2017 - JAMB Chemistry Past Questions and Answers - page 5

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

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

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 105}{0.082 \times 303})

n= 2.536mol

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

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.

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

Chlorine helps to keep water from germs and bacteria.

Balancing the chemical equation.

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

X = NH₃

(\begin{array}{c|c}

\text{Enthalpy Change [ΔH]} & \text{Entropy Change [ΔS]} & \text{Gibbs free Energy[ΔG]} \

\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})

ΔG= ΔH − TΔS.

To determine whether ΔG will be positive or negative, the value of ΔH(change in enthalpy) and ΔS (change in entropy) must be given. Likewise the temperature.