Table 1 records results from a corrosion study on magnesium. Each test tube contained 25.0 cm3 of dilute sulfuric acid at 22 degrees C. A student placed a 0...
Question 1 Report
Table 1 records results from a corrosion study on magnesium. Each test tube contained 25.0 cm3 of dilute sulfuric acid at 22 degrees C. A student placed a 0.60 g piece of magnesium ribbon into each tube and measured the mass of the tube and its contents at intervals. Hydrogen gas escaped through a small plug of cotton wool, so the measured mass decreased as the reaction occurred. The reaction produces magnesium sulfate solution and hydrogen gas.
| Time / s | Mass of tube and contents / g |
|---|---|
| 0 | 48.60 |
| 20 | 48.48 |
| 40 | 48.40 |
| 60 | 48.35 |
| 80 | 48.33 |
| 100 | 48.33 |
Fig. 1 shows the type of apparatus used. The student repeats the investigation using powdered magnesium, while keeping the mass of magnesium, acid volume and acid concentration the same.
(a) State the gas that causes the mass to decrease. [1]
(b) Calculate the mean rate of mass loss during the first 40 s, in g/s. [2]
(c) Explain why the mass stays constant from 80 s to 100 s. [2]
(d) Give the formula of the salt in the final solution. [1]
(e) Explain why powdered magnesium is likely to give a faster reaction than magnesium ribbon. [3]
(f) State one safety precaution, other than wearing eye protection, when carrying out this reaction with acid. [1]
Answer Details
(a) The escaping gas is hydrogen. [1]
(b) Mass loss in the first 40 s:
\[48.60\text{ g}-48.40\text{ g}=0.20\text{ g}\]
\[\text{mean rate}=\frac{0.20\text{ g}}{40\text{ s}}=0.0050\text{ g/s}\]
[2]
(c) The reaction is complete, so no more hydrogen is produced and escapes. All the magnesium or all the acid has been used up. [2]
(d) Magnesium sulfate is \(\mathrm{MgSO_4}\). [1]
(e) Powdered magnesium has a larger surface area than ribbon. More acid particles can collide with magnesium each second, giving more successful collisions per second and therefore a faster reaction. [3]
(f) Use a small volume of dilute acid, keep the tube pointed away from people, clean up spills immediately, or tie back long hair. Any one. [1]
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