January 14, 2019
Q. 1. Why should a magnesium ribbon be cleaned before burning in air?
Answer :
Magnesium ribbon made of pure magnesium metal due to its high reactivity towards oxygen molecule led to the oxidation of magnesium when it come in contact with air this led to formation of layer of oxide on the surface of the magnesium ribbon, this layer acts as a protective layer and prevents further oxidation of pure magnesium to magnesium oxide. This layer is needed to be removed to avail pure magnesium which can be easily be removed by sanding the surface of ribbon using a sandpaper
(magnesium) (oxygen) (magnesium oxide)
Q.2. Write the balanced equations for the following chemical reactions:
(i) Hydrogen + Chlorine → Hydrochloric Acid
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
Answer :
(i) H2 (g) + Cl2 (g) → 2HCl (g)
(ii) 3BaCl2 (s) + Al2(SO4)3 (s) → 3BaSO4 (s) + 2AlCl3 (s)
(iii) 2Na(s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
Q.3.Write balanced chemical equations with state symbols for the following reactions:
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Answer :
(i) Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
(ii) NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
Q.4. A solution of substance X is used for white washing.
(i) Name the substance X and write its formula.
(ii) Write the reaction of the substance X named in (i) above with water.
Answer :
(i) Substance X is Calcium Oxide whose solution we use in water which is used for white washing.
The formula of substance X is CaO.
(ii) Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
Q.5. Why the amount of a gas collected in one of the test-tubes double in volume as compared to other test tube during the electrolysis of water? Name this gas.
Answer :
Electrolysis of Water produces 2 volumes of Hydrogen Gas and 1 Volume of Oxygen gas through which we can conclude that ratio of Hydrogen to Oxygen is 2:1 by Volume in Water. Hence one of test tube has double the amount of gas as compared to other test tube.
Q.6.Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer :
When an iron nail is dipped in copper sulphate solution, then the colour of copper sulphate solution changes because iron displaces copper from copper sulphate solution to form light green solution of iron sulphate. This reaction is known as displacement reaction.
This displacement occurs because iron is more reactive than copper.
The reaction involved here is:
Q.7. Give an example of a double displacement reaction.
Answer :
**Note: In a double displacement reaction, the positive and the negative ions exchange places and form new products, as shown in the figure given below:
Examples:
1) When Barium Chloride is added to Copper Sulphate Solution, a double displacement reaction takes place resulting in the formation of white precipitate of Barium Sulphate along with Copper Chloride Solution
2) Another Example Double Displacement Reaction is as follow:-
Q.8. Identify the substances that are oxidised and the substances that are reduced in the following reactions:
(i) 4Na (s) + O2 (g) → 2Na20 (s)
(ii) CuO (s) + H2 (g) → Cu (s) + H2O (l)
Answer :
(i)
If a substance gain oxygen during a reaction, it is said to be oxidized. During this reaction, the sodium is gaining oxygen and is being oxidized. Oxygen is getting reduced.
(ii)
During this reaction, copper oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidized.
Answer :
Magnesium ribbon made of pure magnesium metal due to its high reactivity towards oxygen molecule led to the oxidation of magnesium when it come in contact with air this led to formation of layer of oxide on the surface of the magnesium ribbon, this layer acts as a protective layer and prevents further oxidation of pure magnesium to magnesium oxide. This layer is needed to be removed to avail pure magnesium which can be easily be removed by sanding the surface of ribbon using a sandpaper
(magnesium) (oxygen) (magnesium oxide)
Q.2. Write the balanced equations for the following chemical reactions:
(i) Hydrogen + Chlorine → Hydrochloric Acid
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
Answer :
(i) H2 (g) + Cl2 (g) → 2HCl (g)
(ii) 3BaCl2 (s) + Al2(SO4)3 (s) → 3BaSO4 (s) + 2AlCl3 (s)
(iii) 2Na(s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
Q.3.Write balanced chemical equations with state symbols for the following reactions:
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Answer :
(i) Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
(ii) NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
Q.4. A solution of substance X is used for white washing.
(i) Name the substance X and write its formula.
(ii) Write the reaction of the substance X named in (i) above with water.
Answer :
(i) Substance X is Calcium Oxide whose solution we use in water which is used for white washing.
The formula of substance X is CaO.
(ii) Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
Q.5. Why the amount of a gas collected in one of the test-tubes double in volume as compared to other test tube during the electrolysis of water? Name this gas.
Answer :
Electrolysis of Water produces 2 volumes of Hydrogen Gas and 1 Volume of Oxygen gas through which we can conclude that ratio of Hydrogen to Oxygen is 2:1 by Volume in Water. Hence one of test tube has double the amount of gas as compared to other test tube.
Q.6.Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer :
When an iron nail is dipped in copper sulphate solution, then the colour of copper sulphate solution changes because iron displaces copper from copper sulphate solution to form light green solution of iron sulphate. This reaction is known as displacement reaction.
This displacement occurs because iron is more reactive than copper.
The reaction involved here is:
Q.7. Give an example of a double displacement reaction.
Answer :
**Note: In a double displacement reaction, the positive and the negative ions exchange places and form new products, as shown in the figure given below:
Examples:
1) When Barium Chloride is added to Copper Sulphate Solution, a double displacement reaction takes place resulting in the formation of white precipitate of Barium Sulphate along with Copper Chloride Solution
2) Another Example Double Displacement Reaction is as follow:-
Q.8. Identify the substances that are oxidised and the substances that are reduced in the following reactions:
(i) 4Na (s) + O2 (g) → 2Na20 (s)
(ii) CuO (s) + H2 (g) → Cu (s) + H2O (l)
Answer :
(i)
If a substance gain oxygen during a reaction, it is said to be oxidized. During this reaction, the sodium is gaining oxygen and is being oxidized. Oxygen is getting reduced.
(ii)
During this reaction, copper oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidized.
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