需要多少亳升4mol/L的HCOOH和多少克NaOH才能配成1L共轭酸碱对的总浓度为1mol/LpH=3.5的缓冲溶液?

今有3种酸ClCHCOOH,HCOOH和(CH)AsOH,它们的电离常数分别为1.40×10,1.77×10和6.40×10,试问:
配制pH=3.50的缓冲溶液选用那种酸最好
需要多少毫升浓度为4.0mol L的酸和多少克NaOH才能配成1L共轭酸碱对的总浓度为1.0mol L的缓冲溶液.
解:(1)pK=-lg1.40×10=2.85
pK=-lg1.77×10=3.75
pK=-lg6.40×10=6.2
所以选用HCOOH最好.
(2) 设所形成的缓冲溶液中HCOOH为xmol,HCOONa为ymol
据pH= pK-lg
3.5=3.75-lg (1)
x+y=1 (2)
解得 x=0.64 y=0.36
所以 m(NaOH)=0.36×40=14.4g
V(HCOOH)==0.25L=250mL
参考资料： http://cache.baidu.com/c?m=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&p=882a915d8c9b50fe0be2977d4a07&user=baidu&fm=sc&query=%B6%E0%C9%D9%D9%F1%C9%FD4mol/L%B5%C4HCOOH%BA%CD%B6%E0%C9%D9%BF%CBNaOH%B2%C5%C4%DC%C5%E4%B3%C91L%B9%B2%E9%EE%CB%E1%BC%EE%B6%D4%B5%C4%D7%DC%C5%A8%B6%C8%CE%AA1mol/LpH%3D3%2E5%B5%C4%BB%BA%B3%E5%C8%DC%D2%BA%3F&qid=d81cba781af618fa&p1=6