Question

An aqueous solution that has 58.5% (w/v) NaCl and $5MMgC{l}_2$ has a density of 1.949 gm/mL. Mark the option(s) which represent the correct molarity or relation of the specified ion(s). (Assume 100% dissociation of each salt)

• A. $\left[C{l}^{-}\right]=20M$
• B. $\left[M{g}^{2+}\right]=10M$
• C. [All the cations] = $15M$
• D. $\frac{\left[\text{All the anions}\right]}{\left[\text{All the cations}\right]}=\frac{4}{3}$

Answer 1

Answer: (A), (C), (D)

The correct options are
A $\left[C{l}^{-}\right]=20M$
C [All the cations] = $15M$
D $\frac{\left[\text{All the anions}\right]}{\left[\text{All the cations}\right]}=\frac{4}{3}$

Let's take 1 L of solution.
Mass of NaCl = 585 gm , moles of NaCl = 10 mol
Moles of $N{a}^{+}=10$ mol and moles of $C{l}^{-}=10$ mol due to NaCl.
Now, in 1 L solution of $5MMgC{l}_2$ ,
moles of $M{g}^{2+}=5$ moles and moles of $C{l}^{-}=10$ mol
So, $\left[C{l}^{-}\right]=\frac{10+10}{1}=20M,\left[N{a}^{+}\right]=\frac{10}{1}=10M,\left[M{g}^{2+}\right]=\frac{5}{1}=5M$
[cations] = 10 + 5 = 15
$\frac{\left[\text{All the anions}\right]}{\left[\text{All the cations}\right]}=\frac{20}{10+5}=\frac{4}{3}$