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Science Answer the questions.[Che-3M]

Acids, Bases and Salts · CBSE STD 10 (CBSE - English Medium). 63 questions.

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Answer the questions.[Che-3M]

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Question 13 Marks
Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is
  1. Neutral?
  2. Strongly alkaline?
  3. Strongly acidic?
  4. Weakly acidic?
  5. Weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
Answer
SolutionpH
Neutral (D)7
Strongly alkaline (C)11
Strongly acidic (B)1
Weakly acidic (A)4
Weakly alkaline (E)9
Arrangement of pH in the increasing order of hydrogen ion concentration is as follows:
pH (11)
C
pH (9)
E
pH (7)
D
pH (4)
A
pH (1)
B
pH in the increasing order of hydrogen ion concentration
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Question 23 Marks
Write chemical equations for what happens when:
  1. Sodium metal is added to ethanol acid.
  2. Solid sodium carbonate is added to ethanol acid.
  3. Ethanol acid reacts with a dilute solution of sodium hydroxide.
Answer

  1. $\text{2 CH}_{3}\text{COOH + 2 Na} \rightarrow \text{2 CH}_{3}\text{COONa + H}_{2}$

  2. $\text{2 CH}_{3}\text{COOH + Na}_{2}\text{CO}_{3} \rightarrow \text{2 CH}_{3}\text{COONa + H}_{2}\text{O + CO}_{2}$

  3. $\text{CH}_{3}\text{COOH + NaOH} \rightarrow \text{CH}_{3}\text{COONa + H}_{2}\text{O}$

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Question 33 Marks
Write the name and molecular formula of an organic compound having its name suffixed with 'ol' and having two carbon atoms in its molecule. Write balanced chemical equation to indicate what happens when this compound is heated with excess conc. H2SO4 and the name of main product formed. Also state the role of conc. H2SO4 in the reaction.
Answer
Molecular formula: CH3-CH2-OH and name: Ethanol.
When it is heated with an excess of conc. Sulphuric acid elimination of water molecule takes place to give ethane.
$\text{C}_2\text{H}_5\text{OH}+\text{H}_2\text{SO}_4\xrightarrow{\Delta}\text{CH}_2=\text{CH}_2+\text{H}_2\text{O}+\text{H}_2\text{SO}_4$
Role of conc. H2SO4-dehydrating agent.
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Question 43 Marks
Write the name and molecular formula of an organic compound having its name suffixed with 'ol' and having two carbon atoms in its molecule. Write balanced chemical equation to indicate what happens when this compound is heated with excess conc. H2SO4 and the name of main product formed. Also state the role of conc. H2SO4 in the reaction.
Answer
Molecular formula: CH3-CH2-OH and name: Ethanol.

When it is heated with an excess of conc. Sulphuric acid elimination of water molecule takes place to give ethane.

$\text{C}_2\text{H}_5\text{OH}+\text{H}_2\text{SO}_4\xrightarrow{\Delta}\text{CH}_2 = \text{CH}_2+\text{H}_2\text{O}+\text{H}_2\text{SO}_4$

Role of conc. H2SO4-dehydrating agent.

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Question 53 Marks
An organic compound ‘P’ is a constituent of wine. ‘P’ on reacting with acidified K2Cr2O7 forms another compound ‘Q’. When a piece of sodium is added to ‘Q’ a gas ‘R’ evolves which burns with a pop sound. Identify P, Q and R and write the chemical equations of the reactions involved.
Answer
P—Ethanol, Q—Ethanoic acid, R—Hydrogen

$\text{CH}_3\text{CH}_2\text{OH}\xrightarrow[] {\text{ }\text{ }\text{ }\text{ }\text{Acidified}\text{ }\text{K}_2\text{Cr}_2\text{O}_7\text{ }\text{ }\text{ }\text{ }}\text{CH}_3\text{COOH}$

$2\text{CH}_3\text{COOH}+\text{2Na}\xrightarrow[] {\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }}2\text{ }\text{CH}_3\text{COONa}+\text{H}_2$

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Question 63 Marks
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. List its two uses.
Answer
  1. The salt is NaHCO3.
  2. Chemical equation for salt formation:

$\text{Na}_2\text{CO}_3+\text{H}_2\text{O}+\text{CO}_2\xrightarrow{\ \ \ \ \ \ \ \ }2\text{NaHCO}_3$

  1. It is used as an antacid and in the bakery industry.
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Question 73 Marks
List three advantages each of:
  1. Exploiting resources with short term aims.
  2. Using a long term perpective in managing our natural resources.
Answer
Three advantages of exploiting resources with short term aims:
  1. Immediate benefit to few people.
  2. Progress in science and technology for development in a country.
  3. Urbanisation and Industrialisation of an area.
Three advantages of using a long time perspective:
  1. Resources will be made available for sustainable development.
  2. Provides valuable contribution to the socio-economic development.
  3. Quality of environment will be conserved.
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Question 83 Marks
List the important products of the Chlor-alkali process. Write one important use of each.
Answer
The chlor-alkali process is used in the electrolysis of NaCl. The important products formed in this process is sodium hydroxide, chlorine and hydrogen gas.
Uses of sodium hydroxide (NaOH):
  • It is used in the manufacturing of paper. 
  • It is used for making soaps and detergents. 
  • It is used for making rayon artificial textile fibres. 
Uses of chlorine (Cl):
  • It is used in the production of bleaching powder.
  • It is used in the production of hydrochloric acid (HCl).
  • It is used to make plastics (PVC), pesticides chlorofluorocarbon (CFCs), chloroform carbon tetrachloride, Paints e.t.c.
Uses of hydrogen gas:
  1. It is used as a fuel for rockets.
  2. It used to make Ammonia for fertilizers.
  3. It is used in the hydrogenation of oils to obtain vegetable ghee.
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Question 93 Marks
Based on the group valency of elements write the molecular formula of the following compounds giving justification for each:
  1. Oxide of first group elements.
  2. Halide of the elements of group thirteen.
  3. Compound formed when an element, A of group 2 combines with an element, B of group seventeen.
Answer
  1. Oxides of the first group elements have the common formula of M2O.

Example- Na2O, K2O. This is because, the first group elements have a common valency of 1, and the valency of Oxygen is 2 so, to satisfy the combining capacity of Oxygen two 1st group metals are required.

  1. Halides of group 13 elements have a common formula of MX3, where M-metal and X-halogen element. 

Example- AlCl3, BF3. This is because the valency of group 13 elements is 3 and that of halogens is 1 so, to satisfy the combining capacity of aluminum or other group 13th elements three of halogens are required in the molecular formula.

  1. The general formula for those kinds of compounds would be AB2.

Example- MgCl2, CaCl2. This is because the valency of group 2 elements is 2 and that of group 17th elements if 1 so to satisfy the combining capacity of group 2 elements two of group 17 elements are required in the molecular formula.

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Question 103 Marks
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 recrystallisation.
$\underset{\text { Sodium Carbonate }}{ Na _2 CO _3}+10 H _2 O \longrightarrow \underset{\text { Washing Soda }}{ Na _2 Ca _3 \cdot 10 H _2 O }$
Washing soda is a basic salt. It is used for removing the permanent hardness of the water.
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Question 113 Marks
Identify the acid and the base from which sodium chloride is obtained. Which type of salt is it? When is it called rock salt? How is rock salt formed?
Answer
NaCl is obtained by the reaction between NaOH and HCl.

$\text{HCl}+\text{NaOH}\xrightarrow{\ \ \ \ \ }\text{NaCl}+\text{H}_2\text{O}$

NaCl is a neutral salt. It is known as rock salt in crystalline form. Rock salt is simply crystallized salt, also known as halite. It is the result of the evaporation of ancient oceans millions of years ago. Sometimes, pressure from deep inside the Earth forces up large masses of rock salt to form salt domes.

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Question 123 Marks
Write the name and formula of one salt each which contains:
  1. Two molecules of water of crystallisation.
  2. Tive molecules of water of crystallisation.
  3. Ten molecules of water of crystallisation.
Answer
  1.  Gypsum (calcium sulphate crystals) contains two molecules of crystallisation in one formula unit and hence is written as CaSO4.2H2O. It is also called calcium sulphate dehydrate.
  2. Copper sulphate crystals contain five molecules of crystallisation in one formula unit. The chemical formula is CuSO4.5H2O (copper sulphate pent hydrate).
  3. Washing soda crystals (sodium carbonate crystals) contain 10 molecules of crystallisation in one formula unit. The chemical formula is Na2CO3.10H2O (sodium carbonate decahydrate).
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Question 133 Marks
Write the formulae of sodium chloride and sodium carbonate. Explain why an aqueous solution of sodium chloride is neutral but an aqueous solution of sodium carbonate is basic (or alkaline). Write chemical equations of the reactions involved.
Answer
Sodium chloride – NaCl.

Sodium carbonate – Na CO.

The aqueous solution of sodium chloride is neutral because it is formed from a strong acid and a strong base.

The aqueous solution of sodium carbonate is basic because it gets hydrolysed to some extent and forms sodium hydroxide which is a strong base and carbonic acid which is a weak acid.

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Question 143 Marks
Write any two natural and two synthetic indicators.
A student dropped few pieces of marble in dilute HCl contained in a test tube. The evolved gas was passed through lime water.
  1. What change would be observed in lime water?
  2. Write balanced chemical equation for the above change.
Answer
  1. Marble is chemically calcium carbonate. When dilute HCl is added to calcium carbonate, it forms calcium chloride, water and carbon dioxide.

The chemical equation for the reaction is as follows:

$\text{CaCO}_3\ +\ 2\text{HCl}\xrightarrow{\ \ \ \ \ \ \ \ \ \ }\text{CaCl}_2\ +\ \text{H}_2\text{O}\ +\ \text{CO}_2$

Carbon dioxide gas turns lime water milky due to the formation of calcium carbonate.

  1. Following is the chemical equation showing the reaction between lime water and carbon dioxide.

$\text{Ca(OH)}_2\ +\ \text{CO}_2\xrightarrow{\ \ \ \ \ \ \ \ \ \ }\text{CaCO}_3\ +\ \text{H}_2\text{O}$

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Question 153 Marks
Which gas is usually liberated when an acid reacts with a metal? How will you test for the presence of this gas?
Answer
Hydrogen gas is liberated when an acid reacts with a metal. When reaction between an acid and a metal occurs, we observe formation of gas bubbles. When these gas bubbles are passed through soap solution, gas filled soap bubbles rise into the air. When a burning candle is brought near a gas-filled soap bubble, the gas present in the soap-bubble burns with a ‘pop’ sound. Only hydrogen gas burns making a ‘pop’ sound. This shows that hydrogen gas is evolved in the process.
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Question 163 Marks
When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved, which is utilised in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.
Answer
Zinc is a metallic element. Metals react with dilute solutions of strong acids to form respective salts and hydrogen gas.

The reaction of zinc with dilute solution of strong acid like HCl forms zinc chloride (ZnCl2) and hydrogen gas is evolved.

$\text{Zn + 2HCl}\rightarrow\text{ZnCl}_2+\text{H}_2\uparrow$

Hydrogen gas is used in hydrogenation of vegetable oil. It can be tested with the help of burning splinter as it burns with a pop sound.

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Question 173 Marks
When a sodium compound X which is also used in soda-fire extinguisher is heated, gives a sodium compound Y along with water and carbon dioxide. Y on crystallisation forms compound Z. Identify X, Y and Z.
Answer
When a sodium compound X which is also used in soda-acid fire extinguisher is heated gives a sodium compound Y along with water and carbondioxide. Y on crytallisation forms a compound Z.

The compound X is NaHCO3 (sodium bicarbonate OR sodium hydrogen carbonate).

The compound Y is Na2CO3(sodium carbonate).

The compound Z is Na2CO3.10H2O (sodium carbonate decahydrate or washing soda).

$2\text{NaHCO}_3\xrightarrow{\text{heat}}\text{Na}_2\text{CO}_3+\text{H}_2\text{O}+\text{CO}_2$

$\text{Na}_2\text{CO}_3+10\text{H}_2\text{O}\rightarrow\text{Na}_2\text{CO}_3.10\text{H}_2\text{O}$

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Question 183 Marks
When a piece of limestone reacts with dilute HCl, a gas X is produced. When gas X is passed through lime water then a white precipitate Y is formed. On passing excess of gas X, the white precipitate dissolves forming a soluble compound Z.
  1. What are X, Y and Z?
  2. Write equations for the reactions which take place:
  1. When limestone reacts with dilute HCl.
  2. When gas X reacts with lime water to form white precipitate Y.
  3. When excess of gas X dissolves white precipitate Y to form a soluble compound Z.
Answer
  1. X is carbon dioxide; Y is calcium carbonate; Z is calcium hydrogen carbonate.
  1.  

  1. $\text{CaCO}_3(\text{S})+2\text{HCl(aq)}\rightarrow2\text{NaCl(aq)}+\text{H}_2\text{O(l)}+\text{CO}_2\text{g}$

  2. $\text{Ca(OH)}_2\text{(aq)}+\text{CO}_2\text{g}\rightarrow\text{CaCO}_3\text{(S)}+\text{H}_2\text{O}(\text{l})$

  3. $\text{CaCo}_3\text{(S)}+\text{H}_2\text{O}\text{l}+\text{CO}_2\text{(g)}\rightarrow\text{Ca}(\text{HCO}_3)_2\text{(aq)}$

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Question 193 Marks
What is washing soda? State two properties and two uses of washing soda.
Answer
Washing soda is:
sodium carbonate decahydrate. Properties:
  1. It is transparent crystalline solid.
  2. It is soluble in water.
Uses:
  1. It is used for removing permanent hardness of water.
  2. It is used in the manufacture of glass, soap and paper.
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Question 203 Marks
What is the effect of dilution on an acid or base?
Answer
Adding water to an acid or base will change its pH. Water is mostly water molecules so adding water to an acid or base reduces the concentration of ions in the solution.
When an acidic solution is diluted with water the concentration of H+ ions decreases and the pH of the solution increases towards 7.
To make the pH change by 1, a tenfold dilution is required.
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Question 213 Marks
What is meant by strong bases and weak bases? Classify the following into strong bases and weak bases:
NH4OH, Ca(OH)2, NaOH, KOH, Mg(OH)2
Answer
Strong base: A base which completely ionises in water and produces a large amount of hydroxide ions.

Strong bases: NaOH, KOH

Weak base: A base which is partially ionised in water and produces a small amount of hydroxide ions.

Weak bases: NH4OH, Ca(OH)2, Mg(OH)2

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Question 223 Marks
What is ‘chlor-alkali’ process and what products are formed during this process?
Answer
When electricity is passed through an aqueous solution of sodium chloride it decomposes to form sodium hydroxide. The process is called the chlor-alkali alkali process because of the products formed: chlor for chlorine and alkali for Sodium Hydroxide. Chlorine gas is given off at the anode and hydrogen gas at the cathode.

An aqueous solution of sodium chloride is called brine.

$2\text{NaCl(aq)}+2\text{H}_2\text{O(l)}\xrightarrow{\text{(electrolysis)}}2\text{NaOH(aq)}+\text{Cl}_2+\text{H}_2\text{(g)}$

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Question 233 Marks
What is baking soda? Write the chemical name of baking soda. Give the important uses of baking soda. How does baking soda differ chemically from washing soda?
Answer
Baking soda is a substance added to food for its faster cooking. Its chemical name is sodium hydrogen carbonate.
Uses:
  1. It is used as an antacid to remove acidity of stomach.
  2. It is used in fire extinguishers. Baking soda is sodium hydrogencarbonate whereas washing soda is sodium carbonate decahydrate.
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Question 243 Marks
What happens when nitric acid is added to egg shell?
Answer
When nitric acid is added to egg shell, it dissolves egg shell. Egg shell is composed of calcium carbonate which dissolves in nitric acid. The reaction between nitric acid and calcium carbonate yields calcium nitrate and carbon dioxide gas.
CaCO3(s) + 2HNO3(aq) → Ca(NO3)2(aq) + CO2(g) + H2O(l)
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Question 253 Marks
What happens when CO2 gas is passed through lime water?
Answer
When carbon dioxide is passed through lime water for a short time, it turns lime water milky due to formation of a white precipitate of calcium carbonate.

The reaction is-

$\text{Ca(OH)}_2+\text{CO}_2\rightarrow\text{CaCO}_3\downarrow+\text{H}_2\text{O}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (\text{white precipate})$

When carbon dioxide gas is passed through lime water for a considerable time ,then the white precipitate of calcium carbonate which is fomed initially as shown in the above reaction ,dissolves due to formation of a soluble salt  calcium hydrogen carbonate and the solution becomes clear again.

The reaction is-

$\text{CaCO}_3\downarrow+\text{H}_2\text{O}+\text{CO}_2\rightarrow\text{Ca(HCO}_3)_2\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {(\text{soluble in water)}}$

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Question 263 Marks
What happens when an acid reacts with a base? Explain by taking the example of hydrochloric acid and sodium hydroxide. Give equation of the chemical reaction which takes place. What is the special name of such a reaction?
Answer
When an acid reacts with a base, then a salt and water are formed. When hydrochloric acid reacts with sodium hydroxide solution, then a neutralisation reaction takes place to form sodium chloride and water.

$\text{NaOH}\text{(aq)}+\text{HCl}\text{(aq)}\rightarrow\text{NaCl}\text{(aq)}+\text{H}_2\text{O}(\text{l})$

Such a reaction is termed as neutralisation reaction.

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Question 273 Marks
What happens when an acid or a base is added to the water? Why does the beaker appear warm? Why should we always add acid or base to the water and not water to the acid or base?
Answer
When an acid or base is added to water:

  1. When we add acid to the water, acid gives H+ or H3O+ (hydronium ion) in water. For example: If we add HCl (an acid) to water, the reaction takes place is given as:

$\text{HCl}+\text{H}_2\text{O}\rightarrow\text{H}_3\text{O}^++\text{Cl}^-\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Hydronium}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{ion}$

  1. When we add base to the water, base produces OH- (hydroxide ions) in water. For example: If we add NaOH to water, the reaction takes place is given as:

$\text{NaOH}+\text{H}_2\text{O}\rightarrow\text{Na}^++\text{OH}^-\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Hydroxy ion}$

The beaker appears warm because the process of dissolving an acid or base in water is a highly exothermic one (releases energy)

We should always add acid or base to the water with constant stirring because if water is added to acid or base, the heat generated may cause the mixture to splash (a small blast) and cause harmful burns.

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Question 283 Marks
What happens when a concentrated solution of sodium chloride is electrolysed? Write the equation of the reaction involved.
Answer
When a concentrated solution of sodium chloride is electrolyzed, it forms sodium hydroxide (NaOH), chlorine gas and hydrogen gas.

Chlorine gas is formed at anode (positively charged) and hydrogen gas at cathode (negatively charged)

The reaction takes place is given as:

$2\text{NaCl}+2\text{H}_2\text{O}\rightarrow2\text{NaOH}+\text{Cl}_2+\text{H}_2$

The above reaction is called chlor-alkali process.

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Question 293 Marks
What are strong and weak acids? In the following list of acids, separate strong acids from weak acids. Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.
Answer
Acids which get completely ionized in aqueous solution are called strong acids, e.g. hydrochloric acid, nitric acid and sulphuric acid.
Acids which do not get completely ionized in aqueous solution are called weak acids, e.g. acetic acid, citric acid, and formic acid.
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Question 303 Marks
The metal salt A is blue in colour. When salt A is heated strongly over a burner, then a substance B is eliminated and a white powder C is left behind. When a few drops of a liquid D are added to powder C, it becomes blue again. What could be A, B, C and D?
Answer
Copper sulphate crystals (A) are blue and have the chemical formula CuSO4.5H2O. When copper sulphate crystals are heated strongly, they lose all the water of crystallisation (B) and form anhydrous copper sulphate (C), which is white.

$\ \ \ \ \text{A}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{C}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{B}\\\text{CuSO}_4.5\text{H}_2\text{O}\rightarrow\text{CuSO}_4+5\text{H}_2\text{O}$

Anhydrous copper sulphate turns blue on addition of a few drops of water (D) because it gets hydrated again.

$\text{CuSO}_4+5\text{H}_2\text{O}\rightarrow\text{CuSO}_4.\text{H}_2\text{O}$

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Question 313 Marks
State some of the uses of mineral acids in industry.
Answer
Uses of mineral acids in industry:
  1. Sulphuric acid is used in the manufacture of fertilizers, paints, dyes, detergents etc.
  2. Nitric acid is used for making fertilizers, explosives, dyes and plastics.
  3. Hydrochloric acid is used for removing oxide film from steel objects, in textile, food and leather industries.
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Question 323 Marks
State in brief the method of preparation of bleaching powder. Write a balanced chemical equation for the reaction involved and state the uses of bleaching powder.
Answer
Chemical formula $\rightarrow\text{CaOCl}_2$
Chemical equation - $\text{Ca(OH)}_2+\text{Cl}_2\rightarrow\text{CaOCl}_2+\text{H}_2\text{O}$
Uses:
  1. For bleaching cotton and linen in textile industry
  2. As an oxidising agent in a chemical industry. 
  3. For disinfecting water.
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Question 333 Marks
Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B and C.
Answer
Salt which is used in bakery product is baking soda or sodium hydrogen carbonate. On heating of baking soda, sodium carbonate is formed with evolution of carbon dioxide gas.

$2\text{NaHCO}_3\rightarrow\text{Na}_2\text{CO}_3+\text{H}_2\text{O + CO}_2\uparrow$

Sodium carbonate is used to remove hardness of water. Another product is carbon dioxide gas that gives lime test in which it turns lime water milky.

Thus, A = NaHCO3; B = Na2CO3 and C = CO2.

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Question 343 Marks
On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue-green.
  1. Predict the new compound formed which imparts a blue-green colour to solution.
  2. Write a balanced chemical equation of the reaction which takes place.
  3. On the basis of the above reaction, what can you say about the nature of copper oxide?
Answer
  1. Copper (II) chloride CuCl2
  2. CuO(s) + 2HCl(aq) → CuCl2(aq) + H2O(l)
  3. Copper oxide is basic in nature
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Question 353 Marks
  1. Name one antacid. How does it help to relieve indigestion in stomach?
  2. A farmer treats the soil with quicklime or calcium carbonate. What is the nature of soil? Why does the farmer treat the soil with quicklime?
Answer

  1. Milk of Magnesia: It is basic in nature. Stomach produces dil. HCI. When suffering from indigestion, more add is produced, this causes irritation. Antacid neutralises some acid and then gives relief.

  2. Soil is acidic: Farmer wants to neutralise some acid and hence adds basic substances like CaO or CaCO3 to it.

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Question 363 Marks
Name three products of the chlor-alkali process. State two uses of each product.
Answer
The three products of thee chlor-alkali process are:

Sodium hydroxide (NaOH):

Uses:

  1. It is mostly used in soaps and detergents.
  2. It is also used to make papers and artificial fibers.

Chlorine gas:

Uses:

  1. It is mostly used in medicines and in fuels.
  2. It is used with ammonia for fertilizers.

Hydrogen gas:

Uses:

  1. It is used in treatment of water in swimming pools.
  2. It is used as disinfectants and pesticides.
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Question 373 Marks
Name three products of the chlor-alkali process. State two uses of each of these products.
Answer
Uses of Sodium hydroxide:
  1. It is used for making soaps and detergents.
  2. It is used in the manufacture of paper.
Uses of chlorine:
  1. It is used in the production of bleaching powder.
  2. It is used in the production of hydrochloric acid.
Uses of hydrogen:
  1. It is used in the production of hydrochloric acid.
  2. It is used in the hydrogenation of oils.
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Question 383 Marks
Name the compound whose one formula unit is associated with 10 water molecules. How is it prepared? Give equations of related reactions. Give two uses of the compound.
Answer
The compound whose one formula unit is associated with 10 water molecules is sodium carbonate (Na2CO3.10H2O) commonly known as washing soda. It is prepared by heating baking soda and then recrystallizing the product so obtained.

The equations related to the above reaction is:

$2\text{NaHCO}_3\xrightarrow{\ \Delta\ \ \ }\text{Na}_2\text{CO}_3\ +\ \text{H}_2\text{O}\ +\ \text{CO}_2$

$\text{Na}_2\text{CO}_3\ +\ 10\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ \ \ \ }\text{Na}_2\text{CO}_3.10\text{H}_2\text{O}$

Two uses of washing soda are:

  1. It is used in glass, soap and paper industries.
  2. It is used for removing permanent hardness of water.
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Question 393 Marks
Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Answer
The gas that extinguishes a burning candle is carbon dioxide, which is formed by the action of dilute hydrochloric acid on a metal carbonate and produces effervescence. Now, since one of the compounds formed is calcium chloride, it shows that the metal compound is calcium carbonate. Thus, the metal compound A is calcium carbonate (CaCO3). Calcium carbonate reacts with dilute hydrochloric acid to form calcium chloride, carbon dioxide and water. This can be written as:

$\text{CaCo}_3+\text{HCl} \xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ } \ \text{CaCl}_{2}\ +\text{Co}_2 + \text{H}_{2}\text{O}\\ \ \ \\ {\text{Calcium}\\{\text{Carbonate}}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {\text{Calcium}\\{\text{Chloride}}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ $

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Question 403 Marks
In one of the industrial processes used for manufacture of sodium hydroxide, a gas X is formed as by product. The gas X reacts with lime water to give a compound Y which is used as a bleaching agent in chemical industry. Identify X and Y giving the chemical equation of the reactions involved.
Answer
‘X’ is chlorine gas.

$2\text{NaCl}+2\text{H}_2\text{O}\xrightarrow{\text{electricity}}2\text{NaOH}+\text{H}_2\text{(g) + Cl}_2\text{(g)}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ '\text{X}'$

$\text{Ca(OH)}_2\ +\ \text{Cl}_2\text{(g)}\ \ \rightarrow\ \ \text{CaOCl}_2\ \ \ +\ \ \ \text{H}_2\text{O}\\\text{Limewater}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ '\text{Y}'\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Bleaching powder}$

‘X’ is Cl2 gas, 'Y' is CaOCl2.

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Question 413 Marks
Identify the compound of calcium which is yellowish white powder and is used for disinfecting drinking water. Write its chemical name and formula. How is it manufactured? Write the chemical equation for the reaction involved. Also, list two other uses of the compound.
Answer
It is bleaching powder.
Chemical name-Calcium oxychloride
Formula- CaOCl₂
It is produced by action of chlorine on dry slaked lime.
Equation- $\text{Ca(OH}_2)\ +\ \text{Cl}_2 \xrightarrow{\ \ \ \ \ \ \ \ \ }\text{CaOCl}_2\ +\ \text{H}_2\text{O}$
Used for washing some clothes.
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Question 423 Marks
Hydrochloric acid reacts with a metal X to form a gas Y which bums with a ‘pop’ sound. Sodium hydroxide solution also reacts with the same metal X (on heating) to form the same gas Y.
  1. Name X and Y.
  2. Write the chemical equation of the reaction of metal X with.
  1. Hydrochloric acid, and
  2. Sodium hydroxide solution.
Answer
  1. X is the metal zinc (Zn) and Y is hydrogen gas. Zinc reacts with hydrochloric acid and forms zinc chloride salt with the liberation of hydrogen gas (Y), which burns with a 'pop' sound. Zinc displaces hydrogen from hydrochloric acid.
    Hence, X is zinc and Y is hydrogen.
  2. The chemical equation is as follows.
  1. Zn + 2HCl →ZnCl2 + H2 ↑
  2. 2NaOH + Zn →Na2ZnO2 + H2
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Question 433 Marks
How will you get relief if an insect bites?
Answer
To treat an insect bite or sting:
  1. Remove the sting, tick or hairs if still in the skin.
  2. Wash the affected area with soap and water.
  3. Apply a cold compress (such as a flannel or cloth cooled with cold water) or an ice pack to any swelling for at least 10 minutes. Raise or elevate the affected area if possible, as this can help reduce swelling.
  4. Apply a mixture of baking soda and water or calamine lotion for itch.
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Question 443 Marks
How toothpaste prevents tooth decay?
Answer
Tooth paste contains fluoride salt which is the active ingredient in preventing tooth decay. The acid released by the bacteria in our mouth react with the basic enamel of our teeth. But when we use tooth paste, the negatively charged fluoride ions are released. These fluoride ions react with the acids in the mouth and prevent the decay of enamel (tooth). It also reduces the loss of minerals from the tooth and promotes repair of early.
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Question 453 Marks
How H3O+ ion is formed in water solution?
Answer
Hydronium ion is a water molecule with an extra hydrogen ion attached to it. $(\text{H}_2\text{O}+\text{H}^+\rightarrow\text{H}_3\text{O}^+)$ It usually used to determine the acidity of a chemical compound. When a compound is put into water solution, the more the hydronium ion is produced, the higher the acidity is.

EX: $\text{HCl(aq)}+\text{H}_2\text{O(l)}\text{Cl}^-+\text{H}_3\text{O}^+$

Hydronium ion is H3O+. It is formed by the combination of hydrogen ion H+ given by an acid and water molecule.

$\text{H}^+\text{H}_2\text{O}\rightarrow\text{H}_3\text{O}^+$

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Question 463 Marks
Here are some results of solutions tested with universal indicator paper:
  1. Sulphuric acid: Red
  2. Metal polish: Dark blue
  3. Washing-up liquid:
  4. Yellow Milk of magnesia:
  5. Light blue Oven cleaner:
  6. Purple Car battery acid: Pink
Arrange the solutions in order of their increasing pH values (starting with the one with the lowest pH).
Answer
 Sulphuric acid < car battery acid < washing up liquid < milk of magnesia < metal polish < oven Cleaner since:
  1. Red: pH = 1
  2. Pink: pH = 3-4
  3. Yellow: pH = 5-6
  4. Light blue: pH = 9
  5. Dark blue: pH = 10
  6. Purple: pH = 11
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Question 473 Marks
Give two important uses of washing soda and baking soda.
Answer
Washing soda:

  1. It is often used as an electrolyte.
  2. Domestically it is used as a water softener during laundry.

Baking soda:

  1. It is used to test garden soil for acidity. If it develops bubbles, the soil is too acidic.
  2. Washing a car with it can remove dead bug bodies without damaging the paint.
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Question 483 Marks
Give reason why solution of sulphuric acid conduct electricity whereas, alcohol does not.
Answer
When acid is dissolved in water it dissociates into ions thus it conducts electricity due to presence of ions.
But alcohol being a very weak acid does not dissociate into ions and so it does not conducts electricity.
Glucose when dissolved in water does not produces ions so it does not conducts electricity.
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Question 493 Marks
Give reasons:
Use of a mild base like baking soda provides relief on the area stung by honeybee.
Answer
When a honeybee stings a person, this means it releases an acidic liquid (formic acid) into the body. This causes too much pain and irritation. As we know that baking soda (sodium hydrogen carbonate NaHCO3) is a mild non-corrosive base. It can be used to neutralize an acid.
Hence, when it is applied to the stung area, it reduces the effect of acid by neutralizing the excess acid. As a result, the pain and irritation is reduced.
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Question 503 Marks
Give reasons:
Baking powder is added to make the cakes spongy and soft.
Answer
Baking soda is converted into baking powder for cooking purpose by adding appropriate amount of tartaric acid to it. This neutralizes sodium carbonate and hence prevents the food item from tasting bitter. 
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