# Chemistry (2017) | Study Mode

Question 41
A
positive ion
B
neutral atom of a metal
C
neutral atom of a non-metal
D
negative ion
##### Explanation
protons = 9

neutrons = 10

electrons = 10

Electronic configuration = 2, 8

Ground state Electronic configuration=2, 7

It means that the atom has gained an electron thereby making it have a negative ion.

When an atom donates an electron, it becomes positively charged.

When an atom accepts an electron, it becomes negatively charged

Question 42
A

Reforming

B

Polymerization

C

Distillation

D

Cracking

##### Explanation

Ethene is produced from cracking which involves breaking up large hydrocarbon molecules into smaller and more useful bits. This is achieved by using high temperatures and pressures without a catalyst.

C15H32 2C2H4 + C3H6 + C8H14
......heat...ethene........propene.........octane

Question 43
A
2.536
B
1.623
C
4.736
D
0.394
##### Explanation
For an ideal gas PV = nRT

Amount in moles = n

Volume v = 10.5dm3

Pressure P = 6atm

Temperature T = 30C + 273 = 303k

R, Gas constant = 0.082 atmdm3k-1 mol

Recall from ideal gas equation

pv = nRT

n = $$\frac{RV}{RT}$$

n = $$\frac{6 \times 105}{0.082 \times 303}$$

n= 2.536mol

Question 44
A
10.0s
B
12.5s
C
17.7s
D
32.0s
##### Explanation
Rate of diffusion $$\frac{\alpha_1}{Density}$$ or $$\frac{1}{\sqrt{Mm}}$$

Rate = $$\frac{1}{time}$$

$$\frac{1}{time}$$ $$\frac{\alpha_1}{Density}$$ or $$\frac{1}{\sqrt{Molarmass}}$$

Time $$\alpha \sqrt{Density}$$ or $$\sqrt{Molarmass}$$

At constant volume of 100cm3

$$\frac{t_{o2}}{\sqrt{Mn_{o2}}}$$ = $$\frac{t_{n2}}{\sqrt{1 \times 2}}$$

$$\frac{50}{4 \sqrt{2}}$$ = $$\frac{t_{n2}}{\sqrt{2}}$$

tn2= 12.5s

Question 45
A
water
B
mercury
C
paraffin
D
phenol
##### Explanation
Na is kept under kerosene (paraffin) to avoid reactivity with air.
Paraffin is also known as Kerosene.
Na(sodium) is kept in kerosene to prevent it from coming in contact with oxygen and moisture. If this happens, it will react with the moisture present in air and form sodium hydroxide.

Question 46
A
calcium hydrogentrioxocarbonate (IV)
B
calcium trioxocarbonate (IV)
C
calcium tetraoxosulphate (VI)
D
calcium hydroxide
##### Explanation
Furring of kettles is caused by the temporary hardness in water. Temporary hardness in water is caused by calcium and magnesium trioxocarbonate (IV)
CaCO3 causes the furring of kettles

Question 47
A
B
bacteria
C
temporary hardness
D
permanent hardness
##### Explanation
Chlorine helps to keep water from germs and bacteria.

Question 48
A

NO2

B

NH3

C

N2O

D

NO2

##### Explanation

Balancing the chemical equation.

Ca[OH]2 + 2NH4Cl CaCl2 + 2H2O + 2NH3

X = NH3

Question 49
A

negative

B

zero

C

positive

D

indeterminate

##### Explanation

$$\begin{array}{c|c} \text{Enthalpy Change [H]} & \text{Entropy Change [S]} & \text{Gibbs free Energy[G]} \\ \hline \text{Positive} & \text{Positive} & \text{depends on T, may be + or -} \\ \hline \text{Negative} & \text{Positive} & \text{always negative} \\ \hline \text{Negative} & \text{Negative} & \text{depends on T, may be + or -} \\ \hline \text{Positive} & \text{Negative} & \text{always positive} \end{array}$$

G= H - TS.
To determine whether G will be positive or negative, the value of H(change in enthalpy) and S (change in entropy) must be given. Likewise the temperature.

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