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Year 9 > Chemistry (Separating Mixtures and Water Treatment) > Flashcards

Chemistry (Separating Mixtures and Water Treatment) Flashcards

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1
Q

The 3 Separation Techniques

A

1) Filtration
2) Evaporation
3) Crystallisation

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2
Q

The Filtration Separation Technique

A

Filtration separates an INSOLUBLE SOLID from a liquid (e.g. salt dissolved in water and sand). The liquid FILTRATE passes through the filter paper, the undissolved solid RESIDUE stays on the paper.
Decantation is another way of separating a liquid from an undissolved solid. When a liquid is decanted it is poured very slowly leaving the solid behind.

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3
Q

What Equipment is used in the Filtration Separation Technique?

A
  • Beaker
  • Salt solution and sand
  • Filter funnel
  • Filter paper
  • Conical flask
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4
Q

The Evaporation Separation Technique

A

Evaporation is used to separate a SOLUBLE SOLID form a solution (e.g. salt in water).
The solution is heated, the solvent evaporates leaving the solid solute behind. Unfortunately this method is only useful when trying to collect the solid.

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5
Q

What Equipment is used in the Evaporation Separation Technique?

A
  • Evaporating Basin
  • Gauze
  • Tripod
  • Bunsen Burner
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6
Q

The Crystallisation Separation Technique

A

Crystallisation is another way of separating a soluble solid from a solution. It is often used when making crystals from a solution where the solvent is water.
Instead of heating the mixture strongly and getting rid of all the water, the solution is put in a warm place and left to evaporate slowly.
When the solution becomes saturated, the crystals will form as more water evaporates. The crystals can be separated from any remaining solution by filtration.
The crystals formed are said to be hydrated and contain water in their structure. If strong heating was used this was would be evaporated away resulting in an anhydrous powder.

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7
Q

What Equipment is used in the Crystallisation Separation Technique?

A
  • Evaporating Basin
  • Gauze
  • Tripod
  • Bunsen Burner
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8
Q

Homogeneous Mixture
(Definition)

A

A combination of two or more substances where the components are evenly dispersed and do not separate over time. The mixture appears uniform throughout, and you cannot visually distinguish the individual components.
E.g. Coffee, Air, Blood

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9
Q

Heterogeneous Mixture
(Definition)

A

When the components of the mixture are not in the same phase or the composition of the mixture is UNEVEN throughout
E.g. Sandwich, Pizza, Chocolate-Chip Cookies

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10
Q

Residue
(Definition)

A

A substance that remains after the main part has gone or been taken or used, maybe after a process such as combustion or evaporation

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11
Q

Filtrate
(Definition)

A

A fluid that has been passed through a filter

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12
Q

Hydrous
(Definition)

A

Containing water as a constituent

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13
Q

Anhydrous
(Definition)

A

Free from water and especially water that is chemically combined in a crystalline substance

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14
Q

Solute
(Definition)

A

A dissolved substance

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15
Q

Solvent
(Definition)

A

The liquid in which a solute is dissolved to form a solution

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16
Q

Soluble
(Definition)

A

Able to be dissolved in a liquid

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17
Q

Insoluble
(Definition)

A

Incapable of being dissolved

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18
Q

Separating copper sulphate and sand
Method

A

Part 1: Filtration-
* Add sand, copper sulphate and distilled water to a beaker
* Stir until the copper sulphate has dissolved
* Filter the mixture into another beaker with a filter funnel and filter paper

Part 2: Evaporation-
* Pour half the contents into an evaporating basin
* Put the evaporating basin on a tripod and gauze and heat strongly with a Bunsen Burner
* When the water has evaporated, stop heating and examine the copper sulphate

Part 3: Crystallisation-
* Pour the remaining half of the solution into a crystallising dish and put it on the windowsill or in a tray so that it can be left undisturbed for a few days for the water to evaporate slowly

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19
Q

What was the colour of the filtrate?
(Separating copper sulphate and sand Experiment)

A

It was bright blue but lighter than the crystals.
This was because copper is a Transition metal, and transition metals are bright coloured solutions.

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20
Q

After the water had been evaporated, copper sulphate was left in the evaporating basin. Describe the appearance of the copper sulphate.
(Separating copper sulphate and sand Experiment)

A

It was a fine, white powder.
It was white as there was no water left because it had all been evaporated off.
It was a powder as it was heated quickly and aggressively - crystals form over time, so it turned into a powder.

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21
Q

Describe the appearance of the copper sulphate that had been formed by slow evaporation of the solution. Is there a difference between how this looks and the copper sulphate made by evaporation?
(Separating copper sulphate and sand Experiment)

A

They were larger, blue and crystalline.
The blue shows it was hydrated, meaning there was still some water left.

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22
Q

Conclusion of Separating copper sulphate and sand Experiment

A

When copper sulphate is obtained by quick evaporation by strong heating of the solution, white anhydrous copper sulphate is formed. This is a powder and is not crystalline. When the solution is allowed to evaporate more slowly, hydrated copper sulphate crystals are formed which are blue. The hydrated copper sulphate contains more water as part of the solid structure which is needed to form the crystal structure.

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23
Q

Distillation

A

Separates a SOLVENT from a solution

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24
Q

Apparatus for Distillation

A
  • Thermometer
  • Round-Bottomed Flask
  • Solution
  • Condenser
  • Delivery Tube
  • Beaker
  • Distillate
  • Solution
  • Bunsen Burner
  • Tripod
  • Gauze
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25
Explain how Distillation works to collect pure water from a sample of salty salt water
1) The sea water is heated in the flask 2) The water the evaporates, goes out of the flask, then into the condenser 3) In the condenser, the water vapour cools and turns from a gas to a liquid. The liquid water is collected in the beaker. Heat - evaporate - cool - condense
26
What Equipment is used in the Separating water from a mixture of copper sulphate and water?
* Boiling Tube * Bung * Solution (copper sulphate) * Anti-bumping Granules * Delivery Tube * Beaker * Ice + water * Distilled / Pure water
27
The apparatus was used to separate water from a solution of copper sulphate. Why is it important not to heat too violently? (Separating water from a mixture of copper sulphate and water Experiment)
The solution you are NOT trying to separate (copper sulphate) boils and bubbles over / goes down suddenly (in the boiling tube) and mixes with the distillate.
28
Describe the physical changes that take place to the water. (Separating water from a mixture of copper sulphate and water Experiment)
It evaporates into gas when heated, and then condenses when cooled (in the ice bath)
29
At what temperature does water distil off?
100 degrees Celsius
30
Describe the appearance of the distillate (Separating water from a mixture of copper sulphate and water Experiment)
It is a clear colourless liquid
31
What has the highest boiling point, the copper sulphate or water? (Separating water from a mixture of copper sulphate and water Experiment)
The copper sulphate
32
Describe a test to prove that the solution you have collected is PURE WATER
Check the boiling point - it has to be EXACTLY 100 degrees Celsius as if the water has impurities, it will have a different boiling point.
33
After the boiling tube has cooled, add some water to the anhydrous copper sulphate in the boiling tube. Describe what happens and the importance of this reaction. (Separating water from a mixture of copper sulphate and water Experiment)
The anhydrous copper sulphate will have a colour change from white to blue. The importance of this reaction is to prove whether it is water of not, NOT if it is pure or not.
34
Separating a liquid form a mixture of miscible liquids
When two liquids (e.g. alcohol and water) they are said to be miscible.
35
Fractional Distillation
Miscible liquids are separated by Fractional Distillation. Fractional Distillation differs from normal distillation because it uses a fractionating column. This allows the separation of liquids that have boiling points that are different but are still quite close together.
36
Separating a liquid from a mixture of miscible liquids (Method)
* The mixture is placed in a flask and heated * The mixture boils. Vapours form both liquids pass into the fractionating column, but there is a higher proportion of the substance with the lower boiling point (the more volatile one). In the fractionating column they condense and rebook many times, each time with a higher proportion of the more volatile liquid. * As a result of this, the vapour of the liquid which has the LOWER BOILING POINT emerges form the top of the columns FIRST, in a pure state, and passes into the condenser. * When all of this liquid has distilled over, it is followed by the liquid having the higher boiling point. * The thermometer measures the boiling point of the liquid distilling over at any moment.
37
Apparatus for Fractional Distillation
* Thermometer * Fractionating Column * Round-Bottomed Flask * Bunsen Burner * Delivery Tube * Condenser * Conical Flask
38
A mixture of two liquids (ethanol and water) is separated by fractional distillation - ethanol has a boiling point 78 degrees Celsius
If you heat the conical flask with the fractionating column to around 78 degrees Celsius, the ethanol will evaporate along with some water. But since the water has a higher boiling point, higher up the fractionating column it will be cooler, meaning it will condense back. But the ethanol will not so it will get to the top, go down the condenser, and end up in a beaker or a conical flask.
39
Separating a mixture of immiscible liquids
When two liquids do not mix (e.g. paraffin and water) they are said to be immiscible liquids. Immiscible liquids are separated using a separating funnel. E.g. Oil and water are separated simply by running off the more dense liquid (water) by opening the tap and collecting the liquids in different beakers.
40
Immiscible Liquids (Definition)
When two liquids do not mix E.g. oil and copper sulphate
41
Chromatography (Definition)
A method for separating several solids that are all soluble in the same solvent
42
How does Chromatography work?
Dyes (and other complex molecules) can be separated using chromatography. They are laced at the bottom of chromatography paper. This is then placed in a solvent, such as water. As the water is drawn up the paper it moves the different dyes at different rates depending on their solubility in water.
43
What does solubility have to do with height reached and speed on chromatography paper?
Dyes which are more soluble in water move more quickly up the paper. Dyes which are less soluble in water move more slowly up the paper. Therefore, the most soluble dye with travel the highest up the paper. If a dye is not soluble in the solvent then it will not move at all - to get it to move a different solvent would be needed.
44
The Mobile Phase in Chromatography
The solvent
45
The Stationary Phase in Chromatography
The paper
46
What do Rf values do?
They are used to identify substances
47
How to calculate the Rf value
Rf = Distance moved by the pigment (measure to the centre of spot) / Distance from pigment origin to solvent front
48
Solvent Front (Definition)
The highest point reached by the solvent
49
Why is the start line drawn in pencil? (Chromatography)
If drawn in pen, it would also stain the chromatography paper, moving upwards with the other ink samples.
50
Why are the spots often labelled at the start? (Chromatography)
To accurately measure the distance needed to calculate the Rf value
51
Why must the water level in the beaker be below the spots? (Chromatography)
If the water reaches the spots, they would dissolve into the solvent at the bottom and not go up the paper. We will not get an Rf value and chromatography will not work / happen.
52
What do chromatograms tell you about pens?
The ink we use is actually made up of multiple different coloured inks
53
Why do some inks move further than others? (Chromatography)
All inks/pigments have different levels of solubility. The more soluble it is, the further upwards they stain.
54
What is Water Treatment?
Water treatment essentially removes insoluble solids from the water and kills any harmful bacteria. It does not remove minerals and water that has been treated is definitely not pure.
55
Why do we do Water Treatment?
Before water can be used to drink it must be treated. Water suitable for drinking is called POTABLE water. This is not necessarily pure water because it contains dissolved substances which are needed in the body. Water supplies obviously come from fresh water. This water, with low levels of dissolved substances (fresh water) collects in the ground and to lakes and rivers and is then treated to make it potable.
56
The 3 main processes used to make water clean enough to drink
1) Sedimentation 2) Filtration 3) Sterilisation
57
What does Sedimentation do?
It gets rid of sediment - this is dirt, sand, small stones, mud, etc.
58
How does Sedimentation work?
Water is put into a tank where the water is very still. Particles of undissolved solid fall to the bottom of the tank where they settle. Sometimes coagulants are added to help particles of solid to stick together to make larger lumps of sediment. Water is removed higher up the tank which now contains less solid matter. This process is a little bit like decanting.
59
Coagulant (Definition)
Chemicals used Sedimentation that help particles of solid to stick together to make larger lumps of solid
60
What does Filtration do?
It removed bigger solid particles (than what sedimentation is able to do)
61
How does Filtration work?
Water is passed through a series of sand (and gravel) filters. These remove small particles of insoluble solid. This process is similar to how lab filtration works.
62
How does Sterilisation work?
Sterilising agents (chlorine, but sometimes either ozone or UV light) are added to the water supply to kill bacteria. Chlorine is also used in greater concentration to sterilise the water in swimming pools.
63
The appearance of tap water after being heated
There were rings of white solid left. This was residue - minerals, mainly calcium and magnesium ions.
64
The appearance of distilled water after being heated
It was completely clear because it was PURE WATER
65
The appearance of sea water after being heated
The abundance of residue left was salt
66
Potable meaning
Safe to drink
67
2 ways to Purify Water
1) Distillation 2) Reverse Osmosis
68
Distillation Method
The sea water is heated. The water evaporates and is then condensed (this produces pure water - distilled water). The salt and other dissolved substances do not evaporate and are left behind. The boiling of the water also kills any bacteria present.
69
Desalinate (Definition)
The process of removing salt in salt water
70
What water is made into solutions?/reacted?
Distilled water. Tap water and Salt water have too many soluble impurities that might cause unwanted side reactions to occur
71
Why is distillation so expensive?
The heat that is used to evaporate the water in the saltwater. This is energy, which is quite costly nowadays in most countries, including the UK.
72
Reverse Osmosis (Method)
Water is pumped through a semi-permeable membrane (like a tiny sieve with holes) that lets the water molecules go through unlike the much larger ions of the dissolved substances.
73
Why is reverse osmosis so expensive?
This is energy, which is quite costly nowadays in most countries, including the UK. It is only suitable for countries where there is no other source of water and energy is cheap.
74
As well as water sterilisation, what else is chlorine used for?
Bleaching - most bleaches are based on chlorine
75
Chlorine is a poisonous gas - how come we use it in both swimming pools and in treating drinking water?
Chlorine kills bacteria - people use very small amounts so it wouldn't be dangerous for humans but still kills bacteria
76
Describe the chemical test for chlorine gas with the results you will see
Blue litmus paper - red - white REMEMBER union jack colours!!

Year 9 (14 decks)

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