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WORKSHEET:
(Paskandy, 2013) (i) PART A: Write examples of mixtures in the empty boxes.
When two or more different materials combine or mix together this forms a mixture. The two (or more) materials that form the mixture DO NOT chemically combine. This means their atoms do not bond (join up), which means that the two substances are not bonded together forever.
Because the substances are only mixed together and not joined by their atoms, these substances can be separated reasonably easily through methods such as filtration and evaporation.
There are three main types of mixtures:
● solutions, ● suspensions and ● colloids(Ext)
Solutions
Solutions are a very common type of mixture. They form when one material dissolves in another. The particles being dissolved in a solution are very, very small. A solution consists of two parts:
● Solute – the substance that dissolves in a liquid ● Solvent – the liquid used to make a solution
If something can dissolve in a liquid it is said to be soluble. If something cannot dissolve in a liquid it is said to be insoluble. If a solution is left for a long time, the solute does not settle to the bottom, it remains dissolved in the solvent. You cannot easily filter a solution neither, this is because the particles are so very small. Light will travel straight through a solution. This is because the rays of light are not blocked by the particles because the particles are too tiny.
Suspensions
Suspensions are formed when one material mixes with another but does not dissolve. The material remains floating or suspended in the liquid. These particles remain floating because they are larger in size. If a suspension is left for a long time the particles of the materials that are floating or suspended in the liquid will eventually settle to the bottom. It is also possible to filter a suspension, separating the liquid from the materials floating within it. Light does not pass easily through a suspension. This is because the large particles scatter the light as it enters the suspension.
Colloids
Colloids fit somewhere between solutions and suspensions. If a colloid is left for an extremely long time, it is possible the medium sized particles may settle to the bottom. However, it is more likely they will not. It is not possible to filter a colloid in order to separate it into its different materials. Colloids scatter light just like a suspension
(ii) ✍ Using the information you just read, fill in the table below about the properties of
Solutions, Suspensions and Colloids. (Paskandy,2013)
Solutions Suspensions Colloids
Particle size
If left, will the mixture settle out?
Can the mixture be filtered?
Light transmission
Examples
PART B: Investigation
(a) You are provided with the following substances : Flour, Salt, oil, powdered food colouring, brown sugar, sand, and breadcrumbs. (i)You are to identify which substances ‘disappeared’ ( dissolved) when mixed and which one did not.
(ii) Construct a table on a word document to record your observations. (iii) Identify which one forms a solution. Are all the solutions colourless?
Worksheet (Wahid, 2015)
Filtration
Filtration is good for separating an insoluble solid from a liquid. (An insoluble substance is one that does not dissolve).Sand, for example, can be separated from a mixture of sand and water using filtration. That's because sand does not dissolve in water.
● You are provided with a mixture of sand and water and you are required to separate the sand from water using the filtration process. ● You have been shown hot to fold a filter paper ● Follow the steps 1,2 and 3 to perform the filtration taking care not to let the liquid overflow in the filter paper
Fill in the blanks: The solid remaining in the filter paper is called the The liquid which passes through the filter paper is called the (choose : Filtrate, Residue)
EXTENDED ACTIVITY:
How will you separate a mixture of salt, sand and water?
Extended Activity:
In groups of 4, make a poster to summarise the different separation techniques.
Model answer
Chromatography
This is good for separating dissolved substances that have different colours, such as inks and plant dyes. It works because some of the coloured substances dissolve in the liquid better than others, so they travel further up the paper.
Evaporation
This is good for separating a soluble solid from a liquid (a soluble substance does dissolve, to form a solution).
For example copper sulphate crystals can be separated from copper sulphate solution using evaporation. Remember that it is the water that evaporates away, not the solution.
Distillation
This is good for separating a liquid from a solution. For example, water can be separated from salty water by simple distillation. This method works because the water evaporates from the solution, but is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.
