The Amazing World of Solutes, Solvents, and Solutions
A solution is a uniform mixture where two or more substances are mixed together. Think about making a glass of lemonade. You add sugar to water, and the sugar disappears, creating a uniform mixture.
The solute dissolves in the solvent to create the solution.
Sometimes, it's not so clear-cut. When two liquids are mixed, the substance present in the smaller amount is considered the solute, and the one in the larger amount is the solvent.
Air is also a solution, but it's a gaseous solution. Nitrogen is the solvent because it's present in the largest amount, and oxygen, argon, carbon dioxide, and other gases are the solutes.
Think about adding sugar to your tea. At first, the sugar dissolves easily. But what happens if you keep adding more and more sugar? Eventually, the sugar will stop dissolving and settle at the bottom of the cup.
The concentration of a solution refers to the amount of solute present in a fixed quantity of solution (or solvent).
Solubility is the maximum amount of solute that can dissolve in a fixed quantity of the solvent.
Temperature plays a significant role in how much solute can dissolve in a solvent.
For most substances, solubility increases with an increase in temperature. A saturated solution at a particular temperature can behave like an unsaturated solution if the temperature is increased.
Many gases, including oxygen, can dissolve in water, although oxygen does so to a small extent. This dissolved oxygen is crucial for aquatic life.
The mixture of gases in water is a uniform mixture because the gases dissolve evenly to form a solution.
Temperature also affects the solubility of gases in liquids. The solubility of gases generally decreases as temperature increases.
You've probably noticed that some things float in water, while others sink. Husk particles float while washing rice, while the rice sinks. Oil floats on water.
Generally, it's believed that objects that float are lighter, and those that sink are heavier. However, it's more about a property called density.
Imagine a crowded bus versus an empty bus. The crowded bus has a high density of people, while the empty bus has a low density. Similarly, a dense forest has trees growing close together, while a less dense forest has trees farther apart.
Density is defined as the mass present in a unit volume of a substance.
The formula for density is:
Density = Mass / Volume
Density is independent of shape or size but depends on temperature and pressure. Pressure primarily affects the density of gases.
The SI unit of density is kilogram per cubic meter (kg/m³). For liquids, gram per milliliter (g/mL) and gram per cubic centimeter (g/cm³) are also used.
Relative density compares the density of a substance to the density of water at the same temperature.
Relative density = Density of substance / Density of water
Relative density has no units.
To determine density, you need to measure mass and volume.
How to measure mass?
Mass is the quantity of matter in an object. A balance is used to measure mass. A digital weighing balance is used to measure mass.
How to measure volume?
Volume is the space occupied by an object. The SI unit of volume is cubic meters (m³). Smaller volumes are expressed in decimeter cubes (dm³) or centimeter cubes (cm³). For liquids, volume is expressed in liters (L), which is equal to 1 dm³, or milliliters (mL), which is equal to 1 cm³.
A measuring cylinder is used to measure the volume of liquids. It's a narrow, transparent container with markings to indicate the volume of liquid.
When measuring volume in a measuring cylinder, the water forms a curved surface called the meniscus. For water and colorless liquids, read the mark at the bottom of the meniscus. For colored liquids, read the mark at the top of the meniscus.
Determining volume of solid objects with regular shapes
For objects with cuboid shapes, volume can be calculated using the formula:
Volume = length × width × height
Determining volume of objects with irregular shapes
For objects with irregular shapes, like a stone, volume can be determined by displacement.
Generally, density decreases with heating and increases with cooling. As temperature increases, the particles of a substance move away and spread, increasing volume but not mass. Since Density = Mass/Volume, density decreases upon heating. This is why hot air rises, as it is less dense than cool air.
Pressure affects density differently depending on the state of matter. For gases, increasing pressure causes particles to move closer, decreasing volume and increasing density. For liquids, pressure has a small effect because they are nearly incompressible. Solids are even less affected by pressure than liquids.
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