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Separation Technique
GCSE chemistry and combined chemistry
Question | Answer |
---|---|
What is chromatography? | A process to separate the constituents of a mixture |
In paper chromatography, what is the stationary phase and what is the mobile phase | Paper is stationary, solvent (usually water or ethanol) is mobile |
How can chromatography show the difference between pure and impure substances? | Pure ones will not separate into a number of spots |
How is the Rf value calculated? | distance moved by spot/distance moved by solvent |
What does a substance's Rf value depend on? | How soluble it is in the solvent |
In chromatography, why must the substances be placed on a pencil line? | Pencil will not dissolve in the solvent |
In chromatography why must the solvent height be lower than the pencil line? | So that the substances do not dissolve into the solvent off the paper |
How is the melting point of a pure substance different from that of an impure substance? | Pure substance has one specific melting point. Impure substance has a melting range. |
What is simple distillation used to separate? | A liquid from a solid |
What is fractional distillation used to separate? | Two liquids with different boiling points. |
What is filtration used to separate? | An insoluble solid from a liquid |
What is crystallisation? | Forming crystals of a soluble solid from a solution. |
What is potable water? | Drinking water |
How can sea water be made potable? | By distillation |
What are the stages used to make water potable. | Sedimentation, filtration and chlorination |
What is a pure substance? | A substance made of one type of atom or molecule only. |
How would you separate water from salt water? | Simple distillation |
How would you separate salt from salt water? | Crystallisation |
Why must analysis be done with pure water? | Because dissolved salts in non pure water would give false positive results. |
How is the melting point of a mixture different from a pure substance? | A pure substance has a single melting temperature, a mixture has a range of melting points. |