A-level Chemistry Questions

Hi, would anyone be able to help with these questions?
1. in what proportions should you mix ethanoic acid and sodium ethanote in order to give a buffer solution of ph 5. pKa for ethanoic acid is 4.76
2. calculate the ph of a buffer solution containing 1.00moldm-3 of ammonia and 0.400moldm-3 ammonium chloride. Ka for the ammonium ion, NH4+, is 5.62 x 10^-10 moldm-3
3. Calculate the effect on the pH of adding a) 5.00 cm3 of 10.0 moldm-3 hydrochloric acid and b) 5.00 cm3 of 10.0 moldm-3 sodium hydroxide solution to 1000 cm3 of the buffer solution from question 2.
4. In what proportions should ammonia and ammonium chloride be mixed in solution to give a buffer solution of ph 10. Pka for nh4+ is 9.25

Help would be appreciated. Thank you

Where exactly are you stuck at? Most of them are solvable by plugging values into henderson hasselbalch formula..

-As for 3. check whether acid base reaction could occur.
If yes, check which is the limiting reagent and identify whether is it acid or base being leftover. if its acid, use the acid dissociation constant formula/ henderson hasselbalch formula to get pH. If its base, use the rule pH + pOH = pKw to get pH

Ohhh okay that makes more sense, I've been able to solve them now. Thank you