Question

The molarity of a 70%(mass/mass) aqueous solution of a monobasic acid (X) is:

Answer 1

Correct Answer: 12.5

To calculate the molarity of the solution, follow these steps:

1. Mass of solute in 100g of solution:
A 70% (mass/mass) solution means 70g of acid (X) is present in 100g of the solution.

2. Volume of 100g of solution:
Using the formula for density:

$ \text{Density} = \frac{\text{Mass}}{\text{Volume}} $
Rearranging to find volume:

$ \text{Volume} = \frac{\text{Mass}}{\text{Density}} $

Substituting the given values:

$ \text{Volume} = \frac{100 \, \text{g}}{1.25 \, \text{g/mL}} = 80 \, \text{mL} = 0.080 \, \text{L} $

3. Moles of solute:
The number of moles is calculated using the formula:

$ \text{Moles} = \frac{\text{Mass}}{\text{Molar Mass}} $

Substituting the values:

$ \text{Moles} = \frac{70 \, \text{g}}{70 \, \text{g/mol}} = 1 \, \text{mol} $

4. Molarity:
Molarity is defined as the number of moles of solute divided by the volume of the solution in liters:

$ \text{Molarity} = \frac{\text{Moles of Solute}}{\text{Volume of Solution (in liters)}} $

Substituting the values:

$ \text{Molarity} = \frac{1 \, \text{mol}}{0.080 \, \text{L}} = 12.5 \, \text{M} $

Final Answer:
The molarity of the solution is $ 12.5 $.