2019 - JAMB Chemistry Past Questions and Answers - page 8
If the cost of electricity required to discharge 10g of an ion X\(^{3+}\) is N20.00, how much would it cost to discharge 6g of ion Y\(^{2+}\)?
[1 faraday = 96,500C, atomic masses are X = 27, Y = 24]
X\(^{3+}\) + 3e\(^-\) \(\to\) X
3F = 27g
xF = 10g
\(\frac{x}{3} = \frac{10}{27} \implies x = \frac{10}{9} F\)
\(\frac{10}{9}\)F \(\equiv\) N20.00
1F is equivalent to x
\(\frac{1}{\frac{10}{9}} = \frac{x}{20}\)
\(\frac{9}{10} = \frac{x}{20} \implies x = N18.00\)
1F is equivalent to N18.00.
Y\(^{2+}\) + 2e\(^-\) \(\to\) Y
2F = 24g
xF = 6g
x = \(\frac{6 \times 2}{24} = \frac{1}{2} F\)
1F = N18.00
\(\frac{1}{2}\)F = \(\frac{1}{2} \times N18.00\)
= N9.00
The cost of discharging 6.0g of a divalent metal, X from its salt is ₦12.00. What is the cost of discharging 9.0g of a trivalent metal, Y from its salt under the same condition?
[X = 63, Y = 27, 1F = 96,500C]
For X: X\(^{2+}\) + 2e\(^-\) \(\to\) X
2F = 63g
xF = 6g
x = \(\frac{6 \times 2}{63} = \frac{4}{21} F\)
\(\frac{4}{21}\)F = N12.00
1F = \(\frac{12}{\frac{4}{21}}\)
= N63.00
1F is equivalent to N63.00.
For Y: Y\(^{3+}\) + 3e\(^-\) \(\to\) Y
3F = 27g
xF = 9g
x = \(\frac{3 \times 9}{27}\)
= 1F
1F = N63.00
How many alkoxyalkanes can be obtained from the molecular formula C\(_4\)H\(_{10}\)O?
4
2
1
3
The 3 alkoxyalkanes are:
- ethoxlethane
- methoxylpropane
- propoxylmethane
The reaction \(2H_2 S + SO_2 \to 3S + 2H_2 O\) is
A solution X, on mixing with AgNO\(_3\) solution gives a white precipitate soluble in aqueous NH\(_3\), a solution Y, when also added to X, also gives a white precipitate which is soluble when heated solutions X and Y respectively contain