Making mixtures

If you put some coloured ink or food dye into some water, you have made a mixture. If you pour some dried peas and some rice into a pan you have made a mixture.
Mixtures contain different substances that are not combined together chemically. For example, if some iron filings are mixed with powdered sulfur, you can see the pieces of grey won and yellow sulfur. If powdered carbon is mixed with table salt, you can see the black carbon powder and the white salt.

How can we separate mixtures?

Mixtures can be separated quite easily because the different substances in the mixture have not combined together to make a new substance. They still each have their own properties. To separate the iron and sulfur mixture in Activity $8/1A$, you used a magnet to pick up the iron because iron is magnetic and sulfu is not.
The evaporating dish in the diagram contains a mixture of water and copper sulfate. If it is left in a warm room the water evaporates into the air and leaves the copper sulfate behind in the dish.

Separating food dye and water

A mixture of food dye and water can be separated using a piece of apparatus called a condenser. It is used to separate mixtures of two liquids.
The water and food dye mixture is heated and boils. The liquid water changes to a gas (steam) and this travels along the tube into the condenser.
The cold water that is circulating around the outside of the condenser cools the gas down. This makes the gas condense back to liquid water, which is collected in the beaker. The food dye remains in the heated container.

Activity 8.3 (Separating sandy, salty water)

 

SE: Your teacher will give you a mixture of water, salt and sand. Your task is to separate the mixture.

1) Prepare a filter paper and place it in a filter  funnel. Place the filter funnel in a conical flask. Pour the mixture into the funnel. Take care to add it slowly so that the mixture does not go down the outside of the filter paper. Do not disturb the wet filter paper-it easily tears. When you have filtered all the mixture, leave the filter paper in a warm place to dry.

2) Place the clear liquid (filtrate) from the conical flask in an evaporating basin. Heat this gently. Wear safety glasses. When this liquid starts to spit remove it from the heat and leave in a warm place to evaporate.

Questions

 

${A_1}$: Suggest why the sand remains in the filter paper.

${A_2}$: One group of students thought their mixture was taking too long to filter so they used a pencil to stir it up while it was in the filter paper. Explain why this is not a good idea.

${A_3}$: What safety precautions should you take when heating the salty water?

${A_4}$: How could you obtain the water from your mixture!

$A+I$: ${A_5}$: The salt left in the evaporating basin is often a little dirty Suggest what you could do to get cleaner salt.