Question

Bài 2 ạ 

Answer 1

a) Gọi $m_{NaCl\ cần\ thêm} = a(gam)$

Sau khi thêm : 

\(m_{NaCl} = a + 500.8\% = a + 40(gam)\\ m_{dd\ sau\ pư} = a + 500(gam)\\ \Rightarrow C\%_{NaCl} = \dfrac{a + 40}{a + 500}.100\% =12\%\\ \Rightarrow a = 22,73(gam)\)

b)

Gọi $m_{H_2O} = a(gam)$

Sau khi thêm : 

$m_{dd}  = a + 500(gam)$
$m_{NaCl} = 500.12\% = 60(gam)$
$\Rightarrow C\%_{NaCl} = \dfrac{60}{a + 500}.100\% = 8\%$

$\Rightarrow a = 250(gam)$