## Chemistry 2018 | Study Mode

Question 11
A
decomposition
B
hydrolysis
C
ozonolysis
D
dehydration
Explanation.

Ethene can be gotten from the dehydration of ethanol in the presence of excess $$H_{2}SO_{4}$$ or $$H_{3}PO_{4}$$.

Question 12
A
a decrease in pressure
B
an increase in pressure
C
a decrease in temperature
D
an introduction of a positive catalyst
Explanation.

The equilibrium position is shifted to the left with a decrease in pressure in this system because the number of gaseous molecules on the right is less. (Le-Chatelier's principle).

Question 13
A
0.490g
B
0.049g
C
0.245g
D
0.0245g
Explanation.

$$500cm^{3} = 0.005moldm^{-3}$$

$$1000cm^{3} = \frac{0.005}{500} \times 1000cm^{3} = 0.010moldm^{-3}$$

Molar concentration = $$\frac{mass in gdm^{-3}}{molar mass in gmol^{-1}}$$

$$0.01moldm^{-3} = \frac{mass in gdm^{-3}}{98.0gmol^{-1}}$$

(Molar mass of $$H_{2}SO_{4}$$ = (2x1) + 32 + (16x4) = 98)

$$mass in gdm^{-3} = 0.980gdm^{-3}$$

$$1000cm^{3} = 0.980g$$

$$500cm^{3} = \frac{0.980}{1000} \times 500 = 0.490g$$

Question 14
A
reducing its quantity
B
decreasing the external pressure
C
distilling it
D
increasing the external pressure
Explanation.

The easiest and most drastic way to change the boiling point is by tampering with the pressure above your water. To lower the boiling point, you need simply to decrease its external pressure.

Question 15
A
0C
B
20C
C
30C
D
40C
Explanation.

From the graph, check for their point of intersection and trace it down to the temperature axis.

Question 16
A
dissolves and the solution becomes super saturated
B
dissolves and the solution becomes unsaturated
C
precipitates and the solution remains unchanged
D
dissolves and crystals are formed
Explanation.

The point of saturation is the point it gets to and from thence, the solution can no longer take in the salt anymore. From this point, it begins to form precipitate while the solution remains unchanged.

Question 17
A
propane
B
propanoic acid
C
propyne
D
propanol
Explanation.

Thus bromine water will be decolorized by alkynes due to the presence of two pi bonds available for reaction!

Question 18
A
mechanism of electrolysis
B
electrolytic reactions
C
nature of the electrode
D
type of electrolytic cell
Explanation.

The preferential discharge of ions is influenced by:

- The position of the ions in the electrochemical series

- The concentration of the ions in the electrolyte

- The nature of the electrode

Question 19
A
3s orbital
B
2p$$_{x}$$
C
2s orbital
D
1s orbital
Explanation.

$$_{12}Mg = 2, 8, 2$$

$$= 1s^{2} 2s^{2} 2p^{6} 3s^{2}$$

Question 20
A
Fe and C
B
Fe and Ni
C
Fe, C and Ni
D
Fe, C and Al
Explanation.

Stainless steel comprises iron (Fe), chromium (Cr), manganese (Mn), silicon (Si), carbon (C) and, in many cases, significant amounts of nickel (Ni) and molybdenum (Mo).

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