CBSE Class 10 Science HOTs Acids Bases And Salts Set 03

PRACTICE QUESTIONS

Question. Select the correct option(s) in the following table. 
Option | Natural source | Acid present
(i) | Tamarind | Tartaric acid
(ii) | Tomato | Lactic acid
(iii) | Ant sting | Oxalic acid
(iv) | Nettle sting | Methanoic acid
(a) (i) only
(b) (iii) only
(c) (i) and (iv)
(d) (i), (ii) and (iv)
Answer: (c) (i) and (iv)

Question. The aqua regia is
(a) \( 3HNO_3(conc.) + 1 HCl (conc.) \)
(b) \( 3HCl (conc.) + 1 HNO_3 (conc.) \)
(c) \( HNO_3 (conc.) + H_2SO_4 (conc.) \)
(d) \( HNO_3(conc.) + HCl (conc.) \)
Answer: (b) \( 3HCl (conc.) + 1 HNO_3 (conc.) \)

Question. The acid having highest hydronium ion concentration is one with 
(a) pH = 2.5
(b) pH = 1.8
(c) pH = 7
(d) pH = 10
Answer: (b) pH = 1.8

Question. The table below has information regarding pH and nature (acidic/basic) for four different solutions. Which one of the option in the table is correct? 
Solution | Colour of pH paper | Approx pH | Nature of solution
(a) Lemon juice | Orange | 3 | Basic
(b) Milk of magnesia | Blue | 10 | Basic
(c) Gastric juice | Red | 6 | Acidic
(d) Pure water | Yellow | 7 | Neutral
Answer: (b) Milk of magnesia | Blue | 10 | Basic

Question. Name the acid present in the following: (a) Tomato (b) Vinegar 
Answer: (a) Oxalic acid (b) Acetic acid

Question. Write any two natural and two synthetic indicators.
Answer: Natural: Litmus, Turmeric. Synthetic: Phenolphthalein, Methyl orange.

Question. A student dropped few pieces of marble in dilute HCl contained in a test tube. The evolved gas was passed through lime water. (a) What change would be observed in lime water? (b) Write balanced chemical equation for the above change.
Answer: (a) Lime water turns milky. (b) \( Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \)

Question. What happens when an acid reacts with metal oxides? Give two chemical equations of the reaction involved.
Answer: It forms salt and water.
(i) \( CuO + 2HCl \rightarrow CuCl_2 + H_2O \)
(ii) \( MgO + H_2SO_4 \rightarrow MgSO_4 + H_2O \)

Question. Name an indicator which is
(a) pink in acidic solution and yellow in basic solution.
(b) colourless in acidic solution and pink in basic solution.
Answer: (a) Methyl orange (b) Phenolphthalein

Question. (a) Which bases are called alkalies? Give an example of alkalies. (b) What is cure for bee sting? Why?
Answer: (a) Water soluble bases are called alkalies, e.g., NaOH. (b) Baking soda because bee sting is acidic and baking soda is a mild base which neutralizes it.

Question. (a) The pH of a sample of vegetable soup was found to be 6.5. How is this soup likely to taste? (b) Which remedy you will suggest if someone in family is suffering from problem of acidity and why?
Answer: (a) Sour. (b) Antacids like milk of magnesia or baking soda because they are basic and neutralize excess acid.

Question. (a) What are antacids? Give one example. (b) State the purpose for which litmus is used in laboratories. 
Answer: (a) Substances which neutralize excess acid in the stomach, e.g., Magnesium hydroxide. (b) To test the acidic or basic nature of a solution.

Question. (a) What is an alkali? Give an example. (b) Why do \( HCl, HNO_3 \), etc. show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer: (a) Water soluble base, e.g., NaOH. (b) Because \( HCl, HNO_3 \) etc. dissociate in water to give \( H^+ \) ions, whereas alcohol and glucose do not dissociate to give \( H^+ \) ions.

Question. Identify the acid and base which form sodium hydrogen carbonate. Write chemical equation in support of your answer. State whether this compound is acidic, basic or neutral. Also write its pH value. 
Answer: Acid: \( H_2CO_3 \), Base: \( NaOH \). \( NaOH + H_2CO_3 \rightarrow NaHCO_3 + H_2O \). It is a basic salt. pH value is greater than 7.

Question. On passing excess carbon dioxide gas through lime water, it first turns milky and then becomes colourless. Explain why? Write all the chemical equations of the reactions involved. 
Answer: First, milkiness is due to formation of \( CaCO_3 \). On passing excess \( CO_2 \), milkiness disappears due to formation of soluble \( Ca(HCO_3)_2 \).
\( Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \)
\( CaCO_3 + H_2O + CO_2 \rightarrow Ca(HCO_3)_2 \)

Question. (a) What is pH value of salt formed by a (i) weak acid and strong base? (ii) strong acid and strong base? (b) 15 mL of water and 10 mL of sulphuric acid are to be mixed in a beaker (i) State the method that should be followed with reason. (ii) What is this process called? 
Answer: (a) (i) pH > 7 (ii) pH = 7. (b) (i) Acid should be added to water slowly with constant stirring because it is highly exothermic. (ii) Dilution.

Question. (c) What is observed when sulphur dioxide is passed through (i) water (ii) lime water? Also write chemical equations for the reactions that take place.
Answer: (i) It forms sulphurous acid. \( SO_2 + H_2O \rightarrow H_2SO_3 \). (ii) Lime water turns milky due to formation of calcium sulphite. \( Ca(OH)_2 + SO_2 \rightarrow CaSO_3 + H_2O \)

Question. (a) The soil in a field is highly acidic. List any two materials which can be added to this soil to reduce its acidity. Give the reason for your choice. 
(b) A gas produced in the laboratory is highly soluble in water. Its colourless solution turns pink when a few drops of phenolphthalein is added to it. What is the nature of this gas?
Answer: (a) Quick lime (CaO) or slaked lime \( (Ca(OH)_2) \). Being basic, they neutralize soil acidity. (b) Basic.

Question. (a) Explain the following chemical properties of acids with the help of balanced chemical equations only. (i) when an acid reacts with a metal carbonate (ii) when an acid reacts with a metal bicarbonate (iii) when an acid reacts with a metal oxide (b) You are given three solutions A, B and C with pH values 2, 10 and 13 respectively. Write which solution has more hydrogen ion concentration among the three and state the nature ‘acidic or basic’ of each solution.
Answer: (a) (i) \( Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2 \) (ii) \( NaHCO_3 + HCl \rightarrow NaCl + H_2O + CO_2 \) (iii) \( MgO + 2HCl \rightarrow MgCl_2 + H_2O \). (b) Solution A (pH 2) has more \( H^+ \) ion concentration. A is acidic, B and C are basic.

Question. (a) A metal compound ‘X’ reacts with dil. \( H_2SO_4 \) to produce effervescence. The gas evolved extinguishes a burning candle. If one of the compounds formed is calcium sulphate, then what is ‘X’ and the gas evolved? Also write a balanced chemical equation for the reaction which occurred. (b) (i) Name one antacid. How does it help to relieve indigestion in stomach? (ii) A farmer treats the soil with quick lime or calcium carbonate. What is the nature of soil? Why does the farmer treat the soil with quick lime?
Answer: (a) X is \( CaCO_3 \), Gas is \( CO_2 \). \( CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2 \). (b) (i) Magnesium hydroxide. It neutralizes excess HCl in stomach. (ii) Soil is acidic. To neutralize the acidity of soil.

More about Salts

Question. Dry slaked lime reacts with \( Cl_2 \) gas to form
(a) \( CaCl_2 \)
(b) \( CaOCl_2 \)
(c) \( Ca(OH)_2 \)
(d) \( CaO \)
Answer: (b) \( CaOCl_2 \)

Question. Which of the following salts do not have the water of crystalisation? 
(i) Bleaching powder (ii) Plaster of Paris (iii) Washing soda (iv) Baking soda
(a) (ii) and (iv)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (i) and (iv)
Answer: (d) (i) and (iv)

Question. Which of the following is not a acidic salt?
(a) \( CuSO_4 \)
(b) \( NH_4Cl \)
(c) \( FeCl_3 \)
(d) \( CH_3COONa \)
Answer: (d) \( CH_3COONa \)

Question. A solution of \( NaCl \)
(i) will turn red litmus blue
(ii) will turn pH paper green
(iii) will turn blue litmus red
(iv) will not affect litmus
(a) (i) and (ii)
(b) (i), and, (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Answer: (d) (ii) and (iv)

Question. Many salts absorbs water from atmosphere. This property is called
(a) deliquescence
(b) efflorescence
(c) hydration
(d) addition
Answer: (a) deliquescence

Question. \( CaOCl_2 \) will liberate \( Cl_2 \) gas in presence of
(i) \( CO_2 \)
(ii) \( HCl \)
(iii) \( CO \)
(iv) \( NO \)
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Answer: (a) (i) and (ii)

Question. Egg shell is made up of
(a) \( CaCO_3 \)
(b) \( CaO \)
(c) \( Ca(OH)_2 \)
(d) \( CaCl_2 \)
Answer: (a) \( CaCO_3 \)

Question. Two salts X and Y are dissolved in water separately. When phenolphthalein is added to these two solutions, the solution ‘X’ turns pink and the solution Y does not show any change in colour, therefore X and Y are 
(a) X: \( Na_2CO_3 \), Y: \( NH_4Cl \)
(b) X: \( Na_2SO_4 \), Y: \( NaHCO_3 \)
(c) X: \( NH_4Cl \), Y: \( Na_2SO_4 \)
(d) X: \( NaNO_3 \), Y: \( Na_2SO_4 \)
Answer: (a) X: \( Na_2CO_3 \), Y: \( NH_4Cl \)

Question. \( NaOH \) is obtained by electrolysis of
(a) Aq. solution of \( NaCl \)
(b) Aq. \( Na_2CO_3 \)
(c) Aq. \( NaHCO_3 \)
(d) Molten \( NaCl \)
Answer: (a) Aq. solution of \( NaCl \)

Question. Baking soda is a mixture of: 
(a) Sodium carbonate and acetic acid
(b) Sodium carbonate and tartaric acid
(c) Sodium hydrogen carbonate and tartaric acid
(d) Sodium hydrogen carbonate and acetic acid
Answer: (c) Sodium hydrogen carbonate and tartaric acid

Question. The chemical formula for Plaster of Paris is: 
(a) \( CaSO_4 \cdot 2H_2O \)
(b) \( CaSO_4 \cdot H_2O \)
(c) \( CaSO_4 \cdot \frac{1}{2} H_2O \)
(d) \( 2CaSO_4 \cdot H_2O \)
Answer: (c) \( CaSO_4 \cdot \frac{1}{2} H_2O \)

Very Short Answer Type Questions

Question. (a) Why does bleaching powder act as bleaching agent?
(b) Write chemical equation representing the action of \( CO_2 \) present in atmosphere on bleaching powder left in open. 
Answer: (a) It is because it is oxidising agent.
(b) \( CaOCl_2 + CO_2 \rightarrow CaCO_3 + Cl_2(g) \)

Question. The pH of a salt used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation.
Answer: (i) The salt is sodium hydrogen carbonate \( (NaHCO_3) \) or sodium bicarbonate (pH = 8.4).
(ii) Manufacture of baking soda is as follows:
\( NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3 \)

Short Answer Type Questions 

Question. How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type of this salt. Name the type of hardness of water which can be removed by it. 
Answer: Washing soda is prepared from sodium carbonate by crystallisation of saturated solution of sodium carbonate.
\( Na_2CO_3 + 10H_2O(l) \rightarrow Na_2CO_3 \cdot 10H_2O(s) \)
Sodium carbonate is basic salt because it is salt of strong base \( (NaOH) \) and weak acid \( (H_2CO_3) \).
It can be used for removal of permanent hardness of water.

Question. (a) Mention the pH of aqueous solution of the following salts as 7, more than 7, less than 7.
\( NH_4Cl, NaNO_3 \)
(b) Two solutions ‘A’ and ‘B’ have pH value 3.0 and 10.5 respectively. Which of these will turn
(i) Blue litmus solution red.
(ii) Phenolphthalein from colourless to pink?
Justify you answer in each case.
Answer: (a) (i) \( NH_4Cl \) pH < 7
(ii) \( NaNO_3 \) pH = 7
(b) (i) pH = 3.0 will turn blue litmus red because it is acidic in nature.
(ii) pH = 10.5 will turn phenolphthalein colourless to pink because solution is basic in nature.

Question. (a) Write the chemical equation involved in the preparation of sodium hydroxide. Name the process.
(b) Why does bleaching powder smell strongly of chlorine and does not dissolve completely in water?
Answer: (a) \( 2NaCl(aq) + 2H_2O(l) \xrightarrow{Electrolysis} 2NaOH(aq) + H_2(g) + Cl_2(g) \)
It is called chlor-alkali process.
(b) When bleaching powder is exposed to air, it gives strong smell of chlorine because bleaching powder reacts with carbon dioxide from the atmosphere to produce calcium carbonate and chlorine.
\( CaOCl_2 + CO_2 \rightarrow CaCO_3 + Cl_2 \)
Bleaching powder is a mixture of different calcium salts which are insoluble in water.

Question. (a) For the preparation of cakes, baking powder is used. If at home your mother uses baking soda instead of baking powder, how will it affect the taste of the cake and why?
(b) How is baking soda be converted into baking powder? 
(c) What makes the cake soft and spongy? 
Answer: (a) Baking powder consists of sodium hydrogen carbonate (baking soda) and tartaric acid. If only baking soda is used in making cake, then sodium carbonate is formed on heating which will give a bitter taste to cake.
(b) Baking soda can be converted into baking powder by adding starch and tartaric acid.
(c) Sodium hydrogencarbonate gives carbon dioxide \( (CO_2) \) gas which makes the cakes soft and spongy.

Question. What is water of crystallisation? Name and give formula two salts which contain water of crystallisation. 
Answer: The water molecules present in crystalline salts are called water of crystallisation.
Hydrated copper sulphate (Blue vitriol) \( CuSO_4 \cdot 5H_2O \)
Hydrated ferrous sulphate (Green vitriol) \( FeSO_4 \cdot 7H_2O \)
Washing soda \( Na_2CO_3 \cdot 10H_2O \)

Question. White chemical compound becomes hard on mixing proper quantity of water. It is also used to maintain broken founts in fixed position. Name the chemical compound and write its chemical formula. Write the chemical equation to show what happens when water is added to this compound in proper quantity? 
Answer: The compound is Plaster of Paris. Its formula is \( CaSO_4 \cdot \frac{1}{2} H_2O \)
It changes into gypsum when proper quantity of water is added to it.
\( CaSO_4 \cdot \frac{1}{2} H_2O + \frac{3}{2} H_2O \rightarrow CaSO_4 \cdot 2H_2O \)
Plaster of Paris \( \rightarrow \) Gypsum