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Science [3 Mark Questions]

Acids, Bases and Salts · MP Board (MPBSE) STD 10 (Madhya Pradesh - English Medium). 63 questions.

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[3 Mark Questions]

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Question 13 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 23 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. $H _2 SO _4$ and the name of main product formed. Also state the role of conc. $H _2 SO _4$ in the reaction.
Answer
Molecular formula: $CH _3- CH _2- OH$ and name: Ethanol. When it is heated with an excess of conc. Sulphuric acid elimination of water molecule takes place to give ethane. $C _2 H _5 OH + H _2 SO _4 \xrightarrow{\Delta} CH _2= CH _2+ H _2 O + H _2 SO _4$
Role of conc. $H _2 SO _4$-dehydrating agent.
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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. $H _2 SO _4$ and the name of main product formed. Also state the role of conc. $H _2 SO _4$ in the reaction.
Answer
Molecular formula: $CH _3- CH _2- OH$ and name: Ethanol. When it is heated with an excess of conc. Sulphuric acid elimination of water molecule takes place to give ethane. $C _2 H _5 OH + H _2 SO _4 \xrightarrow{\Delta} CH _2= CH _2+ H _2 O + H _2 SO _4$ Role of conc. $H _2 SO _4$-dehydrating agent.
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Question 43 Marks
An organic compound ' P ' is a constituent of wine. ' P ' on reacting with acidified $K _2 Cr _2 O _7$ 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 53 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 $NaHCO _3$.
  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 63 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 73 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 83 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
i. Oxides of the first group elements have the common formula of $M _2 O$.

Example- $Na _2 O , K _2 O$. 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. ii. Halides of group 13 elements have a common formula of $MX _3$, where M -metal and X -halogen element.

    Example- $AlCl _3, BF _3$. 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. iii. The general formula for those kinds of compounds would be $A B_2$.

    Example- $MgCl _2, CaCl _2$. This is because the valency of group 2 elements is 2 and that of group 17 th 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 93 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.$\ \ \ \ \ \text{Na}_2\text{CO}_3\ \ \ \ +\ \ \ \ \ 10\text{H}_2\text{O}\ \ \ \xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ }\text{Na}_2\text{Ca}_3.10\text{H}_2\text{O}\\\text{Sodium Carbonate}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Washing Soda}$
Washing soda is a basic salt. It is used for removing the permanent hardness of the water.
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Question 103 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 113 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
a. Gypsum (calcium sulphate crystals) contains two molecules of crystallisation in one formula unit and hence is written as $CaSO _4 \cdot 2 H _2 O$. It is also called calcium sulphate dehydrate.
b. Copper sulphate crystals contain five molecules of crystallisation in one formula unit. The chemical formula is $CuSO _4 \cdot 5 H _2 O$ (copper sulphate pent hydrate).
c. Washing soda crystals (sodium carbonate crystals) contain 10 molecules of crystallisation in one formula unit. The chemical formula is $Na _2 CO _3 \cdot 10 H _2 O$ (sodium carbonate decahydrate).
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Question 123 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 133 Marks
Among sulphurous acid and sulphuric acid, which is stronger and why?
Answer
 Among Sulphurous acid $\left( H _2 SO _3\right)$ and Sulphuric acid, Sulphuric acid $\left( H _2 SO _4\right)$ is stronger because it dissociates into its constituent ions in aqueous solution completely. when sulphuric acid dissociates, it gives more number of $H ^{+}$ions i.e. 2 whereas on dissociation, sulphurous acid gives less number of $H ^{+}$ions i.e. 1.
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Question 143 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 153 Marks
A white shirt has a yellow stain of curry. When soap is rubbed on this shirt during washing, the yellow stain turns reddish-brown. On rinsing the shirt with plenty of water, the reddish-brown stain turns yellow again.
  1. Name the natural indicator present in curry stain.
  2. Explain the changes in colour of this indicator which take place during washing and rinsing the shirt.
  3. What is the nature of soap (acidic/ basic) as shown by the indicator present in curry stain?
Answer
  1. Turmeric.
  2. The yellow stain of curry turns reddish-brown when soap is scrubbed on it because of the fact that soap solution is basic in nature which changes the colour of turmeric in the curry stain to red-brown. This stain turns yellow again when the cloth is rinsed with water because then the basic soap gets removed with water.
  3. Basic.
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Question 163 Marks
Explain why is hydrochloric acid is called, a strong acid and acetic acid, a weak acid? How can it be verified?
Answer
A chemical compound is regarded as strong acid when it gives out maximum $H ^{+}$ions into the solution. HCl is considered as a very strong acid in aqueous media as it completely dissociates into the solution giving $H ^{+}$ions or increasing the concentration of $H ^{+}$ions. $HCl \rightarrow H ^{+} Cl ^{-}$
Acetic acid is a weak acid as it does not completely dissociates into the aqueous solution. The dissociation of acetic acid into acetate ion and $H ^{+}$ion is an equillibrium reaction where concentration of $H ^{+}$ion into the solution is not much increased and the solution is feebly acidic. $CH _3 COOH \leftrightarrow CH _3 COO ^{-}+ H ^{+}$
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Question 173 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 183 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 193 Marks
A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound is also a by–product of chloralkali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide? Write a balanced chemical equation for one such solution.
Answer
‘B’ is NaOH. It absorbs moisture from atmosphere because it is hygroscopic in nature. It is obtained by product of chlor-alkali process.$2\text{NaCl}+2\text{H}_2\text{O}\rightarrow2\text{NaOH}+\text{Cl}_2+\text{H}_2\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ '\text{B}'$
$2\text{NaOH}+\text{CO}_2\rightarrow\text{Na}_2\text{CO}_3+\text{H}_2\text{O}\\ \ \ \ '\text{B}'$
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Question 203 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 213 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 223 Marks
Give one example each of a salt which gives an aqueous solution having:
  1. pH less than 7
  2. pH equal to 7
  3. pH more than 7
Answer
a. Ammonium chloride, $NH _4 Cl$
b. Sodium chloride, NaCl
c. Sodium carbonate, $Na _2 CO _3$​​​​​​​
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Question 233 Marks
A sulphate salt of Group 2 element of the Periodic Table is a white, soft substance, which can be moulded into different shapes by making its dough. When this compound is left in open for some time, it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt and why does it show such a behaviour? Give the reaction involved.
Answer
Calcium sulphate is a white and soft substance. It can be molded into different shapes by making its dough. Calcium is a group 2 element. Calcium sulphate is commonly known as Plaster of Paris. When Plaster of Paris is left in open for some time, it becomes a solid mass and cannot be used for molding purposes. Plaster of Paris has half molecule of water of crystallization. When it is left in open for some time, the number of molecules of water of crystallization in it becomes 2 and the substance is then called gypsum.$\text{CaSO}_4.\frac{1}{2}\text{H}_2\text{O}+1\frac{1}{2}\text{H}_2\text{O}\rightarrow\text{CaSO}_4.2\text{H}_2\text{O}$
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Question 243 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 253 Marks
What is meant by strong bases and weak bases? Classify the following into strong bases and weak bases: $NH _4 OH , Ca ( OH )_2, NaOH , KOH , Mg ( OH )_2$
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: $NH _4 OH , Ca ( OH )_2, Mg ( OH )_2$
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Question 263 Marks
Explain the following chemical properties of acids with the help of balanced chemical equations only.
  1. When an acid reacts with a metal carbonate.
  2. When an acid reacts with a metal bicarbonate.
  3. When an acid reacts with a metal oxide.
Answer
  1. $\text{Zn}+\text{H}_2\text{SO}_4\xrightarrow{\ \ \ \ \ \ \ \ \ }\text{ZnSO}_4+\text{H}_2$
  2. $\text{HCl }+\text{ NaHCO}_3\xrightarrow{\ \ \ \ \ \ \ \ \ \ }\text{NaCl}\ +\ \text{H}_2\text{O}\ +\ \text{CO}_2$
  3. $\text{HCl}\ +\ \text{NaOH}\xrightarrow{\ \ \ \ \ \ \ \ }\text{NaCl}\ +\ \text{H}_2\text{O}$
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Question 273 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 283 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 293 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
i. 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.
ii. Soil is acidic: Farmer wants to neutralise some acid and hence adds basic substances like CaO or $CaCO _3$ to it.
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Question 303 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 313 Marks
A compound which is prepared from gypsum has the property of hardening when mixed with proper quantity of water.
  1. Identify the compound.
  2. Write the chemical equation for its preparation.
  3. Mention one important use of this compound.
Answer
  1. The name of the compound is Plaster of Paris.
  2. Its chemical formula is $\text{CaSO}_4.\frac{1}{2}\text{H}_2\text{O}$
Equation:
$\text{CaSO}_4.2\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ \ \ \ }\text{CaSO}_4.\frac{1}{2}\text{H}_2\text{O}\ +\ 1\frac{1}{2}\text{H}_2\text{O}$
  1. It is used in the hospitals mainly as plaster for supporting fractured bones in the right position.
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Question 323 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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Question 333 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 $\left( Na _2 CO _3 \cdot 10 H _2 O \right)$ 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 343 Marks
For making cake, baking powder is taken. If at home your mother uses baking soda instead of baking powder in cake,
  1. How will it affect the taste of the cake and why?
  2. How can baking soda be converted into baking powder?
  3. What is the role of tartaric acid added to baking soda?
Answer
  1. Baking soda is sodium hydrogen carbonate which decomposes to sodium carbonate, water and carbon dioxide on heating. Baking powder is a mixture of sodium hydrogen carbonate with tartaric acid which readily reacts with sodium carbonate and neutralizes it. Therefore use of baking soda will give a bitter taste to cake due to presence of sodium carbonate.
  2. Baking powder is formed by addition of tartaric acid to baking soda.
  3. Presence of tartaric acid in baking powder neutralizes the effect of sodium carbonate formed during decomposition of baking soda.
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Question 353 Marks
A compound X which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water.
  1. Identify the compound X,
  2. Write the chemical equation for its preparation.
  3. For what purpose is it used in hospitals?
Answer
  1. Compound X is plaster of Paris, or calcium sulphate half hydrate $(\text{CaSO}_4.\frac{1}{2}\text{H}_2\text{O})$
  2. $\text{CuSO}_4.2\text{H}_2\text{O}\rightarrow\text{CaSO}_4.\frac{1}{2}\text{H}_2\text{O}+\frac{3}{2}\text{H}_2\text{O}$
  3. Plaster of Paris is used in hospitals for setting fractured bones in the right position to ensure correct healing. Casts made of plaster of Paris help keep the fractured bone straight.
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Question 363 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 373 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.
$CaCO _3(s)+2 HNO _3( aq ) \rightarrow Ca \left( NO _3\right)_2( aq )+ CO _2(g)+ H _2 O ( I )$
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Question 383 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
a. Copper (II) chloride $CuCl _2$
b. $CuO ( s )+2 HCl ( aq ) \rightarrow CuCl _2( aq )+ H _2 O ( l )$
c. Copper oxide is basic in nature
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Question 393 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 403 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 413 Marks
How $H _3 O ^{+}$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 $H _3 O ^{+}$. 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 423 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 433 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.
i. $Zn +2 HCl \rightarrow ZnCl _2+ H _2 \uparrow$
ii. $2 NaOH + Zn \rightarrow Na _2 ZnO _2+ H _2$​​​​​​​
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Question 443 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 453 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 463 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 $NaHCO _3$ (sodium bicarbonate OR sodium hydrogen carbonate). The compound Y is $Na _2 CO _3$ (sodium carbonate). The compound Z is $Na _2 CO _3 \cdot 10 H _2 O$ (sodium carbonate decahydrate or washing soda). $2 NaHCO _3 \xrightarrow{\text { heat }} Na _2 CO _3+ H _2 O + CO _2$ $Na _2 CO _3+10 H _2 O \rightarrow Na _2 CO _3 \cdot 10 H _2 O$
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Question 473 Marks
Fill in the missing data in the following table.
 
Name of the salt
Formula
Salt obtained from
Base
Acid
1.
Ammonium chloride
$NH_4Cl$
$NH_4OH$
-
2.
Copper sulphate
-
-
$H_2SO_4$
3.
Sodium chloride
$NaCl$
$NaOH$
-
4.
Magnesium nitrate
$Mg(NO_3)_2$
-
$HNO_3$
5.
Potassium sulphate
$K_2SO_4$
-
-
6.
Calcium nitrate
$Ca(NO_3)_2$
$Ca(OH)_2$
-
Answer
 
Name of the salt
Formula
Salt obtained from
Base
Acid
1.
Ammonium chloride
$NH_4Cl$
$NH_4OH$
 $HCl$
2.
Copper sulphate
 $CuSO_4$ $Cu(OH)_2$
$H_2SO_4$
3.
Sodium chloride
$NaCl$
$NaOH$
 $HCl$
4.
Magnesium nitrate
$Mg(NO_3)_2$
 $Mg(OH)_2$
$HNO_3$
5.
Potassium sulphate
$K_2SO_4$
 $KOH$ $H_2SO_4$
6.
Calcium nitrate
$Ca(NO_3)_2$
$Ca(OH)_2$
 $HNO_3$
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Question 483 Marks

Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formulae of A, B and C.
Answer
X must be a compound which forms water with acids. It means it must be a base which reacts with acids to form salt and water. This base also reacts with zinc metal and releases hydrogen gas. So it must be NaOH (sodium hydroxide).
  1. $2\text{NaOH}\ \ +\ \ \text{Zn}\ \rightarrow\ \text{Na}_2\text{ZnO}_2+\text{H}_2\\\text{Sodium}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Sodium}\\\text{hydroxide(x)}\ \ \ \ \ \ \ \ \ \ \ \ \ \text{zincate(A)}$
  2. $\text{NaOH}\ \ +\ \ \text{H}\ \rightarrow\ \text{NaCl}+\text{H}_2\text{O}\\\text{Sodium}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Sodium}\\\text{hydroxide(x)}\ \ \ \ \ \ \ \text{chloride(B)}$
  3. $\text{NaOH}\ \ +\ \ \text{CH}_3\text{COOH}\ \rightarrow\ \text{CH}_3\text{COONa}\ \ \ +\ \ \ \text{H}_2\text{O}\\\text{Sodium}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Sodium acetate(C)}\\\text{hydroxide(x)}$
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Question 493 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 $Cl _2$ gas, ' $Y$ ' is $CaOCl _2$.
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Question 503 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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