Purity (Purification). Flashcards
What is a mixture?
Two or more substances mixed together but not chemically combined.
NOTE - The chemical properties of each substance in a mixture are unchanged.
How do we know if a substance is pure?
Pure substances have a sharp melting point and boiling point whereas if a substance is impure, the impurities will have an effect on the melting and boiling point.
FURTHER EXPLAINATION : Pure water has an exact boiling point of 100°C whereas impure water could have a boiling point of 103°C.
Why is purity important (for consumption)?
Medical drugs and food additives must be pure to avoid harming people. To have a pure substance for food and drugs is very important as impurities could be dangerous even in small amounts.
A solution contains a solid dissolved in a solvent. Which is the solute and which is the solvent?
The dissolved solid is called the solute and the liquid that dissolves the solid is the solvent.
Define filtration.
Separating a solid from a liquid by using filter paper (the precipitate is insoluble).
What is the filtrate and what is the residue?
The solution which passes through the filter paper is called the filtrate and the solid that stays on the filter paper is called the residue.
Define decanting.
To gradually pour another liquid from one container into another in order to separate out sediment.
What is centrifugation/ what is the use of a centrifuge machine?
The separation of a solid from a liquid by rapid spinning during the solid collects at the bottom of the test tube - the liquid can then be decanted off carefully.
What is crystallization?
The formation of crystals when a saturated solution is left to cool.
If you were to have produced a soluble salt, how would you separate this salt from the solution that it was dissolved in?
- Warm the solution in an open container allowing the solvent to evaporate, leaving a saturated solution..
- Allow this solution to cool.
- The solid will come out of the solution and crystals will start to grow, these can be collected and allowed to dry.
What is simple distillation?
Used to separate a liquid and soluble solid from a solution or a pure liquid from a mixture of liquids.
When does simple distillation work?
Works when the liquids have different boiling points.
What is the sequence of events in distillation?
Heating → evaporating → cooling → condensing.
What is the sequence of events in distillation?
Heating → evaporating → cooling → condensing.
How do you separate ethanol and water?
Ethanol has a lower boiling point than water (ethanol boiling point 78°C VS water boiling point 100°C) so it evaporates first. The ethanol vapor is then cooled and condensed inside the condenser to form a pure liquid.
