Question

Question #a286d

Answer 1

There will be 0.116 g of HCN gas theoretically formed with complete reaction of the KCN.

Explanation:

The limiting reagent is potassium cyanide because hydrochloric acid is in excess. This means that the number of moles of hydrogen cyanide gas formed will be equal to the number of moles of potassium cyanide. We can see this from the chemical equation, as the mole ratio of KCN to HCN is 1:1.

`KCN_"(aq)"+HCl_"(aq)"rarrKCl_"(aq)"+HCN_"(g)"`

So, now we need to know the number of moles of KCN used. We need to find the molar mass (MM) of KCN and the use the mole/mass relationship (n=mass/MM). This is calculated as follows

`MM(KCN)=39.1+12.0+14.0=65.1" g/mol"`

`n(KCN)="mass"/"MM"=0.279/65.1=4.29*10^-3" mol"`

As mentioned above, the mole ratio is 1:1 so we can say

`n(KCN)=n(HCN)=4.29*10^-3" mol"`

Finally, we need to find the mass of HCN formed in grams. We need to calculate the molar mass of HCN and then rearrange the mole/mass relationship

`MM(HCN)=1.0+12.0+14.0=27.0" g/mol"`

`mass(HCN)=n(HCN)*MM(HCN)=4.29*10^-3*27.0=0.116" g"`