A student is given 500.mL of a 0.10M HCN solution. Ka = 4.9 X 10^−10 What...

A student is given 500.mL of a 0.10M HCN solution. Ka = 4.9 X 10^−10

What mass of NaCN should the student dissolve in the HCN solution to turn it into a buffer with pH = 9.86?

Expert Solution

[HCN] = molarity x volume in Litres = 0.1 M x 0.5 L = 0.05 mol

[NaCN] = ?

pH = pKa + log [NaCN]/[HCN]

pH = - log Ka + log [NaCN]/[HCN]

9.86 = - log (4.9 x 10⁻¹⁰) + log [NaCN]/ 0.05

On solving,

[NaCN] = 0.177 mol

Hence,

mass of NaCN = moles x molar mass = 0.177 mol x 49 g/mol = 8.67 grams

Therefore,

mass of NaCN required= 8.67 grams

queen_honey_blossom answered 2 years ago

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