Introduction to Chemistry

Q.

When dilute hydrochloric acid is heated with iron-sulphide, a gas with rotten egg smell is evolved. This gas is

1. hydrogen

2. oxygen

3. hydrogen sulphide

4. sulphide

Q.

Oxygen is used by living organisms during respiration but it also supports_____________.

1. Combustion

2. Evaporation

3. Condensation

4. Distillation

Q.

Which zone represents the partial combustion in a candle flame?

1. 
   

   Outer zone

2. 
   

   Middle zone

3. 
   

   Inner zone

4. 
   

   Lower zone

Q. Evaporation occurs only at the surface of the liquid.

1. False
2. True

Q.

Define Enthalpy of Combustion.

Q.

The effervescence when vinegar is added to baking soda is due to the evolution of

1. carbon monoxide

2. carbon dioxide

3. nothing is evolved

4. oxygen

Q.

Equations that contain an equal number of atoms of each element on the two sides of the arrow head are called ___________ (skeleton/ balanced).

Q. What are the factors affecting evaporation?

Q. During a science activity, the teacher arranged a test tube as shown in the figure and asked students to predict the effect of various indicators on the given solutions. Which of the following statements are correct?
I. Turmeric solution will turn red in test tube B and C.
II. Litmus solution will turn blue in test tube A.
III. Red cabbage extract will turn green in test tube A.
IV. Litmus solution will turn red in test tubes Band C.

1. I, II and IV only
2. II, III and IV only
3. I and II
4. III and IV only

Q. Evaporation is a phenomenon that occurs:

1. only at boiling point
2. only above boiling point
3. below boiling point
4. at melting point

Q. Roshni uses a solution of ammonia and water to clean tiles in the kitchen. What would happen to the cleaning action if vinegar is used in place of water?

1. Improves the cleaning action
2. Reduces the cleaning action
3. No change in the cleaning action
4. Shouldn't be mixed as the product formed is toxic

Q. An arrow pointing downwards in a chemical reaction shows

(a) evolution of gas
(b) formation of precipitae
(c) oxidation
(d) displacement

Q. When an ionic compound dissolves in water, the compound is separated into individual _________(1). When one element substitutes another element in a compound, the reaction is known as a ____________(2) reaction. When the interchange of two ions in a reaction produces a solid compound or a molecular compound, the reaction is known as a ____________(3) reaction.

1. (1) molecules (2) decomposition (3) double displacement
2. (1) ions (2) displacement (3) double displacement
3. (1) atoms (2) exothermic (3) displacement
4. (1) atoms (2) endothermic (3) displacement

Q.

Oxygen supports the process of combustion.

1. True
2. False

Q.

_{What will you observe when barium chloride is added to sodium sulphate solution.}

Q.

Give an example of a reaction in which colour change occurs.

Q.

how does 2Mg + O2(two atoms of oxygen)becomes magnesium oxide(2MgO)?

Q.

Which zone represents the partial combustion in a candle flame?

1. 
   

   Outer zone

2. 
   

   Middle zone

3. 
   

   Inner zone

4. 
   

   Lower zone

Q.

Complete the following chemical equation and balance.

${\mathrm{Cl}}_2\left(\mathrm{g}\right)+\mathrm{KBr}\left(\mathrm{aq}\right)\to \mathrm{\_\_\_\_}+{\mathrm{Br}}_2\left(\mathrm{g}\right)$

Q.

Answer the question related to the chemical equation given below

$\mathrm{Mg}+{\mathrm{O}}_2\to \mathrm{MgO}$

1. Identify the reactants and products.
2. Balance the above and also make it more informative.
3. What is the valency of two elements involved in the reaction.

Q.

What happens when:

a) A solution of calcium hydroxide is added to red litmus paper

b) A solution of sodium chloride is added to red litmus paper

c) A solution of lemon juice is added to blue litmus paper

d) A solution of distilled water is added to red litmus paper

e) A solution of sodium hydroxide is added to turmeric [5 MARKS]