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Chemistry G10 > Mixtures and Separations > Flashcards

Mixtures and Separations Flashcards

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1
Q

What is a pure substance

A

A pure substance is a single substance not physically mixed with anything else.

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2
Q

2 examples of pure substances

A

Sugar and table salt are examples of pure substances.

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3
Q

Can a pure substance be an element or a compound.

A

Yes

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4
Q

Does a pure substance have a fixed melting point and boiling point.

A

Yes

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5
Q

Is a mixture a pure substance?

A

No, a mixture is an impure substance.

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6
Q

Does a Mixture have a fixed melting and boiling point?

A

No, it does not have a fixed melting point and boiling point.

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7
Q

Are most substances in nature pure or impure.

A

Impure

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8
Q

Can pure substances get separated by physical means

A

No

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9
Q

Can impure substances be separated by physical means?

A

Yes

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10
Q

Is air a mixture?

A

Yes

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11
Q

Homogenous Mixtures

A

A homogenous mixture is a mixture that has the same composition all the area of the mixture.

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12
Q

Heterogenous mixtures

A

A mixture that doesn’t have the same composition in all parts of it.

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13
Q

The different types of heterogenous mixtures

A

Suspensions and colloids

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14
Q

Difference between suspensions and colloids

A
  1. Suspensions usually have bigger particles than colloids
  2. Solvent and solute don’t separate in colloids when they are left to stand.
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15
Q

Solubility

A

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.

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16
Q

The rate of dissolving of a solute depends on:

A

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.)

17
Q

Explain why air is a mixture but water is a compound.

A

Water is chemically bonded together unlike air

18
Q

State two reasons why a mixture of iron filings and sulfur before heating is a mixture

A

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.

19
Q

When the mixture of iron filings and sulphur is heated strongly, state two reasons why the solid formed is a compound.

A

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.

20
Q

Name 8 different separation techniques

A

Filtration
Evaporation
Crystallisation
Sublimation
Simple distillation
Fractional distillation
Use of separating funnel
Chromatography

21
Q

Filtration + example

A

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.

22
Q

Evaporation + example + method

A

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.

23
Q

Crystalization + method

A

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.

24
Q

Sublimation + method + examples

A

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.

25
Q

Simple distillation + Example + method

A

Distillation is the method used to obtain a pure solvent from a solution. E.g. pure water from seawater.

It is done by heating the solution in a distillation flask and collecting the vapour that boils off.
A condenser is used to condense the hot vapour and change it to a liquid.
The condenser is cooled by the flow of cold water (in the condenser) from the tap.

26
Q

Fractional distillation + method example

A

Fractional distillation is used to separate two or more miscible liquids with different boiling points.

Example: Mixture of ethanol and water
When the thermometer reaches a steady temperature of 78 oC,
ethanol is collected.
Water is collected when the
thermometer reaches a steady
temperature of 100 oC.

27
Q

Separation funnel + method + method example

A

This method is used to separate a mixture of immiscible liquids.

The mixture is placed into a separating funnel and allowed to settle into two layers.

Example: Mixture of oil and water
The tap is first opened to allow the water to drain out of the funnel.
After all the water has drained out, another beaker is placed below the funnel and oil is now drained out.

28
Q

Chromatography + types + method idea

A

Chromatography is a method used to separate and identify small quantities of substances.

There are different kinds of chromatography techniques, such as gas chromatography, liquid chromatography and paper chromatography.

It is based on the principle that
different substances have different
solubilities in the same solvent.
The more soluble substance will get
carried along faster by the solvent
and move further ahead than the
less soluble substances.

29
Q

Set up/ method for chromatography

A

The starting line must be drawn in pencil, not ink. This is because unlike ink, pencil lead is insoluble in the solvent and will not interfere with the chromatogram.

-The spots of mixtures must be placed above the solvent level, so that they will not immediately dissolve in the solvent, and the solvent has time to slowly move up.

30
Q

Rf value formula

A

Distance substance has moved
_____________________________________
Distance the solvent front has moved

Chemistry G10 (1 decks)

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