Question

`25.3 g` sodium carbonate, `Na_(2)CO_(3)`, was dissolved in enough water to make `250 mL` of solution. If sodium carbonate dissociates completely, molar concentration of `Na^(+)` and carbonate ions are respectively:
A. 0.955 M and 1.910 M
B. 1.910 M and 0.955 M
C. 1.90 M and 1.910 M
D. 0.477 M and 0.477 M

Answer 1

Correct Answer - B
Molarity `= ("Number of moles of solute")/("Volume of solution (in mL)")xx1000`
`=(25.3xx1000)/(106xx250)=0.9547 ~~ 0.955 M`
`Na_(2)CO_(3)` in aqueous solution remains dissociated as
`{:(Na_(2)CO_(3),hArr,2Na^(+),+,CO_(3)^(2-)),(" x",," 2x",," x"):}`
Since, the molarity of `NA_(2)CO_(3)` is 0.955 M, the molarity of `CO_(3)^(2-)` is also 0.955 M and that of `Na^(+)` is `1xx0.955=1.910 M`