Question 1. Why is magnesium ribbon cleaned before burning in air?
Answer: Magnesium is a reactive metal. When it comes in contact with air, it reacts with O 2 present in the air. Therefore, there is usually a layer of magnesium oxide on its surface.  Therefore, before burning magnesium in air, it is necessary to remove the coating on it.

Question 2. Write balanced equations for the following chemical reactions
(i) Hydrogen + chlorine → hydrogen chloride
(ii) Barium chloride + aluminum sulphate → barium sulphate + aluminum chloride
(iii) Sodium + water → sodium hydroxide + hydrogen
Answer – (i) H 2 (hydrogen) + Cl 2 (chlorine) → 2HCl (hydrogen chloride)
(ii) 3BaCl 2 (barium chloride) + Al 2 (SO 4 ) 3 (aluminium sulphate) → 3BaS 4 (barium sulphate) + 2AIC 3 (aluminium Chloride)
(iii) 2Na(Sodium) + 2H 2 O(Water) → 2NaOH (Sodium Hydroxide) + H 2 (Hydrogen)

Question 3. Write balanced chemical equations for the following reactions with their state symbols:
(i) Solutions of barium chloride and sodium sulphate react in water to form a solution of sodium chloride and a precipitate of insoluble barium sulphate.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to form sodium chloride solution and water.
Answer- (i)  BaCl3(aq)(barium chloride) +  Na3SO4(aq) (sodium sulphate) → BaSO4(s)(barium sulphate) + 2NaCl(aq) (sodium chloride)
(ii) NaOH( aq)(sodium hydroxide) + HCI(aq) (hydrochloric acid) → NaCl(aq) (cadmium chloride) + H 2 O(l)(water)

Question 1. The solution of a substance ‘X’ is used for whitening.
(i) Write the name of substance ‘x’ and its formula.
(ii) Write the reaction of substance ‘X’ mentioned in (l) above with water.
Answer – (i) Substance ‘X’ is quicklime. Its chemical name is calcium oxide and formula is CaO.
(i) CaO(s)(calcium oxide) + H 2 O(l)(water) → Ca(OH) 2 (aq) (calcium hydroxide)

Question 1. When an iron nail is dipped in copper sulphate solution, why does the color of the solution change?
Answer: When copper sulphate solution reacts with iron, the following reaction occurs:
CuSO 4 (aq)(copper sulphate) + Fe(s)(iron) → FeSO 4 (aq)(ferrous/iron sulphate) + Cu(s) ) (Copper)
Copper sulphate solution is blue in colour. Iron, being more reactive than copper, displaces copper from its salt solution. Therefore, due to the formation of ferrous sulphate, the blue color disappears and a light green color is formed.

Question 2. Give an example of a double displacement reaction different from Activity 1.10 (textbook). Answer: An example of double displacement reaction is
BaCl 2 + ZnSO 4 → ZnCl 2 + BaSO 4

Question 3. What happens when dilute hydrochloric acid is added to iron powder? Tick ​​the correct answer.
(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 formed.
Answer – (a) Hydrogen gas and iron chloride are formed
Fe + 2HCl → FeCl 2 + H 2

Question 4. What is a balanced chemical equation? Why is it necessary to balance a chemical equation?
Answer: Balanced chemical equation: A chemical equation in which the number of atoms of elements is equal towards reactants and products.
Example- 2NaOH + H 2 SO 4 → Na 2 SO 4 + 2H 2 O
The chemical equation is balanced because according to the law of mass conservation, atoms can neither be created nor destroyed. .
Therefore the mass should be equal on both sides. This can be possible only if the number of atoms on both sides is equal.

Question 5. Convert the following statements into chemical equations and balance them.
(a) Nitrogen combines with hydrogen gas to form ammonia.
(b) When hydrogen sulphide gas burns in air, water and sulfur dioxide are formed.
(c) Barium chloride reacts with aluminum sulphate to give precipitate of aluminum chloride and barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Answer – (a) Skeletal equation N 2 (g) + H 2 (g) → NH 3 (g)
Balanced equation N 2 (g) + 3H 2 (g) → 2NH 3 (g)
(b) Skeletal equation H 2 S(g) + O 2 (g) (air) → H 2 O (g) SO 2 (g)
Balanced equation 2H 2 S(g) + 3O 2 (g) → 2H 2 O (l) + 2SO 2 ( g)
(c) Skeletal equation- Al 2 (SO 4 ) 3 (s) + BaCl 2 (aq) → AICI 2 (aq) + BaSO 4
Balanced equation- Al 2 (SO 4 ) 3 (s) + 3BaCla (aq) ) → 2AICIg (aq) + 3BaSOAL
(d) Skeletal equation K(s) + H 2 O(l) → KOH (aq) + H 2 (g)
Balanced equation 2K(s) + 2H 2 O (l) → 2KOH (g) + H 2 (g)

Question 6. Balance the following chemical equations
(a) HNO 3 + Ca(OH) 2 → Ca(NO 3 ) 2 + H 2 O
(b) NaOH + H 2 SO 4 → Na 2 SO 4 + H 2 O
( c) NaCl + + AgNO 3 → AgCl + NaNO 3
(d) BaCl 2 + H 2 SO 4 → BaSO 4 + HCI
Answer-(a) 2HNO 3 + Ca(OH) 2 → Ca(NO 3 ) 2 + 2H 2 O
(b) 2NaOH + – H 2 SO 4 → Na 2 SO 4 a + 2H 2 0
(c) NaCl . + AgNO 3 → AgCI . + NaNO 2
(d) BaCl 2 + H 2 SO 4 → BaSO 2 + 2HCI

Question 7. Write balanced chemical equations for the following reactions
(a) Calcium hydroxide + carbon dioxide → calcium carbonate + water
(b) Zinc + silver nitrate → Zinc nitrate + silver
(c) Aluminum + copper chloride → Aluminum chloride + copper
(d) ) Barium chloride + potassium sulphate → Barium sulphate + potassium chloride
Answer – (a) Ca (OH) 2 + CO 2 → CaCO 3 + H 2 O
(b) Zn + 2AgNO 2 → Zn (NO 3 ) 2 + 2Ag
(c ) 2Al + 3CuCl 2 → 2AICl 2 + 3Cu
(a) BaCl 2 + K 2 SO 4 → BaSO 4 + 2KCl

Question 8. Write balanced chemical equations for the following reactions and describe the type of each reaction
(a) Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide (s) (b) Zinc carbonate (s) ) →Zinc oxide (s) + Carbon dioxide (g)
(c) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)
Answer – (a) 2KBr (aq) + Bal 2 (aq) → 2KI (aq) + BaBr 3 (s)
Type of reaction – Double displacement reaction
(b) ZnCO 3 (s) → ZnO (s) + CO 2 (g)
Type of reaction – decomposition/dissociation reaction
(c) H 2 (g) + CI 2 (g) → 2HCl (g)
Type of reaction – addition reaction
(d) Mg (s) + 2HCI (aq) ) → MgCl 2 (aq) + H 2 (g)
Type of reaction – Single displacement reaction

Question 9. What is the meaning of exothermic and endothermic reaction? Give examples.
Answer-Exothermic reaction-Those reactions in which heat is also emitted along with the products, are called exothermic reactions.
C(s) coal + O 2 (g) → CO 2 (g) + heat
Endothermic reactions-those reactions in which the reactants absorb heat or for which heat is absorbed to occur. Are called endothermic reactions.
Example- N 2 (g) +O 2 (g) + heat → 2NO (g) (nitric oxide).
2AgBr (s)→ 2Ag + Br 2 (g)

Question 10. Why is respiration called an exothermic reaction? Describe.
Answer: Respiration means oxidation of glucose in cells in which complete decomposition of glucose occurs after several reactions. This process takes place in the mitochondria inside the cells through enzymes.
2 H 12 O 6 (aq)(glucose) + 6O 2 (aq) → 6CO 2 (aq) +6H 2 O (l) + Energy
In this reaction, energy is released, which can be stored in the cells in the form of ATP. is taken. Therefore respiration is called exothermic reaction.

Question 11. Why is decomposition reaction called the opposite of combination reaction? Write equations for these reactions.
Answer: Decomposition reaction is said to be the opposite of combination reaction because in decomposition reaction a single reactant forms two or more products whereas in combination reaction two or more reactants combine to form a single product.
This can be described with the help of the following example:
Combination reaction- 2H 2 (8) +O 2 (g)→ 2H 2 O (g) + Energy
Dissociation reaction- 2H 2 O (l) → 2H 2 (g) + O 2 (g)

Question 12. Write one equation each of those decomposition reactions in which energy is provided in the form of heat, light and electricity.
Answer: The dissociation reactions which require different types of energy are-
(i) CaCO 3 (s)→CaO(s)+CO 2 (g)
(ii) 2AgCI(s) →2Ag(s)+ Cl 2 (g)
(iii) 2H 2 O)→2H 2 (g)+O 2 (8)

Question 13. What is the difference between displacement and didisplacement reactions? Write the equations of these reactions.
Answer: Displacement reactions – Those reactions in which an atom or group of atoms in a compound is replaced by another atom or group of atoms are called displacement reactions.
Example- CuSO 4 (aq) + Fe (s) – FeSO 4 (aq) + Cu (s)
Here iron displaces copper from copper sulphate solution.
Double displacement reactions: Those reactions in which ions of reactants are exchanged are called double displacement reactions.
Example- BaCl 2 (aq) Barium chloride + H 2 SO 2 (aq) Sulfuric acid →BaSO 4 (s) Barium sulphate + HCl(aq) Hydrochloric acid.

Question 14. In the purification of silver, silver is displaced by copper metal to obtain silver from silver nitrate solution. Write the reaction for this process.
Answer Cu (s)+2AgNO 3 (aq)→ Cu (NO 3 ) 2 (aq) + 2Ag (s)

Question 15. What do you understand by precipitation reaction? Explain by giving examples.
Answer: Precipitation reaction: A reaction in which white colored precipitate is formed is called precipitation reaction.
Na 2 SO 4 (s)Sodium sulphate + BaCl 2 (aq)Barium chloride → BaSO 4 (s)Barium sulphate↓1 + 2 NaCl(aq)Sodium chloride
Pb(NO 3 ) 2 (aq)Lead nitrate + 2KI(aq )Potassium iodide →2KNO 3 (aq)Potassium nitrate + PbI 2 Lead iodide

Question 16. Explain the following terms on the basis of addition or loss of oxygen. Give two examples for each.
(a) Oxidation, (b) Reduction
Answer – (a) Oxidation – If a substance accepts oxygen or loses hydrogen during the reaction, then the reaction is called oxidation reaction.
CCarbon + O 2 Oxygen → CO 2 Carbon Dioxide + Heat
2CuCopper + O 2 Oxygen → 2CuoCopper (II) Oxide
(b) Reduction – If during any reaction there is loss of oxygen or increase of hydrogen, then this reaction is called reduction. .
Znozinc oxide + ccoke/carbon → Znzinc + cocarbon monoxide
CuOCopper oxide + H 2 hydrogen → Cucopper +H 2 OWater
Copper oxide is reduced to copper.

Question 17. When a brown colored shiny element ‘X’ is heated in the presence of air, it turns black. , Name this element ‘X’ and that black colored compound.
Answer: Element ‘X’ is copper and the black colored compound is copper oxide. When the brown element copper was heated in air. When this happens, a black colored compound called copper oxide is formed. The equation can be written as follows –
2Cu (s) Copper (brown) oxide (black) + O 2 (g) 2CuO(s) Copper (II) oxide (black)

Question 18. Why do we paint iron objects?
Answer: Iron is a reactive metal. It easily reacts with oxygen gas in the presence of moisture present in the air, causing a brown layer (rust) to form on iron objects. This process is called corrosion or rusting of iron. is called the process of.
4Fe + xH 2 O+ 3O 2 → 2Fe 2 O 3 . xH 2 O
(Rust) Therefore, iron is painted to protect it from coming in contact with oxygen.

Question 19. Why are oil and fatty foods affected by nitrogen?
Answer: Oily and fatty foods are affected by nitrogen because nitrogen is an inert gas. It protects such foods from getting oxidized. Therefore it prevents food items from spoiling.

Question 20. Iron + Steam → Ferric Oxide + Hydrogen Balance this equation and write the equation. Answer-Equation-3Fe(s) + 4H 2 O(g) → Fe 2 O(g) + 4H 2 (g)


Question 21. Tell the type of reaction 2Fesoa→ Fe,os+So, + so,
Answer-Dissociation ) reaction.

Question 22. What are displacement reactions?
Answer: Those reactions in which a reactive element displaces a less reactive element from its compound are called displacement reactions.

Question 23. Write an equation in which a reactive metal displaces hydrogen from water.
Answer-2Na + 2H 2 O → 2NaOH + H 2

Question 24. Give an example where a reactive metal displaces hydrogen from dilute acids. Answer-Zn + dilute 2HCl → ZnCl 2 + H 2

Question 25. Write a displacement reaction in which metallic magnesium and copper sulphate solutions are involved.
Answer – Mg (s) + CuSO 4 (aq) + MgSO 4 (aq) + Cu (s)

Question 26. Name a metal which when kept in ferrous sulphate solution, loses its light green color. . Write the chemical equation for this.
Answer: Those metals which are more reactive than iron (Mg, Zn etc.) can discolor the green color of ferrous sulphate.
Zn (s) + FeSO 4 (aq) →ZnSO 2 (aq) + Fe (s)

Question 27. A person accidentally stored ferrous sulphate solution in an aluminum vessel. After a few days he found that there were some holes in the vessel. What reaction could possibly have occurred?
Answer-2AI (s) + 3FeSO 4 (aq) → AI 2 (SO 4 ) 3 + 3Fe Aluminum is more reactive than iron, hence it displaces iron from ferrous sulphate solution due to which there is a hole in the aluminum vessel. Let’s go.

Question 28. Write the electrolysis equation of Alumina.
Answer-Equation- 2AI 2 O 3 Aluminum oxide (alumina in molten state) → 4AI Aluminum + 30 2 Oxygen

Question 29. Write the chemical reaction of slaking lime.
Answer – Chemical reaction of slaking lime
CaOCalcium oxide + H 2 OWater → Ca(OH) 2 Calcium hydroxide + heat

Question 30. Write the chemical equation for heating potassium chlorate.
Answer-2KCIO 2 (s)Potassium chloride →2KCI(s)Potassium chlorate + 30 2 (g) Oxygen

Question 31. Give an equation to show double displacement.
AgNO 3 (aq) + KBr(aq) →AgBr ↓ +KNO 3 (aq) . 
Silver Nitrate Potassium Bromide Silver Bromide Potassium Nitrate

Question 32. Is the following reaction possible? If not, why?
Cu (s) + ZnSO 4 (aq) → CuSO 4 (aq) + Zn (s)
Answer – No, this reaction is not possible because copper is less reactive than zinc, hence it cannot displace zinc from zinc sulphate solution. Could.

Question 33. Give an example of a precipitation reaction.
Answer- NaCl (aq) + AgNO 3 (aq) → AgClSilver chloride (white precipitate) ↓+ NaNO 3 (aq)

Question 34. Give an example of an anti acid.
Answer: Baking soda, (sodium hydrogen carbonate) (NaHCO 3 ) is an antacid.

Question 35. Define oxidation process on the basis of gain/loss of hydrogen/oxygen.
Answer: A chemical reaction in which there is loss of hydrogen or gain of oxygen is called oxidation reaction.

Question 36. Give an example of oxidation reaction.
Answer- S+O 2 → SO 2 Sulfur has been oxidized into sulfur dioxide.

Question 37. Write and balance the dissociation process of lead nitrate.
Answer-2Pb(NO 3 ) 2 Lead Nitrate → 2Pbo(s)Lead Oxide + ANO 2 (g)Nitrogen Dioxide + O 3 2(g) Oxygen

Question 38. Which reactant is being oxidised in the following chemical reaction?
ZnO + C → Zn + CO
Answer- Carbon (C) is being oxidised.

Question 39. What are metabolic (reduction – oxidation) reactions?
Answer: Those chemical reactions in which reduction and oxidation occur simultaneously are called metabolic reactions.

Question 40. Give an example of metabolic reaction.
Answer- 2AI +.Fe 2 O 3 → Al 2 O 3 + 2Fe

Question 41. What happens when silver chloride is kept in sunlight, write the chemical equation.
Answer-2AgCI (s) → 2Ag (s) + Cl 2 (g) When silver chloride is kept in sunlight, silver chloride gets decomposed.

Question 42. What type of reaction occurs between an acid and a base, when they together form salt and water? Answer: This is a double displacement (and neutralization) reaction.
NaOHAlkali + HCl Acid → NaClSalt + H 2 OWater

Question 43. What happens when dilute HCI is poured on iron powder?
Answer: Iron reacts with dilute HCI and H2 gas is evolved.
Fe + dilute 2HCl → FeCl 2 + H 2 ↑

Question 44. In silver refining, silver is displaced by copper to obtain silver from silver nitrate solution. Write the reaction.
Answer- 2AgNO 3 (aq) + Cu (s) → 2Ag(s) Pure silver + Cu (NO 3 ) 2 (aq)

Question 45. What are oxidizing substances?
Answer: Those substances which get reduced and oxidize other substances are called oxidizing agents.

Question 46. What are reducing substances?
Answer: Those substances which themselves get oxidized and reduce other substances are called reducing substances.

Question 47. Name the reduced and oxidized substances in the following reaction
CuO(s)+CO(g) → Cu (s)+CO 2 (g).
Answer- CuO has been reduced to Cu.
Oxidation of CO has taken place into CO 2 .

Question 48. Write the formula for quicklime and slaked lime.
Answer – Quicklime, Calcium Oxide – CaO
Slaked Lime, Calcium Hydroxide – Ca(OH) 2

Question 49. Why does the green color of ferrous sulphate disappear when it is heated in a test tube?
Answer: The green color of ferrous sulphate, FeSO 4 .7H 2 O is due to the water of crystallization present in it. When it is heated, the crystal water escapes from it, due to which its green color disappears, even if it does not decompose.

Question 50. Which substance of calcium is used in making cement? Answer: Quicklime – Calcium oxide (Cao) is used in making cement.

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