Ok so here is an example of an activity in my cell molec lab. We\'re supposed to

Question

Ok so here is an example of an activity in my cell molec lab. We're supposed to calculate final concentrations and pH of both acetic acid and sodium acetate, but the process my lab TA gave me keeps giving me the same number for both concentrations, and it just doesn't seem right.

If someone could help me figure out how to do this, it would help me with the rest of the worksheet. I've been using C1V1=C2V2 and the pH=pKa + log[A-]/[HA] but I don't understand why these numbers are ALL the same.

Acetic acid sodium acetate Final concentration(AA) Final Concentration SA CalculatedpH ActualpH 0mL 10mL 0 0 7.39 2mL 8mL .04 .04 5.25 4mL 6mL .08 .08 4.83

Explanation / Answer

In the begining you have only SA, its a salt of weakacid,stringbase.

pH = 7+1/2(pka+log C)

   7.39 = 7+(1/2(4.75+log C))

C = concentration of SA = 0.0001 M

the standard concentration of SA = 0.01 M,

That means at first 10 ml of 0.01 M SA is taken.

2.) By the addition of aceticacid gives buffer formation.

pH=pKa + log[A-]/[HA]

5.25 = 4.75 + log((8/10*0.01)/(2/10*x))

final concentration of SA = 0.008 M

concentration of original AA = 0.012 M

final concentration of AA = 2/10*0.012 = 0.0024 M

3) x = 4.75 + log((6/10*0.01)/(4/10*0.012))

   x = pH = 4.83

final concentration of SA = 0.006 M

final concentration of AA = 0.0048 M

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