3.
欲配制\(\rm{100ml 1.0 mol/L Na_{2}SO_{4}}\)溶液,正确的方法是( )
\(\rm{①}\) 将\(\rm{14.2 g Na_{2}SO_{4}}\)溶于\(\rm{100ml}\)水中
\(\rm{②}\)将\(\rm{20 ml 5.0 mol/L Na_{2}SO_{4}}\)溶液用水稀释至\(\rm{100 ml}\)
\(\rm{③}\)将\(\rm{32.2g Na_{2}SO_{4}·10H_{2}O}\)溶于少量水中,再用水稀释至\(\rm{100 ml}\)