Chemistry problems!Help!

来源：学生作业帮编辑：作业帮分类：英语作业时间：2024/04/27 15:09:38

Chemistry problems!Help!
1.Calculate the pH when we add 0.001 mole of HAc to 0.02 mole of NaAc and bring the volume up to 100ml with pure water.
HAc ↔ H+ + Ac− pKa = 4.76
2.Consider the following two systems:
(a) 0.1 litre of pure water at pH 7.0
(b) 0.1 litre of 0.1M phosphate buffer at pH 7.2
H2PO4 ↔ HPO42− + H+ pKa = 7.2
If we add 10ml of 0.01 M HCl to each,what will be the pH in each solution.
p/s:Solve the questions,not translate it for me!Thanks!
I need the answer in English,please..Help!

1.suppose [H+]=x mol/L
before ionization
[HAc]=0.01mol/L [Ac-]=0.2mol/L
HAc ↔ H+ + Ac−
before 0.01 0 0.2
after 0.01-x x 0.2+x
thus -lg[(0.2+x)*x/(0.01-x)]=4.76
note that x is quite small
therefore 0.2+x=0.2 0.01-x=0.01
-lg20x=4.76
pH=-lgx=6.06
2.HCl=H+ +Cl-
(a) [H+]=0.01*10/(10+100)=9.09*10^-4mol/L
pH=-lg[H+]=3.04
(b) suppose ionized[H+]=xmol/L
H2PO4 ↔ HPO42− + H+ pKa = 7.2
before 0.1/1.1 0.1/1.1 0.01/11
after 0.1/1.1-x 0.1/1.1+x 0.01/11+x
thus -lg[(0.01/11+x)*(0.1/1.1+x)/(0.1/1.1-x)]=7.2
note that x is quite small
thus 0.1/1.1+-x=0.1/1.1
pH=-lg(0.01/11+x)=7.2

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