(a) (i) What is meant by hardness of water? (ii) Describe briefly how you would determine what proportion of hardness in a given sample of water is due to p...

Answer Details

(a)
(i) Hardness of water refers to the presence of dissolved metal ions, mainly calcium and magnesium, in water. These ions can form insoluble salts with soap, reducing its effectiveness, and can also cause scale buildup in pipes and appliances.
(ii) To determine the proportion of hardness due to permanent hardness in a sample of water, we can first determine the total hardness by titrating the water sample with a solution of ethylenediaminetetraacetic acid (EDTA) using an indicator such as Eriochrome Black T. The EDTA will react with all the metal ions present in the water. Then, we can remove the temporary hardness by boiling the water sample to precipitate out the calcium and magnesium bicarbonates. The difference between the total hardness and the hardness after boiling will give us the proportion of permanent hardness.
(iii) Hardness of water is undesirable because it can cause scale buildup in pipes and appliances, leading to decreased efficiency and increased maintenance costs. It can also reduce the effectiveness of soaps and detergents, requiring more of these products to achieve the desired cleaning results.

(b)
(i) Reagents for the laboratory preparation of trioxonitrate (V) acid include concentrated sulfuric acid and a nitrate salt, such as potassium nitrate or sodium nitrate.
(ii) Trioxonitrate (V) acid can be prepared in the laboratory by adding a nitrate salt to concentrated sulfuric acid while cooling the mixture in an ice bath. The mixture is then gently warmed until trioxonitrate (V) acid fumes appear.
(iii)
(I) When concentrated trioxonitrate (V) acid reacts with sulfur, it produces nitrogen dioxide gas, sulfur dioxide gas, and oxygen gas.
(II) When concentrated trioxonitrate (V) acid reacts with aluminum, it produces aluminum nitrate, water, and nitrogen dioxide gas.

(c)
One example of an amphoteric oxide is aluminum oxide (Al2O3). An amphoteric oxide is a type of oxide that can react with both acids and bases to form salts and water. Aluminum oxide can react with acids to form salts such as aluminum nitrate, and can also react with bases to form salts such as sodium aluminate.