If 20ml of 0.1m naoh is added to 30ml of 0.2m ch3cooh (ka=4.74) , the ph of the resulting solutions is
a) 4.44 b) 9.56. c) 5.04. d) 8.96

The answer should be 5.35 not 5.04. C.

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Explanation:

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the answer is either b or c

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%