CBSE 10th Standard Science Subject Acids, Bases and Salts Chapter Case Study Questions With Solution 2021
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CBSE 10th Standard Science Subject Acids, Bases and Salts Case Study Questions With Solution 2021
10th Standard CBSE
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Reg.No. :
Science
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The acidic behaviour of acids is due to the presence of hydrogenil(H+)ions in them. They produce hydrogen ions in the presence of water. Water is a polar solvent and this property of water helps in weakening the bond between the ions and makes them soluble. Hence, acids and bases produce ions in aqueous solutions.
It may be noted that a dry Hel gas or a solution of hydrogen chloride in organic, nonpolar solvents like toluene or benzene do not show acidic properties. This is because hydrogen chloride does not undergo ionization in toluene.
The reason why Hel splits into H+ and CI- ions in presence of water lies in the fact that water molecules, being polar, pull the H+ and Cl - ions apart and thus, the bond in Hel is broken
(i) Identify the wrong statement.(a) Higher the hydronium ion concentration, lower is the pH value (b) Universal indicator is used to judge how strong a given acid or base is (c) As the pH value increases from 7 to 14, it represents increase in H+ ion concentration in the solution (d) Value less than 7 on the pH scale represents an acidic solution (ii) If the pH of a solution is 8, then its [H+] ion is
(a) log 10- 8 (b) 108 (c) 10- 8 (d) 8 (iii) In terms of acidic strength, which one of the following is in the correct increasing order?
(a) Water < Acetic acid < Hydrochloric acid (b) Water < Hydrochloric acid < Acetic acid (c) Acetic acid < Water < Hydrochloric acid (d) Hydrochloric acid < Water < Acetic acid (iv) Which of the following compounds does not give H+ ions in aqueous solution?
(a) H3 PO4 (b) C2H5OH (c) H2CO3 (d) CH3COOH (v) Four solutions labelled as P, Q, Rand Shave pH values 1, 9, 3 and 13 respectively.
Which of the following statements about the given solutions is incorrect?(a) Solution P has higher concentration of hydrogen ions than solution R. (b) Solution Q has lower concentration of hydroxide ions than solution S. (c) Solutions P and Q will turn red litmus solution blue. (d) Solution P is highly acidic while solution Q is weakly basic. -
A compound, X of sodium forms a white powder. It is a constituent of baking powder and is used in some antacids. When heated it gives a compound, Y which is anhydrous and absorbs water to become a hydrated salt. When this salt is kept in open air, it loses water molecules in a process called efflorescence. When dissolved in water it forms a strong base and a weak acid, Z.
(i) What is the compound, X?(a) NaHCO3 (b) Na2CO3 (c) NaOH (d) NaCl (ii) The compound, Y is
(a) NaHCO3 (b) Na2CO3 (c) Na2CO3 10H2O (d) NaCI (iii) What is the nature of the solution formed by dissolving Y in water?
(a) Alkaline (b) Acidic (c) Neutral (d) It remains insoluble (iv) Identify the compound, Z.
(a) CO2 (b) H2CO3 (c) NaOH (d) H2O (v) Sodium carbonate is a basic compound because it is a salt of a
(a) strong acid and strong base (b) weak acid and weak base (c) strong acid and weak base (d) weak acid and strong base -
Sodium chloride obtained from sea water or from lakes contains many impurities such as sulphates of sodium and magnesium along with chlorides of calcium and magnesium. The chlorides of calcium and magnesium are particularly undesirable on account of their deliquescent nature.
For its purification, common salt is dissolved in minimum quantity of water to get a saturated solution from which insoluble impurities are filtered off. Then hydrogen chloride gas is passed through the saturated solution and the crystals of pure NaCl separate out. The soluble impurities remain in the mother liquor. The crystals are filtered, washed and dried.
(i) Select the correct statement regarding salt NaCl.(a) Pure NaCI is hygroscopic in nature (b) It is soluble in alcohol (c) Pure NaCI is not hygroscopic, it shows hygroscopic nature due to impurities (d) It is a brown crystalline solid (ii) Nature of aqueous solution of common salt is
(a) acidic (b) alkaline (c) basic (d) neutral (iii) In the given series of reactions, Y and Z respectively are
2(a) NaHCO3 , NaOCl2 (b) NH4CI, Na2CO3 (c) Na2CO3 , NH4CI (d) Na2CO3, NaHCO3 (iv) Which of the following compounds is alkaline in aqueous medium?
(a) Na2CO3 (b) NaCI (c) H2CO3 (d) CuSO4 (v) Some statements regarding salt NaCI are given below
(I) It is prepared by chlor-alkali process
(II) It is a white crystalline substance
(III) It also exists in the form of rocks and is called rock salt
(IV) It is a neutral salt, pH value of NaCI is 7(a) II and III only (b) III and IV only (c) I and IV only (d) II, III and IV only -
Chemically, Plaster of Paris (POP) is calcium sulphate hemihydrate, i.e., containing half molecule of water of crystallisation. It is represented by the formula, CaSO4 ·1/2H2O. Half molecule of water of crystallisation means that one water molecule is shared by two formula units of CaSO4. Hence, we also represent its formula as (CaSO4)2·H2O. The name, plaster of Paris, was given to this compound because for the first time, it was made from gypsum which was mainly found in Paris.
(i) The difference of water molecules in gypsum and plaster of Paris is(a) 5/2 (b) 2 (c) 1/2 (d) 3/2 (ii) Plaster of Paris hardens by
(a) giving off CO2 (b) changing into CaCO3 (c) combining with water (d) giving out water (iii) Which of the following statements is incorrect?
(a) Plaster of Paris is used to ornate designs on walls and ceilings (b) On heating gypsum above 373 K, CaSO4 is obtained (c) Dead burnt plaster is CaSO4 ·2H2O (d) Setting of plaster is due to its hydration into gypsum (iv) Select the incorrect statement with respect to gypsum
(a) It is slightly soluble in water (b) It is also known as alabaster (c) On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate (d) Chemical formula of gypsum is CaSO4 ·1/2H2O (v) Plaster of Paris is obtained by
(a) adding water to calcium sulphate. (b) adding sulphuric acid to calcium hydroxide (c) heating gypsum to a very high temperature (d) heating gypsum to 100° C -
pH is quite useful to us in a number of ways in daily life. Some of its applications are:
Control of pH of the soil: Plants need a specific pH range for proper growth. The soil may be acidic, basic or neutral depending upon the relative concentration of H+ and OH-. The pH of any soil can be determined by using pH paper. If the soil is too acidic, it can be corrected by adding lime to it. If the soil is too basic, it can be corrected by adding organic manure which contains acidic materials
Regaining shine of a tarnished copper vessel by use of acids: A copper vessel gets tarnished due to formation of an oxide layer on its surface. On rubbing lemon on the vessel, the surface is cleaned and the vessel begins to shine again. This is due to the fact that copper oxide is basic in nature, which reacts with the acid (citric acid) present in lemon to form a salt (copper citrate) which is washed away with water. As a result, the layer of copper oxide is removed from the surface of the vessel and the shining surface is exposed
(i) When black copper oxide placed in a beaker is treated with dilute HCl, its colour changes to(a) white (b) dark red (c) bluish green (c) bluish green (d) no change (ii) P is an aqueous solution of acid and Q is an aqueous solution of base. When these two are diluted separately, then
(a) pH of P increases while that of Q decreases till neutralisation (b) pH of P decreases while that of Q increases till neutralisation (c) pH of both P and Q decrease (d) pH of both P and Q increase (iii) Which of the following acids is present in bee sting?
(a) Formic acid (c) Citric acid (b) Acetic acid (b) Acetic acid (d) Hydrochloric acid (iv) Sting of ant can be cured by rubbing the affected area with soap because
(a) it contains oxalic acid which neutralises the effect of formic acid (b) it contains aluminium hydroxide which neutralises the effect of formic acid (c) it contains sodium hydroxide which neutralises the effect of formic acid (d) none of these (v) The pH of soil X is 7.5 while that of soil Y is 4.5. Which of the two soils, should be treated with powdered chalk to adjust its pH?
(a) X only (b) Y only (c) Both X and Y (d) None of these
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CBSE 10th Standard Science Subject Acids, Bases and Salts Case Study Questions With Solution 2021 Answer Keys
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(i) (c): As the pH value increases from 7 to 14, it represents decrease in H+ ion concentration in the solution.
(ii) (c): pH = -logl0 [H+] = 8
logl0 [H+] =-8
[H+] = 10- 8 mol/L
(iii) (a)
(iv) (b): C2H5OH is not an ionic compound, it is a covalent compound and hence does not give H+ ions in aqueous solution.
(v) (c): (a) Lower the pH of the solution, more acidic is the solution and higher is the [H+] ions
Thus, solution P (pH = 1) has higher [H+] ions than solution R (pH = 3).
(b) Higher the pH of the solution, more basic is the solution and higher is the [OH-] ions
Thus, solution Q (pH = 9) has lower [OH-] ions than solution S (pH = l3).
(c) Solution P (pH = 1) is acidic which turns blue litmus solution red whereas solution Q (pH = 9) is basic which turns red litmus solution blue.
(d) Solution P (pH = 1) is highly acidic while solution S (pH = l3) is highly basic and solution Q (pH = 9) is weakly basic. -
(i) (a): The compound of sodium that is a constituent of baking powder and is used in antacids, is sodium hydrogen carbonate (NaHC03).
\(\text { (iii) }(\mathrm{a}): \mathrm{Na}_{2} \mathrm{CO}_{3}+2 \mathrm{H}_{2} \mathrm{O} \ \ \longrightarrow 2 \mathrm{NaOH}+ \mathrm{H}_{2} \mathrm{CO}_{3}\)
Strong base (Z)Weak acid
NaOH ionises completely to give a large amount of OH- ions whereas H2CO3 ionises partially to give a small amount ofH+ ions. Hence, the solution is overall alkaline.
(iv) (b): Z is carbonic acid, a weak acid formed when Na2CO3 is dissolved in water.
(v) (d) -
(i) (c): NaCI is insoluble in alcohol and it is a white crystalline solid. Pure NaCI is not hygroscopic in nature
(ii) (d): Aqueous solution of common salt is neutral in nature.
\(\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O} \ \ \ \longrightarrow \mathrm{NaOH} \ + \ \ \ \ \ \mathrm{HCl}\)
Strong base Strong acid
(iv) (a): When Na2CO3 (sodium carbonate) is dissolved in water then it forms alkaline aqueous solution due to the formation of NaOH which is a strong alkali.
(v) (d): Sodium hydroxide (NaOH) is prepared by chlor-alkali process. -
(i) (d): Gypsum is CaSO4 ·2H2Oand plaster of Paris is CaSO4\(\frac{1}{2}\) H2O. Difference in number of water molecules \(=\frac{3}{2}\).
(ii) (c): Plaster of Paris is hardened by combining with water.
(iii) (c): Dead burnt plaster is CaSO4 (anhydrous calcium sulphate).
(iv) (d): Gypsum: CaSO4 ·2H2O Plaster of paris: CaSO4 ·1/2H2O
(v) (d): Gypsum on heating upto lOO°C gives plaster of Paris.
\(\begin{array}{c} \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \stackrel{100^{\circ} \mathrm{C}}{\longrightarrow} \mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}+1 \frac{1}{2} \mathrm{H}_{2} \mathrm{O} { } \end{array}\)
Gypsum Plaster of Paris
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\(\text { (i) }(\mathrm{c}): \mathrm{CuO}+2 \mathrm{HCl} \longrightarrow \mathrm{CuCl}_{2}+2 \mathrm{H}_{2} \mathrm{O}\)
(Bluish green)
(ii) (a): On diluting, H+ ion concentration reduces per unit volume thus, pH increases. On the other hand, on diluting, OH- concentration also reduces, pOH increases and pH decreases. As, pOH + pH = 14. Thus, pH of Q (basic solution) decreases while that of P (acidic solution) increases on dilution
(iii) (c): Formic acid is the common name of methanoic acid, and it is present in bee sting
(iv) (c)
(v) (b): Soil Y is acidic. Hence, it should be treated with powdered chalk to reduce its acidity
