WAEC Chemistry Past Questions & Answers - Page 43

-Potassium dichromate solution is acidified with dilute sulphuric acid to oxidise ethanol into ethanoic acid.

- Endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products.

-  A system of reactants that absorbs heat from the surroundings in an endothermic reaction has a positive ΔH.

-  examples of endothermic processes:

• Melting ice cubes.
• Melting solid salts.
• Sublimation of dry ice into carbon dioxide gas.
• Evaporating liquid water.

- When quicklime is added to water, it forms slaked lime along with the evolution of heat. There will be a rise in the temperature of the bucket. Calcium oxide reacts with water to form calcium hydroxide, also called slaked lime.

- That is adding water to quicklime produces an exothermic reaction (gives out heat) and hydrated lime.

In other terms, the stronger the acid the greater the amount of hydrogen ions present in the solution, and hence the more alkali that should be required to neutralise the solution, hence increasing the enthalpy

Where 3mols of H2So4 = 1 mol of (Al2SO4)3
y mols of H2SO4 = 0.5 mol of (Al2SO4)3
Then cross multiply to have:
y = \(\frac{3×0.5}{1}\)
y = 1.5 moles