Class ten acids, bases and salt short answers

Class 10 Chapter 4: Acids, Bases and Salt

TOPIC-1: Acids: Indicators, General characteristic properties of acids, chemical nature of acids. 


Q.1. What are the indicators ?

Ans. The substances which indicate the acidic or basic nature of the solution by the colour changes are known as indicators.

 Q.2. How will you test with litmus paper that the given solution is acidic? 

Ans. An acidic solution turns blue litmus red.

 Q.3. What happens to blue litmus when it is added to soda water? “HOTS” ]

Ans. The colour of the blue litmus will turn red because soda water contains carbonic acid (HCO3). 

Q.4. What is the colour of methyl orange in an acidic medium? 

Ans. Methyl orange gives a red colour in acidic medium. 

Q.5. What is the name given to the indicators giving different odours in the acidic and basic medium? 

Ans. Olfactory indicators. 

Q. 6. What is the colour of phenolphthalein in soap solution? 

Ans. Colour of phenolphthalein will be pink because the soap solution provides an alkaline medium.

Q. 7. What is the colour of methyl orange in baking soda?

Ans. The colour of methyl orange will be yellow because baking soda provides a basic medium.

Q.8. Which gas is evolved when an acid reacts with a metal? 

Ans. Hydrogen (H) gas.

Q.9. What is Arrhenius’ definition of Acids’? [HOTS]

Ans. Acids are the substances which give H+ ions in water, (aqueous solution).

Q. 10. Which acid is present in sour milk or curd? 

Ans. Lactic acid.

Q.11. Why is the solution of HCl in water conduct electricity but that of glucose in water does not though both contain hydrogen? [HOTS]

Ans. HCl solution conducts electricity but glucose solution does not because HCl in aqueous solution dissociates to give. H+ and Cl ions, but glucose (C6H12O6) do not.

Q. 12. Name the acid present in: 

(1) nettle sting 

(ii) curd

Ans. (i) Methanoic acid or formic acid (HCOOH) 

(ii) Lactic acid

Q. 13. Name the indicator which tells the various levels of H+ ions concentration.

Ans. It is a mixture of a number of indicators known as universal indicators.

Q. 14. How should a concentrated acid be diluted? 

Ans. It should be diluted by adding concentrated acid into water. 

Q. 15. What are weak acids? Give two examples. 

Ans. An acid which gives a small amount of H+ ions in water is a weak acid. 

e. g. Acetic acid and carbonic acid. 

Q. 16. What are the strong acids ? Give two examples? 

Ans. An acid that gives a large amount of H+ ions in aqueous solution is a strong acid. Example: Sulphuric Acid ( H2SO4) and Hydrochloric Acid (HCl).

Q. 17. How do H+ ions exist in water? 

Ans. Exist as hydronium ion (H2O*). H+ ion in water combines with water (H2O). 

H2O + H+ —–>H3O+

Q. 18. What is the effect of dilution on H+ ion concentration of an acid? 

The H+ ion concentration per unit volume decreases on dilution.

 Q. 19. How will you test a gas which is liberated when hydrochloric acid reacts with an active metal? [CBSE 2008]

Ans. Hydrogen gas is produced when an active metal reacts with diluted hydrochloric acid. When a burning candle is brought near hydrogen gas, a popping sound is heard due to the combustion of hydrogen to form water. 

2H2 (g) + O2(g) — 2H2O(g)

 Q. 20. Name the gas evolved when diluted sulphuric acid acted on sodium carbonate. [CBSE 2006]

Ans. Carbon dioxide (CO) gas released. 

Na2CO3 (s) + H2SO4 (aq)——-> Na2SO4 (aq) + CO2(g) + H2O(l)

Q. 21. Is dilution of concentrated acid or base exothermic or endothermic? 

Ans. Exothermic.

Q. 22. Why should water never be added dropwise to concentrated sulphuric acid? [CBSE 2007]

Ans. Adding water to acid is an exothermic process. Thus, a large amount of heat is liberated which results in splashing out of the acid. 

Q. 23. Give one example of a strong acid and one of a weak acid. 

Ans. Hydrochloric acid (HCl) is a strong acid and acetic acid ( CH2COOH) is a weak acid.

Q.24. What acid is produced in the stomach? 

Ans. Hydrochloric acid (HCl). 

Q.1. Give the name and formula of two

(i) Strong monobasic acids 

(ii) Weak dibasic acids 

Ans. 1. Hydrochloric acid (HCI), Nitric acid (HNO3). : Strong monobasic acids 

2. Carbonic acid ( H2CO3), oxalic acid (C2H4O4): Weak dibasic


Q.1. Give the name and formula of two

(i) Strong monobasic acids 

(ii) Weak dibasic acids 

Ans. 1. Hydrochloric acid (HCl), Nitric acid ( HNO3). : Strong monobasic acids 

2. Carbonic acid (H2CO3), oxalic acid (C2H4O4).: Weak dibasic acids.

Q.2. Kazi and Priyam want to prepare dil H2SO4. Kazi added conc. H2SO4 to water slowly with constant stirring and cooling whereas Priyam added water to conc. H2SO4. Name the student who was correct and why? [HOTS]

 Ans. Kazi was correct. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

Q.3. Why does not an acid show any acidic behaviour in the absence of water?

 Ans. Acid gets ionized only in aqueous solution which means in the presence of water. It also releases H+ ions and shows acidic behaviour in the presence of water.

Q.4. Name the acid present in “ant sting” and give its chemical formula. Also, give the common method to get relief from the discomfort caused by the “ant sting”. [NCERT Exemplar] 

Ans. The acid present in ‘ant sting’ is: Methanoic acid 

The chemical formula of methanoic acid: HCOOH Method to get relief from the discomfort caused by the ant sting: Rubbing of baking soda over the location of ant sting, will soothe the pain instantly. Baking soda is a base. Therefore, while rubbing baking soda over the ant sting, it neutralizes the methanoic acid present in ant sting and gives relief from pain. 

Q.5 A first aid manual suggests the vinegar should be used to treat wasp stings and baking soda for bee stings. 

(i) What does this information tell you about the chemical nature of the wasp stings? (ii) If there were no baking soda in the house, what other household substance could you use to treat bee stings? [HOTS]

Ans. (i) Since vinegar (acetic acid) is used to heal or neutralize the effect of wasp sting which this means that the chemical present in the stings must be some base. (ii) – NH4OH Ammonium hydroxide.

Q.6. You might have seen lemon or tamarind juice being used to clean the tarnished surface of copper vessels. Explain why these sour substances are effective in cleaning the vessels. [CBSE 2011] 

Ans. Lemon juice contains citric acids and tamarind contains tartaric acid. These acids react with a layer of copper carbonate on the surface of vessels to form soluble salts which are washed away by water. i.e. these acids act as cleansing agents.

Q.7. What happens when nitric acid is added to the eggshell? [NCERT Exemplar]

Ans. Eggshells contain calcium carbonate. When nitric acid is added to it, carbon dioxide gas is evolved. The reaction can be given as: 

Q.8. A few drops of phenolphthalein indicator were added to an unknown solution A. It acquired a pink colour. Now another unknown solution B was added to it drop by drop and the solution becomes colourless. Predicting the nature of A and B. [HOTS]

Ans. A is basic in nature as phenolphthalein has imparted pink colour to it. Solution ‘B’ is acid. It has made solution A colourless by neutralizing its basic effect. Q.9. The knife, which was used to cut fruit, was immediately dipped into water containing a drop of blue litmus solution. If the colour of the solution is changed to read, what inference can be drawn about the nature of the fruit and why? (CBSE 2011]

Ans. The substance (solution) sticking to the knife is acid which turns blue litmus into red. The fruit is a citrus fruit because citrus contains acid.

 Q. 10. How will you show that acetic acid is monobasic acid? 

 Ans. When acetic acid is added to the aqueous solution (water) only one H+ ions is released. Due to this, it is monobasic acid also. When acetic acid reacts with NaOH solution only one atom of the acid gets replaced which shows acetic acid is a monobasic acid. 


Q. 12. Dry HCl gas does not change the colour of dry blue litmus paper. Give reason. [CBSE 2013, 2013]

Ans. Because dry HCl gas does not furnish H’ ions. H+ ions are produced when HCl gas comes into contact with water. 

H+ ions or H2O+ ions react with blue litmus and changes to red.