42 + Interview Questions in CHEMICAL CHANGE IN GENERAL AWARENESS Page 1 InterviewSolution

1.	Kindling fire by pouring oil. Heap up some potassium permanganate on a tile. Keep a piece of dry cotton wick on top of it. Pour one or two drops of glycerine on the wick. Observe the changes.
Answer» potassium permanganate heap burns

Discussion

2.	Give two examples of covalent compounds.
Answer» Covalent compounds: Hydrogen (H₂), Water (H₂O).

Discussion

3.	Write a chemical equation (unbalanced) for the following reaction:Magnesium salts during the softening of hard water.Magnesium chloride + Sodium carbonate \(\longrightarrow\) Magnesium carbonate + Sodium chloride
Answer» MgCl₂ + Na₂CO₃ → MgCO₃ + 2NaCl

Discussion

4.	Name the salts present in hard water.
Answer» Salts present in hard water are calcium chloride, magnesium chloride, calcium sulphate and magnesium sulphate.

Discussion

5.	Give two examples of ionic compounds.
Answer» Ionic compounds: Sodium chloride (NaCl), Potassium fluoride (KF).

Discussion

6.	State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)(i) H2O Molecule is an ionic compound.(ii) The bond between two chlorine atoms is a covalent band(iii) Arrow indicates the direction of the reaction.
Answer» (i) False. (H₂O molecule is a covalent compound.) (ii) True. (iii) True.

6.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)(i) H2O Molecule is an ionic compound.(ii) The bond between two chlorine atoms is a covalent band(iii) Arrow indicates the direction of the reaction.

Answer»

(i) False. (H₂O molecule is a covalent compound.)

(ii) True.

(iii) True.

Discussion

7.

Distinguish between the following:Physical change and Chemical change:

Answer»

Physical change	Chemical change
1. In this change, the composition of the substance does not change. No new substance is formed.	1. In this change, the composition of the compounds change and new compounds are formed.
2. In this case, physical properties such as state, colour, density, etc. are changed.	2. In this case, physical and chemical properties are entirely changed.
3. This change is temporary.	3. This change is permanent.
4. In this case, the original substance can be recovered by simple means or by merely reversing the process.	4. In this case, the original substance cannot be recovered by easy means or by reversing the process.

Discussion

8.	What are the methods of classification of changes?
Answer» The methods of classification of changes: Physical change and chemical change.

Discussion

9.	State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)(i) The preparation of cold drink soda- lemon is a physical change.(ii) Hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state.(iii) Combustion of fuel is a fast and irreversible manmade chemical change.(iv) Photosynthesis reaction is a man-made chemical change.
Answer» (i) False. [The preparation of cold drink soda-lemon is a chemical change.] (ii) True. (iii) True. (iv) False. [Photosynthesis reaction is a natural chemical change.]

9.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)(i) The preparation of cold drink soda- lemon is a physical change.(ii) Hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state.(iii) Combustion of fuel is a fast and irreversible manmade chemical change.(iv) Photosynthesis reaction is a man-made chemical change.

Answer»

(i) False. [The preparation of cold drink soda-lemon is a chemical change.]

(ii) True.

(iii) True.

(iv) False. [Photosynthesis reaction is a natural chemical change.]

Discussion

10.	What is the difference between physical and chemical change?
Answer» 1. In physical change, the composition of substance does not change. No new substance is formed. 2. In chemical change, the composition of compounds change and new compounds are formed.

10.

What is the difference between physical and chemical change?

Answer»

1. In physical change, the composition of substance does not change. No new substance is formed.

2. In chemical change, the composition of compounds change and new compounds are formed.

Discussion

11.	Classify the following changes into physical and chemical change. Ripening of mango, melting of ice, boiling of water, dissolution of salt in water, Ripening of banana, fragrance on ripening fruit, darkening of a cut potato, bursting of an inflated balloon, sound of bursting fire cracker, foul smell from a portion of spoiled food.
Answer» Physical change: Melting of ice, boiling of water, dissolution of salt in water. Chemical change: Ripening of mango, ripening of banana, fragrance of ripening fruit, darkening of a cut potato, bursting of an inflated balloon, sound of bursting firecracker, foul smell from a spoiled food.

Discussion

12.	Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms.Sodium Chloride.
Answer» 1. Sodium has atomic number 11 and electronic configuration 2, 8, 1. 2. Sodium atom has 1 electron in its outermost shell. 3. It loses one electron from its outermost shell, i.e., M shell. Then its L shell becomes the outermost shell with a stable octet. The nucleus of sodium atom has 11 protons but the number of electrons in the atom has become 10. So, there is a net unit positive charge giving a sodium cation (Na⁺). 4. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet. 5. Thus, the electron lost by sodium is taken up by chlorine. 6. When chlorine atom gains one electron, octet of chlorine is completed and its K, L, M shells have together 18 electrons and the nucleus has 17 protons. This leads to the formation of an ion (CP). 7. Thus, a chlorine atom accepts one electron from a sodium atom and consequently a chloride ion with one unit negative charge and a sodium ion with one unit positive charge are formed. 8. Sodium and chloride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of sodium chloride (NaCl) molecule.

12.

Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms.Sodium Chloride.

Answer»

1. Sodium has atomic number 11 and electronic configuration 2, 8, 1.

2. Sodium atom has 1 electron in its outermost shell.

3. It loses one electron from its outermost shell, i.e., M shell. Then its L shell becomes the outermost shell with a stable octet. The nucleus of sodium atom has 11 protons but the number of electrons in the atom has become 10. So, there is a net unit positive charge giving a sodium cation (Na⁺).

4. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.

5. Thus, the electron lost by sodium is taken up by chlorine.

6. When chlorine atom gains one electron, octet of chlorine is completed and its K, L, M shells have together 18 electrons and the nucleus has 17 protons. This leads to the formation of an ion (CP).

7. Thus, a chlorine atom accepts one electron from a sodium atom and consequently a chloride ion with one unit negative charge and a sodium ion with one unit positive charge are formed.

8. Sodium and chloride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of sodium chloride (NaCl) molecule.

Discussion

13.	What is the observation when two drops of phenolphthalein is added to the solution obtained after the reaction of sodium with water? Justify your answer.
Answer» The solution becomes pink in colour. The product of the reaction is sodium hydroxide which is alkaline.

Discussion

14.	Write a chemical equation (unbalanced) for the following reaction:Calcium carbonate + Hydrochloric acid \(\longrightarrow\) Calcium chloride + carbon dioxide + water
Answer» Chemical equation: CaCO₃ + HCl → CaCl₂ + CO₂ + H₂O

14.

Write a chemical equation (unbalanced) for the following reaction:Calcium carbonate + Hydrochloric acid \(\longrightarrow\) Calcium chloride + carbon dioxide + water

Answer»

Chemical equation:

CaCO₃ + HCl → CaCl₂ + CO₂ + H₂O

Discussion

15.	Write a chemical equation for combustion of fuel.
Answer» Chemical equation: C + O₂ → CO₂

15.

Write a chemical equation for combustion of fuel.

Answer»

Chemical equation:

C + O₂ → CO₂

Discussion

16.	State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)(i) The atoms with incomplete electron octet/duplet form chemical bonds.(ii) Electronic configuration of chlorine is 2, 8, 6.(iii) One ionic bond is formed due to the electrical change +1 or -1 on an ion.
Answer» (i) True. (ii) False. (Electronic configuration of chlorine is 2, 8, 7.) (iii) True.

16.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)(i) The atoms with incomplete electron octet/duplet form chemical bonds.(ii) Electronic configuration of chlorine is 2, 8, 6.(iii) One ionic bond is formed due to the electrical change +1 or -1 on an ion.

Answer»

(i) True.

(ii) False. (Electronic configuration of chlorine is 2, 8, 7.)

(iii) True.

Discussion

17.	Explain :Combustion of fuel is a fast and irreversible chemical change.
Answer» Wood, coal, petrol or cooking gas are burnt for producing energy. Carbon is the common substance that burns in all these fuels. The product carbon dioxide is formed when carbon combines with oxygen in the air during the combustion process. We cannot obtain fuel from carbon dioxide by employing any other method. Properties of carbon dioxide are altogether different from those of fuel. Hence, this change is a irreversible chemical change. Word equation: Carbon + Oxygen → Carbon dioxide

17.

Explain :Combustion of fuel is a fast and irreversible chemical change.

Answer»

Wood, coal, petrol or cooking gas are burnt for producing energy. Carbon is the common substance that burns in all these fuels. The product carbon dioxide is formed when carbon combines with oxygen in the air during the combustion process. We cannot obtain fuel from carbon dioxide by employing any other method. Properties of carbon dioxide are altogether different from those of fuel. Hence, this change is a irreversible chemical change.

Word equation:

Carbon + Oxygen → Carbon dioxide

Discussion

18.	Name the products of photosynthesis.
Answer» Glucose and oxygen are the products of photosynthesis.

Discussion

19.	Name the reactants in photosynthesis.
Answer» Carbon dioxide and water are the reactants in photosynthesis.

Discussion

20.	Write name the products of respiration.
Answer» Carbon dioxide and water are the products of respiration.

Discussion

21.	Name the reactants in respiration.
Answer» Glucose and oxygen are the reactants in respiration.

Discussion

22.

Match the columns:Column IColumn II1. Respirationa. Potassium and fluorine2. Acid + Baseb. Glucose and oxygen3. Photosynthesisc. Carbon dioxide and water4. Ionic bondd. Salt and water

Answer»

Column I	Column II
1. Respiration	c. Carbon dioxide and water
2. Acid + Base	d. Salt and water
3. Photosynthesis	b. Glucose and oxygen
4. Ionic bond	a. Potassium and fluorine

Discussion

23.

Match the pair :Column IColumn II1. Photosynthesisa. Tendency to lose electrons2. Waterb. Reactant in combustion process3. Sodium chloridec. Chemical change4. Dissolution of salt in waterd. Covalent bond5. Carbone. Ionic bond6. Fluorinef. Physical change7. Magnesiumg. Tendency to form anion

Answer»

Column I	Column II
1. Photosynthesis	c. Chemical change
2. Water	d. Covalent bond
3. Sodium chloride	e. Ionic bond
4. Dissolution of salt in water	f. Physical change
5. Carbon	b. Reactant in combustion process
6. Fluorine	g. Tendency to form anion
7. Magnesium	a. Tendency to lose electrons

Discussion

24.	Consider the correlation between the words of the first pair, match the third word/words with the most appropriate answer:(i) K : 2, 8, 8, 1 : : Mg : ………………(ii) MgCl2 : Ionic bond : : CaO : …………….(iii) Photosynthesis : Natural chemical change : : Cold drink, soda lemon : ………(iv) Respiration: Glucose + Oxygen : : Neutralization : ………….
Answer» (i) 2, 8, 2 (ii) Covalent bond (iii) Man-made chemical change (iv) Acid + alkali.

24.

Consider the correlation between the words of the first pair, match the third word/words with the most appropriate answer:(i) K : 2, 8, 8, 1 : : Mg : ………………(ii) MgCl2 : Ionic bond : : CaO : …………….(iii) Photosynthesis : Natural chemical change : : Cold drink, soda lemon : ………(iv) Respiration: Glucose + Oxygen : : Neutralization : ………….

Answer»

(i) 2, 8, 2

(ii) Covalent bond

(iii) Man-made chemical change

(iv) Acid + alkali.

Discussion

25.	What is elecroplating? How are the electrode and the electrolyte selected when a metallic object is to be plated with another special metal?
Answer» To obtain a thin coating of a particular metal on another metallic object using electricity is known as electroplating. The metal to be plated is taken as the positive electrode. The electrolyte is a solution of salt containing the metal to be plated. The negative electrode is the metallic object to be plated.

25.

What is elecroplating? How are the electrode and the electrolyte selected when a metallic object is to be plated with another special metal?

Answer»

To obtain a thin coating of a particular metal on another metallic object using electricity is known as electroplating.

The metal to be plated is taken as the positive electrode. The electrolyte is a solution of salt containing the metal to be plated. The negative electrode is the metallic object to be plated.

Discussion

26.	Give an example each for exothermic and endothermic reactions.
Answer» Exothermic reaction: Magnesium + hydrochloric acid → magnesium chloride + hydrogen + heat Endothermic reaction: Potassium permanganate + heat → potassium manganate + manganese dioxide + oxygen

26.

Give an example each for exothermic and endothermic reactions.

Answer»

Exothermic reaction:

Magnesium + hydrochloric acid → magnesium chloride + hydrogen + heat

Endothermic reaction:

Potassium permanganate + heat → potassium manganate + manganese dioxide + oxygen

Discussion

27.

List out the instruments that use electrochemical cells. What are the merits and demerits of using such cells?

Answer»

Cells	Equipment used
Dry cell	• Radio
	• Camera
	• Clocks
	• Toys
Mercury cell	• Watches
	• Calculators
	• Electric instruments
Nickel-cadmium cell	• Rechargeable torches
Nickel-cadmium cell	• Cameras
Lithium-iron cell	• Mobile phones
Lithium-iron cell	• Laptops

Discussion

28.	Some medicines and chemicals are kept in dark bottles, why?
Answer» To prevent the chemical change due to the absorption of light

Discussion

29.	Some chemical reactions are given below. Identify the energy change involved and write down what type of chemical reaction takes place here.a. Burning of a candle b. Glowing of a fire fly c. Plating a copper ring with gold d. Reaction between potassium hydroxide and sulphuric acide. Burning of fuels
Answer» a. Thermochemical reactions b. Photochemical reaction c. Electrochemical reaction d. Thermochemical reactions e. Thermochemical reactions

29.

Some chemical reactions are given below. Identify the energy change involved and write down what type of chemical reaction takes place here.a. Burning of a candle b. Glowing of a fire fly c. Plating a copper ring with gold d. Reaction between potassium hydroxide and sulphuric acide. Burning of fuels

Answer»

a. Thermochemical reactions

b. Photochemical reaction

c. Electrochemical reaction

d. Thermochemical reactions

e. Thermochemical reactions

Discussion

30.	Give scientific reason:Ionic compounds are formed due to the combination of metallic and nonmetallic atoms.
Answer» Metallic atoms have a tendency to lose electrons from their outermost orbits to establish the octet state in their penultimate orbits. Conversely, nonmetallic atoms gain electrons to establish the octet state of their outermost orbits. When a metallic atom and a nonmetallic atom come close together, the metallic atom loses electrons and gets c converted into positively charged ion, while the nonmetallic’ atom gets converted into negatively charged ions so formed, develop an ionic bond and this results in the formation of an ionic compound. Hence, ionic compounds are formed due to the combination of metallic and nonmetallic atoms.

30.

Give scientific reason:Ionic compounds are formed due to the combination of metallic and nonmetallic atoms.

Answer»

Metallic atoms have a tendency to lose electrons from their outermost orbits to establish the octet state in their penultimate orbits. Conversely, nonmetallic atoms gain electrons to establish the octet state of their outermost orbits.

When a metallic atom and a nonmetallic atom come close together, the metallic atom loses electrons and gets c converted into positively charged ion, while the nonmetallic’ atom gets converted into negatively charged ions so formed, develop an ionic bond and this results in the formation of an ionic compound. Hence, ionic compounds are formed due to the combination of metallic and nonmetallic atoms.

Discussion

31.

Distinguish between the following:Ionic bond and Covalent bond.

Answer»

Ionic bond	Covalent bond
1. Ionic bond is formed due to the transfer of electrons from one atom to another.	1. Covalent bond is formed due to the sharing of electrons between two or more atoms.
2. Atoms of metals and nonmetals combine to form ionic bonds.	2. Atoms of nonmetals combine to form covalent bonds.
3. Molecules of the compounds formed due to ionic bond split up into ions in aqueous solution.	3. Molecules of the compounds formed due to covalent bond so not split up into ions in a solution.

Discussion

32.	Tabulate the following changes into physical and chemical changesWater changes to water vapour burning wood rusting the iron explosion of crackers cutting the wood Magnesium burns in air Ice is melting
Answer» Water changes to water vapour – Physical change Burning wood – Chemical change Rusting the iron – Chemical change Explosion of crackers – Chemical change Cutting the wood – Physical change Magnesium burns in air – Chemical change Ice is melting – Physical change

32.

Tabulate the following changes into physical and chemical changesWater changes to water vapour burning wood rusting the iron explosion of crackers cutting the wood Magnesium burns in air Ice is melting

Answer»

Water changes to water vapour – Physical change

Burning wood – Chemical change

Rusting the iron – Chemical change

Explosion of crackers – Chemical change

Cutting the wood – Physical change

Magnesium burns in air – Chemical change

Ice is melting – Physical change

Discussion

33.	i. sodium + water → sodium hydroxide + hydrogenii. Magnesium + oxygen → magnesium oxideWrite the reactants and products of these reactions.
Answer» i. Reactants: sodium, water Products: sodium hydroxide, hydrogen ii. Reactants: magnesium, oxygen products: Magnesium oxide

33.

i. sodium + water → sodium hydroxide + hydrogenii. Magnesium + oxygen → magnesium oxideWrite the reactants and products of these reactions.

Answer»

i. Reactants: sodium, water

Products: sodium hydroxide, hydrogen

ii. Reactants: magnesium, oxygen

products: Magnesium oxide

Discussion

34.	Assess the chemical reactions given below and answer the questions.1. Calcium carbonate + heat → Calcium oxide + Carbon dioxide2. Calcium oxide + water → Calcium hydroxide + heata. Mention the reactants and products in each case.b. Which among these is endothermic?Which one is exothermic?
Answer» a. Reactants: 1. Calcium carbonate 2. Calcium oxide, water Products 1. Calcium oxide, carbon dioxide 2. Calcium hydroxide b. First reaction is endothermic and second is exothermic reaction.

34.

Assess the chemical reactions given below and answer the questions.1. Calcium carbonate + heat → Calcium oxide + Carbon dioxide2. Calcium oxide + water → Calcium hydroxide + heata. Mention the reactants and products in each case.b. Which among these is endothermic?Which one is exothermic?

Answer»

a. Reactants:

1. Calcium carbonate

2. Calcium oxide, water

Products

1. Calcium oxide, carbon dioxide

2. Calcium hydroxide

b. First reaction is endothermic and second is exothermic reaction.

Discussion

35.	Classify the following into physical changes and chemical changes. 1. Melting of ice. 2. Heating magnesium in water. 3. Silver bromide kept exposed to sunlight. 4. Change happening to soda water on opening its bottle.
Answer» 1. physical change 2. chemical change 3. chemical change 4. physical change

35.

Classify the following into physical changes and chemical changes. 1. Melting of ice. 2. Heating magnesium in water. 3. Silver bromide kept exposed to sunlight. 4. Change happening to soda water on opening its bottle.

Answer»

1. physical change

2. chemical change

3. chemical change

4. physical change

Discussion

36.	Tabulate the important energy change in the following reactions.1. Magnesium burns in air 2. Heating potassium permanganate 3. Photosynthesis 4. Electroplating 5. Reaction between Sodium hydroxide and Hydrochloric acid 6. Glittering the fire fly 7. Reaction in electrochemical cells
Answer» 1. Liberates heat energy 2. Absorbs heat energy 3. Absorbs light energy 4. Absorbs electric energy 5. Liberates heat energy 6. Liberates light energy 7. Liberates electric energy

36.

Tabulate the important energy change in the following reactions.1. Magnesium burns in air 2. Heating potassium permanganate 3. Photosynthesis 4. Electroplating 5. Reaction between Sodium hydroxide and Hydrochloric acid 6. Glittering the fire fly 7. Reaction in electrochemical cells

Answer»

1. Liberates heat energy

2. Absorbs heat energy

3. Absorbs light energy

4. Absorbs electric energy

5. Liberates heat energy

6. Liberates light energy

7. Liberates electric energy

Discussion

37.	What is your observation when a glowing in inscent stick is brought to the mouth of test tube containing potassium permanganate which is heated? Give reason.
Answer» The stick flares up. When potassium permanganate is heated, it decomposes to form potassium manganate, manganese dioxide and oxygen.

Discussion

38.	Acid is added to water for its electrolysis. Why?
Answer» Pure water is not an electric conductor. But if some acid, alkali or salt is added, lot of ions are formed in it and water will become an electric conductor.

Discussion

39.	How electrical energy is produced by batteries?
Answer» Tn a battery, electrical energy is produced by the chemical reaction between zinc and sulphuric acid or by zinc and carbon. Electrical energy is produced by chemical reactions. Here chemical energy is converted to electrical energy.

Discussion

40.	Give an example each for the reaction of liberation of heat and absorption of heat from daily life.
Answer» Exothermic reaction: Burning of wood Endothermic reaction: Marble is heated to quick lime

40.

Give an example each for the reaction of liberation of heat and absorption of heat from daily life.

Answer»

Exothermic reaction: Burning of wood

Endothermic reaction: Marble is heated to quick lime

Discussion

41.	Photosynthesis is the reaction that responsible to sustain life on the earth. Write the equation of the reaction. What is the energy change in it?
Answer» 6H₂O + CO₂ → C₆H₁₂ O₆ + 6O₂ Light energy is absorbed in it.

41.

Photosynthesis is the reaction that responsible to sustain life on the earth. Write the equation of the reaction. What is the energy change in it?

Answer»

6H₂O + CO₂ → C₆H₁₂ O₆ + 6O₂

Light energy is absorbed in it.

Discussion

42.	Take sodium chloride solution in a beaker. Add to it a few drops of phenolphthalein. With the help of two carbon rods, let electricity pass through the solution. Record your observations. What is your inference?
Answer» Sodium chloride is decomposed into sodium and chlorine

Discussion

Explore topic-wise InterviewSolutions in .

Kindling fire by pouring oil. Heap up some potassium permanganate on a tile. Keep a piece of dry cotton wick on top of it. Pour one or two drops of glycerine on the wick. Observe the changes.

Give two examples of covalent compounds.

Write a chemical equation (unbalanced) for the following reaction:Magnesium salts during the softening of hard water.Magnesium chloride + Sodium carbonate \(\longrightarrow\) Magnesium carbonate + Sodium chloride

Name the salts present in hard water.

Give two examples of ionic compounds.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)(i) H2O Molecule is an ionic compound.(ii) The bond between two chlorine atoms is a covalent band(iii) Arrow indicates the direction of the reaction.

Distinguish between the following:Physical change and Chemical change:

What are the methods of classification of changes?

What is the difference between physical and chemical change?

Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms.Sodium Chloride.

What is the observation when two drops of phenolphthalein is added to the solution obtained after the reaction of sodium with water? Justify your answer.

Write a chemical equation (unbalanced) for the following reaction:Calcium carbonate + Hydrochloric acid \(\longrightarrow\) Calcium chloride + carbon dioxide + water

Write a chemical equation for combustion of fuel.

Explain :Combustion of fuel is a fast and irreversible chemical change.

Name the products of photosynthesis.

Name the reactants in photosynthesis.

Write name the products of respiration.

Name the reactants in respiration.

Match the columns:Column IColumn II1. Respirationa. Potassium and fluorine2. Acid + Baseb. Glucose and oxygen3. Photosynthesisc. Carbon dioxide and water4. Ionic bondd. Salt and water

Match the pair :Column IColumn II1. Photosynthesisa. Tendency to lose electrons2. Waterb. Reactant in combustion process3. Sodium chloridec. Chemical change4. Dissolution of salt in waterd. Covalent bond5. Carbone. Ionic bond6. Fluorinef. Physical change7. Magnesiumg. Tendency to form anion

What is elecroplating? How are the electrode and the electrolyte selected when a metallic object is to be plated with another special metal?

Give an example each for exothermic and endothermic reactions.

List out the instruments that use electrochemical cells. What are the merits and demerits of using such cells?

Some medicines and chemicals are kept in dark bottles, why?

Give scientific reason:Ionic compounds are formed due to the combination of metallic and nonmetallic atoms.

Distinguish between the following:Ionic bond and Covalent bond.

Tabulate the following changes into physical and chemical changesWater changes to water vapour burning wood rusting the iron explosion of crackers cutting the wood Magnesium burns in air Ice is melting

i. sodium + water → sodium hydroxide + hydrogenii. Magnesium + oxygen → magnesium oxideWrite the reactants and products of these reactions.

Assess the chemical reactions given below and answer the questions.1. Calcium carbonate + heat → Calcium oxide + Carbon dioxide2. Calcium oxide + water → Calcium hydroxide + heata. Mention the reactants and products in each case.b. Which among these is endothermic?Which one is exothermic?

Classify the following into physical changes and chemical changes. 1. Melting of ice. 2. Heating magnesium in water. 3. Silver bromide kept exposed to sunlight. 4. Change happening to soda water on opening its bottle.

Tabulate the important energy change in the following reactions.1. Magnesium burns in air 2. Heating potassium permanganate 3. Photosynthesis 4. Electroplating 5. Reaction between Sodium hydroxide and Hydrochloric acid 6. Glittering the fire fly 7. Reaction in electrochemical cells

What is your observation when a glowing in inscent stick is brought to the mouth of test tube containing potassium permanganate which is heated? Give reason.

Acid is added to water for its electrolysis. Why?

How electrical energy is produced by batteries?

Give an example each for the reaction of liberation of heat and absorption of heat from daily life.

Photosynthesis is the reaction that responsible to sustain life on the earth. Write the equation of the reaction. What is the energy change in it?

Take sodium chloride solution in a beaker. Add to it a few drops of phenolphthalein. With the help of two carbon rods, let electricity pass through the solution. Record your observations. What is your inference?