Question

$2mL$ 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 a dilute solution of a strong acid.

Answer 1

Hint : When any alkali reacts with a metal it produces a salt and hydrogen gas. Since $Zn$ is a metal, it reacts with $NaOH$ to form a coordination compound called Sodium Zincate ( $N{a_2}Zn{O_2}$ ) with the evolution of ${H_2}$ gas.
Hydrogen can be easily distinguished from other gases because hydrogen produces a pop sound when introduced to a flame.

Complete Step By Step Answer:
It is given in the question that we are adding $Zn$ granule to sodium hydroxide.
As mentioned earlier when alkali is added to a metal it produces hydrogen gas. The complete chemical equation for this reaction is given as follows:
$\Rightarrow NaOH + Zn \to N{a_2}Zn{O_2} + {H_2} \uparrow$
Thus we can see that the gas evolved in this reaction is hydrogen gas. The production of a gas causes bubbling in the soap solution mentioned in the question.
Now we need to test the gas evolved and confirm that it is in fact hydrogen gas
To do that introduces a lighted splint on the way of the gas produced. If there is a squeaky pop sound, then hydrogen gas is present. The squeaky pop sound is a result of the hydrogen reacting with oxygen in the air causing a small explosion.
When the same metal, $Zn$ is reacted with a dilute solution of a strong acid like ${H_2}S{O_4}$ we will again obtain Hydrogen gas and the metal salt.
In this case the chemical equation is given as:
$\Rightarrow Zn + {H_2}S{O_4} \to ZnS{O_4} + {H_2} \uparrow$

Note :
Most of the metals will give hydrogen gas when they are reacted with acids, bases and even water to give off Hydrogen gas. This is because most of the metals (Active metals) are above hydrogen in the activity series. So metals act as reducing agents and reduce ${H^ + }$ to ${H_2}$
$Zn$ when reacted with $HCl$ will produce $ZnC{l_2}$ and hydrogen gas
$\Rightarrow Zn + HCl \to ZnC{l_2} + {H_2} \uparrow$