Science 7: Solutions, Solubility, and Concentration study guide

A mixture is formed by combining two or more substances physically. Unlike chemical compounds, the components of a mixture retain their individual identities and can generally be separated by physical means.

There are two primary categories of mixtures based on the distribution of their particles:

Homogeneous Mixture: In this type of mixture, the substances are evenly spread throughout the mixture, resulting in a uniform appearance. The different components are not distinguishable to the naked eye. Examples include:
- Juices
- Coffee
- Synthetic Vinegar (specifically noted in a container of $500\,ml$ )
Heterogeneous Mixture: In this type of mixture, the different parts or particles are visible and the composition is not uniform. The individual components can often be seen as separate phases. Examples include:
- Cookies (where chocolate chips or nuts are distinct from the dough)
- Salad (where individual vegetables are visible)
- Milktea (where pearls or tea layers can be seen)

A solution is specifically defined as a homogeneous mixture composed of two or more substances. It consists of two essential parts: the solvent and the solute.

Solvent: This is any substance, usually a liquid, which is capable of dissolving one or several substances and creating a solution. It is typically the component present in the largest amount.
Solute: This is the substance that is dissolved into a solution by a solvent. It is typically the component present in the smaller amount.

When a small amount of salt is added to water:
- The Water acts as the solvent.
- The Salt acts as the solute.
- Together, they form a Saltwater solution.

Solubility is defined as the ability of a specific solute to dissolve in a specific solvent at a given set of conditions.

Solubility is governed by the principle that substances with similar chemical properties will dissolve in each other.
Polar substances will dissolve other polar substances.
Non-polar substances will dissolve other non-polar substances.

Concentration refers to the precise amount of solute present in a given amount of solvent or total solution.

Concentrated: A solution that contains a relatively large amount of solute and a smaller amount of solvent.
Diluted: A solution that contains a relatively small amount of solute and a larger amount of solvent.

Solutions can be categorized by their level of saturation:

Unsaturated Solution: A solution that can still dissolve more solute at a given temperature. In this state, added solute will continue to dissolve.
Saturated Solution: A solution that contains the maximum amount of solute that can be dissolved under normal conditions. In this state, no more solute will dissolve even if added.
Supersaturated Solution: A solution that contains more solute than would normally be possible at a certain temperature. These solutions are generally unstable, and the excess solute will form crystals if the solution is disturbed or seeded.

Several physical and chemical factors influence how quickly or how much of a solute can dissolve in a solvent.

Solids in Liquids: For most solids, a higher temperature increases the solubility. For example, sugar or salt dissolves faster when the water is warmer.
Gases in Liquids: Unlike solids, gases become less soluble as the temperature increases.
Measurement context: Temperature scales often involve ranges such as $0\,^{\circ}C$ to $100\,^{\circ}C$ ( $32\,^{\circ}F$ to $212\,^{\circ}F$ ).

Gases in Liquids: Higher pressure increases the solubility of gases in liquids.
- Example: In a sealed soda bottle, the liquid is under high pressure, allowing a significant amount of carbon dioxide gas to remain dissolved, making the drink fizzy.
Solids and Liquids: For solid and liquid solutes, changes in pressure have a minimal effect on solubility.

Stirring helps the solute mix with the solvent at a faster rate, which increases the speed of dissolution.
It is critical to note that while stirring makes a solute dissolve faster, it does not change the maximum amount of solute that the solvent can eventually hold (the saturation point).

The size of the solute particles directly impacts the rate of dissolution. Smaller particles dissolve faster than larger ones.
This occurs because smaller particles provide a greater surface area relative to their volume, allowing for more interactions between the solvent and the solute particles.
Example: Powdered sugar (such as Peotraco Confectioners' Powdered Sugar, available in $450\,g$ net weight) will dissolve much faster than a solid sugar cube.