When potassium cyanide (kcn) reacts with acids, a deadly poisonous gas, hydrogen cyanide (hcn), is given off: kcn(aq) + hcl(aq) → hcn(g) + kcl(aq) if a sample of 0.420 g of kcn is treated with an excess of hcl, calculate the amount of hcn formed in grams.

The mass of hydrogen cyanide formed is 0.17 grams

Explanation:

To calculate the number of moles, we use the equation:

     .....(1)

Given mass of KCN = 0.420 g

Molar mass of KCN = 65.12 g/mol

Putting values in equation 1, we get:

The given chemical equation follows:

As, hydrochloric acid is present in excess. So, it is considered as an excess reagent.

Thus, potassium cyanide is a limiting reagent because it limits the formation of products.

By Stoichiometry of the reaction:

1 mole of potassium cyanide produces 1 mole of hydrogen cyanide.

So, 0.0064 moles of potassium cyanide will produce = of hydrogen cyanide

Now, calculating the mass of hydrogen cyanide from equation 1, we get:

Molar mass of HCN = 27.02 g/mol

Moles of HCN = 0.0064 moles

Putting values in equation 1, we get:

Hence, the mass of hydrogen cyanide formed is 0.17 grams