The solubility of a solute is primarily determined quantitatively by measuring the maximum amount of solute that can dissolve in a specific quantity of solvent at a given temperature, commonly expressed in grams per 100 grams of solvent (g/100g).
To determine the solubility of a solute precisely, a specific calculation is employed that involves the masses of both the solute and the solvent. This method provides a standardized way to compare the solubilities of different substances.
The standard unit for reporting solubility is grams of solute per 100 grams of solvent (g/100g). This unit makes it easy to understand how much solute can be dissolved in a typical amount of solvent.
Formula for Solubility Determination
The determination of solubility involves a straightforward calculation using the masses of the solute (the substance being dissolved) and the solvent (the substance doing the dissolving) when a saturated solution is formed.
Here are the steps to calculate the solubility:
- Measure the mass of the solute: Determine the exact mass (in grams) of the solute that has dissolved to form a saturated solution.
- Measure the mass of the solvent: Determine the exact mass (in grams) of the solvent in which the solute is dissolved.
- Divide the mass of the solute by the mass of the solvent.
- Multiply the value by 100 to report the solubility in g/100g.
This can be expressed by the following formula:
Solubility (g/100g) = (Mass of Solute (g) / Mass of Solvent (g)) × 100
Practical Example
Let's illustrate this with an example. Suppose you are determining the solubility of sodium chloride (NaCl) in water.
| Component | Mass (g) |
|---|---|
| Dissolved Solute | 36 g |
| Solvent (Water) | 100 g |
Calculation Steps:
- Mass of Solute (NaCl): 36 g
- Mass of Solvent (Water): 100 g
- Divide Solute Mass by Solvent Mass: 36 g / 100 g = 0.36
- Multiply by 100: 0.36 × 100 = 36
Therefore, the solubility of sodium chloride in water under these conditions is 36 g/100g. This means that 36 grams of sodium chloride can dissolve in 100 grams of water to form a saturated solution at the given temperature.
Key Considerations in Determination
While the calculation is direct, the actual experimental determination of solubility requires careful control of certain factors:
- Temperature: Solubility is highly dependent on temperature. Most solids become more soluble as temperature increases, while gases become less soluble. Therefore, the temperature at which the solubility is determined must always be specified.
- Saturation: The measurement must be taken when the solution is saturated, meaning no more solute can dissolve in the given amount of solvent at that temperature. Any undissolved solute present indicates saturation has been reached.
