Extra Questions for Class 10 Science Chapter 2 Acids, Bases and Salts

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Extra Questions On Class 10 Science Chapter 2 Acids, Bases and Salts

Q.1. The pH of a sample of vegetable soup was found to be 6.5. How is this soup likely to taste?

Answer Answer. The taste will be slightly sour as it is weakly acidic.

Q.2. Which bases are called alkalies? Give an example of alkalies.

Answer Answer. Soluble bases are called alkalies, e.g. sodium hydroxide (NaOH).

Q.3. Write a balanced chemical equation for the reaction between sodium carbonate and hydrochloric acid indicating the physical state of the reactants and the products.

Answer

Q.4. Write a balanced chemical equation for a neutralisation reaction, mentioning the physical state of the reactants and the products.

Answer

Q.5. What happens when chlorine is passed over slaked lime at 313K? Write chemical equation
of the reaction involved and state two uses of the product obtained.

Answer Answer. Bleaching powder is formed.
(i) It is used as bleaching agent in paper and textile industries.
(ii)It is used as disinfectant in purification of drinking water.

Q.6. What would be the colour of red litmus in a solution of sodium carbonate?

Answer Answer. The red litmus will change to blue in sodium carbonate solution.

Q.7. Which gas is evolved when sodium hydrogen carbonate reacts with dilute hydrochloric acid?

Answer Answer. Carbon dioxide gas is evolved.

Q.8. Curd is not kept in copper and brass utensils. Why?

Answer Answer. Curd and sour substances contain acids which react with brass and copper vessels to form poisonous salts which are harmful for our health.

Q.9. Name the gas usually liberated when a dilute acid reacts with a metal. What happens when
a burning candle is brought near this gas?

Answer Answer. H2 gas is liberated. It burns with pop sound when burning candle is brought near the gas.

Q.10. What effect does an increase in concentration of H+(aq.) in a solution have on the pH of solution?

Answer Answer. Higher the concentration, lower will be pH of the solution.

Q.11. Which one of these has a higher concentration of H+ ions ? 1 M HCl or 1 M CH3COOH

Answer Answer.1 M HCl has higher concentration of H+ ions.

Q.12. Why does 1 M HC1 solution have a higher concentration of H+ ions than 1 M CH3COOH solution?

Answer Answer.1 M HCl has higher cone, of (H+) because it ionises completely in aqueous solution whereas CH3COOH does not as it is weak acid.

Q.13. Which gas is generally liberated when a dilute solution of hydrochloric acid reacts with an active metal?

Answer Answer. Hydrogen gas is liberated when active metal reacts with dilute hydrochloric acid

Q.14. What is the colour of litmus in a solution of ammonium hydroxide?

Answer Answer. Red litmus will turn blue in ammonium hydroxide.

Q.15. Name the natural source of each of the following acid
(i) Citric acid.
(ii) Oxalic acid.
(iii) Lactic acid.
(iv) Tartaric acid.

Answer Answer. (i) Lemon and orange.(ii)Tomatoes and Guava. (iii)Sour milk (curd).(iv)Tamarind.

Q.16. A student detected the pH of four unknown solution A, B, C and D as follows 11, 5, 7 and 2. Predict the nature of the solution.

Answer Answer. A is basic ‘B’ is acidic ‘C’ is natural and ‘D’ is strongly acidic.

Q.17. (i) Give the constituents of baking powder
(ii) Why cake or bread swells on adding baking powder? Write chemical equation.

Answer Answer.
(i) Baking powder containg sodium hydrogen carbonate and tartaric acid.
(ii)It is due to carbon dioxide

Q.18. How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?

Answer Answer. Bring a burning matchstick near the gas. It burns with ‘pop’ sound showing that it is hydrogen.

Q.19. Name the acid present in the following:
(i) Tomato (ii) Vinegar (iii) Tamarind

Answer Answer. (i) Oxalic acid (ii) Acetic acid (iii) Tartaric acid

Q.20. Explain how antacid works.

Answer Answer. Hyperacidity is caused by excess of hydrochloric acid in stomach. Antacid is basic in nature. It neutralizes excess of acid and gives relief from pain caused by hyperacidity.

Q.21. (a) Define olfactory indicators. Name two substances which can be used as olfactory indicator.
(b) Choose strong acids from the following:
CH3COOH, H2SO4, H2CO3, HNO3

Answer Answer.
(a) Those substances whose smell (odour) changes in acidic or basic solution are called olfactory indicators, e.g. onion and vanilla.
(b) H2SO4 and HNO3 are strong acids.

Q.22. A white coloured powder is used by doctors for supporting fractured bones.
(a) Write chemical name and formula of the powder.
(b) When this white powder is mixed with water a hard solid mass is obtained. Write balanced chemical equation for the change.

Answer

Q.23. Explain the action of dilute hydrochloric acid on the following with chemical equation:
(i) Magnesium ribbon (ii) Sodium hydroxide (iii) Crushed egg shells

Answer

Q.24. State reason for the following statements:
(i) Tap water conducts electricity whereas distilled water does not.
(ii) Dry hydrogen chloride gas does not turn blue litmus red whereas dilute hydrochloric acid does.
(iii) During summer season, a milk man usually adds a very small amount of baking soda to fresh milk.
(iv) For a dilution of acid, acid is added into water and not water into acid.
(v) Ammonia is a base but does not contain hydroxyl group.

Answer Answer.
(i) Tap water contains ions which conduct electricity, distilled water does not contain ions.
(ii)Dry HCl does not form ions but HCl gives H+ and Cl–.
(iii) Baking soda does not allow milk to change to lactic acid which makes milk sour.
(iv) Adding water to acid is highly exothermic. Therefore water is added to acid very slowly with cooling.
(v) Ammonia dissolves in water and forms H– Therefore, it is basic in nature.

Q.25. (a) Write the chemical formula of hydrated copper sulphate and anhydrous copper sulphate. Giving an activity illustrate how these are inter convertible.
(b) Write chemical names and formula of plaster of paris and gypsum.

Answer Answer.
(a)CuSO4.5H2O is hydrated copper sulphate. CuSO4 is anhydrous copper sulphate. Aim: To show crystalline salts contain water of crystallization. Material Required: CuSO4.5H2O (Blue vitriol), boiling tube, burner, cork, delivery tube, test tube, clamp stand.
Procedure: 1.Take 2g of CuSO4.5H2O in a boiling tube fitted in a clamp stand.
2.Observe its colour. Fit it with cork and delivery tube bent at two right angles which dips into a test tube.
3.Heat crystals in boiling tube.
4.Observe vapours being condensed in test tube.
5.Cool the crystals and add few drops of water into it.
Observation: Water vapours get condensed in a test tube and colour of blue crystals changes into white. On adding water to anhydrous copper sulphate it changes into blue again.
Chemical Reaction :

Conclusion : Crystalline substances have water of crystallization which are lost on heating. When we add water in CuSO4 till a saturated solution is formed. On cooling, it gets converted into CuSO4.5H2Ocrystals and it shows that both are inter convertible.

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