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Study

Guide

Chemistry

(Paper 6)

-0620-

By: TooMuch1995

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Contents of the book

General Information.............................................................................................................................03

Test for Water......................................................................................................................................04

Basic knowledge of .Electrolysis...........................................................................................................04

Chemical Analysis.................... ............................................................................................................06

Labelling of Apparatus..........................................................................................................................08

Salt Preparation: Soluble Salts.............................................................................................................10

Salt Preparation: InsolubleSalts...........................................................................................................15

Rates of reaction..................................................................................................................................16

Fermentation .......................................................................................................................................18

Frequent questions ..............................................................................................................................18

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General Information As Per the syllabus of Cambridge IGCSE (0620) for Chemistry it’s your third Paper which you have

chosen to appear for instead of the coursework or the practical test.

It’s Called Alternative to practical paper (ATP)

Its duration is for one hour only

It’s weighted at 20% of total available marks

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Test for Water Not all Colourless liquids are water; therefore there is a test for identification and purity.

It can be detected by using:-

Anhydrous copper(II) Sulphate

Anhydrous cobalt (II)Chloride

Water will turn anhydrous copper (II) Sulphate from white to blue

Water will turn anhydrous cobalt (II) Chloride from blue to pink

Cobalt chloride paper contains blue anhydrous cobalt chloride which turns pink with presence

of water

To decide if water is pure or not, you would need to test that the boiling is 100oC exactly

A Solid pure substance has a Sharp Melting point (as in Ice form of water)

Electrolysis Electrolysis is the process of electrically inducing chemical changes in a conducting melt or

solution example: splitting an ionic compound into the metal and non-metal.

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Electrons flow from the battery to the cathode

Positive ions ( Metallic or Hydrogen ) in the liquid are attracted to this negative electrode

The positive ions accept electrons from the cathode, and metals or hydrogen are formed at

the cathode.

Electrons flow from the anode to the battery or power supply

Negative ions (non- metals except hydrogen) are attracted to this positive electrode

When the electrode is inert ( carbon or platinium ) the negative ions lose electrons to the

anode

Electrolysis separates an ionic compound back to the elements that form it. For example by

electrolysis we can obtain sodium and chlorine from sodium chloride.

When the current is turned on, the negative ion in the electrolyte gets attracted to the

positive electrode because they are oppositely charged. When this happens, the negative

ion loses the electrons it gained from the positive ion during bond formation and becomes

an atom. The electrons lost are transferred through the wire in the outer circuit from the

anode to the cathode. At the same time, the positive ion from the electrolyte is attracted to

the cathode, where it gains the electrons lost by the negative ion and becomes an atom too.

In ionic compounds the positive ion is a metal and it is collected at the cathode. And the

negative ion is a non-metal and collected at the anode.

The electrons are transferred from the anode to the cathode through the wires.

The electrolyte is an ionic compound either in its molten or aqueous form. Ionic compounds

conduct electricity only when they are in these forms because they contain free mobile ions

which can carry the current but they don’t in solid form.

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Chemical Analysis The following Test Analysis Should be learnt by heart as they are asked frequently in the

exam.

Flame test colour

Test for gases

Test for positive ions (Cations)

Test for negative ions (anions)

Some flame test Colours

Metal Ions Formula Colour of flame Sodium Na+ Yellow

Potassium K+ Lilac

Calcium Ca2+ Brick red

Lithium Li+ crimson

Copper Cu2+ Blue-green

Barium Ba2+ Apple green

Test for gases

Gas Description Test Test result Ammonia (NH3) Colourless and

pungent smell Hold damp red litmus paper (or universal indicator) in gas

Indicator paper turns blue

Carbon dioxide (CO2) Colourless and odourless

Bubble gas through lime water (calcium hydroxide solution)

White precipitate of calcium carbonate formed (solution turns milky)

Chlorine (Cl2) Pale green, chocking smell

Hold damp litmus paper ( or universal indicator) in gas

Indicator paper is bleached white (blue litmus will turn red first)

Hydrogen (H2) Colourless, odourless Hold a lighted splint in gas

Hydrogen burns with a pop squeaky sound

Oxygen (O2) Colourless, odourless Hold a glowing wooden splint in gas

The splint re-lights

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Test for negative ions (anions)

Negative ion Test Test results Carbonate (CO3

2-) Add dilute hydrochloric acid to solid

Effervescence (fizzes), carbon dioxide produced ( test with lime water)

Chloride (in solution) (Cl-)

Acidify solution with dilute nitric acid, then add aqueous silver nitrate

White precipitate of silver chloride formed, precipitate soluble in ammonia solution

Bromide (in solution) (Br-)

Acidify solution with dilute nitric acid, then add silver nitrate

Cream precipitate of silver bromide, only slightly soluble in ammonia solution

Iodide (in solution) (I-)

Acidify solution with dilute nitric acid, then add aqueous silver nitrate

Yellow precipitate of silver iodide formed insoluble in ammonia solution

Sulphate (in solution) (SO4

2-) Acidify solution with dilute hydrochloric acid , then add barium chloride solution

White precipitate of barium sulphate formed

Nitrate (in solution) (NO-

3) Make solution alkaline with sodium hydroxide solution then add aluminium foil and warm carefully

Ammonia gas given off (test with moist red litmus)

Test for positive ions (Cations)

Positive ion (in solution) Effect of adding Sodium Hydroxide

Effect of adding ammonia solution

Ammonium (NH+4) Ammonia produced on warming (test

with damp red litmus paper) -

Copper(II) (Cu2+) Light blue gelatinous precipitate of copper hydroxide, insoluble in excess sodium hydroxide

Light blue gelatinous precipitate; dissolves giving a deep blue solution

Iron (II) (Fe2+) Green gelatinous precipitate of Iron (II) hydroxide insoluble in excess

Green gelatinous precipitate, insoluble in excess

Iron (III) (Fe3+) Rust-brown gelatinous precipitate of Iron (III) hydroxide, insoluble in excess

Rust-brown gelatinous precipitate, insoluble in excess

Calcium (Ca2+) White precipitate of calcium hydroxide, insoluble in excess

No precipitate ( or only very slight precipitate)

Magnesium (Mg2+) White precipitate of magnesium hydroxide, insoluble in excess

White precipitate , insoluble in excess

Zinc (Zn2+) White precipitate of zinc hydroxide, insoluble in excess

White precipitate , soluble in excess

Aluminium (Al3+) White precipitate of aluminium hydroxide, soluble in excess giving a colourless solution

White precipitate , insoluble in excess

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Apparatus you will have to name and Describe

# Name Description 1 Beaker Used to hold and heat liquids. Multipurpose and

essential in the lab.

2 Bottle Bottles can be used for storage, for mixing and for displaying.

3 Bunsen Burner

Bunsen burners are used for heating and exposing items to flame. They have many more uses than a hot

plate, but do not replace a hot plate.

4 burette The burette is used in titrations to measure precisely how much liquid is used.

5 Crucible Crucibles are used to heat small quantities to very high temperatures.

6 Erlenmeyer Flask

The Erlenmeyer Flask is used to heat and store liquids. The advantage to the Erlenmeyer Flask is that the bottom is wider than the top so it will heat quicker because of the greater surface area exposed to the

heat.

7 Evaporating Dish

The Evaporating Dish is used to heat and evaporate liquids.

8 Florence Flask The Florence Flask is used for heating substances that need to be heated evenly. The bubbled bottom allows the heat to distribute through the liquid more evenly.

The Florence Flask is mostly used in distillation experiments.

9 Food Colouring

Food Colouring is used in many experiments to show colour change and to make the experiment more

exciting.

10 Funnel The Funnel is a piece of equipment that is used in the lab but is not confined to the lab. The funnel can be

used to target liquids into any container so they will not be lost or spilled.

11 Micro spatula The Micro spatula, commonly called a spatula, is used for moving small amounts of solid from place to place.

12 Mortar and Pestle

The Mortar and Pestle are used to crush solids into powders for experiments, usually to better dissolve the

solids.

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13 Paper Towels Paper Towels are essential to the lab environment. They will be used in almost every lab.

14 Pipet The pipet is used for moving small amounts of liquid from place to place. They are usually made of plastic

and are disposable

15 Ring Stand Ring stands are used to hold items being heated. Clamps or rings can be used so that items may be placed above the lab table for heating by bunsen

burners or other items.

16 Stir Rod The stir rods are used to stir things. They are usually made of glass. Stir Rods are very useful in the lab

setting.

17 Stopper Stoppers come in many different sizes. The sizes are from 0 to 8. Stoppers can have holes for thermometers

and for other probes that may be used.

18 Test tube Brush

The test tube brush is used to easily clean the inside of a test tube.

19 Test tube Holder

The holder is used to hold test tubes when they are hot and untouchable.

20 Test tube Rack The test tube rack is used to hold test tubes while reactions happen in them or while they are not needed.

21 Thermometer The thermometer is used to take temperature of solids, liquids, and gases. They are usually in oC, but can also

be in oF

22 Tongs Tongs are used to hold many different things such as flasks, crucibles, and evaporating dishes when they are

hot.

23 Triangle The triangle is used to hold crucibles when they are being heated. They usually sit on a ring stand

24 Volumetric Flask

The Volumetric flask is used to measure one specific volume. They are mostly used in mixing solutions where

a one litter or one half a litter is needed.

25 Watch Glass The watch glass is used to hold solids when being weighed or transported. They should never be heated.

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Salt Preparation Here are a few general points on Salts:

Salts are ionic Compounds

A Salt compound is formed from an acid by the replacement of hydrogen in the acid

by a metal

How is salt produced?

Salt deposits were formed by the evaporation of ancient seas millions of years ago therefore

Solid rock salt is directly mined from those areas.

Another technique known as solution mining in which the salt is dissolved underground and

the solution. This solution is known as the brine solution and it’s pumped to the surface

Preparing Salts

Number 1: you should know that there are two types of salts

Soluble Salts

Insoluble Salts

Number 2: you should know that each has a different way of producing

Number 3: When preparing a Salt, you should keep two things in your mind

Is the salt soluble or insoluble in water?

Do crystals of the salt contain water of crystallisation?

These points influence the preparation method chosen and how crystals are handled at the end

of the experiment

Preparing Soluble Salts

Number 4: Soluble Salts can be made by either

Characteristic Reaction ( with base or carbonate or metal)

Titration Method (involves neutralisation)

The three Characteristic Reactions

Soluble Salts are prepared using a

Insoluble Solid

Dilute Acid

The Insoluble solid can be one of those three

A Metal

A Base

A Carbonate

Number 5: Remember that the acid you use (parent acid) affects what type of salt you get

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To make chloride Salts use Hydrochloric Acid

To make Nitrate Salts use Nitric Acid

To make Sulphate Salts use Sulphuric Acid

To make Ethanoate Salts use Ethanoic Acid

Reacting dilute acid with fairly reactive metal

Dilute Acid + Metal Metal Salt + Hydrogen gas

Reacting dilute acid with insoluble base

Dilute acid + Insoluble base Metal Salt + Water

Reacting dilute acid with insoluble Carbonate

Dilute acid + Insoluble Carbonate Metal Salt + Water + Carbon dioxide

Steps of Preparing (using Characteristic Reactions Method)

Step 1:

Add Excess of the insoluble Solid to the dilute acid in a beaker until reaction stops (no

fizzing)

Step 2:

The Excess Solid is filtered out and collect the filtrate

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Step 3:

The Filtrate is gently evaporated to concentrate the Salt solution

This can be done using a water bath

Step 4:

When Crystals are seen Forming, heating is stopped

Step 5:

The concentrated solution is left to cool to from crystals completely

Step 6:

The crystals are filtered off and washed with distilled water

Step 7:

Dry crystals between filter papers

The Titration Method

Reacting dilute Acid with soluble Base (Alkali)

Dilute acid + Alkali Metal Salt + Water

This involves the neutralisation of acid with an alkali (to produce a soluble Salt)

Number 6: Since both the reactants are colourless an indicator should be used

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Steps of Preparing (using the titration method)

Step 1:

Fill the Burette with the dilute acid till the zero mark

Step 2:

A known value of an alkali is placed in a conical flask using a pipette

Step 3:

Add few drops of indicator to the conical flask of alkali

(Methyl orange will be used as an example here)

Step 4: The acid solution is run from the burette to the flask conating alkali until indicator

colour changes

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(Methyl orange will turn pink here)

Step 5:

The Volume of acid used to neutralise the alkali is noted

Step 6:

The process is repeated with the volume noted from the acid and same volume of alkali but

this time without the addition of the indicator

Step 7:

Evaporate most of the solution using a water bath

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Step 8:

When crystals are seen stop heating, and leave it to cool then dry between filter paper

Preparing Insoluble Salts

Insoluble salts are prepared by mixing 2 soluble salts together, each containing half the

needed salt.

This process is called precipitation.

Example: Preparation of insoluble lead sulphate (PbSO4):

Step 1:

Choose 2 suitable soluble salts, e.g. lead nitrate and sodium sulphate. Make aqueous solutions

of both.

Step 2:

Mix the two aqueous solutions together. An insoluble precipitate of lead sulphate is formed.

Step 3:

Filter the solution formed to get lead sulphate in filter paper.

Step 4:

Wash the filter paper with distilled water to remove trace of soluble salt.

Step 5:

The filter paper is dried in a warm oven. The salt is then scraped off it.

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Rates of reaction

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Fermentation You should know about Fermentation fully (only Definition is provided here)

Definition:

It is an anaerobic process. It takes place under condition where there is no air or oxygen

available.

Therefore, there is no oxygen (O2) present in the equation for the reaction taking place.

Carbon dioxide is the gas produced in the reaction.

Separation Techniques The most common ones are:

Filtration

Distillation (fractional and normal one)

Chromatography

Precipitation

You should know about the above all too

Frequent Questions

In this Section, there will be a collection of 60 questions from the past paper

exams of paper 6 which are repeated every year.

It would be a great help for you if you try to read and understand them because they also

might come in a different way (Indirectly)

They are numbered for you from 1-60 to make it easier for you

Question 1:

What is the purpose of ice or cold water?

Answer: To cool down the gas so that it condenses and turns into a liquid.

Question 2:

When the gas collecting tube is upside down, give a property of this gas.

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Answer: It is less dense than air.

Question 3:

Why is a pencil used in drawing the origin line in chromatography?

Answer: because pencil will dissolve as it will not give collies which makes the experiment

more accurate

Question 4:

When using ethanol, give a better apparatus arrangement, and why?

Answer: Cover apparatus with a lid, because ethanol is volatile.

Question 5:

In the tests and observation tables, when in the first row, they tell you that upon heating

condensation occurred, there will be a question asking

What does this show about the solid?

Answer: It is hydrated.

Question 6:

When copper is used in the test and the answer is four marks, (the best answer is...)

Answer: light blue precipitate (ppt.) which is soluble in excess to form dark blue solution.

Question 7:

Why is this experiment done in a fume cupboard?

Answer: It releases harmful gases that are poisonous. It is toxic.

Question 8:

Which result appears to be inaccurate? ( In graph drawing)

Answer: It is the point not appearing on the drawn graph, you read its x-axis and write it with

a reason indicating that it doesn't occur in the graph.

Question 9:

Why should the solid be crushed?

Answer: It increases surface area for a faster rate of reaction.

Question 10:

Why is the experiment made in a well-ventilated room?

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Answer: To prevent the burning of the substance.

Question 11:

Explain the term (decant)

Answer: Filter/Pour the liquid leaving the solid alone.

Question 12:

Why is concentrated sulphuric acid not used to dry ammonia?

Answer: because it will reach the base ammonia, which is neutralization reaction.

Question 13:

Why should samples be taken from different parts of the field?

Answer: to get more accurate results.

Question 14:

Suggest why it is important to know the pH of the soil.

Answer: to see which is a better place for growing, and what kind of base to use for

neutralizing it.

Question 15:

What is necessary for rusting?

Answer: water (humidity) and oxygen (air).

Question 16:

Suggest why in an experiment for rusting the water level increases.

Answer: Oxygen is used up, and water is used to take its place.

Question 17:

For electrolysis, state the observations.

Answer: The bulb will light - A metal is formed on the cathode - Fizz of gases produced.

Question 18:

Suggest a suitable material for electrodes.

Answer: Graphite - Carbon – Steel- Platinum.

Question 19:

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When copper oxide is reacted with hydrogen, what is the colour change?

Answer: black to brown, because copper oxide is reduced to copper.

Question 20:

How can you distinguish between water and ethanol?

Answer: use cobalt chloride paper, it turns from pink to blue with water, but there will be no

change with ethanol.

Question 21:

How can you distinguish between sulphuric acid and aqueous sodium sulphate?

Answer: there are three tests, you can use a metal carbonate in which carbon dioxide will be

produced with sulphuric acid but there will be no change with sodium sulphate. You can add

a metal, in which hydrogen is produced with sulphuric acid, but no change in sodium

sulphate. Finally, you could use an indicator like litmus paper, it will change to red with

sulphuric acid, but there will be no change with sodium sulphate..

Question 22:

How can you distinguish between hydrochloric acid and nitric acid?

Answer: add silver nitrate, in which white ppt. will be formed with hydrochloric acid, but

there will be no reaction with nitric acid.

Question 23:

What is the purpose of the mineral wool?

Answer: to absorb and hold the liquid.

Question 24:

When there is a delivery tube involved in a question, what precaution should be taken in the

experiment when the heat is removed?

Answer: remove the delivery tube from water to prevent suck-back.

Question 25:

In rate of reactions, always include the word "collisions between particles".

Question 26

How can you distinguish between alkanes and alkenes?

Answer: Use bromine water, in which the alkene will decolourise it to colourless, but

nothing, happens with an alkane,

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Question 27

How can you distinguish between chlorine and sodium chloride?

Answer: add litmus paper, it will bleach with chlorine, but nothing happens to it with sodium

chloride.

Question 28

How can you distinguish between copper sulphate and copper carbonate?

Answer: acidify with hydrochloric acid, and add barium chloride, there will be white ppt with

sulphate, but no white ppt. with carbonate. OR just add hydrochloric acid, in which nothing

happens with sulphate, but a fizz or effervescence of carbon dioxide will occur with

carbonate.

Question 29:

When a measuring cylinder is used, and they ask for a change in apparatus to get more

reliable results,

Answer: you should say that a biuret can be used instead as it is more accurate.

Question 30:

Why Volume of reagent is used?

Answer: volume of reagent used decreases if it is more concentrated.

Question 31:

In an experiment observation of pH value, and they ask what type of acid/base is used, your

Answer: should be weather weak or strong. A strong acid lies between pH values of 0 and 2,

and a weak one lies between 3 and 6. 7 are neutral. A weak base lies between 8 and 11, while

a strong one lies between 12 and 14.

Question 32:

What is a concentrated acid?

Answer: a concentrated acid is an acid that contains a large number of H+, hydrogen ions.

Vice versa with dilute acid.

Question 33:

What is a concentrated base?

Answer: a concentrated base is a base that contains a large number of OH-' hydroxide ions.

Vice versa with dilute base.

Question 34

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What is a strong acid?

Answer: a strong acid is one that ionizes completely giving H+ in solutions. Vice versa with a

weak one.

Question 35:

What is a strong base?

Answer: a strong base is one that ionizes completely giving OH- in solutions. Vice versa with

a weak one.

Question 36:

What is meant by the term Concentrated?

Answer: concentrated: is a solution that contains a large number of solute or little amount of

water is involved.

Question 37:

How can you make crystals?

Answer: 1) heat till point of crystallization. 2) Leave to cool gradually. 3) Filter, dry and

collect the crystals!

Question 38:

How can you detect the point of crystallization?

Answer: Place a stirring rod in the solution and see the formation of the first crystals on it.

Question 39:

What is used to crush a substance?

Answer: when you crush, you use a pestle and mortar.

Question 40

Why ethanol is used but not water? (grass)

Answer: grass is ground with ethanol rather than water because chlorophyll is more soluble in

ethanol.

Note 41:

Colour of rusty iron fillings is brown (orange and red are I think accepted)

Note 42:

If pure oxygen was used instead of air, rusting will be faster.

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Note 43:

You can speed up the drying process by using a fan or by increasing temperature or by using

a hair-drier if you have one) NOT a catalyst.

Note 44:

The action of a lie big condenser is to change steam to water.

Note 45:

To check for the purity for a collected solvent, test it's melting or boiling point.

Note 36:

The chromatogram needs to be sprayed with locating agent is amino acids are investigated

because they are colourless.

Note 37:

If water contained salt, this will have no effect on rusting, however if a bigger substance is

being rusted, it will be slower.

Note 38:

Hydrated copper sulphate will turn from whit to blue upon heating.

49) Saturated: no more solute can be dissolved in a solvent AT A CONSTANT

TEMPERATURE.

50) An excess amount of reactant is used to make sure all the other reactant will be used.

51) Sometimes, crystals are dried using filter paper instead of heating to prevent the complete

loss of water from crystals, and to prevent crystals from breaking.

52) How could you know which reactant is in excess? At the end of the reaction, the excess

reactant will be visible.

53) Excess means more than what is needed.

54) When lead bromide is used, you can use a fume cupboard or use goggles, lab coat, gloves

because it is toxic.

55) To separate two different solutions with different boiling point, use fractional distillation.

56) Physical test of water: heat, it will boil at 100 degrees Celsius, or heat ice and it will melt

at 0 degrees Celsius.

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57) Chemical test of water: Add blue cobalt chloride paper, it turns pink OR add anhydrous

copper sulphate, it turns blue.

Question 58

Why is it dangerous to heat alcohol directly?

Answer: fire will be produced if alcohol is touched with lighted splint, therefore a water bath

should be used when heating it. Lagging or cloth can be used to control temperature for

accurate results.

Question 59

What is the name given to unreacted material?

Answer: unreacted reactant is called excess.

Question 60

What happens to the particles when they get heated?

Answer: the particles gain energy, move faster, and their kinetic energy increases therefore

there will be more collisions and rate increases.

DONE

Pray for me