`a)` `m_{CuSO_4} = 5 \cdot \frac{160}{250} = 3,2` (g)

`m_{H_2O} = 5 - 3,2 = 1,8` (g)

`m_{ct} = 3,2 - 2,75 = 0,45` (g)

`C\%_{bh} = \frac{0,45}{0,45 + 1,8} \cdot 100 = 20\%`

`b)` Gọi `m_{ct} = a`; `m_{H_2O} = b` (ban đầu).

Sau khi bay hơi `20\%` nước, dung dịch bão hòa ($20\%$):

`\frac{a}{a + 0,8b} = 0,2`

`a = 0,2a + 0,16b`

`0,8a = 0,16b \Rightarrow b = 5a`

`X\% = \frac{a}{a + 5a} \cdot 100 = \frac{1}{6} \cdot 100 \approx 16,67\%`

Đáp số:

`a) 20%;`

`b) 16,67%`

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