Which of the following solutions when mixed with 25.0 cm^3 of 1.0M hydrochloric acid would result in a a change of pH?
(1)50cm^3 of 1.0M nitric acid
(2)50cm^3 of 1.0M ethanoic acid
(3)50cm^3 of 1.0 M sulphuric acid
answer is (2) and (3) only
why?
CHEM ACID&ALKALI MC 1題
2011-04-28 6:20 pm
回答 (1)
2011-04-30 11:48 pm
✔ 最佳答案
HCl ---> H+ + Cl-Originally, no. of moles of [H+] in HCl = 25/1000 * 1 = 0.025 mol
and molarity of [H+] = 1.0 M
(1) HNO3 ---> H+ + NO3-
=> no. of moles of [H+] in HNO3 = 50/1000 * 1 = 0.05 mol
=> total no. of moles of [H+] in mixture = 0.075 mol
=> molarity of [H+] = 0.075 / (25+50)/1000 = 1.0 M
So there is no change in pH because of no change in [H+] concentration.
(2) CH3COOH ≒ H+ + CH3COO-
Not all CH3COOH molecules are completely ionized, so [H+] concentration must be lower than 1.0M. So there is a change in pH.
(3) H2SO4 ---> 2H+ + SO4^2-
=> no. of moles of [H+] in H2SO4 = 50/1000 * 1 * 2 = 0.1 mol
=> total no. of moles of [H+] in mixture = 0.125 mol
=> molarity of [H+] = 0.125 / (25+50)/1000 = 1.667M
So there is an increase in [H+] concentration, resulting in a change in pH.
參考: Knowledge is power.
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