Question

How to prepare a 100mL buffer solution of pH 8.5 using glycine and sodium hydroxide ?

Answer 1

How to prepare a 100mL buffer solution of pH 8.5 using glycine and sodium hydroxide?

Since glycine is a neutral molecule it does not contribute for the pH of the solution so only NaOH should be consider for pH of buffer.

Now for 8.5 pH of buffer how much NaOH should be use can be calculated as follows,

Sodium hydroxide is a strong base dissociate completely in water giving following ions,

NaOH     àà        Na⁺       +       OH^-

X moles/L-----------x--------------x--------complete dissociation

Now;   pOH = -log [OH^-]

Given is; pH= 8.5

Now, [OH^-] = -antilog pOH = 3.1622 × 10^-6 moles/L

To prepare 100 ml of buffer with pH 8.5; 3.1622 × 10^-6 moles/L of NaOH should be use,

g of NaOH= 3.1622 × 10^-6 * molecular weight of NaOH (40g/mol)= 126.488× 10^-6 g of NaOH in 1000ml

For 100 ml= 1.26 × 10^-9 g of NaOH should be used