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1)calculate the change in ph when 4 ml of .1 m HCl is added to 100...

1)calculate the change in ph when 4 ml of .1 m HCl is added to 100 ml of a buffer solution that is .1 m in NH3 and .1 m in NH4Cl

2 calculate the change in ph when 4ml of .1 m NaOH is added to the original buffer solution.

Solutions

Expert Solution

The buffer solution is 100mL ofNH3 and NH4 Cl buffer

the Pkb of ammonia is 4.74.

For a buffer the pH is calculated using Hendersen equation as

pH = 14- pOH

= 14 -[ pkb + log [conjugate acid]/[base]]

The initial pH of the buffer = 14-[4.74 + log 0.1/0.1]

= 9.26

case 1) 4 mL of 0.1 M HCl is added

NH3 + HCl ------------------> NH4Cl

100 x0.1 0 100x0.1 initial mmol

4x0.1 change

9.6 0 104 after reaction

Thus pH = 14 -[4.74 + log 104/96]

= 9.225

The chang ein pH = 9.26-9.225

= 0.03476

the pH decrease by 0.03476 units

case2

NH4Cl +Na OH -----------------------> NH3 + NaCl + H2O

100 x0.1 0 100x0.1 initial mmol

4x0.1 change

9.6 0 104 after reaction

Thus the pH of the solution

pH = 14 -[4.74 + log 96/104]

= 9.29476

Thus the pH increases by 0.03476 units

queen_honey_blossom answered 1 year ago

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