Question

How many gram moles of hcl will be required to prepare 1 litre of a buffer solution (nacn +hcl) of ph 8.5 using 0.1 gram formula mass of nacn?

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Answer 1

NaCN+HCI  is not a buffer but if HCI is in less amount then it gives a buffer as it produces HCN.

                                    NaCN +HCL----->NaCL + HCN

Mole added.                0.01       α              0               0

Mole after reaction   (0.01-α)   0              α               α

This is buffer of HCN + NaCN.

Let a mole of HCI be used for this purpose.

∴pH=−logKa+log(0.01−aa)

8.5=−log4.1×10−10+log( $\frac{0.01-\alpha }{\alpha }$)

∴a=8.85×10−3 mole of HCI`