C5 Purity And Mixtures Flashcards
What does it mean when you refer to a substance as being pure in chemistry?
A pure substance is something that only contains one compound or element throughout (not mixed with anything)
What does melting point tell us about a substance?
How pure it is.
How can you test purity using melting point?
By sample measuring a substances melting point and comparing it with the reference melting point of the pure substance ( found in a data book)
The closer your measured value is to the actual melting point, the purer your sample is.
What effect will impurities in the sample have on the melting point?
They will lower the melting point and increase the melting range of the substance.
What is a substance that isn’t pure called?
A mixture
What are mixtures?
Substances that contain more than one element or compound which aren’t chemically bonded together.
The elements or compounds in a mixture can be separated out by what?
Physical methods such as Filtration Crystallisation Simple distillation Fractional distillation Chromatography
What is crude oil a mixture of?
Different length hydrocarbon molecules.
How are the chemical properties of a substance affected by being part of a mixture?
The chemical properties aren’t affected.
What are the properties of a mixture?
A mixture of the properties of the separate parts.
What is a physical method?
One that doesn’t involve a chemical reaction.
What are formulations?
Mixtures with exact amounts of components.
How are formulations made?
By following a formula.
Complete the sentence.
Each component in a formulation is present in a ……………, and contributes to the properties of the formulation so that it meets its required function.
Measured quantity
Paint is a formulation. Name the 4 parts.
Pigment (gives colour)
Solvent (dissolves the other components)
Binder (holds the pigment in place after it’s been painted on)
Additives (to change the physical and chemical properties of the paint)
Why are the chemicals used and the amounts used changed in different types of paint?
So the paint is right for its job.
Examples of everyday products that are formulations 9
Medicines Cleaning products Fuels Cosmetics Hygiene products Fertilisers Alloys Food Drink
Why is it important that the substances used to make a formulation, such as drugs and cosmetics, is pure?
If impurities get into the formulation, people could be harmed when they use them.
Ratios can be used to describe the composition of formulations. See p59 for an example
.
The melting point of pure aspirin is 136degree C. The melting point of a sample of aspirin is measured as being between 128-132 degree C.
Give two reasons why this suggest that the sample is not pure aspirin (2 marks)
The sample melts over a range of temperatures (1 mark).
The melting point is lower than that of pure aspirin (1mark)
