CBSE Class 10 Science Acids Bases and Salts VBQs Set 02

PRACTICE QUESTIONS

Question. Which of the following salts does not contain water of crystallisation?
(a) Blue vitriol
(b) Baking soda
(c) Gypsum
(d) Washing soda
Answer: (b) Baking soda

Question. Select the washing soda from the following: 
(a) \( NaHCO_3 \)
(b) \( Na_2CO_3 \cdot 5H_2O \)
(c) \( Na_2CO_3 \cdot 10H_2O \)
(d) \( NaOH \)
Answer: (c) \( Na_2CO_3 \cdot 10H_2O \)

Question. Few drops of aqueous solution \( NH_4Cl \) are put on universal indicator paper. The paper turns pink. Study the following table and choose the correct option. \( NH_4Cl \) is salt of
(a) Nature: Acidic | Acid and Base: Weak acid and strong base | Range of pH: < 7
(b) Nature: Basic | Acid and Base: Weak acid and strong base | Range of pH: > 7
(c) Nature: Acidic | Acid and Base: Strong acid and weak base | Range of pH: < 7
(d) Nature: Basic | Acid and Base: Strong acid and strong base | Range of pH: 7
Answer: (c) Nature: Acidic | Acid and Base: Strong acid and weak base | Range of pH: < 7

Question. When dilute hydrochloric acid reacts with sodium hydrogen carbonate, then ____________, carbon dioxide and water are formed.
(a) sodium chloride
(b) calcium chloride
(c) sodium carbonate
(d) calcium carbonate
Answer: (a) sodium chloride

Question. Which of the following salts does not contain water of crystallisation?
(a) Alum
(b) Bleaching powder
(c) Gypsum
(d) Washing soda
Answer: (b) Bleaching powder

Question. List four uses of sodium bicarbonate.
Answer: (i) Used as an antacid to treat acidity.
(ii) Used in baking powder for making soft cakes.
(iii) Used in soda-acid fire extinguishers.
(iv) Used as a mild disinfectant.

Question. 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: (a) Calcium sulphate hemihydrate, \( CaSO_4 \cdot \frac{1}{2} H_2O \).
(b) \( CaSO_4 \cdot \frac{1}{2} H_2O + \frac{3}{2} H_2O \rightarrow CaSO_4 \cdot 2H_2O \)

Question. A gas ‘X’ reacts with lime water and forms a compound ‘Y’ which is used as a bleaching agent in the chemical industry. Identify ‘X’ and ‘Y’. Give the chemical equation of the reactions involved.
Answer: X is Chlorine \( (Cl_2) \), Y is Bleaching Powder \( (CaOCl_2) \).
\( Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O \)

Question. A compound which is prepared from gypsum has the property of hardening when mixed with proper quantity of water.
(a) Identify the compound.
(b) Write the chemical equation for its preparation.
(c) Mention one important use of this compound.
Answer: (a) Plaster of Paris.
(b) \( CaSO_4 \cdot 2H_2O \xrightarrow{373K} CaSO_4 \cdot \frac{1}{2} H_2O + \frac{3}{2} H_2O \).
(c) Used for supporting fractured bones in the right position.

Question. List the important products of the Chlor-alkali process. Write one important use of each. 
Answer: (i) Sodium hydroxide: Used in making soaps and detergents.
(ii) Chlorine: Used for water treatment (as a disinfectant).
(iii) Hydrogen: Used as fuel or in making margarine.

Question. (a) Crystals of a substance changed their color on heating in a closed test tube but regained it after some time when they were allowed to cool down. Name the substance and write its formula. Explain the phenomenon.
(b) How is sodium carbonate prepared? Give two uses of the compound. 
Answer: (a) Hydrated copper sulphate, \( CuSO_4 \cdot 5H_2O \). On heating, it loses water of crystallisation and turns white. On cooling, it absorbs moisture from air and regains its blue color.
(b) It is prepared by heating sodium hydrogen carbonate (Solvay process intermediate). Uses: (i) Manufacture of glass. (ii) Cleaning agent for domestic purposes.

INTEGRATED (MIXED) QUESTIONS

Question. Answer the following questions:
(a) State the colour of phenolphthalein in soap solution.
(b) Name the by-product of chlor-alkali process which is used for the manufacture of bleaching powder.
(c) Name one indicator which specifies the various levels of \( H^+ \) ion concentration. 
Answer: (a) Pink (since soap is basic).
(b) Chlorine gas.
(c) Universal indicator.

Question. (a) Which property do acids and bases have in common? Explain with the help of example.
(b) A compound which is prepared from Gypsum has the property of hardening when mixed with water. Identify the compound and write its formula. How is compound prepared? Describe in form of chemical equation only. 
Answer: (a) Both acids and bases conduct electricity in aqueous solutions because they produce ions.
(b) Plaster of Paris, \( CaSO_4 \cdot \frac{1}{2} H_2O \). Preparation:
\( CaSO_4 \cdot 2H_2O \xrightarrow{373K} CaSO_4 \cdot \frac{1}{2} H_2O + 1 \frac{1}{2} H_2O \)

Question. Consider the following salts
(i) \( YCl \)
(ii) \( NH_4X \) and (iii) \( ZCO_3 \).
(a) What would be pH of salt solution of \( YCl \) if Y is \( Na \)?
(b) If salt \( NH_4X \), X is nitrate, then the solution will give what colour with universal indicator and why?
(c) What will be change in colour in blue litmus solution if \( ZCO_3 \) is added to it and ‘Z’ is potassium. 
Answer: (a) pH will be 7 because \( NaCl \) is a neutral salt.
(b) The solution will turn pink/red because \( NH_4NO_3 \) is a salt of a strong acid and a weak base, making it acidic.
(c) No change in colour because \( K_2CO_3 \) is a basic salt, and bases do not change blue litmus red.

Question. (a) Given below are the pH values of four different liquids: 7.0, 14.0, 4.0, 2.0. Which of these could be that of
(i) lemon juice,
(ii) distilled water,
(iii) 1 M sodium hydroxide solution,
(iv) tomato juice? 
(b) (i) What is the role of toothpastes in preventing cavities? 
(ii) How washing soda is prepared from baking soda? 
Answer: (a) (i) lemon juice: 2.0; (ii) distilled water: 7.0; (iii) 1 M sodium hydroxide: 14.0; (iv) tomato juice: 4.0.
(b) (i) Toothpastes are basic and neutralize the acid produced by bacteria in the mouth.
(ii) By heating baking soda to get sodium carbonate, followed by recrystallization.
\( 2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2 \)
\( Na_2CO_3 + 10H_2O \rightarrow Na_2CO_3 \cdot 10H_2O \)

Question. (a) What is chlor – alkali process? Give chemical equation of the reaction involved.
(b) Write any two uses of bleaching powder.
(c) Write equations to show the reaction between:
(i) acid and bases
(ii) acid and hydrogen carbonates 
Answer: (a) It is the electrolysis of brine solution to produce \( NaOH, Cl_2 \) and \( H_2 \).
\( 2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g) \)
(b) (i) Bleaching cotton in textile industry. (ii) Disinfecting drinking water.
(c) (i) \( HCl + NaOH \rightarrow NaCl + H_2O \)
(ii) \( HCl + NaHCO_3 \rightarrow NaCl + H_2O + CO_2 \)

Question. (a) Identify the acid and the base whose combination forms the common salt that you use in your food. Write its formula and chemical name of this salt. Name the source from where it is obtained.
(b) What is rock salt? Mention its colour and the reason due to which it has this colour.
(c) What happens when electricity is passed through brine? Write the chemical equation for it. 
Answer: (a) Acid: Hydrochloric acid (\( HCl \)); Base: Sodium hydroxide (\( NaOH \)). Formula: \( NaCl \); Chemical Name: Sodium Chloride. Source: Sea water.
(b) Large crystals of sodium chloride found in nature. It is often brown in colour due to impurities.
(c) It decomposes to form sodium hydroxide, chlorine gas, and hydrogen gas.
\( 2NaCl(aq) + 2H_2O(l) \xrightarrow{electricity} 2NaOH(aq) + Cl_2(g) + H_2(g) \)

ASSERTION AND REASON QUESTIONS

Direction: In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: Sodium hydrogen carbonate is used as an ingredient in antacids. 
Reason: \( NaHCO_3 \) is a mild non-corrosive basic salt.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Carbonic acid is weak acid
Reason: It ionised completely in aqueous solution.
Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: Copper sulphate is acidic salt.
Reason: It is a salt of weak base \( [Cu(OH)_2] \) and strong acid \( (H_2SO_4) \).
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Ammonium hydroxide is weak base.
Reason: Phenolphthalein becomes pink in \( NH_4OH \).
Answer: (b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Bleaching power liberate chlorine when kept in atmosphere.
Reason: \( CaOCl_2 \) reacts with \( CO_2 \) present in atmosphere to form \( CaCO_3 \) and chlorine gas.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Universal indicator gives green colour with distilled water.
Reason: pH of distilled water is 7 and it is neutral and universal indicator gives green colour with neutral solution.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: The aqueous solutions of glucose and alcohol do not show acidic character.
Reason: Aqueous solutions of glucose and alcohol do not give \( H^+ \) ions.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: After white washing the walls, a shiny white finish on walls is obtained after two or three days.
Reason: Calcium oxide reacts with carbon dioxide to form Calcium hydrogen carbonate which gives shiny white finish. 
Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: Ferrous sulphate is acidic salt.
Reason: It is a salt of weak base \( Fe(OH)_2 \) and strong acid \( (H_2SO_4) \).
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Salts are formed by reaction of acid and base.
Reason: Salts may be acidic, basic or neutral.
Answer: (b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Baking powder is used for making cake instead of baking soda.
Reason: Baking powder contains tartaric acid which reacts with \( Na_2CO_3 \) and remove bitter taste.
Answer: (a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Question. Assertion: Pure water is neither acidic nor basic.
Reason: The pH of solution is inversely proportional to conc. of \( [H_3O]^+ \).
Answer: (b) Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: A gas is produced when conc. \( H_2SO_4 \) is added to \( NaCl \) in a test tube. The gas is passed over dry blue litmus paper, it changed to red.
Reason: Blue colour of dry litmus paper does not change to red.
Answer: (d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: A white coloured powder is used by doctors for supporting fractured bone. It is plaster of paris.
Reason: It is gypsum.
Answer: (c) Assertion is true but the Reason is false.

Question. Assertion: It is advised while diluting an acid, one should add water to acid, not acid to water keeping the solution continuously stirred.
Reason: The process of dissolving an acid into water is highly exothermic.
Answer: (d) The statement of the Assertion is false but the Reason is true.

CASE-BASED QUESTIONS

Read the given passage and answer the questions based on passage and related studied concepts.
Taj Mahal, the great wonder of the world, is made of white marble which is composed of calcium carbonate. About 60 years ago it was discovered that this monument is being eaten away by acid rain. The Archeological survey of India, that looks after this building of historical importance is of the opinion that the atmospheric pollution due to vehicular traffic and industries, mainly Mathura Refinery may be a major cause of acid rain in and around the monument. Normal rain is slightly acidic because it absorbs some \( CO_2 \) from the atmospheric air. Acid rain is more acidic than normal rain because it also has absorbed oxides of nitrogen and sulphur. 

Question. (a) What is the formula of calcium carbonate?
(b) Name two gases which contribute to acid rain.
(c) What happens when acid rain falls on Taj Mahal? Write balanced chemical equation.
Or
(c) Name the acids and bases which will form calcium carbonate. What is nature of salt? Give reason.
Answer: (a) \( CaCO_3 \).
(b) Nitrogen dioxide \( (NO_2) \) and Sulphur dioxide \( (SO_2) \).
(c) The marble reacts with acid rain and gets corroded (marble cancer).
\( CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2 \)
Or
(c) Acid: Carbonic acid \( (H_2CO_3) \); Base: Calcium hydroxide \( (Ca(OH)_2) \). Nature: Basic. It is a salt of a strong base and a weak acid.

Salts are formed by reactions of acids and bases, strong acids react with strong bases to form neutral salt. Weak acids react with strong bases to form basic salts whose aqueous solution turned red litmus blue, phenolphthalein pink and universal indicator blue. Acidic salts are formed by strong acids and weak bases. \( Na_2CO_3 \) and \( NaHCO_3 \) are salts of \( NaOH \) (strong base) and \( H_2CO_3 \) (Carbonic acid) weak acid and are basic in nature. Electrolysis of brine solution gives caustic soda \( (NaOH) \), \( H_2 \) gas and \( Cl_2 \). Bleaching powder \( (CaOCl_2) \) is prepared when slaked lime reacts with dry chlorine gas used as disinfectant, washing soda is used to remove permanent hardness of water. Crystalline salts are hydrated and lose water of crystallisation on heating, may change colour and become amorphous (powdery). Gypsum on heating at 373K gives Plaster of Paris, used in making chalk, plastering fractured bones. \( NaHCO_3 \) is baking soda used in making crisp pakora and as antacid.

Question. (a) What is formula of plaster of paris?
(b) What is composition of baking powder?
(c) What happens when milk of magnesia reacts with sulphuric acid? Write balanced chemical equation.
Or
(c) (i) Name an indicator used by visually impaired children.
(ii) Give one use of bleaching powder.
Answer: (a) \( CaSO_4 \cdot \frac{1}{2} H_2O \).
(b) It is a mixture of baking soda \( (NaHCO_3) \) and a mild edible acid like tartaric acid.
(c) It undergoes neutralization to form magnesium sulphate and water.
\( Mg(OH)_2 + H_2SO_4 \rightarrow MgSO_4 + 2H_2O \)
Or
(c) (i) Vanilla essence or Onion (olfactory indicators). (ii) Used as a disinfectant for water.

The sour and bitter taste of food is due to acids and bases, respectively present in them. If some person is suffering from a problem of acidity after overeating, we give baking soda solution (ENO) to the person to give relief. Vinegar contains acetic acid, sour milk (curd) contains lactic acid, lemon contains citric acid where as nettle sting contains methanoic acid. Bitter gourd, cucumber, fenugreek are bitter in taste due to presence of bases in them.

Question. (a) What is nature of bitter gourd juice?
(b) It soil is acidic in nature, which chemical is added to make it neutral?
(c) What happens when ammonium sulphate is warmed with aq. \( NaOH \)? What will be the nature of gas evolved and effect on litmus solution?
Or
(c) Identify nature of A, B, C and D based on Universal Indicator colour:
A: Blue | B: Green | C: Red | D: Violet
Answer: (a) Basic.
(b) Slaked lime or quick lime.
(c) Ammonia gas is evolved. It is basic in nature and turns red litmus blue.
Or
(c) A: Basic, B: Neutral, C: Strongly acidic, D: Strongly basic.

Lime is an alkaline substance. The figure shows some of the properties of a calcium compound ‘X’. The letters are not chemical symbols of substances. Answer the questions that follow:
[Flowchart: A colourless compound 'X' \( \xrightarrow{heat} \) White solid 'Y' + Gas 'P'. Gas 'P' mixed with lime water turns it milky. White solid 'Y' dissolves in water to form Colourless aqueous solution 'Z'. 'Z' turns universal indicator blue.]

Question. (a) Name an acid which can liberate ‘P’ from ‘X’.
(b) Identify ‘X’ and ‘Y’.
(c) Write chemical reaction from ‘X’ to ‘Y’ and identify ‘P’.
Or
(c) Identify ‘Z’ and write equation between ‘Z’ and ‘P’.
Answer: (a) Hydrochloric acid (\( HCl \)).
(b) X is Calcium Carbonate \( (CaCO_3) \); Y is Calcium Oxide \( (CaO) \).
(c) \( CaCO_3 \xrightarrow{\Delta} CaO + CO_2 \). P is Carbon dioxide.
Or
(c) Z is Calcium hydroxide \( [Ca(OH)_2] \). Reaction: \( Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \).

Mineral acids are strong acids as compared to organic acids. Mineral acids are \( HCl, H_2SO_4, HNO_3 \) which are obtained from minerals such as chlorides, sulphates and nitrates. Organic acids are present in living organisms. Strong acids are completely ionised in aqueous solution and their pH is close to 2. Weak acids do not ionise completely, their pH is close to 4. Acids combine with bases to form salts, which may be acidic, basic or neutral depending upon strength of acid and base.

Question. (a) Name on organic acid.
(b) Give two examples of weak acids.
(c) What is nature of gastric juice secreted in our stomach? What is its pH?
Or
(c) Name one antacid. Give its pH in aqueous solution.
Answer: (a) Citric acid.
(b) Acetic acid and Carbonic acid.
(c) Acidic. pH is about 1.2.
Or
(c) Milk of Magnesia. pH is about 10.5.

Crystalline salts have water of crystallisation. The number of water molecules associated with crystals depends upon size of cation. The colour and physical state may be different for crystalline and amorphous salt. Crystalline salts have well defined geometrical shape, sharp melting point. Amorphous compounds do not have well defined shape.

Question. (a) What is colour of hydrated copper sulphate?
(b) What is formula of washing soda?
(c) What happens when hydrated copper sulphate is heated? Write chemical equation.
Or
(c) What happens when water is added to anhydrous copper sulphate? Write chemical equation involved.
Answer: (a) Blue.
(b) \( Na_2CO_3 \cdot 10H_2O \).
(c) It loses water of crystallisation and becomes white.
\( CuSO_4 \cdot 5H_2O \xrightarrow{\Delta} CuSO_4 + 5H_2O \)
Or
(c) It regains its blue colour.
\( CuSO_4 + 5H_2O \rightarrow CuSO_4 \cdot 5H_2O \)

The teacher was conducting practicals in laboratory divided the students in three groups and gave them various solutions to find their pH and classify them into acidic, basic and neutral solutions.
Group A: Lemon juice, vinegar, colourless aerated drink.
Group B: Tomato juice, coffee, ginger juice.
Group C: Sodium hydroxide, sodium chloride lime water.

Question. (a) For the solution provided, which group is/are likely to have pH value (i) < 7 (ii) > 7.
(b) List two ways of determining pH of a solution.
(c) Explain, why the sour substances such as lemon juice are effective in cleaning the tarnished copper vessels.
Or
(c) “pH has great importance in our daily life.” Justify this statement giving two examples. 
Answer: (a) (i) Groups A and B (ii) Group C (specifically NaOH and lime water).
(b) Using pH paper and using a pH meter.
(c) Copper vessels get tarnished due to formation of basic copper carbonate layer. The acid in lemon juice reacts with this layer and dissolves it.
Or
(c) (i) pH of soil for plant growth. (ii) pH in our digestive system.

Question. 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: Dip red litmus paper in all the three test tubes. The one which changes its colour to blue contains basic solution. Now dip this blue litmus paper to each of the remaining two test tubes. The one which changes blue litmus back to red is acidic. The one which has no effect on either is distilled water.