Question

Given,2 mL of sodium hydroxide solution is added to a few pieces of granulated zinc metal taken in a test tube. When the contents are warmed, a gas evolves which is bubbled through a soap solution before testing. Write the equation of the chemical reaction involved and the test to detect the gas. Name the gas which will be evolved when the same metal reacts with dilute solution of strong acid.

Answer 1

Hint: A chemical equation tells us the exact products formed by the reaction of various compounds, also it tells the nature of the products. Zinc is a transition metal that is moderately reactive so it will not displace the sodium from sodium hydroxide as Na is highly reactive. Sulfuric acid can be used as a strong acid by diluting it.

Complete answer:
When zinc granules are taken in a test tube and we add 2 mL of sodium hydroxide (NaOH), then a compound called sodium zincate will be formed. Zinc is not more reactive than sodium, so displacement will not occur. Apart from sodium zincate a gas called hydrogen gas will be evolved. The reaction is:
$2NaOH+Zn\to N{{a}_{2}}Zn{{O}_{2}}+{{H}_{2}}\uparrow $
This hydrogen gas can be detected by its burning sound. As we bring a matchstick near the mouth of the test tube, the hydrogen gas will burn with a pop sound.
When this same metal Zn reacts with strong acid which is diluted that is sulfuric acid ${{H}_{2}}S{{O}_{4}}$, then a displacement reaction occurs, where zinc displaces hydrogen and forms zinc sulfate and again the hydrogen gas is evolved, the reaction is:
$Zn+{{H}_{2}}S{{O}_{4}}\to ZnS{{O}_{4}}+{{H}_{2}}\uparrow $
So, when 2 mL sodium hydroxide is added to zinc then hydrogen gas is evolved that burns with a pop sound, and the same gas is evolved on reaction of zinc with strong dilute acid.

Note:
Sodium hydroxide is considered as a strong base, which has a capability to liberate more hydroxide ions. While sulfuric acid is a strong acid that readily liberates all its hydrogen ions. The reactivity of metals is responsible for the reaction between metals. Metals above the reactivity series are more reactive and can displace the metals below that are less reactive.