydroxide + Sodium chloride
Q2. Name the three products of 'chlor-alkali process. Write one commercially or industrially important material each that can be prepared from each of these products.
Answer
The three products are: Sodium hydroxide (NaOH), Chlorine (Cl2) and Hydrogen (H2).
NaOH: used in making soaps and detergents and also in paper making or artificial fibres.
Cl2: PVC, pesticides, CFCs.
H2: fuels, margarine, NH3 for fertilizers.
Q3. Draw a neat and labelled diagram to show the following activity: Action of dilute sulphuric acid on zinc granules
(i) Name the gas evolved.
(ii) How will you test for the gas.
Answer
(i) The gas evolved is hydrogen.
(ii) Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
Test for H2 gas: The presence of H2 gas can be tested by passing the gas through soap solution and then bringing a burning splinter near the soap bubbles filled with the gas. If the gas burns with a pop sound, it is hydrogen.
Long Answer Questions (LAQs): 5 Marks
1. (i) Explain why is hydrochloric acid a strong acid and acetic acid, a weak acid. How can it be verified?
(ii) Explain why aqueous solution of an acid conducts electricity.
(iii) You have four solutions A, B, C and D. The pH of solution A is 6, B is 9, C is 12 and D is 7.
(a) Identify the most acidic and most basic solutions.
(b) Arrange the above four solutions in the increasing order of H+ ion concentration.
(c) State the change in colour of pH paper on dipping in solution C and D.
Answer
(i) HCI will give rise to more H+ ions and CH3COOH produces less H+ ions on dissociation. The colour of pH paper depends on the concentration of H+ ion. Colour becomes red for high H+ concentration.
(ii) Aqueous solution of acids have H+ which carry electric current through the solution.
(iii) (a) Most acidic: A and Most basic: C
(b) C, B, D, A/C < B < D < A
(c) In C: blue, In D: green
2. Give suitable reasons for the following statements:
(i) Rain water conducts electricity but distilled water does not.
(ii) We feel burning sensation in the stomach when we over eat.
(iii) A tarnished copper vessel regains its shine when rubbed with lemon.
(iv) The crystals of washing soda change to white powder on exposure to air.
(v) An aqueous solution of sodium chloride is neutral but an aqueous solution of sodium carbonate is basic.
Answer
(i) Distilled water is a pure form of water, is neither acidic nor basic in nature. So distilled water does not dissociate into ions, since, conduction of electricity requires free ions so, distilled water does not conduct electricity. While rain water being an impure form of water, contains many ionic species. These ions are responsible for electrical conductivity of rain water.
(ii) Because when we over eat too much HCI is produced in our stomach which causes burning sensation.
(iii) Copper vessels tarnish is due to the formation of basic copper carbonate [Cu2(OH)2CO3] which gets neutralized when rubbed with lemon and the copper vessel regains its shine.
(iv) Washing soda (sodium carbonate decahydrate), Na2CO3.10H2O when exposed to air, it loses 10 molecules of water and changes to white powder.
(v) Sodium chloride is a salt of strong acid HCI and strong base NaOH, so it is neutral. Sodium carbonate is a salt of weak acid H2CO3 and strong base NaOH, so it is basic.
NaCI + H2O → NaOH + HCI
Na2CO3 + H2O → NaOH + H2CO3