# Chemistry 2018 | Study Mode

Question 21
A
$$1.2 \times 10^{22}$$
B
$$1.2 \times 10^{23}$$
C
$$2.4 \times 10^{22}$$
D
$$2.4 \times 10^{23}$$
##### Explanation

$$1mole = 6.02 \times 10^{23} ions$$

$$0.02moldm^{-3} = 0.02 \times 6.02 \times 10^{23}$$

=$$0.1204 \times 10^{23} = 1.204 \times 10^{22}$$

$$\approxeq 1.2 \times 10^{22}$$

Question 22
A
water
B
carbon(IV) oxide
C
fire blanket
D
sand
##### Explanation

In order to extinguish a petrol fire, you have to cut off the oxygen. This can be done by using carbon dioxide gas to dilute the oxygen available and stop the burning.

Question 23
A
production of ammonia
B
manufacture of cement
C
photosynthesis
D
combustion
##### Explanation

Photosynthesis is the process of food-making in plants, it doesn't have any by-products that pose a threat to the environment. Infact, the plants use our waste product of respiration (Carbon dioxide) and uses it for the photosynthetic process and gives off oxygen as by-product.

Question 24
A
particle size of the reactants
B
vigorous stirring of the reaction mixture
C
presence of a catalyst
D
change in concentration of the reactants
##### Explanation

The position of equilibrium will shift under the effects of changes in temperature, pressure and concentration.

Question 25
A
The water is at lower temperature than the ice
B
Energy is absorbed when the ice changes to water
C
Energy is released when the ice changes to water
D
The water molecules vibrate about a fixed point
##### Explanation

Heat energy near the ice gets absorbed into the ice. The energy breaks the bonds of the ice, causing it to melt into liquid water. On other words, when ice melts, the energy gets absorbed into the water.

Question 26
A

Unlike gases, vapours are liquids at room temperature

B

Unlike gases, vapour can easily be condensed into liquids

C

Unlike gases, vapour is readily converted into solids

D

Vapours are generally denser than gases

##### Explanation

Vapour is the equilibrium state between the gases and liquid, and it can bounce back to its original form, liquid with constant temperature and pressure exerted on it.

Question 27
A
150$$cm^{3}$$
B
75$$cm^{3}$$
C
30$$cm^{3}$$
D
25$$cm^{3}$$
##### Explanation

Using the formula, $$\frac{C_{A}V_{A}}{C_{B}V_{B}} = \frac{N_{A}}{N_{B}}$$, we have

$$\frac{0.1 \times V_{A}}{0.3 \times 25} = \frac{2}{1}$$

$$V_{A} = \frac{0.3 \times 25 \times 2}{0.1 \times 1}$$

$$V_{A} = 150cm^{3}$$

Question 28
A
reactivity and oxidation respectively
B
conductivity and corrosiveness respectively
C
melting point and reduction respectively
D
electronegativity and solubility respectively
##### Explanation

Copper is not active enough to replace hydrogen in an acid. Also, nitric acid is a strong oxidizing agent which quickly oxidises hygrogen to water.

Question 29
A
$$CH$$
B
$$CH_{2}$$
C
$$P_{2}O_{5}$$
D
$$N_{2}O_{4}$$
##### Explanation

The empirical formula is always in the ratio of the smallest positive integer, hence, $$N_{2}O_{4}$$ has an empirical formula $$NO_{2}$$.

Question 30
A
heat capacity
B
boiling point
C
mass
D
colour
##### Explanation

Any pure substance will have a specific melting and boiling point. The presence of impurities alters the boiling point of benzene.

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