# Acids and pH

1. Jan 21, 2006

### sci0x

Question: Aspirin is a weak acid.

(a) Calculate pH of 0.2M solution of aspirin at 25 degrees celsius (Ka = 3.0 x 10^-4 at 25 degrees celcius).

(b) Determine the percent ionisation

(c) Explain qualitatively the effect of adding 0.01M hydrochloric acid to the aspirin solution.

(d) Calculate the pH of the resulting solution

(e) Determine the percent ionisation of the aspirin under these conditions

2. Jan 25, 2006

### niz

hmmm
well formula goes.. pH=-log[H+]
am not sure what about aspirine...i am is Ka also meant as concentration of H+ ??
if yes ...then

pH=-log[H+]
pH=-log(3.0 x 10^-4)=3.5228

and it is acid....but wouldnt say that weak

3. Jan 25, 2006

### Gokul43201

Staff Emeritus
Sci0x : Please read the forum guidelines for getting help with schoolwork. See my signature.

4. Jan 29, 2006

### benzun_1999

here is the most effective way with which u must proceed---

1) the conc is given as .2 M and ka is given so find the $$H^+$$ conc using the formula $$[H^+] = \sqrt{K_a * c}$$
2) percentage ionisation is given by the formula $$\sqrt{\frac{k_a}{c}}$$
3)Explain common ion effect
4) due to addition of hydrochloric acid the conc of H+ will now be 0.01 + the conc of H+ u got in the 1st question
5) repeate the 2 question but now with the new conc of H+ note use formula $$\frac{[H^+]}{c}$$