Question

Find the mass of an organic compound of molar mass 84, required to prepare 250 ml solution of molarity 0.4

Hint:

Always ensure your volume is converted to Liters before plugging it into the molarity formula $n = M \times V$.

Answer 1

Step 1: Understanding the Concept:
Molarity ($M$) is defined as the number of moles of solute dissolved per liter of solution. To find the mass required, we first calculate the moles needed using the molarity formula, and then convert moles to mass using the molar mass.

Step 2: Key Formula or Approach:
$\text{Molarity } (M) = \frac{\text{moles of solute } (n)}{\text{Volume of solution in liters } (V)}$
$\text{Moles } (n) = \frac{\text{Mass } (w)}{\text{Molar Mass } (M_w)}$
Combining these: $w = M \times V \times M_w$

Step 3: Detailed Explanation:
Given values:
- Molarity ($M$) = $0.4 \text{ mol/L}$
- Volume of solution ($V$) = $250 \text{ ml} = 0.250 \text{ L}$
- Molar mass of solute ($M_w$) = $84 \text{ g/mol}$
First, find the number of moles required:
$n = M \times V$
$n = 0.4 \text{ mol/L} \times 0.250 \text{ L}$
$n = 0.1 \text{ moles}$
Now, calculate the mass from the number of moles:
$\text{Mass} = \text{moles} \times \text{Molar mass}$
$\text{Mass} = 0.1 \text{ mol} \times 84 \text{ g/mol}$
$\text{Mass} = 8.4 \text{ g}$

Step 4: Final Answer:
The required mass of the organic compound is 8.4 g.