20 g of common salt is dissolved in 180 g of water. What is the mass percentage of the salt in the solution?
10%
Calculating Mass Percentage of Salt in Solution
The question asks us to find the mass percentage of common salt when 20 g of salt is dissolved in 180 g of water. This is a common calculation in chemistry to express the concentration of a solution.
Understanding the Terms
- Solute: The substance that is dissolved. In this case, it is common salt (20 g).
- Solvent: The substance in which the solute is dissolved. Here, it is water (180 g). Water is often called the universal solvent.
- Solution: The homogeneous mixture formed when a solute is dissolved in a solvent. The solution is the combination of salt and water.
Formula for Mass Percentage Concentration
Mass percentage of a component in a solution is defined as the mass of the component divided by the total mass of the solution, multiplied by 100%.
The formula is:
\(\text{Mass Percentage of Solute} = \frac{\text{Mass of Solute}}{\text{Mass of Solution}} \times 100\%\)
Step-by-Step Calculation
First, we need to find the total mass of the solution. The mass of the solution is the sum of the mass of the solute and the mass of the solvent.
- Mass of solute (common salt) = 20 g
- Mass of solvent (water) = 180 g
- Mass of solution = Mass of solute + Mass of solvent
- Mass of solution = 20 g + 180 g = 200 g
Now, we can use the mass percentage formula:
\(\text{Mass Percentage of Salt} = \frac{\text{Mass of Salt}}{\text{Mass of Solution}} \times 100\%\)
\(\text{Mass Percentage of Salt} = \frac{20 \text{ g}}{200 \text{ g}} \times 100\%\)
\(\text{Mass Percentage of Salt} = \frac{1}{10} \times 100\%\)
\(\text{Mass Percentage of Salt} = 0.1 \times 100\%\)
\(\text{Mass Percentage of Salt} = 10\%\)
Therefore, the mass percentage of the salt in the solution is 10%.
| Component | Mass (g) |
|---|---|
| Common Salt (Solute) | 20 |
| Water (Solvent) | 180 |
| Solution (Salt + Water) | 20 + 180 = 200 |
Using the formula with the calculated mass of the solution:
\(\text{Mass Percentage} = \frac{20 \text{ g}}{200 \text{ g}} \times 100\% = 10\%\)
The mass percentage of common salt in the solution is 10%.
Revision Table: Mass Percentage Calculation
| Concept | Definition/Formula | Application |
|---|---|---|
| Solute | Substance being dissolved | Common Salt (20 g) |
| Solvent | Substance doing the dissolving | Water (180 g) |
| Solution | Solute + Solvent | 20 g + 180 g = 200 g |
| Mass Percentage | \(\frac{\text{Mass of Solute}}{\text{Mass of Solution}} \times 100\%\) | \(\frac{20 \text{ g}}{200 \text{ g}} \times 100\% = 10\%\) |
Additional Information: Solution Concentration Units
Mass percentage is just one way to express the concentration of a solution. Other common units include:
- Volume Percentage (\(\text{v/v}\%\)): \(\frac{\text{Volume of Solute}}{\text{Volume of Solution}} \times 100\%\)
- Mass by Volume Percentage (\(\text{w/v}\%\)): \(\frac{\text{Mass of Solute (g)}}{\text{Volume of Solution (mL)}} \times 100\%\)
- Molarity (M): Moles of solute per liter of solution (\(\frac{\text{Moles of Solute}}{\text{Volume of Solution (L)}}\))
- Molality (m): Moles of solute per kilogram of solvent (\(\frac{\text{Moles of Solute}}{\text{Mass of Solvent (kg)}}\))
- Mole Fraction (\(\chi\)): Moles of a component divided by the total moles of all components in the solution.
Choosing the right unit depends on the specific application and the properties being measured (mass or volume).
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