JAMB Chemistry Past Questions & Answers - Page 76

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

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.

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

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

\(\frac{50}{4 \sqrt{2}}\) = \(\frac{t_{n2}}{\sqrt{2}}\)

t_n2= 12.5s

For an ideal gas PV = nRT

Amount in moles = n

Volume v = 10.5dm3

Pressure P = 6atm

Temperature T = 30°C + 273 = 303k

R, Gas constant = 0.082 atmdm3k-1 mol

Recall from ideal gas equation

pv = nRT

n = \(\frac{RV}{RT}\)

n = \(\frac{6 \times 10.5}{0.082 \times 303}\)

n= 2.536mol

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
......Δheat...ethene........propene.........octane