Solutions, suspensions and colloids

Introduction to mixtures

In your kitchen, you mix many things together. When you stir sugar into water until it disappears, you have a solution. If you mix sand and water, the sand eventually settles at the bottom; that is a suspension. Sometimes, you have something in the middle, like thick pap or milk, which we call a colloid.

Understanding solutions

A solution is a uniform mixture where the substance you dissolve (solute) completely disappears into the liquid (solvent). Think of how salt disappears in water when you are cooking soup. You cannot see the salt anymore because the particles are very tiny, even smaller than what a microscope can see.

In simple terms, a solution is a perfect blend where everything looks the same from top to bottom.

Understanding suspensions

A suspension is like muddy water from a borehole that hasn't been filtered. The particles are large and heavy. If you leave it to stand, the mud will settle at the bottom of the bucket. You can easily separate it by using a filter cloth or filter paper.

Simply put, a suspension is a 'temporary' mixture where the heavy pieces eventually fall to the bottom.

Understanding colloids

A colloid is the 'middle child.' The particles are larger than those in a solution but smaller than those in a suspension. Examples include milk, fog, and the foam on top of your malt drink. They look uniform to the eye, but the particles are actually floating and do not settle down.

In short, a colloid is a mixture that looks smooth like a solution but contains hidden particles that are too light to sink.

Differences between the three types

1. Particle Size: Solutions have the smallest particles, colloids are medium, and suspensions have the largest particles.

2. Appearance: Solutions are clear and transparent. Colloids are usually cloudy or opaque. Suspensions are murky and become clear only after the dirt settles.

3. Filtration: You cannot filter a solution or a colloid with ordinary filter paper, but you can easily filter a suspension.

4. Stability: Solutions and colloids are stable (they don't separate on their own), but suspensions are unstable.

Calculation of solubility

Sometimes we need to calculate how much solute is in a solution. Let us look at this example:

If 25 g of common salt (NaCl) is dissolved in 100 g of water at 25 degrees Celsius, what is the percentage by mass of the salt in the solution?

1. First, find the total mass of the solution: Mass of solute + Mass of solvent = 25 g + 100 g = 125 g.

2. Use the formula: (Mass of solute / Total mass of solution) x 100.

3. (25 / 125) x 100 = 0.2 x 100 = 20 percent.