WAEC Chemistry Past Questions & Answers

1 Faraday of electricity is equal to the charge of 1 mole of electrons, which is 96,485 coulombs. The reduction of copper(II) ions in solution to copper metal requires 2 electrons per ion, so 1 Faraday of electricity will deposit 0.5 moles of copper.
1 Faraday * (2 electrons/Cu ion) / (1 mole electrons/96,485 coulombs) * (1 mole Cu/2 electrons) = 0.5 moles Cu

Amount (in moles) = Molarity × Volume
Amount (in moles) = 0.20 mol/dm³ × 100.0 cm³ / 1000 cm³/dm³ = 0.020 moles
Now, we can calculate the mass using the formula:
Mass = Amount × Molar Mass
Mass = 0.020 moles × 40.0 g/mol = 0.80 g
So, the correct answer is:0.80 g

Thermal cracking is a process used in the petroleum industry to break down long-chain alkanes (hydrocarbons) into smaller, more useful hydrocarbons. It involves the decomposition of high-molecular-weight hydrocarbons, such as heavy crude oil fractions or long-chain alkanes, into lower-molecular-weight hydrocarbons, like smaller alkanes and alkenes. During thermal cracking, high temperatures and sometimes pressure are applied to the feedstock (such as crude oil or natural gas) to initiate the decomposition reactions.

Vapour density = Relative molar mass / 2
Vapour density = 30 / 2 = 15
Therefore, the vapour density of the gaseous hydrocarbon is 15.

Phenolphthalein is an indicator that is commonly used in acid-base titrations. It is colorless in acidic solutions (pH below 8.2) and turns pink or magenta in alkaline solutions (pH above 10). In the titration of ethanoic acid (acetic acid) with sodium hydroxide (a strong base), the pH will change from acidic to alkaline as the acid is neutralized by the base