C1.3 - R* Separating mixtures Flashcards
When analytical chemists working on forensic or medical investigations are given an unknown sample to identify, what often is it?
When analytical chemists working on: 1. Forensic Or, 2. Medical investigations are given an unknown sample to identify, it is often a mixture of different substances
Mixture
A mixture is made up of: 1. 2 Or, 2. More substances (elements or compounds) that are not chemically combined together
Compounds have a fixed composition.
What does this mean?
This means that the ratio of elements present is always the same in any particular compound
Mixtures have no fixed composition.
What does this mean?
This means that the proportions vary depending on the amount of each substance mixed together
What must be used, to separate the elements in a compound?
To separate the elements in a compound, chemical reactions must be used
How can the different elements or compounds in a mixture be separated again?
The different: 1. Elements Or, 2. Compounds in a mixture can be separated again by physical means
What are there between atoms of the different elements in the compound?
Between atoms of the different elements in the compound, there are chemical bonds
What are there between atoms of the different substances in a mixture?
Between atoms of the different substances in a mixture, there are no chemical bonds
Before the substances in a mixture are identified, what happens?
Before the substances in a mixture are identified, they are separated from each other by physical means
What physical techniques are available to separate substances in a mixture?
To separate substances in a mixture, the physical techniques available are:
- Filtration
- Crystallisation
- Simple distillation
- Fractional distillation
- Chromatography
What do the physical techniques to separate substances in a mixture rely on?
The physical techniques to separate substances in a mixture rely on differences in the physical properties of the substances in the mixture
What is the technique of filtration used for?
The technique of filtration used to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent
(Insoluble solids from liquids)
If your product is an insoluble solid that needs to be separated from a liquid reaction mixture, what can be used?
If your product is an insoluble solid that needs to be separated from a liquid reaction mixture, filtration can be used
If your product is an insoluble solid that needs to be separated from a liquid reaction mixture, filtration can be used.
When else can filtration be used?
Filtration can also be used in purification
What is the method of filtration?
The method of filtration is that filter paper is folded into a cone shape
How can you separate a soluble salt from a solution?
To separate a soluble salt from a solution, there are 2 methods:
- Evaporation
- Crystallisation
What is evaporation a really quick way of doing?
Evaporation is a really quick way of separating a soluble salt from a solution
You can use evaporation only if what?
You can use evaporation only if the salt doesn’t decompose when its heated
Decompose
Decompose means to break down
If you want to make big crystals of your salt, what method should you use?
If you want to make big crystals of your salt, you should use the method of crystallisation
The point of crystallisation
The point of crystallisation is:
1. When small crystals first appear around the edge of the solution/or you see crystals start to form
Or,
2. When crystals appear in a drop of solution extracted from the dish with a glass rod
Rock salt
Rock salt is a mixture of:
- Salt
- Sand
What method can be used to separate rock salt?
To separate rock salt, the methods of:
1. Filtration
2. Crystallisation
can be used
Sand and salt are both what?
- Sand
2. Salt are both compounds
To separate a soluble salt from a solution, there are 2 methods: Evaporation and crystallisation.
What is a gentler way of heating the evaporating dish rather than using a Bunsen burner and directly on a tripod and gauze?
During evaporation and crystallisation, a gentler way of heating the evaporating dish rather than:
1. Using a Bunsen burner
2. Directly on a tripod and gauze
is by using a water bath
What does simple distillation allow us to do?
Simple distillation allows us to collect the solvent itself
Simple distillation is used for what?
Simple distillation is used for separating out a liquid from a solution
A condenser (part of the distillation apparatus)
A condenser (part of the distillation apparatus) is an outer glass tube with water flowing through it that acts as a cooling ‘jacket’ around the inner glass tube from the flask
Water goes what of the condenser?
Water goes:
1. In at the bottom
2. Out at the top
of the condenser
The problem with simple distillation
The problem with simple distillation is that you can only use it to separate things with very different boiling points
What do you do to separate a mixture of liquids with similar boiling points?
To separate a mixture of liquids with similar boiling points, you use fractional distillation
Filtration
Filtration is the technique used to separate substances that are insoluble in a particular solvent from those that are soluble
Simple distillation
Simple distillation is separation of a liquid from a mixture by evaporation followed by condensation
Fractional distillation
Fractional distillation is a way to separate liquids from a mixture of liquids by:
- Boiling off the substances at different temperatures
- Then condensing
- Collecting the liquids
Chromatography
Chromatography is the process whereby small amounts of dissolved substances are separated by running a solvent along a material such as absorbent paper
What is air?
Air is a mixture of gases, mainly:
- Nitrogen
- Oxygen
- Carbon dioxide
- Argon
Air is a mixture of gases, mainly nitrogen, oxygen, carbon dioxide and argon.
These gases all can be what?
These gases all can be separated out fairly easily
What is crude oil?
Crude oil is a mixture of different length hydrocarbon molecules
The properties of a mixture
The properties of a mixture are a mixture of the properties of the separate parts
The properties of a mixture are a mixture of the properties of the separate parts.
The chemical properties of a substance aren’t affected by it being part of a mixture.
Example
For example, a mixture of iron powder and sulfur powder will show the properties of both:
- Iron
- Sulfur
Simple distillation allows us to collect the solvent itself instead of just letting it evaporate off into the air.
Example
For example, some countries with a lack of fresh water sources purify seawater to obtain usable water
What can you use simple distillation to do?
You can use simple distillation to get pure water from seawater
How can you use simple distillation to get pure water from seawater?
You can use simple distillation to get pure water from seawater, because the water:
- Evaporates
- Is condensed and collected
The problem with simple distillation is that you can only use it to separate things with very different boiling points.
If the temperature goes higher than the boiling point of the substance with the higher boiling point, they will mix again.
If you have a mixture of liquids with similar boiling points, what do you need?
If you have a mixture of liquids with similar boiling points, you need another method instead of simple distillation to separate this
Heating —> Evaporating —>
Heating —> Evaporating —> Cooling —> Condensing
The physical techniques to separate substances in a mixture rely on differences in the physical properties of the substances in the mixture.
Examples
For example:
1. Different solubilities in a solvent
Or,
2. Different boiling points
If your product is an insoluble solid that needs to be separated from a liquid reaction mixture, filtration can be used.
Filtration can also be used in purification.
Example
For example, solid impurities in the reaction mixture can be separated out using filtration
You can use evaporation only if the salt doesn’t decompose when its heated.
If it does, then what will you have to use?
If the salt decomposes when its heated, then you will have to use crystallisation
Decompose means to break down.
What does thermal decomposition mean?
Thermal decomposition means to break down with heat
Sand and salt are both compounds, but salt dissolves in water, whereas sand doesn’t.
What does this vital difference in their physical properties give?
This vital difference in their physical properties gives a great way to separate them
The different elements or compounds in a mixture can be separated again by physical means, using what?
The different: 1. Elements Or, 2. Compounds in a mixture can be separated again by physical means, using the differences in properties of each substance in the mixture
The method of filtration is that filter paper is folded into a cone shape.
What happens to the solid?
The solid is left in the filter paper
The method of filtration is that filter paper is folded into a cone shape.
What happens to the solid?
The solid is left in the filter paper
If you want to make big crystals of your salt, you should use the method of crystallisation, rather than what?
If you want to make big crystals of your salt, you should use the method of crystallisation, rather than evaporation
Rock salt is a mixture of salt and sand.
It is what in water?
Rock salt is spread on the roads in winter
Sand and salt are both compounds, but what?
Sand and salt are both compounds, but salt dissolves in water, whereas sand doesn’t
During evaporation and crystallisation, a gentler way of heating the evaporating dish rather than using a Bunsen burner and directly on a tripod and gauze is by using a water bath, but you could also use what?
During evaporation and crystallisation, a gentler way of heating the evaporating dish rather than:
1. Using a Bunsen burner
2. Directly on a tripod and gauze
is by using a water bath, but you could also use an electric heater
Simple distillation allows us to collect the solvent itself, instead of just what?
Simple distillation allows us to collect the solvent itself, instead of just letting it evaporate off into the air
The problem with simple distillation is that you can only use it to separate things with very different boiling points.
What happens if the temperature goes higher than the boiling point of the substance with the higher boiling point?
If the temperature goes higher than the boiling point of the substance with the higher boiling point, they will mix again
The properties of a mixture are a mixture of the properties of the separate parts,
The chemical properties of a substance aren’t affected by it what?
The chemical properties of a substance aren’t affected by it being part of a mixture
For example, a mixture of iron powder and sulfur powder will show the properties of both iron and sulfur.
It will contain what?
A mixture of iron powder and sulfur powder will contain:
- Grey magnetic bits of iron
- Bright yellow bits of sulfur
You can use simple distillation to get pure water from seawater, because the water evaporates and is condensed and collected.
Eventually you’ll end up with what?
Eventually you’ll end up with just the salt left in the flask
You can use simple distillation to get pure water from seawater, because the water evaporates and is condensed and collected.
Eventually you’ll end up with what?
Eventually you’ll end up with just the salt left in the flask
The problem with simple distillation is that you can only use it to separate things with very different boiling points.
If the temperature goes higher than the boiling point of the substance with the higher boiling point, they will mix again.
If you have a mixture of liquids with similar boiling points, you need another method instead of simple distillation to separate this, like what?
If you have a mixture of liquids with similar boiling points, you need another method instead of simple distillation to separate this, like fractional distillation
