Indicators or Identifiers

Q. Which amongst the following observations may indicate the occurrence of a chemical reaction?

1. Formation of precipitate
2. Evolution of gas
3. Evolution of heat or light energy
4. All of the above.

Q.

Changing of water into the gases hydrogen and oxygen by electrolysis is a physical change

1. True
2. False

Q.

State the visible change and give the equation for the reaction:

A coil of Mg is heated in steam

Q. When iron filings are added to copper sulphate solution, a confirms the occurrence of a chemical change.

1. evolution of gas
2. evolution of heat
3. change in colour

Q.

What information do you get from the equation? [3 Mark]
${\text{N}}_2\text{(g)}+3{\text{H}}_2\text{(g)}\to 2{\text{NH}}_3\text{(g)}$

Q.

Which of the following is a catalyst that accelerates the decomposition of ${\mathrm{KClO}}_3$?

1. ${\mathrm{MgO}}_2$

2. $\mathrm{MnO}$

3. $\mathrm{MgO}$

4. ${\mathrm{MnO}}_2$

Q. is the catalyst used in the reaction $2H_2{O}_2\to 2H_{2}O+O_2$

1. ${\mathrm{CuSO}}_4$
2. ${\mathrm{FeSO}}_4$
3. ${\mathrm{NH}}_4\mathrm{OH}$

Q.

Observing the changes, in which of the following would you say a chemical reaction may be occurring?
(i) Heating iodine changes the colour from bluish black to purple
(ii) Mixing ammonia and hydrogen chloride gases gives fumes containing a white powdery substance
(iii) Mixing an acid and a base solution raises the temperature.
(iv) Mixing ferrous sulphide and hydrochloric acid gives off a gas with a rotten egg smell

1. (i), (ii), (iii)

2. (i), (ii), (iv)

3. (ii), (iii), (iv)

4. (i), (ii), (iii), (iv)

Q.

In which of the following reaction the physical state of the reactants or the product is not correctly represented?

1. ${\text{N}}_2\text{(g)}+3{\text{H}}_2\text{(g)}\leftrightharpoons 2{\text{NH}}_3\text{(g)}$

2. ${\text{SO}}_2\text{(g)}+{\text{Cl}}_2\text{(g)}\leftrightharpoons {\text{SO}}_2\text{(g)}$

3. $\text{Zn (s)}+\text{HCl (aq)}\leftrightharpoons {\text{ZnCl}}_2\text{(aq)}+{\text{H}}_2\text{(g)}$

4. ${\text{NH}}_3\text{(s)}+\text{HCl (aq)}\leftrightharpoons {\text{NH}}_4\text{Cl (s)}$

Q.

By giving a reason state why chemical change takes place in the following case:

Heating of zinc oxide in a hard glass test tube

Q.

Which of the following observations helps to determine whether a chemical reaction has taken place or not?

(i) Change in state.

(ii) Change in colour.

(iii) Change in shape

(iv) Evolution of gas.

(v) Change in temperature.

1. (ii), (iii), (iv), (v)

2. (iii), (v)

3. (i), (ii), (iv), (v)

4. (i), (ii), (iii), (v)

Q. Burning of wood is a chemical reaction in which heat is released.

1. False
2. True

Q. When ferrous sulphate $\left({\text{FeSO}}_4\right)$ solution combines with sodium hydroxide $\text{(NaOH)}$, the chemical change is identified by the .

1. formation of gas
2. formation of ppt
3. absoprtion of heat

Q. Match the following reactions with the changes observed during each of them.

1. Change in colour
2. Gas is evolved
3. Formation of ppt

Q.

To make the chemical reaction more informative, ___________ of reactant & product are mentioned.

1. Physical state
2. Chemical name
3. Chemical formulae
4. Chemical equation