$$\begin{array}{l} 1)\\ a)\\ {m_{CuS{O_4}}} = 400 \times 4\%  = 16g\\ {m_{{H_2}O}} = 400 - 16 = 384g\\ b)\\ {m_{NaCl}} = 40 \times 1\%  = 0,4g\\ {m_{{H_2}O}} = 40 - 0,4 = 39,6g\\ 2)\\ a)\\ {m_{{\rm{dd}}NaOH}} = 30 + 120 = 150g\\ {C_\% }NaOH = \dfrac{{30}}{{150}} \times 100\%  = 20\% \\ b)\\ {n_{KN{O_3}}} = 0,5 \times 2 = 1\,mol\\ {m_{KN{O_3}}} = 1 \times 101 = 101g\\ c)\\ {n_{NaCl}} = 2,5 \times 0,9 = 2,25\,mol\\ {m_{NaCl}} = 2,25 \times 58,5 = 131,625g \end{array}$$

$$\begin{array}{l} 3)\\ tt:\\ {m_{Mg}} = 24g\\ {m_{{\rm{dd}}HCl}} = 200g\\ a)\\ Mg + 2HCl \to MgC{l_2} + {H_2}\\ {n_{Mg}} = \dfrac{{2,4}}{{24}} = 0,1mol\\ {n_{HCl}} = 2{n_{Mg}} = 0,2mol\\ {m_{HCl}} = 0,2 \times 36,5 = 7,3g\\ C{\% _{HCl}} = \dfrac{{7,3}}{{200}} \times 100\% = 3,65\% \\ b)\\ {n_{MgC{l_2}}} = {n_{Mg}} = 0,1mol\\ {m_{MgC{l_2}}} = 0,1 \times 95 = 9,5g\\ c)\\ {n_{{H_2}}} = {n_{Mg}} = 0,1mol\\ {V_{{H_2}}} = 0,1 \times 22,4 = 2,24l\\ 4)\\ tt:\\ {m_{Zn}} = 3,25g\\ {V_{HCl}} = 200ml = 0,2l\\ a)\\ Zn + 2HCl \to ZnC{l_2} + {H_2}\\ {n_{Zn}} = \dfrac{{3,25}}{{65}} = 0,05mol\\ {n_{HCl}} = 2{n_{Zn}} = 0,1mol\\ {C_{{M_{HCl}}}} = \dfrac{{0,1}}{{0,2}} = 0,5M\\ b)\\ {n_{ZnC{l_2}}} = {n_{Zn}} = 0,05mol\\ {m_{ZnC{l_2}}} = 0,05 \times 136 = 6,8g\\ c)\\ {n_{{H_2}}} = {n_{Zn}} = 0,05mol\\ {V_{{H_2}}} = 0,05 \times 22,4 = 1,12l \end{array}$$