Chemistry_Grade_10-12 (1).pdf

The air we breathe is another example of a

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or from the bottom. The air we breathe is another example of a homogeneous mixture since it is made up of different gases which are in a constant ratio, and which can’t be distinguished from each other. Definition: Homogeneous mixture A homogeneous mixture is one that is uniform, and where the different components of the mixture cannot be seen. An alloy is a homogeneous mixture of two or more elements, at least one of which is a metal, where the resulting material has metallic properties. Alloys are usually made to improve on the properties of the elements that make them up. Steel for example, is much stronger than iron, which is its main component. 1.1.3 Separating mixtures Sometimes it is important to be able to separate a mixture. There are lots of different ways to do this. These are some examples: Filtration A piece of filter paper in a funnel can be used to separate a mixture of sand and water. Heating / evaporation Sometimes, heating a solution causes the water to evaporate, leaving the other part of the mixture behind. You can try this using a salt solution. Centrifugation This is a laboratory process which uses the centrifugal force of spinning objects to separate out the heavier substances from a mixture. This process is used to separate the cells and plasma in blood. When the test tubes that hold the blood are spun round in the machine, the heavier cells sink to the bottom of the test tube. Can you think of a reason why it might be important to have a way of separating blood in this way? Dialysis This is an interesting way of separating a mixture because it can be used in some important applications. Dialysis works using a process called diffusion . Diffusion takes place when one substance in a mixture moves from an area where it has a high concentration to an area where its concentration is lower. This movement takes place across a semi-permeable membrane. A semi-permeable membrane is a barrier that lets some things move across it, but not others. This process is very important for people whose kidneys are not functioning properly, an illness called renal failure . Interesting Fact erest Fact Normally, healthy kidneys remove waste products from the blood. When a person has renal failure, their kidneys cannot do this any more, and this can be life- threatening. Using dialysis, the blood of the patient flows on one side of a semi-permeable membrane. On the other side there will be a fluid that has no waste products but lots of other important substances such as potassium ions ( K + ) that the person will need. Waste products from the blood diffuse from where their concentration is high (i.e. in the person’s blood) into the ’clean’ fluid on the other side of the membrane. The potassium ions will move in the opposite direction from the fluid into the blood. Through this process, waste products are taken out of the blood so that the person stays healthy.
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