Types of Solutions
Now we have identified and defined what a solution is, we can look at the specific types of solutions.
Here’s a scenario
How much sugar can you dissolve in a small 250ml cup of water?
10g? 50g? 100g? 1000g? 5000g?
Each of the different amounts above indicates a different type of solution.
If we were to dissolve 10g of sugar, we know that the 10g will dissolve completely because 10g are not too much for a 250ml of water.
This solution is said to be unsaturated solution.
- An unsaturated solution is a solution in which a solution can still hold more solute in the solution at a given temperature.
If we were to dissolve more sugar into the 250ml of water, it will eventually reach to a point where no more sugar can be dissolved; this point is called the saturation point. The solution created is then called saturated solution.
- A saturated solution is a solution in which the maximum amount of solute is dissolved at a given temperature.
If we wanted to dissolve a substantial amount of sugar such as 1000g or 5000g, the only way possible is to heat the solution. Heating the solution increases the energy, which allows the compound to dissolve “easier”.
A supersaturated solution is a solution in which the solution holds more than the maximum amount of solute at a given temperature.
How do you create a saturated or supersaturated solution?
In order to saturate a solution, two ways can accomplish this feat:
- Add more solute. Add enough solute that the solvent can no longer dissolve at a given temperature.
- Evaporate the solvent. By evaporating the solvent, ONLY the solvent is taken out of the solvent. However, if the solution such as siphoning or taking a spoon to scoop out the solution were to be done, this would not only take the solvent but the solute as well. Therefore, only evaporating would work.
In order to supersaturate a solution,
- Heat heat heat! By adding heat to the solution, both the solute and the solvent gain kinetic energy allowing more collisions between the atoms, thus making them dissolve at a faster rate. Once the temperature is allowed to fall back to the original temperature, the solute has already dissolved into solvent, thus making a supersaturated solution! But if the solution is “disturbed”, the excess amounts of solute will crystal out of solution. See an example!
The next part is to analyze and quantify (to put into numbers) how much solid can a solvent hold.
A solubility curve is useful in showcasing the amounts of solute that can be dissolved and also at which specific temperature.
The solubility curve on the right is basic standard curves on dissolving various amounts of various compounds dissolve in 100g of water (100ml of water).
For example: Look at KNO3 Potassium nitrate.
The line of Potassium nitrate indicates the amount of solute (KNO3) in grams that can be dissolved at that particular temperature.
At 20C, approximately 34g can be dissolved to reach saturation point. Any amount below the line represents unsaturation, and anything above the line indicates super saturation.
- Describe and give examples of various types of solutions. Include: all nine possible types
- Describe the structure of water in terms of electronegativity and the polarity of its chemical bonds.
- Explain the solution process of simple ionic and covalent compounds, using visual, particulate representations and chemical equations. Include: crystal structure, dissociation, hydration
- Interpreting a a solubility curve of a pure substance in water and differentiate among saturated, unsaturated, and supersaturated solutions.
- Explain how a change in pressure affects the solubility of gases.
- Explain freezing-point depression and boiling-point elevation at the molecular level. Examples: antifreeze, road salt…
- Include: grams per litre (g/L), % weight-weight (% w/w), % weight-volume (% w/v), % volume/volume (% v/v), parts per million (ppm), parts per billion (ppb), moles per litre (mol/L) (molarity)
- Prepare a solution, given the amount of solute (in grams) and the volume of solution (in millilitres), and determine the concentration in moles/litre. (Molarity)
- Solve problems involving the dilution of solutions.
Include: dilution of stock solutions, mixing common solutions with different volumes and concentrations