Question

Granulated zinc is preferred to metallic zinc in the preparation of hydrogen using dilute acid.

Answer 1

Hint:This question depends on surface area of reactants. As the exposed surface area of reactants is increased more and more product is formed.

Complete step-by-step answer:
We should first know about the reaction between granulated zinc and dilute acid.
Here in place of dilute acid we are taking dilute hydrochloric acid. When this hydrochloric acid is added to granulated zinc placed in a test tube, a colourless and odourless gas is evolved with bubbles.
The chemical reaction can be written as:
\[Zn\text{ }+\text{ }2HCl\text{ }\to \text{ }ZnC{{l}_{2}}+\text{ }{{H}_{2}}\]​
This colourless and odourless gas is hydrogen. It is identified by pop sound when we bring flame near it.
Now, coming back to our question granulated zinc is preferred to metallic zinc in the preparation of hydrogen because granulated zinc has more surface area exposed to the acid, so the reaction can occur more rapidly. It should be noted also that granulated zinc is preferred over metallic zinc because granulated Zinc has impurities of copper which acts as a catalyst and speeds up the process.
We should know that the surface area of a catalyst most certainly does affect the rate of reaction. We should understand this as that when particles collide they have a greater chance of reacting with each other. But during a reaction, not all of the reaction will take place on the catalyst itself. Only those particles in contact with the catalyst will be catalysed. So, by increasing the surface area of the catalyst, by using a powdered catalyst we ensure that there are a greater number of collisions on the catalyst itself and thus the reaction will proceed at a faster rate. A catalyst with a small surface area would not work as well as there would be fewer collisions between particles in contact with the catalyst.
Industrial processes such as the Haber process will use powdered catalysts to ensure that the reaction proceeds as fast as possible while keeping yields high.
So, from this above discussion we came to know that it is the surface area of granulated zinc that we prefer.

Note: We should note that there are other factors on which reaction rate depends such as concentration, surface area, pressure, temperature, and the addition of catalysts. We should understand that when the concentrations of the reactants are raised, the reaction proceeds more quickly. This is due to an increase in the number of molecules that have the minimum required energy. For gases, increasing pressure has the same effect as increasing concentration. And when we increase the reaction temperature by 10 °C, it can double or triple the reaction rate. This is due to an increase in the number of particles that have the minimum energy required. The reaction rate decreases with a decrease in temperature.