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.
How does the fractional distillation of crude oil (petroleum) and products for fermentation work?
- The oil is heated in the fractionating column and the oil evaporates and condenses at a number of different temperatures.
- The many hydrocarbons in crude oil can be separated into fractions each of which contains molecules with a similar number of carbon atoms.
- The fractionating column works continuously, heated crude oil is piped in at the bottom. The vaporized oil rises up the column and the various fractions are constantly tapped off at the different levels where they condense.
- The fractions can be processed to produce feuls and feedstock for the petrochemical industry.
NOTE - The separation of the components in petroleum is achieved by fractional distillation on an industrial scale.
What is fractional distillation used for?
Used to separate two or more liquids that are miscible with one another.
What are the steps to separating liquids using fractional distillation?
- The solution is heated to the temperature of the substance with the lowest boiling point.
- This substance will rise and evaporate first, and vapors will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker.
- All of the substance is evaporated and collected, leaving behind the other components.
What are the steps to separating liquids using simple distillation?
- The solution is heated and pure water evaporates producing a vapor which rises through the neck of the round-bottomed flask.
- The vapor passes through the condenser, where it cools and condenses, turning into pure water which is collected in a beaker.
- After all the water is evaporated from the solution, only the solid solute will be left behind.
What can simple distillation be used to do?
Simple distillation can be used to separate the products of fermentation, such as alcohol and water.
How can immiscible liquids (oil and water) be separated?
Immiscible liquids can be separated using a separating funnel or by decanting.
What are the steps of separating undissolved solid from a liquid using filter paper?
- Filter paper is placed in a filter funnel above another beaker.
- The mixture of insoluble solid and liquid is poured into the filter funnel.
- Filter paper will only allow small liquid particles to pass through in the filtrate.
- Solid particles are too large to pass through the filter paper so will stay behind as a residue.
Appropriate apparatus for measuring:
- Time.
- Temperature.
- Mass.
- Volume.
- Time = stopwatch/ clock.
- Temperature = thermometer.
- Mass = balance.
- Volume = measuring cylinder/ burette/ pipette.
What is paper chromatography used for?
Used to separate mixtures and give information to help identify substances.
