Solutions and Suspensions Made Simple! (Lower Sec Chemistry)

Here is a quick and easy guide on understanding mixtures – solutions and suspensions – using common examples and a mind map!

When we talk about mixtures, there are two types that we can consider: homogeneous & heterogeneous.

In fact, Solutions and Suspensions are a subset of the concept of mixtures – and they are homogenous and heterogenous respectively.

For a quick recap on the basic properties of mixtures, check out this article on elements, compounds and mixtures!

Elements, Compounds, Mixtures Made Easy! (Lower Sec Chem)

If not, let’s delve deeper into the topic of solutions and suspensions.

Some key terms to take note of are:

• Solute (Substance dissolved in Solvent)
• Solvent (Substance that dissolves solute – remember that water is commonly known as our universal solvent!)
• Homogenous mixture (Substances are evenly distributed, mixture has the same appearance and composition throughout) – refer to Solutions
• Heterogenous mixture (Substances are not evenly distributed, mixture does not have the same appearance and composition throughout) – refer to Suspensions

Solutions 

Solutions are when two different substances are mixed together physically, to form a homogenous mixture. In this case, homogenous means equal/same, and that relates to the fact that the particles in solutions are distributed evenly throughout.

For example, one can relate this to mixing sugar (glucose – C6H12O6) with water🚰, after some stirring, the sugar will be dissolved and the sugar solution will have a uniform appearance and composition (homogenous).

Concentration of Solution

Concentration (g/cm³) → Amount of solute (g) ➗ Volume of solvent (cm³)

Goldilocks and The Three Bears

• Dilute – too bland! 😐
• Concentrated – just right 🙂
• Saturated – too sweet! 😵‍💫

To begin with, a concentrated solution contains a large amount of solute dissolved in a specific amount of solvent.

On the other hand, a dilute solution contains a small/trace amount of solute.

Lastly, a saturated solution contains the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature.

Rate of Dissolving 

In addition, a concept to consider when discussing solutions is the rate of dissolving, which is affected by a few factors.

Let’s choose a solution of sugared water as an example: For this, sugar is your solute (substance being dissolved) and water is your universal solvent (substance that dissolves another substance). 

Factors affecting Rate of Dissolving

How fast the sugar molecules dissolve in water depends on:

1. Temperature – If sugar molecules are put in hot water as compared to ice cold water, it will naturally dissolve faster. You can picture the sugar cubes just melting in the hot sun and dissolving into the water.
2. Size of particle – Imagine trying to dissolve a sugar cube vs sugar powder of equal mass. The sugar powder is bound to dissolve faster due to a larger exposed surface area to the solvent, which is associated with the smaller particle size it has.
3. Rate of Stirring – If you vigorously stir your drinks to dissolve the sugar, you will be able to enjoy the drink first
4. Amount of Solvent – In order for the sugar molecules to dissolve in the water, it must be able to bind to/ stick to the water molecules. If you have more solvent, sugar can bind to more water molecules. This results in a faster rate of dissolving!

In summary, to dissolve sugar in water faster:

• Use hot water
• Break/Grind sugar cubes into small pieces/use sugar powder instead
• Stir the mixture
• Use more/enough water

I think it helps when you associate and group different factors together using an example you are familiar with – give it a try!

Solubility 

Solubility refers to the maximum amount of solute which can dissolve in 100g water at a fixed temperature. In a sense, you can link this to the definition of a saturated solution. In this case, the solubility of coffee measures how much coffee powder can be dissolved in 100g of water until it is saturated, and further addition of coffee powder in that fixed amount of water (solvent) will settle in the cup as residue/undissolved solute.

Differentiating the terms (rate of dissolving, concentration & solubility)

• The rate of dissolving measures the speed (how fast the solute dissolves)
• Concentration of solution measures how MUCH solute is dissolved in the solvent
• Solubility of solution measures how much solute can be dissolved 

Suspension

The other type of mixture is a suspension – where solute particles are suspended in the solvent. Even after vigorous mixing, after leaving the suspension on its own for a while, there will be large insoluble solute particles that settle to the bottom of the beaker.

Therefore, we label suspensions as heterogeneous, as they do NOT have a uniform appearance and composition throughout the mixture. 

It will contain seawater, together with many fine grains of sand (solute), which do not dissolve in water, as well as other impurities – algae, that will be suspended in the bucket of seawater.

You can use a filter funnel to remove some of the larger insoluble impurities and substances using the method below: by pouring the suspension through a filter funnel with filter paper.

Now, let’s break down some of the main differences between solutions and suspensions.

Comparison: Solutions and Suspensions

Solution	Suspension
Dissolved Solute in the solvent has a small particle size	Contains large insoluble/undissolved solute particles
Usually Transparent & Clear – allows light to pass through (with exceptions: coffee)	Opaque – does not allow light to pass through easily
No residue is formed after filtration	Residue is left behind after filtering

Using the two examples we have named above, let’s summarise the above points.

Comparing a [sugar + water] solution and a [sea water + sand] suspension, we can see that when sugar is dissolved in water, the solution becomes clear and transparent. However, for the sea water + sand suspension, the large sand particles are undissolved in the sea water. Thus, the suspension is opaque (and will have the sand particles settling down in the mixture after some time).

For a quick summary and to visualise some of the links between the different topics in chemistry, I drew a quick mind map for these three topics: 

Mind Map for Lower Sec Chemistry: Solutions and Suspensions

1. Atoms, Ions and Molecules

2. Elements, Compounds and Mixtures

3. Solutions and Suspensions

For more information on how to use mind maps to effectively consolidate information, check out this article below!

5 Quick Tips to Use Mind Maps when learning science

Hope you found this useful, one way or another ~