This mine water is acidic because it has flowed through rock containing iron sulfide. Fig. 1 shows a treatment tank where powdered limestone is added before...
Question 1 Report
This mine water is acidic because it has flowed through rock containing iron sulfide. Fig. 1 shows a treatment tank where powdered limestone is added before the water enters a stream. The pH is measured during treatment.
(a) Name the type of substance added to neutralise the acid. [1]
(b) Give the pH number of a neutral solution. [1]
(c) Suggest why acidic water containing dissolved iron compounds can harm fish. [1]
(d) Complete the word equation: acid + carbonate → salt + water + ............ . [1]
(e) Use the information to suggest why limestone is added as a powder rather than large pieces. [1]
The table below shows the mass of iron wool before and after it was heated in air in a crucible. Fig. 1 shows the crucible held with tongs above a Bunsen burner.
| measurement | mass / g |
|---|---|
| empty crucible | 24.60 |
| crucible + iron wool before heating | 26.10 |
| crucible + product after heating | 26.74 |
(a) Use Table 1 to calculate the mass of iron wool used. [1]
(b) Use Table 1 to calculate the mass gained during heating. [1]
(c) Suggest why the mass increases. [1]
(d) Name the compound formed when iron reacts with oxygen. [1]
(e) Give one reason why tongs are used. [1]
Answer Details
Labelled answer diagram:
Neutralising mine water
- (a) A substance used to neutralise an acid is an alkali, base, or carbonate. Limestone is calcium carbonate. [1]
- (b) A neutral solution has pH 7. [1]
- (c) Acidic water containing dissolved iron compounds can kill fish or damage aquatic organisms. [1]
- (d) acid + carbonate → salt + water + carbon dioxide. [1]
- (e) Limestone powder has a larger surface area, so it reacts faster with the acidic water. [1]
Heating iron wool in air
- (a) \[26.10\text{ g}-24.60\text{ g}=\mathbf{1.50\text{ g}}\]
This is the mass of iron wool used. [1] - (b) \[26.74\text{ g}-26.10\text{ g}=\mathbf{0.64\text{ g}}\]
This is the mass gained during heating. [1] - (c) The mass increases because oxygen atoms combine with the iron. [1]
- (d) The compound formed is iron oxide. [1]
- (e) Tongs are used because the crucible is hot and they prevent burns. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
