Question

In a chemical equation the symbol ‘⇣’ represents

• A. the rise in temperature
• B. a fall in temperature
• C. the evolution of a gas
• D. the formation of precipitates

Answer 1

The correct option is D

the formation of precipitates

Explanation for correct option:

D:

• In a chemical equation, the downward arrow represents the formation of a precipitate.
• The formation of a solid product is indicated by the downward arrow.
• Example: Lead (II) nitrate $\left[\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\right]$ reacts with potassium iodide $\left(\mathrm{KI}\right)$ to form potassium nitrate $\left({\mathrm{KNO}}_3\right)$ and solid Lead (II) iodide $\left({\mathrm{PbI}}_2\right)$. The chemical equation is:

$\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+\mathrm{KI}\left(\mathrm{s}\right)\to {\mathrm{KNO}}_3\left(\mathrm{aq}\right)+{\mathrm{PbI}}_2\left(\mathrm{s}\right)⇣$

Here, lead iodide is an insoluble solid called precipitate.

Explanation for incorrect options:

A: There is no such symbol to indicate the rise in temperature in a chemical equation. However, the change in temperature, in general, is represented by $∆\mathrm{T}$.

B: There is no such symbol to indicate the fall in temperature in a chemical equation. However, the change in temperature, in general, is represented by $∆\mathrm{T}$.

C: In a chemical equation, the upward arrow ($⇡$) shows that a gas is liberated. Example: when zinc ($\mathrm{Zn}$) reacts with sulfuric acid (${\mathrm{H}}_2{\mathrm{SO}}_4$), zinc sulfate (${\mathrm{ZnSO}}_4$) is formed along with the liberation of hydrogen gas (${\mathrm{H}}_2$). The chemical equation is:

$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)⇡$

Final Answer:

Hence, the correct option is (D).