In: Chemistry
Add 10 mL of 0.1 M HCl to one liter of a 0.10 M sodium acetate buffer, pH 6.76 (pKa = 4.76 for acetic acid). Does the pH of the solution change? Determine the effect of the addition of 20.0 mL of 0.100 M HCl?
moles of acetate = 1L * 0.10mol/L = 0.10mol
moles of acetic acid = 0.10 mol
H+ + CH3COO-
<---------> CH3COOH
moles of acetate after adding 10mL of 0.1M HCl = 0.10 -
1*10-3 = 0.099mol
moles of acetic acid after adding HCl= 0.1+ 1*10-3 =
0.101 mol
PH = Pka + log [acetate/acetic acid]
PH = 4.76 + log [0.099/0.101] = 4.75
Therefore the PH changes after adding 10mL of 0.1M HCl to 1L of
buffer
Similarly you can do it for 20mL adition,
moles of acetate after adding 20mL = 0.1 - 2*10-3 =
0.098 mol
moles of acetic acid after adding HCl = 0.1 + 2*10-3 =
0.102 mol
PH = 4.76 + log [0.098/0.102] = 4.74