Summary
Highlights
Solubility curves are visual representations showing the dissolution of solids and gases in water at specific temperatures. They are based on meticulously collected data, making them useful tools in laboratory and industrial settings. The y-axis indicates grams of solute dissolved per 100 milliliters (or grams) of water, while the x-axis represents temperature in degrees Celsius.
For solids, solubility generally increases with temperature. Pressure has no significant effect on the solubility of solids. For example, more salt or sugar dissolves in warmer water. This is why sugar may settle out of sweet tea as it cools, because cooler temperatures reduce the amount of solute the water can hold.
Unlike solids, the solubility of gases in liquids decreases as temperature increases. Gases prefer to dissolve in cold liquids. Pressure, however, greatly affects gas solubility; higher pressure leads to higher solubility. Carbonated drinks and dissolved oxygen in lakes are common examples. Fish require dissolved oxygen, and colder water or deeper parts of a lake tend to have higher oxygen levels.
The line on a solubility curve represents a saturated solution, which holds the maximum amount of solute at a given temperature. Points below the curve indicate an unsaturated solution, meaning less than the maximum amount of solute is dissolved. Points above the curve represent a supersaturated solution, where more than the maximum amount of solute is present, often requiring agitation to prevent precipitation.
The video provides examples of how to read a solubility curve. When asked for the mass of a substance to form a saturated solution at a specific temperature (e.g., sodium nitrate at 40°C), find the temperature on the x-axis, trace up to the substance's curve, and then over to the y-axis to find the mass. For potassium iodide at 20°C, a highly soluble substance, it is shown to dissolve around 147 grams in 100 grams of water.
If the amount of water differs from the standard 100 grams on which the curve is based, the dissolved solute amount must be adjusted proportionally. For instance, if 200 grams of water are used, the amount of dissolved solute will be double what the curve indicates for 100 grams of water.
The video also demonstrates how to find the temperature required for a specific mass of solute to form a saturated solution (e.g., 50 grams of potassium chloride). It also shows how to determine if a solution is saturated, unsaturated, or supersaturated by plotting the given coordinates (mass and temperature) relative to the substance's curve.
In summary, for solids, solubility increases with temperature, while for gases, solubility decreases with temperature. Solubility curves are straightforward visual tools to understand how much of a substance can dissolve in water at various temperatures.