3.71 When potassium cyanide (KCN) reacts with acids, a deadly poisonous gas,
hydrogen cyanide (HCN), is given off. Here is the equation:
KCN(aq) + HCl(aq) -> KCl(aq) + HCN(g)
If a sample of 0.140 grams of KCN is treated with an excess of HCl,
calculate the amount of HCN formed, in grams.
To calculate the amount of HCN formed in grams, we need to determine the moles of KCN and then use the balanced equation to calculate the moles and grams of HCN.
Step 1: Convert the mass of KCN to moles.
To do this, we need to use the molar mass of KCN, which is the sum of the individual atomic masses of potassium (K), carbon (C), and nitrogen (N).
The molar mass of K is 39.1 g/mol, the molar mass of C is 12.0 g/mol, and the molar mass of N is 14.0 g/mol.
Molar mass of KCN = (39.1 g/mol) + (12.0 g/mol) + (14.0 g/mol) = 65.1 g/mol
Now, we can calculate the moles of KCN using the formula:
moles of KCN = mass of KCN / molar mass of KCN
moles of KCN = 0.140 g / 65.1 g/mol
Step 2: Use the balanced equation to determine the moles of HCN.
According to the balanced equation:
1 mole of KCN produces 1 mole of HCN.
So, the moles of HCN formed will be the same as the moles of KCN.
Therefore, the moles of HCN = moles of KCN calculated in step 1.
Step 3: Convert the moles of HCN to grams.
To do this, we need to use the molar mass of HCN, which is the sum of the individual atomic masses of hydrogen (H), carbon (C), and nitrogen (N).
The molar mass of H is 1.0 g/mol, the molar mass of C is 12.0 g/mol, and the molar mass of N is 14.0 g/mol.
Molar mass of HCN = (1.0 g/mol) + (12.0 g/mol) + (14.0 g/mol) = 27.0 g/mol
Now, we can calculate the grams of HCN using the formula:
grams of HCN = moles of HCN * molar mass of HCN
Inserting the values:
grams of HCN = moles of HCN * 27.0 g/mol
Therefore, to calculate the amount of HCN formed in grams, you need to multiply the moles of HCN (which is equal to the moles of KCN) by the molar mass of HCN, which is 27.0 g/mol.