\(\begin{array}{l}
5)\\
a)\\
C\% NaOH = \dfrac{{mct}}{{mdd}} \times 100\% = \dfrac{{40}}{{200}} \times 100 = 20\% \\
b)\\
mddNaCl = 15 + 85 = 100g\\
C\% NaCl = \dfrac{{mct}}{{mdd}} \times 100\% = \dfrac{{15}}{{100}} \times 100\% = 15\% \\
6)\\
a)\\
mNaCl = n \times M = 1 \times 58,5 = 58,5g\\
b)\\
nCuS{O_4} = \dfrac{m}{M} = \dfrac{{320}}{{160}} = 2\,mol\\
{C_M}CuS{O_4} = \dfrac{n}{V} = \dfrac{2}{{0,4}} = 5M\\
c)\\
nNaCl = 2 \times 0,2 + 3 \times 0,3 = 1,3\,mol\\
Vdd = 2 + 3 = 5l\\
{C_M}NaCl = \dfrac{n}{V} = \dfrac{{1,3}}{5} = 0,26M
\end{array}\)