(1)碳酸钠物质的量=
=0.1mol,故溶液中c(Na2CO3)=10.6g 106g/mol
=0.1mol/L,溶液中c(Na+)=2c(Na2CO3)=0.1mol/L×2=0.2mol/L,0.1mol 1L
故答案为:0.1mol/L;0.2mol/L;
(2)Na+ 的物质的量=1L×0.4mol/L=0.4mol,故加入NaCl物质的量=0.4mol-0.1mol×2=0.2mol,故加入氯化钠的质量=0.2mol×58.5g/mol=11.7g,溶液中c(Cl-)=
=0.2mol/L,0.2mol 1L
故答案为:11.7g;0.2mol/L.