Chemistry Form 1 Coursework e-Content CD

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CLASSIFICATION OF SUBSTANCES

DECANTATION, FILTRATION AND EVAPORATION

 

SEPARATION OF MIXTURES

Separation of an insoluble solid from a liquid/solid mixture

Insoluble solids can be obtained from liquid/solid mixture by Decantation.Click to play the video to observe the process of decantation.


This method is based on density, sand being denser than water settles at the bottom and water being less dense remains at the top.

Decantation is therefore the process of separating an insoluble solid from a liquid-solid mixture.

SEPARATION OF MIXTURES

Separation of an insoluble solid from a liquid/solid mixture

Insoluble solids can be obtained from liquid/solid mixture by the methods below:

(i) Decantation

(ii) Filtration


EVAPORATION

Separation of salt from sea water

Procedure

Put sea water in an evaporating dish and heat it to dryness.

Clip

Evaporation is a method used to separate soluble solid from its solution.

 

SIMPLE CLASSIFICATION OF SUBSTANCES

MiXTURES

A mixture is made up of two or more substances. There are different types of mixtures as shown below:


Scroll down to identify other types of mixtures.

Other types of mixtures include


Mixtures can be separated using different methods.

The methods used will depend on the nature of the mixture.

OBJECTIVES

By the end of this lesson you should be able to explain how to carry out simple experiments to obtain pure substances from mixtures.

FILTRATION

Separation of sand and water using Filtration method.

This method uses a filter paper placed in a funnel.The filter paper is folded into two. It is then folded again into a quadrant. The paper is then opened to form a cone and placed in a filter funnel after wetting it.

To separate sand and water using Filtration

A mixture of sand and water can be separated by filtration

Play the video to observe the process.



To separate sand and water using Filtration

The following apparatus are used:

Clip

Procedure:

Fold the filter paper and place it in the filter funnel.

Clip

Place the filter funnel on the conical flask.

Clip

pour the sand and water mixture to the filter funnel

Clip

Allow the filtration to take place.


The liquid collected in the conical flask is the filtrate and the solid that remains on the filter paper is the residue.

Clip

The process of separating a solid-liquid mixture using a filter paper is called filtration. This method is more suitable than the decantation method.

DISTILLATION

Miscible liquid- liquid mixtures and liquid-solid mixtures can be separated using Simple and Fractional distillation.Click to play the video to observe how ethanol is separated from water by simple distllation.


Simple distillation can be used to obtain a solvent from its solution.The process of distillation involves both evaporation and condensation.In the distillation flask, evaporation takes place.The vapour rises through the delivery tube and into the Lie big condenser filled with cold water which cools the vapour making it to condense to liquid.
Simple distillation can also be used to separate two miscible liquids with wider range in boiling points.

OBJECTIVE

By the end of this activity you should be able to explain how salt and water are separated from salt solution.

FRACTIONAL DISTILLATION

Ethanol and water are miscible Liquids.

Miscible liquids can be separated by fractional distillation.

The mixture is heated.


Ethanol whose boiling point is 78 degree centigrade boils first. Water whose boiling point is 100 degree centigrade boils too.

The fractionating column is packed with glass beads to increase the surface area for condensation.

The vapour from the mixture rises up the fractionating column. At about 78 degree centigrade, water vapour condenses and drops back to the flask while ethanol vapour rises and is condensed in the lie-big condenser.

When the thermometer reading rises above 78 degree centigrade , most of the ethanol will have separated.

We distinguish the two products by the smell and burning i.e. ethanol is

flammable and water does not burn.

 


APPLICATION OF FRACTIONAL DISTILLATION

REFINING OF CRUDE OIL

Crude oil is a mixture of several substances with different boiling points.

These include, Crude oil consists of

Petrol (0 - 65 degrees centigrade) , Naphtha (65 - 170 degrees centigrade),Kerosene ( 170 - 250 degrees centigrade), Diesel oil (250 - 340 degrees centigrade),Lubricating oil (340 - 500 degrees centigrade), Fuel oil (over 500 degrees centigrade).The fractions in crude oil are separated by fractional distillation.

 


PROCESS OF FRACTIONAL DISTILLATION

Observe the following animation and note how different components of crude oil are separated.

FRACTIONAL DISTILLATION OF LIQUID AIR

Air is a mixture of nitrogen, oxygen, carbon (IV) oxide, noble gases and water vapour.These gases can be obtained by fractional distillation of liquid air.


Step 1

Air is puified by passing it through filters

Step2

Carbon (IV) Oxide gas is removed by passing the air through Concentrated Sodium Hydroxide solution

Step 3

The remaining air is condensed to about -25 degree centrigrades to remove water vapour which solidies out as ice

Step 4

The air is compressed to about 200atmospheres. The cooled compressed air is allowed to expand rapidly. This process is repeated until all the air liquidifies

Step 5

The liquified air is then passed into a the fractionating column containing compartments

Each compartment is slightly at a higher temperature than the one above it.The components of the liquid air then separates according to their boiling points

Nitrogen distills off first because it has a lower boiling point of -196 degrees centrigrade followed by Argon at -186 degree centrigrade and finally Oxygen at -183 degree centigrade.

Liquid Oxygen is transported in large insulated metal tanks.


SEPARATION OF IMMISCIBLE LIQUIDS

Immiscible liquids do not mix. Water and oil are poured into a separating funnel and shaken thoroughly. The two liquids are allowed to settle until they form two layers. The stopper at the top is removed to allow the lower liquid to run into the beaker below. Stop running the layer before the dividing line touches the tap.


OBJECTIVE

By the end of this lesson you should be able to explain how oil can be separated from water.

The two liquids were separated using this method because they do not mix. Immiscible liquids form separate layers due to differences in their densities e.g. water settles below oil because it is denser than oil.

SUBLIMATION

One spatula end full of Iodine is placed in a boiling tube and heated gently.Click on the video clips below to observe the process of sublimation



When solid Iodine is heated,it changes to purple vapour which solidifies on the cooler parts of the boiling tube.


The process of change of state from solid to gas and from gas to solid without passing through the liquid state is called Sublimation.

Other examples of solids which sublime on heating include  Ammonium Chloride , Solid Carbon (IV) Oxide, Iron (III) Chloride and Aluminium Chloride

SEPARATION OF COMMON SALT AND IODINE

A mixture of solid common salt and Iodine is placed in a boiling tube. The boiling tube is heated gently. Solid Iodine forms a purple vapour which condenses on the funnel to sublimate of Iodine leaving salt on the evaporating dish.The process is used in the purification of Iodine. During the experiment, glass funnel was used instead of plastic funnel because the plastic cannot withstand high temperature.


EXTRACTION OF OIL FROM NUTS

Groundnuts are crushed in a mortar using a pestle. Propanone or ethanol is added. The solution is decanted and then put into an evaporating dish. A drop of the extract is placed on a piece of paper which is held against some light.


Groundnuts contain oil. Propanone is used because oil dissolves in it.The solution is left in the sun so that propanone can evaporate.The oil having a higher boiling point than the solvent is left in the evaporating dish.This method of extraction is known as solvent extraction.Oil leaves a translucent patch on the filter paper (Test for oil)


ACTIVITY

 

OBJECTIVES

By the end of this lesson you should be able to

  • Explain how oil can be extracted from nuts
  • Show how dyes can be separated from green leaves.


APPLICATION OF SOLVENT EXTRACTION

Solvent extraction can also be used in the removal of stains from fabrics e.g. in dry cleaning.



Other solvents that can be used include acetone, Benzene, carbon tetrachloride

CHROMATOGRAPHY

This is a method of separating coloured substances.

To separate various dyes from flowers.

Flowers are crushed and about 4cm3 of ethanol is added.


The solution obtained is decanted into a beaker. One drop of the solution is then placed at the centre of the filter paper and let to dry.


The green colouring matter in the leaves is a mixture of two substances. The green spot is the Chlorophyll and the orange yellow colour is due to Xanthophyll. The filter paper which contains the separated colored substances is called a Paper Chromatogram. Observe the following animation showing separation of dyes.

Column Chromatography

If a rectangular filter paper is used in place of the circular filter paper,it appears as below

Each coloured substance has a different solubility in the solvent and sticks on the filter paper to a different extent.Substances which are more soluble and less sticky are carried furthest.Less soluble and more sticky substances are left behind.


APPLICATION OF CHROMATOGRAPHY

Chromatography can be used to test the presence of substances in a mixture.

It is also used to analyze dyes used in food colourings and components in blood .



Blood being analyzed.


ACTIVITY


ACTIVITY


ACTIVITY


ACTIVITY


CRYSTALLIZATION

A saturated solution can be prepared by adding a solute to solution until no more can dissolve.A solution that can not dissolve any more of the same solute at a given temperature is referred to as a saturated solution.Using 50 cm3 of warm water a saturated solution of Copper (II) Sulphate.Filter off the undissolved solid.Allow the filtrate to stand.


A Crystal can be defined as regular shaped solid formed when a

saturated solution is allowed to cool or evaporate at room

temperature.

Crystals contain water molecule attached to the compound. e.g. CUSO4:5 H2O

Crystallization is the process of separating salt mixtures from

their solutions through formation of crystals.

 When solutions of two or more solutes are cooled, the one with the lowest solubility crystallizes first, while the most soluble remains in solution.

To obtain a large crystal, the saturated solution is covered

with a perforated filter paper and allowed to stand (undisturbed) for 2-3 weeks.

APPLICATION OF CRYSTALLIZATION

Crystallization is applied in:

Extraction of salts from sea and lake water e.g. at Lake Magadi.


EFFECT OF IMPURITIES ON SUBSTANCES

When substances are subjected to various temperatures they undergo change of state. The temperature at which melting occurs is referred to as melting point and the temperature at which boiling occurs is referred to as boiling point.
Impurities affect the melting point of a substance.

Effect of impurities on the melting point of naphthalene.Equal amounts of naphthalene and camphor are placed on a piece of paper and mixed thoroughly and placed in a boiling tube.

Turn to the next page to see the diagram.

 

Melting point of pure and impure Naphthalene


The melting point of pure naphthalene is 80.2 degrees Centigrade while the impure naphthalene melts over a temperature range below 80.2 degrees Centigrade .Impurities therefore lower the melting point of naphthalene.


BOILING POINT OF PURE AND IMPURE WATER

Pure water is poured into a boiling tube and heated.

Water containing salt is also poured into another boiling tube and heated.

The temperature at which boiling occurs in both experiments is recorded.

The impure water starts boiling at above 100 degrees centigrade.
The boiling point of pure water is 100 degrees centigrade at sea level.
The temperature continues rising as impure water boils.
Impure water therefore boils over a range of temperature.It is concluded that impurities raise the boiling point of liquids.
Pure substances melt and boil at constant temperatures that are specific for a particular substance.
Melting point and boiling point are therefore used to determine
 the purity of substances.


ACTIVITY


STATES OF MATTER

 

STATES OF MATTER

BACKGROUND KNOWLEDGE

ACTIVITY

Matter is anything that has weight and occupies space  (volume).The three states of matter are SOLID, LIQUID AND GAS. Matter undergoes changes when heated or cooled. .For example: Ice changes to liquid and then to vapour

OBJECTIVES


By the end of the lesson you should be able:

  • Explain the three states of matter in terms of kinetic theory
  • State the effects of heat on substances


Experiment: Effect of heat on ice

Ice is put in a beaker and a thermometer placed inside the ice cubes. The ice is heated and the temperarure recorded in intervals of 1 minute.


Time(min)

Temp 0c

The results obtained can be used to plot a graph of temperature against time (min).

Sample results.


At pointAB the Solid ice is gaining heat.
At point BC the ice is melting. The heat energy supplied changes the solid ice into a liquid.
At the point CD the water formed absorbs heat and the temperature increases.
At point DE the water changes into a vapour. The heat energy supplied is used to overcome the force of attraction between the water particles.During change of state the temperature of a substance remains constant but the substance continues to absorb heat energy.The temperature remains constant because the heat energy is used to overcome the force of attraction between the particles in a substance.


Particles in ice (solid) are closely held together in fixed positions by intermolecular forces.

When ice (solid) is heated the particles vibrate more vigorously in the same fixed position.On further heating the particles continue vibrating even more until the intermolecular forces are weakened.The temperature at which this occur is called the Melting point.At this point the particles are separated forming a liquid.On further heating the particles continue vibrating even more until the intermolecular forces are overcome.At this point the particles are separated forming a liquid.

On further heating the liquid particles move faster and finally overcome intermolecular forces and the particles separate forming a gas (steam)

The temperature at which this occurs is called the boiling point.The changes that occur in the particles can be shown as follows.

These observations can be interpreted in terms of a heating curve as shown.

Temperature rises steadily as ice absorbs heat energy.Temperature remains constant as all the ice meltsThe temperature rises steadily as heat energy is absorbed until the liquid boils.The temperature remains constant as boiling continues.From the graph constant temperature represent change of state.


These changes can be summarised as below


These changes can be reversed by cooling.

ACTIVITY


PERMANENT AND TEMPORARY CHANGES

Background knowledge

When ice and naphthalene are heated they undergo change of state as temperature is varied.

 

Objective

By the end of the lesson you should be able:

 Distinguish between permanent and temporary changes

QUIZ


QUIZ


TEMPORARY CHANGES

OBJECTIVES


By the end of the lesson you should be able:


    Distinguish between permanent and temporary changes

     

What happens when different substances are heated?

Place a small amount of Zinc Oxide in a test tube and heat until no further change. Allow it to cool and observe the animation to note what happens.

When Zinc Oxide is heated its co lour changes from white to yellow. On cooling the yellow solid turns white.

What happens when candle wax is heated?

Wax melts on heating and solidifies on cooling.


Iodine sublimes on heating.When cooled the Iodine vapour changes to solid.Click to play the video to observe what hapens when Iodine is heated.


Note that when Iodine is heated it changes directly from a solid to vapour. This process is called sublimation. Sublimation is the process of changing a solid directly to vapour without going through the liquid state.

ACTIVITY

To be inserted

CONCLUSION

In the above experiment cooling reverses the changes these substances undergo. These changes are called temporary changes.

Temporary changes have the following characteristics.


1.easily reversible


2. No new substance is formed.


3. Mass of the substance does not change.


4. Not accompanied by great heat changes.

PERMANENT CHANGES


QUIZ


What happens when Copper (II) nitrate is heated?

A small amount of Copper (II) nitrate is placed in a dry test-tube and weighed

The Copper (II) nitrate is heated strongly and allowed to cool.

 

 

 

 

When green Copper (II) Nitrate is heated Black Copper (II) Oxide is formed.

 

 

What happens when Potassium Manganate (VII) is heated?

 

 


What happens when Potassium Mangnate (VII) is heated?

ACTIVITY


CONCLUSION

From the results the substances formed did not change on cooling and the formed substances weighed less.

These changes are referred to as permanent changes. They have the following characteristics.


1.New substance is formed.


2. Change is irreversible.


3.Change is accompanied by apparent change in mass.


4.Heat is released or absorbed.

CONSTITUENTS OF MATTER

Some substances cannot be split into Simpler substances by any chemical means.

When Iron reacts with Sulphur, Iron (II) Sulphide solid is formed.

Sulphur and Iron are elements.

An element can therefore be defined as a substance which cannot be split into anything simpler by any chemical process.

Pure substances are obtained using various methods

Pure substances are classified into elements and compounds

An element can therefore be defined as a pure substance which cannot be split into simpler substance by any chemical means.

OBJECTIVES

By the end of the lesson you should be able to:

Define an element, compund , atom and Molecule

Name and write chemical symbols of common elements

Distinguish between mixtures and compounds.

QUIZ


In Chemistry elements are represented by symbols.

Some elements derive their names from their English names..

Others are derived from their Latin names.

The chemical symbol of an element represents one atom of the element.

For example:

H represents one atom of Hydrogen


An atom is the smallest particle of an element which can take part in a chemical reaction.

Two or more elements may combine to form a molecule

Carbon and Oxygen are both elements and they combine chemically to form a new substance known as Carbon (IV) Oxide.

A compound is a substance made up of two or more elements chemically combined.

All compounds consists of two or more elements chemically combined together and exist as single particles.

The smallest particle of an element or compound

which can exist in a free and separate state is called a Molecule.


Two or more elements may combine to form a molecule

Carbon and Oxygen are both elements and they combine chemically to form a new substance known as Carbon (IV) Oxide.

A compound is a substance made up of two or more

elements chemically combined.


All compounds consists of two or more elements chemically combined together and exist as single particles.

The smallest particle of an element or compound

which can exist in a free and separate state is

called a Molecule.

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