125876 + Interview Questions in General QA

1.	Three beakers labelled as A, B and C each containing 25 ml of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is (are) correct?(i) In beakers A and B, exothermic process has occurred.(ii) In beakers A and B, endothermic process has occurred.(iii) In beaker C, exothermic process has occurred.(iv) In beaker C, endothermic process has occurred.(A) (i) only (B) (ii) only(C) (i) and (iv) (D) (ii) and (iii)
Answer» (C) (i) and (iv)

Discussion

2.	Why do fire flies glow at night?
Answer» Fire flies have a protein which in the presence of an enzyme undergoes aerial oxidation. This is a chemical reaction which involves emission of visible light. Therefore, fire flies glow at night.

Discussion

3.	Which among the following are physical or chemical changes?(a) Evaporation of petrol(b) Burning of Liquefied Petroleum Gas (LPG)(c) Heating of an iron rod to red hot.(d) Curdling of milk(e) Sublimation of solid ammonium chloride
Answer» (a), (c) and (e) are physical changes. (b) and (d) are chemical changes (a) Evaporation of petrol is a physical change because no new chemical substance is formed. (b) Burning of LPG is a chemical change because on burning, LPG forms CO₂ and H₂O. (c) Heating of an iron rod to red hot is a physical change.

3.

Which among the following are physical or chemical changes?(a) Evaporation of petrol(b) Burning of Liquefied Petroleum Gas (LPG)(c) Heating of an iron rod to red hot.(d) Curdling of milk(e) Sublimation of solid ammonium chloride

Answer»

(a), (c) and (e) are physical changes.

(b) and (d) are chemical changes

(a) Evaporation of petrol is a physical change because no new chemical substance is formed.
(b) Burning of LPG is a chemical change because on burning, LPG forms CO₂ and H₂O.
(c) Heating of an iron rod to red hot is a physical change.

Discussion

4.	Which of the following gases puts off the matchstick when calcium carbonate is heated ? A) H2B) O2 C) CO2 D) NO2
Answer» Correct option is C) CO₂

Discussion

5.	Marble chips or calcium carbonate react with hydrochloric acid as :CaCO3 + 2HCl → CaCl2, + H2O + CO2The reaction is carried out twice and following graphs were obtained :Which of the following statements is incorrect? (A) Reaction is faster in experiment ll. (B) Marble chips taken in experiment ll are smaller in size than the marble chips taken in experiment l. (C) Same amount of marble chips and hydrochloric acid is used for both the experiments. (D) None of these
Answer» Correct option (D) None of these Explanation: Graph ll is steeper than graph I which shows that reaction is faster in experiment ll. Both graphs level off at the same value which shows that same amount of marble chips and hydrochloric acid is used for both experiments and marble chips in experiment ll must have been of smaller size as the reaction is faster.

5.

Marble chips or calcium carbonate react with hydrochloric acid as :CaCO3 + 2HCl → CaCl2, + H2O + CO2The reaction is carried out twice and following graphs were obtained :Which of the following statements is incorrect? (A) Reaction is faster in experiment ll. (B) Marble chips taken in experiment ll are smaller in size than the marble chips taken in experiment l. (C) Same amount of marble chips and hydrochloric acid is used for both the experiments. (D) None of these

Answer»

Correct option (D) None of these

Explanation:

Graph ll is steeper than graph I which shows that reaction is faster in experiment ll. Both graphs level off at the same value which shows that same amount of marble chips and hydrochloric acid is used for both experiments and marble chips in experiment ll must have been of smaller size as the reaction is faster.

Discussion

6.	(a) Substitute formulae for names and balance the following equation : Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide gas. (b) Write balanced chemical equation with state symbols for the following reaction : Sodium hydroxide solution reacts with hydrochloric acid solution to produce sodium chloride solution and water.
Answer» (a) CaCO₃ + 2HCl —–> CaCl₂ + H₂O + CO₂ (b) NaOH (aq) + HCl(aq) —–> NaCl (aq) + H₂O (l)

6.

(a) Substitute formulae for names and balance the following equation : Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, water and carbon dioxide gas. (b) Write balanced chemical equation with state symbols for the following reaction : Sodium hydroxide solution reacts with hydrochloric acid solution to produce sodium chloride solution and water.

Answer»

(a) CaCO₃ + 2HCl —–> CaCl₂ + H₂O + CO₂

(b) NaOH (aq) + HCl(aq) —–> NaCl (aq) + H₂O (l)

Discussion

7.	Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or physical change?
Answer» i. Microbes can grow in plucked grapes and under anaerobic conditions these grapes can get fermented. ii. It is a chemical change.

Discussion

8.	Ammonia reacts with oxygen to form nitrogen and water. Write a balanced chemical equation for this reaction. Add the state symbols for all the reactants and products.
Answer» 4NH₂ (g)+ 3O₂ (g) —–> 2N₂ (g) + 6H₂O (l)

Discussion

9.	What do you understand by a physical change? OR Define physical change.
Answer» The change in which only the physical state of a substance is changed; no new substance is formed. This change is temporary. During this change the composition of the substance does not change.

Discussion

10.	Write a balanced chemical equation for the process of photosynthesis giving the physical states of all the substances involved and the conditions of the reaction.
Answer» 6CO₂ (g) + 6H₂O C₆ —–> H₁₂O₆ (aq) + 6O₂ (g) Carbon dioxide Water Glucose Oxygen

10.

Write a balanced chemical equation for the process of photosynthesis giving the physical states of all the substances involved and the conditions of the reaction.

Answer»

6CO₂ (g) + 6H₂O C₆ —–> H₁₂O₆ (aq) + 6O₂ (g)

Carbon

dioxide Water

Glucose Oxygen

Discussion

11.	What is meant by a chemical reaction?
Answer» A process in which some substances undergo bond breaking and are transformed into new substances by formation of new bonds is called a chemical reaction.

Discussion

12.

Fill the following table.ElementAtomic MassOxygenSodiumAluminiumPhosphorusArgonPotassium

Answer»

Element	Atomic Mass
Oxygen	16
Sodium	23
Aluminium	27
Phosphorus	31
Argon	39.9
Potassium	39

Discussion

13.	When hydrogen burns in oxygen, water is formed and when water is electrolysed, then hydrogen and oxygen are produced. What type of reaction takes place : (a) in the first case ? (b) in the second case ?
Answer» (a) Combination reaction. (b) Decomposition reaction.

13.

When hydrogen burns in oxygen, water is formed and when water is electrolysed, then hydrogen and oxygen are produced. What type of reaction takes place : (a) in the first case ? (b) in the second case ?

Answer»

(a) Combination reaction.

(b) Decomposition reaction.

Discussion

14.	In the above image, an experiment is performed where 3 g of lead nitrate powder is heated in a boiling tube over the flame. We observe fumes of some gas and some solid compound is percipitated at bottom of the boiling tube.1. What is the colour of the fumes formed?(i) Brown(ii) Red(iii) Yellow(iv) White2. What is the colour of the solid compound percipitated at bottom of the boiling tube?(i) Brown(ii) Red(iii) Yellow(iv) White3. What is the chemical formula of the gas whose fumes are formed ?(i) No(ii) N2O2(iii) N2O(iv) NO24. What is the chemical formula of the compound percipitated at the bottom of the boiling tube?(i) PbO2(ii) PbO(iii) Pb2O2(iv) Pb2O5. What is the type of the chemical reaction happening in the above experiment?(i) Thermal decomposition(ii) Combination(iii) Displacement(iv) Redox
Answer» 1. (i) Brown 2. (iii) Yellow 3. (iv) NO₂ 4. (ii) PbO 5. (iv) Redox

14.

In the above image, an experiment is performed where 3 g of lead nitrate powder is heated in a boiling tube over the flame. We observe fumes of some gas and some solid compound is percipitated at bottom of the boiling tube.1. What is the colour of the fumes formed?(i) Brown(ii) Red(iii) Yellow(iv) White2. What is the colour of the solid compound percipitated at bottom of the boiling tube?(i) Brown(ii) Red(iii) Yellow(iv) White3. What is the chemical formula of the gas whose fumes are formed ?(i) No(ii) N2O2(iii) N2O(iv) NO24. What is the chemical formula of the compound percipitated at the bottom of the boiling tube?(i) PbO2(ii) PbO(iii) Pb2O2(iv) Pb2O5. What is the type of the chemical reaction happening in the above experiment?(i) Thermal decomposition(ii) Combination(iii) Displacement(iv) Redox

Answer»

1. (i) Brown

2. (iii) Yellow

3. (iv) NO₂

4. (ii) PbO

5. (iv) Redox

Discussion

15.	Which of the following is the colour of hydrous copper sulphate (CuSO4) ? A) Red B) White C) Yellow D) Blue
Answer» Correct option is D) Blue

Discussion

16.	Write the Balanced equation for the reaction of iron with steam.
Answer» 3Fe(s) + 4H₂O(g) ➝ Fe₃O₄(s) + 4H₂(g)

Discussion

17.	State whether the following statement is true or false :A chemical equation can be balanced easily by altering the formula of a reactant or product.
Answer» Statement is false

Discussion

18.	Why is photosynthesis considered an endothermic reaction ?
Answer» Photosynthesis is an endothermic reaction because sunlight energy is absorbed by green plants during this process.

Discussion

19.	When dilute hydrochloric acid is added to iron filings A) hydrogen gas and iron chloride are formed B) chlorine gas and iron hydroxide are formed C) no reaction takes place D) iron salt and water are produced
Answer» A) hydrogen gas and iron chloride are formed

Discussion

20.	How do you determine whether a chemical reaction has taken place?
Answer» Following observations helps us to determine whether a chemical reaction has taken place 1. Change in state 2. Change in colour 3. evolution of a gas 4. Change in temperature.

20.

How do you determine whether a chemical reaction has taken place?

Answer»

Following observations helps us to determine whether a chemical reaction has taken place

1. Change in state

2. Change in colour

3. evolution of a gas

4. Change in temperature.

Discussion

21.	A water-insoluble substance X on reaction with dilute hydrochloric acid released a colourless and odourless gas accompanied by brisk effervescence. When the gas passed through water, the solution obtained turns blue litmus red. On bubbling the gas through lime water, it initially became milky and milkiness disappeared when the gas was passed in excess. Identify the substance X. Write the chemical equation of the reaction involved.
Answer» Here we will first find out the gas. It is stated that this gas turns lime water milky so it is sure that the gas is carbon dioxide (CO₂). When CO₂ reacts with water then carbonic aid is formed (H₂CO₃), which turns blue litmus red. CO₂ + H₂O → H₂CO₃ When CO₂ is passed through lime water (Ca(OH)₂) it turns it milky and on excess passing of carbon dioxide it forms calcium bicarbonate which forms a colourless solution, so the reaction is: Ca(OH)₂ + CO₂→ CaCO₃ + H₂O On passing in an excess amount CaCO₃ + H₂O + CO₂→ Ca(HCO₃)₂ For the identification of substance X, we know that in product carbon dioxide is there so there must be something of carbon must be there in reactant and X is water-insoluble so it should be calcium carbonate that is insoluble. So the reaction is: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ X= CaCO₃

21.

A water-insoluble substance X on reaction with dilute hydrochloric acid released a colourless and odourless gas accompanied by brisk effervescence. When the gas passed through water, the solution obtained turns blue litmus red. On bubbling the gas through lime water, it initially became milky and milkiness disappeared when the gas was passed in excess. Identify the substance X. Write the chemical equation of the reaction involved.

Answer»

Here we will first find out the gas. It is stated that this gas turns lime water milky so it is sure that the gas is carbon dioxide (CO₂).

When CO₂ reacts with water then carbonic aid is formed (H₂CO₃), which turns blue litmus red.

CO₂ + H₂O → H₂CO₃

When CO₂ is passed through lime water (Ca(OH)₂) it turns it milky and on excess passing of carbon dioxide it forms calcium bicarbonate which forms a colourless solution, so the reaction is:

Ca(OH)₂ + CO₂→ CaCO₃ + H₂O

On passing in an excess amount

CaCO₃ + H₂O + CO₂→ Ca(HCO₃)₂

For the identification of substance X, we know that in product carbon dioxide is there so there must be something of carbon must be there in reactant and X is water-insoluble so it should be calcium carbonate that is insoluble.

So the reaction is:

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

X= CaCO₃

Discussion

22.	When a copper wire was left in silver nitrate solution for sometime, it was observed that the solution turned bluish green.(i) Explain the observation.(ii) Write the balanced chemical equation to represent the change taking place.
Answer» (i) Copper is more reactive than silver. Hence, when copper wire is dipped in silver nitrate solution, it displaces silver from AgNO₃ solutions forming copper nitrate which is bluish green in colour (ii) Cu+2AgNO₃ → Cu(NO₃)₂ +2Ag Cu(NO₃)₂-Copper (II) nitrate bluish green 2Ag -Silver

22.

When a copper wire was left in silver nitrate solution for sometime, it was observed that the solution turned bluish green.(i) Explain the observation.(ii) Write the balanced chemical equation to represent the change taking place.

Answer»

(i) Copper is more reactive than silver. Hence, when copper wire is dipped in silver nitrate solution, it displaces silver from AgNO₃ solutions forming copper nitrate which is bluish green in colour

(ii) Cu+2AgNO₃ → Cu(NO₃)₂ +2Ag

Cu(NO₃)₂-Copper (II) nitrate bluish green

2Ag -Silver

Discussion

23.	Ethane (C2H6) on complete combustion gave CO2 and water. It shows that the results are in accordance with the law of conservation of mass. Then, the coefficient of oxygen is equal to A. 3 B. 5/2 C. 2 D. 7/2
Answer» According to law of conservation of mass, the mass of the elements on the product side should be equal to the mass of the elements on reactant side. In simple words, the number of atoms of each element should be same on the both sides. This can be achieved by balancing a chemical reaction. Unbalanced chemical equation for combustion of ethane: C₂H₆ + O₂ → CO₂ +H₂O The balanced chemical equation: C₂H₆ + \(\frac72\)O₂ → 2CO₂ +3H₂O From the balanced chemical equation, we can observe that the coefficient of O₂ is \(\frac72\)

23.

Ethane (C2H6) on complete combustion gave CO2 and water. It shows that the results are in accordance with the law of conservation of mass. Then, the coefficient of oxygen is equal to A. 3 B. 5/2 C. 2 D. 7/2

Answer»

According to law of conservation of mass, the mass of the elements on the product side should be equal to the mass of the elements on reactant side. In simple words, the number of atoms of each element should be same on the both sides. This can be achieved by balancing a chemical reaction.

Unbalanced chemical equation for combustion of ethane:

C₂H₆ + O₂ → CO₂ +H₂O

The balanced chemical equation:

C₂H₆ + \(\frac72\)O₂ → 2CO₂ +3H₂O

From the balanced chemical equation, we can observe that the coefficient of O₂ is \(\frac72\)

Discussion

24.	State the law of conservation of mass as applicable in a chemical reaction.
Answer» Total mass of the elements present in the products in a chemical reaction has to be equal to the total mass of elements present in the reactants or Mass can neither be created nor destroyed in a chemical reaction.

Discussion

25.	With the help of an activity; demonstrate how do we know that a chemical reaction has taken place?
Answer» For a chemical reaction to take place some chemical change must occur. So, here is the activity to demonstrate a chemical reaction: Step-1: Take a magnesium ribbon around 2cm long by rubbing it with sand paper. Step-2: Hold it with tongs. Step-3: Burn the ribbon and collect the ash in a watch glass which is white in pair. Precaution must be taken while performing the experiment to keep the burning ribbon far away from eye. The experiment should be under some expert supervision. In the activity we observed that magnesium ribbon burns with a white flames and changes into white powder. This powder is magnesium oxide. There was a change in state, change in colour, change in temperature all of these are chemical changes and this proves that chemical reaction takes places here in which magnesium was converted into magnesium dioxide.

25.

With the help of an activity; demonstrate how do we know that a chemical reaction has taken place?

Answer»

For a chemical reaction to take place some chemical change must occur. So, here is the activity to demonstrate a chemical reaction:

Step-1: Take a magnesium ribbon around 2cm long by rubbing it with sand paper.

Step-2: Hold it with tongs.

Step-3: Burn the ribbon and collect the ash in a watch glass which is white in pair.

Precaution must be taken while performing the experiment to keep the burning ribbon far away from eye. The experiment should be under some expert supervision.

In the activity we observed that magnesium ribbon burns with a white flames and changes into white powder. This powder is magnesium oxide.

There was a change in state, change in colour, change in temperature all of these are chemical changes and this proves that chemical reaction takes places here in which magnesium was converted into magnesium dioxide.

Discussion

26.	Write a balanced chemical equation :FeSO4(s) + heat→ Fe2O3(s) + SO2(g) + SO3(g)
Answer» 2FeSO₄(s) + heat→ Fe₂O₃(s) + SO₂(g) + SO₃(g)

Discussion

27.	Identify the type of chemical reaction in the following statements and define each of them :(i) Digestion of food in our body(ii) Rusting of iron(iii) Heating of manganese dioxide with aluminium powder(iv) Blue colour of copper sulphate solution disappears when iron filings are added to it(v) Dilute hydrochloric acid is added to sodium hydroxide solution to form sodium chloride and water.
Answer» (i) Decomposition Reaetion: Carbohydrates are broken down to form glucose. (ii) Oxidation Reaction: When an iron object is left in moist air for a considerable time, it get covered with a red-brown flaky substance called rust. (iii) Displacement reaction: More reactive metal displaces less reactive metal from its salt solution. (iv) Displacement reaction: More reactive metal displaces less reactive metal from its salt solution. (v) Double displacement reaction: Reaction in which two compounds react by an exchange of ions to from two new compounds.

27.

Identify the type of chemical reaction in the following statements and define each of them :(i) Digestion of food in our body(ii) Rusting of iron(iii) Heating of manganese dioxide with aluminium powder(iv) Blue colour of copper sulphate solution disappears when iron filings are added to it(v) Dilute hydrochloric acid is added to sodium hydroxide solution to form sodium chloride and water.

Answer»

(i) Decomposition Reaetion: Carbohydrates are broken down to form glucose.

(ii) Oxidation Reaction: When an iron object is left in moist air for a considerable time, it get covered with a red-brown flaky substance called rust.

(iii) Displacement reaction: More reactive metal displaces less reactive metal from its salt solution.

(iv) Displacement reaction: More reactive metal displaces less reactive metal from its salt solution.

(v) Double displacement reaction: Reaction in which two compounds react by an exchange of ions to from two new compounds.

Discussion

28.	Mention the four informations given by an equation.
Answer» (i) Physical state of reactants and products. (ii) Conditions such as temperature, pressure, heat etc. (iii) Catalyst involved. (iv) Change in the state.

28.

Mention the four informations given by an equation.

Answer»

(i) Physical state of reactants and products.

(ii) Conditions such as temperature, pressure, heat etc.

(iii) Catalyst involved.

(iv) Change in the state.

Discussion

29.	Zinc oxide reacts with carbon, on heating to form zinc metal and carbon monoxide. Write a balanced chemical equation for this reaction. Name (i) Oxidising agent (ii) The reducing agent in this reaction.
Answer» The reaction mentioned in the question is as follows: ZnO + C \(\overset{heat}\longrightarrow\) Zn + CO The oxidising agent is the substance which oxidises other substance and gets reduced. Reducing agent is the substance which reduces other substance and gets oxidised. i) In the reaction zinc oxide (ZnO) is oxidising agent as it oxidises the carbon to carbon monoxide (CO) and zinc oxide gets reduced to zinc. ii) Carbon is the reducing agent as it reduces zinc oxide to zinc and gets oxidised to carbon monoxide.

29.

Zinc oxide reacts with carbon, on heating to form zinc metal and carbon monoxide. Write a balanced chemical equation for this reaction. Name (i) Oxidising agent (ii) The reducing agent in this reaction.

Answer»

The reaction mentioned in the question is as follows:

ZnO + C \(\overset{heat}\longrightarrow\) Zn + CO

The oxidising agent is the substance which oxidises other substance and gets reduced.

Reducing agent is the substance which reduces other substance and gets oxidised.

i) In the reaction zinc oxide (ZnO) is oxidising agent as it oxidises the carbon to carbon monoxide (CO) and zinc oxide gets reduced to zinc.

ii) Carbon is the reducing agent as it reduces zinc oxide to zinc and gets oxidised to carbon monoxide.

Discussion

30.	List any three observations which determine that a chemical reaction has taken place. Also list three informations that cannot be obtained about a chemical reaction, merely by its chemical equation,
Answer» Three observations which determine that a chemical reaction has taken place are : (i) Change in state and colour. (ii) Evolution of gas. (iii) Change in temperature. Three informations that cannot be obtained about a chemical reaction, merely by its chemical equation (i) The state of a matter of the reactants and products. (ii) Amount of heat evolved or absorbed in a reaction (iii) The change of colour after the chemical reaction.

30.

List any three observations which determine that a chemical reaction has taken place. Also list three informations that cannot be obtained about a chemical reaction, merely by its chemical equation,

Answer»

Three observations which determine that a chemical reaction has taken place are :

(i) Change in state and colour.

(ii) Evolution of gas.

(iii) Change in temperature.

Three informations that cannot be obtained about a chemical reaction, merely by its chemical equation

(i) The state of a matter of the reactants and products.

(ii) Amount of heat evolved or absorbed in a reaction

(iii) The change of colour after the chemical reaction.

Discussion

31.	List four observations that help us to determine whether a chemical reaction his taken place.
Answer» (i) Evolution of a gas (ii) Change in temperature (iii) Change in state (iv) Change in colour.

31.

List four observations that help us to determine whether a chemical reaction his taken place.

Answer»

(i) Evolution of a gas

(ii) Change in temperature

(iii) Change in state

(iv) Change in colour.

Discussion

32.	Write a balanced chemical equation with state symbols for the following reactionsi) Solutions of Barium chloride and Sodium sulphate in water react to give insoluble Barium sulphate and solution of Sodium chloride.ii) Sodium hydroxide solution in water reacts with hydrochloric acid solution to produce Sodium chloride solution and water.
Answer» i) BaCl₂+ Na₂SO₄→ BaSO₄+ 2NaCl ii) NaOH + HCl → NaCl + H₂O

32.

Write a balanced chemical equation with state symbols for the following reactionsi) Solutions of Barium chloride and Sodium sulphate in water react to give insoluble Barium sulphate and solution of Sodium chloride.ii) Sodium hydroxide solution in water reacts with hydrochloric acid solution to produce Sodium chloride solution and water.

Answer»

i) BaCl₂+ Na₂SO₄→ BaSO₄+ 2NaCl

ii) NaOH + HCl → NaCl + H₂O

Discussion

33.	Write the balanced chemical equations for the following reactions.(a) Calcium hydroxide +Carbon dioxide → Calcium carbonate + Water(b)Zinc + Silver nitrate →Zinc nitrate + Silver(c) Aluminium + Copper chloride → Aluminium chloride + Copper(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Answer» (a) Ca(OH)₂+CO₂ → CaCO₃+H₂O (b) Zn+2AgNO₃ → Zn(NO₃)₂+2Ag (c) 2Al+3CuCl₂ → 2AlCl₃+3Cu (d) BaCl₂+ K₂SO₄ → BaSO₄+2KCl

33.

Write the balanced chemical equations for the following reactions.(a) Calcium hydroxide +Carbon dioxide → Calcium carbonate + Water(b)Zinc + Silver nitrate →Zinc nitrate + Silver(c) Aluminium + Copper chloride → Aluminium chloride + Copper(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Answer»

(a) Ca(OH)₂+CO₂ → CaCO₃+H₂O

(b) Zn+2AgNO₃ → Zn(NO₃)₂+2Ag

(c) 2Al+3CuCl₂ → 2AlCl₃+3Cu

(d) BaCl₂+ K₂SO₄ → BaSO₄+2KCl

Discussion

34.	Write the balanced equations for the following reactions, and add the state symbols : (a) Magnesium carbonate reacts with hydrochloric acid to produce magnesium chloride, carbon dioxide and water. (b) Sodium hydroxide reacts with sulphuric acid to produce sodium sulphate and water.
Answer» (a) MgCO₂ (s) + 2HCl (aq) MgCl₂ (aq) + CO₂ (g) + H₂O (l) (b) 2NaOH (aq) + H₂SO₄ (aq) Na₂SO₄ (aq) + 2H₂O (l)

34.

Write the balanced equations for the following reactions, and add the state symbols : (a) Magnesium carbonate reacts with hydrochloric acid to produce magnesium chloride, carbon dioxide and water. (b) Sodium hydroxide reacts with sulphuric acid to produce sodium sulphate and water.

Answer»

(a) MgCO₂ (s) + 2HCl (aq) MgCl₂ (aq) + CO₂ (g) + H₂O (l)

(b) 2NaOH (aq) + H₂SO₄ (aq) Na₂SO₄ (aq) + 2H₂O (l)

Discussion

35.	Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.
Answer» 1. Evolution of gas. For example: When sodium carbonate reacts with dilute hydrochloric acid, carbon dioxide gas is evolved. 2. Formation of a precipitate. For example: When potassium iodide solution is added to a solution of lead nitrate, yellow precipitate of lead iodide is formed.

35.

Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.

Answer»

1. Evolution of gas.

For example: When sodium carbonate reacts with dilute hydrochloric acid, carbon dioxide gas is evolved.

2. Formation of a precipitate.

For example: When potassium iodide solution is added to a solution of lead nitrate, yellow precipitate of lead iodide is formed.

Discussion

36.

Distinguish between the following:Combination reaction and Decomposition reaction.

Answer»

Combination reaction	Decomposition reaction
1. In a combination re‐ action, two or more reactants take part in the chemical reaction.	1. In a decomposition reaction there is only one reactant in the chemical reaction.
1. In the combination reaction, only one product is formed.	2. In a decomposition reaction, two or more products are formed.

Discussion

37.	Convert the following statements into balanced chemical equations :(i) Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas.(ii) Magnesium burns in oxygen to form magnesium oxide.
Answer» (i) Zn + H₂SO₄ → ZnSO₄+ H₂ (ii) 2Mg + O₂ → 2MgO

37.

Convert the following statements into balanced chemical equations :(i) Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas.(ii) Magnesium burns in oxygen to form magnesium oxide.

Answer»

(i) Zn + H₂SO₄ → ZnSO₄+ H₂

(ii) 2Mg + O₂ → 2MgO

Discussion

38.	(a) Aluminium hydroxide reacts with sulphuric acid to form aluminium sulphate and water. Write a balanced equation for this reaction. (b) Balance the following chemical equation : MnO2 + HCl —–> MnCl2 + Cl + H2O.
Answer» (a) 2Al(OH)₃ + 3H₂SO₄ —–> Al₂(SO₄) + 6H₂O. (b) MnO₂ + 4HCl —–> MnCl₂ + Cl₂ + 2H₂O

38.

(a) Aluminium hydroxide reacts with sulphuric acid to form aluminium sulphate and water. Write a balanced equation for this reaction. (b) Balance the following chemical equation : MnO2 + HCl —–> MnCl2 + Cl + H2O.

Answer»

(a) 2Al(OH)₃ + 3H₂SO₄ —–> Al₂(SO₄) + 6H₂O.

(b) MnO₂ + 4HCl —–> MnCl₂ + Cl₂ + 2H₂O

Discussion

39.	Classify the following reaction as combination, Decomposition, displacement and double displacement reaction :(a) BaCl2+H2SO4 → BaSO4+2HCl(b) C+O2 → CO2(c) 3CuSO4+2Al → Al2(SO4)3+3Cu(d) ZnCO3 → ZnO+CO2
Answer» (a) Double displacement reaction. (b) Combination reaction. (c) Dispiacement reaction. (d)Decomposition reaction

39.

Classify the following reaction as combination, Decomposition, displacement and double displacement reaction :(a) BaCl2+H2SO4 → BaSO4+2HCl(b) C+O2 → CO2(c) 3CuSO4+2Al → Al2(SO4)3+3Cu(d) ZnCO3 → ZnO+CO2

Answer»

(a) Double displacement reaction.

(b) Combination reaction.

(c) Dispiacement reaction.

(d)Decomposition reaction

Discussion

40.	i. Classify the following reactions into different types:a. AgNO3(aq) + NaCl(aq) →AgCl(s) + NaNO3(aq)b. CaO(s) + H2O(l) → Ca(OH)2(aq)c. 2KClO3(s) →2KCl(s) + 3O2(g)ii. Which of the above reaction(s) is/are precipitation reaction(s)? Why is a reaction called precipitation reaction?
Answer» i. a. Double displacement reaction b. Combination reaction c. Thermal decomposition reaction ii. Reaction (a) is a precipitation reaction because precipitate of silver chloride is formed as the product. When a product of a chemical reaction is obtained in the form of a precipitate (insoluble substance), then that reaction is called as precipitation reaction.

Discussion

41.	Which of the following is Lewis acid ?a. BaCl2b. KCl c. BeCl2d. LiCl
Answer» Option : c. BeCl₂

Discussion

42.	What happens when crystalline Na2CO3 is heated ?a. releases CO2b. loses H2O c. decomposes into NaHCO3d. colour changes.
Answer» Option : b. loses H₂O

Discussion

43.	What are the various letters used by Bohr to represent electron shell in an atom?
Answer» K, L, M, N were the letters used by Bohr to represent electron shells in an atom.

Discussion

44.	Name the central part of an atom where protons and neutrons are held together.
Answer» Nucleus is the central part of an atom in which protons and neutrons are held together.

Discussion

45.	An atom with 3 protons and 4 neutrons will have a valency of:A. 3B. 7C. 1D. 4
Answer» An atom with 3 protons would have 2 electrons in its innermost shell and 1 proton in its outermost shell. The outermost proton could be easily given away by the atom to attain a stable two electron inner shell configuration. So, the valency would be 1. Hence the correct option is C.

45.

An atom with 3 protons and 4 neutrons will have a valency of:A. 3B. 7C. 1D. 4

Answer»

An atom with 3 protons would have 2 electrons in its innermost shell and 1
proton in its outermost shell. The outermost proton could be easily given away by the
atom to attain a stable two electron inner shell configuration. So, the valency would be
1.

Hence the correct option is C.

Discussion

46.	Fill in the blanks in the following statements: (a) The number of protons in the nucleus of an atom is called its ______. (b) The total number of protons and neutrons in the nucleus of an atom is called ______.(c) An atom has atomic mass number 23 and atomic number 11. The atom has ______ electrons. (d) An atom of an element has 11 protons, 11 electrons and 12 neutrons. The atomic mass of the atom is ______. (e) If the nucleus of an atom has atomic number 17 , mass number 37 and there are 17 electrons outside the nucleus, the number of neutrons in it is ______. (f) Almost all the mass of an atom is concentrated in a small region of space called the ______. (g) Cathode rays are a beam of fast moving ______. (h) The anode rays obtained from hydrogen gas consist of particles called ______. (i) The maximum number of electrons that can be accommodated in L shell are ______. (j) The maximum number of electrons that can go into the M shell is ______. (k) The subatomic particle not present in a hydrogen atom is ______. (l) The electron has ______ charge, the proton has ______ charge, and the neutron has______ charge.
Answer» (a) Atomic number (b) Mass number (c) 11 (d) 23 (e) 20 (f) Nucleus (g) Electrons (h) Protons (i) 8 (j) 18 (k) Neutron (l) Negative; Positive; No

46.

Fill in the blanks in the following statements: (a) The number of protons in the nucleus of an atom is called its . (b) The total number of protons and neutrons in the nucleus of an atom is called .(c) An atom has atomic mass number 23 and atomic number 11. The atom has electrons. (d) An atom of an element has 11 protons, 11 electrons and 12 neutrons. The atomic mass of the atom is . (e) If the nucleus of an atom has atomic number 17 , mass number 37 and there are 17 electrons outside the nucleus, the number of neutrons in it is . (f) Almost all the mass of an atom is concentrated in a small region of space called the . (g) Cathode rays are a beam of fast moving . (h) The anode rays obtained from hydrogen gas consist of particles called . (i) The maximum number of electrons that can be accommodated in L shell are . (j) The maximum number of electrons that can go into the M shell is . (k) The subatomic particle not present in a hydrogen atom is . (l) The electron has charge, the proton has charge, and the neutron has charge.

Answer»

(a) Atomic number

(b) Mass number

(c) 11

(d) 23

(e) 20

(f) Nucleus

(g) Electrons

(h) Protons

(i) 8

(j) 18

(k) Neutron

(l) Negative; Positive; No

Discussion

47.	Fill in the blanks:The total number of protons and neutrons in the nucleus of an atom in known as ……….
Answer» The total number of protons and neutrons in the nucleus of an atom in known as Atomic mass.

Discussion

48.	Which of the following is true about the value of refractive index of quartz glass?(i) Same in all directions(ii) Different in different directions(iii) Cannot be measured(iv) Always zero
Answer» (i) Same in all directions

Discussion

49.	The nucleus of an atom contains 19 protons and 21 neutrons. The atomic mass number of the element is ………….. . (a) 19(b) 21 (c) 40 (d) 39
Answer» Correct option is (c) 40

Discussion

50.	Name the element whose atom contain six protons in the nucleus.
Answer» Carbon contain six protons in the nucleus.

Discussion

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