(1)
混合后m(NaCl) = 20*14% + 30*24% = 10g
m(溶液) = 20+30 = 50g
所以混合液氯化钠的质量分数 = 10/50 * 100% = 20%
(2)
n(NaCl) = 10/58.5 = 0.17mol
V(溶液) = 50/1.17 = 42.7ml = 0.0427L
所以混合液氯化钠的物质的量的浓度 = 0.17/0.0427 = 4mol/L
(3)
设加入x gNaCl,则有：
x/(1000+x) = 20%
解得x = 250g
所以n(NaCl) = 250/58.5 = 4.3mol
所以需加入4.3mol NaCl