A solution contains 20 g of solute in 180 g of solvent. If the solvent is water, what is the concentration of the solution in terms of mass by mass percentage ?
10%
Understanding Solution Concentration: Mass by Mass Percentage
This question asks us to calculate the concentration of a solution in terms of mass by mass percentage. The solution is formed by dissolving a specific amount of solute in a specific amount of solvent. We are given the mass of the solute and the mass of the solvent (water).
What is Mass by Mass Percentage?
Mass by mass percentage is a way to express the concentration of a solution. It is defined as the mass of the solute divided by the total mass of the solution, multiplied by 100%.
The formula for mass by mass percentage concentration is:
\(\text{Mass percentage} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100\%\)
Applying the Formula to the Given Problem
We are given the following information:
- Mass of solute = 20 g
- Mass of solvent = 180 g (Since the solvent is water, this is the mass of water)
To use the formula, we first need to find the 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 solution = Mass of solute + Mass of solvent
Let's calculate the mass of the solution:
Mass of solution = 20 g + 180 g = 200 g
Now we have the mass of the solute and the total mass of the solution. We can plug these values into the mass by mass percentage formula:
\(\text{Mass percentage} = \frac{20\text{ g}}{200\text{ g}} \times 100\%\)
Simplifying the fraction \(\frac{20}{200}\):
\(\frac{20}{200} = \frac{1}{10}\)
Now, multiply by 100%:
\(\text{Mass percentage} = \frac{1}{10} \times 100\%\)
\(\text{Mass percentage} = 0.1 \times 100\%\)
\(\text{Mass percentage} = 10\%\)
So, the concentration of the solution in terms of mass by mass percentage is 10%.
Summary of Calculation
| Component | Mass (g) |
|---|---|
| Solute | 20 |
| Solvent (Water) | 180 |
| Solution (Solute + Solvent) | 20 + 180 = 200 |
Calculation:
\(\text{Mass by mass percentage} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100\%\)
\(\text{Mass by mass percentage} = \frac{20\text{ g}}{200\text{ g}} \times 100\%\)
\(\text{Mass by mass percentage} = 0.1 \times 100\%\)
\(\text{Mass by mass percentage} = 10\%\)
Revision Table: Key Concepts
| Term | Definition | How it relates here |
|---|---|---|
| Solute | The substance being dissolved. | 20 g is the solute. |
| Solvent | The substance doing the dissolving (usually present in a larger amount). | 180 g of water is the solvent. |
| Solution | A homogeneous mixture of solute and solvent. | The total mixture of solute and water. |
| Mass by Mass Percentage | (Mass of solute / Mass of solution) x 100%. | The concentration measure we calculated. |
Additional Information: Other Concentration Units
Besides mass by mass percentage, there are other ways to express the concentration of a solution. Some common ones include:
- Volume by Volume Percentage: (Volume of solute / Volume of solution) \(\times\) 100%. Used for solutions where both solute and solvent are liquids.
- Mass by Volume Percentage: (Mass of solute / Volume of solution) \(\times\) 100%. Commonly used in pharmacy and medicine.
- Molarity (M): Moles of solute per liter of solution. This is a very common unit in chemistry as it relates concentration to the number of particles (moles).
- Molality (m): Moles of solute per kilogram of solvent. This unit is useful because it is independent of temperature changes (volume can change with temperature, mass does not).
- Parts per Million (ppm) and Parts per Billion (ppb): Used for very dilute solutions, often for environmental measurements.
Choosing the right concentration unit depends on the nature of the substances involved and the application of the solution.
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