Rita added dilute hydrochloric acid to four metals. She recorded her observations in the table given below. While noting her observations she made some errors.
| Metals | Observations | |
|---|---|---|
| 1 | copper | a gas was given off |
| 2 | iron | a gas was given off |
| 3 | magnesium | no gas was given off |
| 4 | zinc | a gas was given off |
Which observation(s) made by Rita is/are correct?
(a) 1 only
(b) 3 only
(c) Both 1 and 4
(d) Both 2 and 4
(d) Both 2 and 4
Explanation –
The reactivity of these metals with dilute HCl depends on their position in the activity series:
Copper lies below hydrogen in the activity series, so it does not react with dilute HCl. Hence, no gas is given off — observation (1) is incorrect.
Iron is above hydrogen in the activity series, hence it reacts with dilute HCl liberating hydrogen gas — observation (2) is correct.
\mathrm{Fe + 2HCl \rightarrow FeCl_2 + H_2 \uparrow}Magnesium is highly reactive and reacts vigorously with dilute HCl liberating hydrogen gas — observation (3) is incorrect.
\mathrm{Mg + 2HCl \rightarrow MgCl_2 + H_2 \uparrow}Zinc is above hydrogen in the activity series and reacts with dilute HCl liberating hydrogen gas — observation (4) is correct.
\mathrm{Zn + 2HCl \rightarrow ZnCl_2 + H_2 \uparrow}Hence, observations 2 and 4 are correct.
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