Mixtures and Separations Flashcards
What is a pure substance
A pure substance is a single substance not physically mixed with anything else.
2 examples of pure substances
Sugar and table salt are examples of pure substances.
Can a pure substance be an element or a compound.
Yes
Does a pure substance have a fixed melting point and boiling point.
Yes
Is a mixture a pure substance?
No, a mixture is an impure substance.
Does a Mixture have a fixed melting and boiling point?
No, it does not have a fixed melting point and boiling point.
Are most substances in nature pure or impure.
Impure
Can pure substances get separated by physical means
No
Can impure substances be separated by physical means?
Yes
Is air a mixture?
Yes
Homogenous Mixtures
A homogenous mixture is a mixture that has the same composition all the area of the mixture.
Heterogenous mixtures
A mixture that doesn’t have the same composition in all parts of it.
The different types of heterogenous mixtures
Suspensions and colloids
Difference between suspensions and colloids
- Suspensions usually have bigger particles than colloids
- Solvent and solute don’t separate in colloids when they are left to stand.
Solubility
Solubility of a solution refers to the amount of solute that is able to dissolve in a given quantity of solvent at a fixed temperature and pressure.
The rate of dissolving of a solute depends on:
Temperature (e.g. Solubility increases with temperature.)
Surface area of solute (e.g. Fine sugar dissolves faster than rock sugar.)
Rate of agitation (e.g. Stirring the solution increases the rate of dissolving.)
Explain why air is a mixture but water is a compound.
Water is chemically bonded together unlike air
State two reasons why a mixture of iron filings and sulfur before heating is a mixture
It is a mixture because the iron and sulphur can be separated by physical means e.g. by using a magnet. Also, no heat or light is given out when the iron filings and sulphur are mixed together.
When the mixture of iron filings and sulphur is heated strongly, state two reasons why the solid formed is a compound.
When the mixture of iron filings and sulphur is heated strongly, a compound is formed because a chemical reaction occurs e.g. heat and light are given off. Also, the sulphur and iron in the compound can no longer be separated by physical means such as by using a magnet.
Name 8 different separation techniques
Filtration
Evaporation
Crystallisation
Sublimation
Simple distillation
Fractional distillation
Use of separating funnel
Chromatography
Filtration + example
Filtration is the method used to separate an insoluble solid from a liquid.
An example would be to separate a mixture of sand and water.
Evaporation + example + method
Evaporation is the method used to separate a solute from a solution.
It can only be used for solids which do not decompose under heat e.g. table salt (sodium chloride).
It is done by heating the solution in an evaporating dish until it is completely dry.
Crystalization + method
Crystallisation is the method used to obtain pure crystals from a solution.
It is done by heating the solution in an evaporating dish until it is saturated.
The hot solution is then allowed to cool.
Crystals will be formed on cooling. They are then dried between sheets of filter paper.
Sublimation + method + examples
Sublimation is the method used to separate a substance which sublimes from a mixture.
Examples of substances which sublime are: iodine, ammonium salts, naphthalene and dry ice.
The mixture is heated in an
evaporating dish covered with
a filter funnel.
The substance which sublimes
will be changed into a vapour
and then formed back on the
inside of the funnel.
