Question

What mass of zinc metal is required to evolve a `30*mL` volume of dihydrogen gas from a `30*mL` volume of hydrochloric acid at `1.00*mol*L^-1` concentration?

Answer 1

From the equation you can see that one mole of Zn will react with two moles of HCl.

Explanation:

Calculate the number of moles of HCl in 30mL of 1.00M solution, and divide by 2 for moles of Zn. Then multiply that by the molecular weight of Zn.

1M = 1mole/L 0.030L * 1mole/L = 0.030 moles HCl. 0.015 moles of Zn will react.

Answer 2

Nearly `1` `"gram"` zinc metal is required.

Explanation:

`Zn(s) + 2HCl(aq) rarr ZnCl_2(aq) + H_2(g)uarr`.

Each equiv of zinc metal requires 2 equiv of hydrochloric acid for complete oxidation. This gives this molar quantity: we simply take half of the molar quantity of hydrochloric acid used.

`n_(HCl)` `=` `30xx10^-3Lxx1.00*mol*L^-1` `=` `??`

`n_(HCl)` `=` `n_(Zn)/2`.

So the mass of zinc is simply:

`30xx10^-3Lxx1.00*mol*L^-1xx("1 equiv of zinc")/("2 equiv of acid")xx65.38*g*mol^-1` `=` `??g`