simple classification of substances notes free download

simple classification of substances

simple classification of substances notes free download

By the end of the topic, the learners should be able to:

  1. Define mixture, element, atom, molecule, compound, melting point, boiling point and sublimation.
  2. Write chemical symbols of common elements and identify the constituents of compounds.
  • Determine the purity of a substance and use separation techniques to obtain pure substances.
  1. Differentiate
  2. Permanent change and non-permanent changes.
  3. Physical and chemical changes.
  4. Explain the arrangement of particles of matter in the three states in terms of the kinetic theory of matter.

MIXTURES

  • A mixture is a combination of two or more substances that are not chemically combined and therefore can be separated by physical means.
  • Matter can be classified into solids, liquids and gases.
  • There are various mixtures from these categories

Mixture

 

Solid/Solid                  solid/Liquid             Liquid/Liquid

Mixture                       Mixture                    Mixture

  • The method used to separate mixtures depends on the physical states and properties of the constituent substances.
  • There are various ways in which mixtures are separated, namely;
  1. Use of a magnet
  2. Decantation
  • Filtration
  1. Evaporation
  2. Crystallization
  3. Sublimation
  • Use of a separating funnel
  • Use of teat pipette/Dropper
  1. Simple distillation
  2. Fractional distillation
  3. Paper chromatography
  • Solvent extraction
  1. Use of a magnet
  • This method is used to separate magnetic material from a mixture of magnetic material and non-magnetic materials e.g. separating iron from a mixture of iron and Sulphur.
  1. Decantation
  • This method is used in separating insoluble substances from liquids e.g. sand and water. However, it is not efficient because some solids still pass into the liquid in the process of decanting.
  • Filtration
  • It is used to separate an insoluble solid substance from a soluble one e.g. common table salt can be obtained from a mixture of sand and common table salt by dissolving the mixture in water and filtering off the sand.
  • The liquid collected in the evaporating basin is called a filtrate and the solid particles remaining behind are known as the
  • This method is used to separate solute from a solution.
  • It involves heating to dryness of a solution to propel away the solvent into the atmosphere.
  • When crystals start forming, the evaporating basin is transferred to a sand bath, so that the salt does no spurt out of the basin as heating continues which upon cooling, the crystals are recovered.
  • Crystalline substances are separated from their solutions by the method of crystallization.
  • In this process, a solution is heated to form a concentrated solution known as saturated solution. The concentrated solution is left to cool and the solid crystallizes out e.g. copper (II) Sulphate crystals are obtained from their solution by crystallization.
  • A saturate solution is one that cannot dissolve any more of the solute at given temperature and contains undissolved solute.

Exp: Preparation of saturated solution

Apparatus and chemicals

  • Beaker
  • Sodium chloride
  • Stirring rod
  • Water

Procedure

  1. Put 100cm3 of water in a beaker.
  2. Add sodium chloride a little at a time while stirring well with a glass rod until no more can be dissolve. One can tell it is saturated when undissolved salt settles down even after vigorous stirring.
  3. Filter off the undissolved salt. The filtrate is called a saturated solution.
  4. Allow the filtrate to cool and form crystals.
  5. Sublimation
  • This method is used to separate a mixture of solids, one of which changes directly to vapour on heating.
  • The following are some of the compounds that sublime on heating;-
  • Naphthalene
  • Ammonium chloride
  • Iodine
  • Solid carbon(IV) oxide
  • Aluminium chloride
  • Anhydrous iron(III) chloride
  • Benzoic acid
  • Use of a separating funnel
  • This method is used to separate immiscible liquids.
  • The denser liquid forms the bottom layer and can be easily run off e.g. water and kerosene mixture. [diagram pg ,klb bk 1]
  • Use of a teat pipette/dropper
  • This method is used to separate immiscible liquids.
  • The dropper is used to suck one layer transferring it to another beaker or container repeatedly.
  1. Simple distillation
  • This method is used to separate two miscible liquids with widely different boiling points.
  • The mixture is heated and the liquid with the lower boiling point distils first.
  • It is then condensed and collected as shown below.

[diagram showing all alt; pg klb bk 1].

simple classification of substances notes free download

  1. Fractional distillation
  • This method is used to separate miscible liquids with close boiling points e.g. chlorobenzene from water, ethanol from water and crude oil into various components.
  • In this method fractionating column is used and liquids with lower boiling points are collected first.

[diagram pg 28,klb bk 1]

NB:  Simple and fractional distillations are similar in that they both separate miscible liquids. However, they have some differences which are;

Simple distillation Fractional distillation
1 The liquids must have widely different Bpts 1 The Bpts of component are close
2 Does not have a fractionating column 2 Has a fractionating column
3 Can separate solid/liquid mixture 3 Only liquid/liquid mixtures are separated
  1. Paper chromatography
  • This method is used to separate substances which have several pigments (colours) e.g. grass, ink, leaf or petals extracts.

Exp: How can a mixture of pigments be separated?

Aim

To separate green colour into its various components from grass extract.

Apparatus and materials

  1. Mortar and pestle
  2. Teat pipette
  3. Filter paper
  4. Stop watch
  5. Beaker

simple classification of substances notes free download

Procedure

  1. Crush some green leaves or grass in a mortar using a pestle.
  2. Add ethanol/propanone/methylated spirit as you continue crushing the leaves.
  3. Decant the extract into a beaker.
  4. Place one drop of the extract on the centre of a piece of filter paper as shown below and let it dry. [diagram pg 31,klb bk 1]
  5. Place the filter paper on a beaker half filled with the solvent.
  6. Lower the strip of paper into the solvent in the beaker.
  7. Leave the set-up in this state for twenty minutes.
  8. Draw the diagram of the filter paper showing the results obtained.

Results

[diagram pg 33,klb bk 1]

Discussions

  • The colouring matter of plants, flowers, ink and dyes is composed of different substances.
  • Each coloured material moves different distances on the filter paper. The distance moved by each coloured material/substance is determined by:
  1. Solubility of the material in the solvent used.
  2. Stickiness to the paper by the substance.
  • The colour in the grass separated out into two substances;
  1. Green colour
  2. Yellow colour

Applications of chromatography

  1. In detecting illegal drug usage in games e.g. Samples of urine from three participants F, G and H at an international sports meeting were spotted onto a chromatography paper alongside two from illegal drugs A1 and A2. A chromatogram was run using methanol.  The figure below shows the chromatogram.

 

  1. Identify the athletes who had used an illegal drug. =G and H
  2. Which drug or drugs had they used?=G used A2;H used A1
  3. Which drug is more soluble in methanol? =A1
  4. Identifying impurities from a substance.
  5. In hospital for testing HIV and AIDS.
  • Solvent extraction.
  • This method of extracting a solute from a solution using a second solvent.
  • The second solvent should be immiscible with the first solvent and the solute to be extracted should be soluble in the second solvent.
  • It is used to extract oil from peanuts and castor seeds, chlorophyll from leaves etc.
  • Tetrachloromethane, chloroform and benzene are the most commonly used solvents since they are insoluble in many organic solvents.

simple classification of substances notes free download

Exp: Extraction of oil from nut seeds

Apparatus and reagents

  • Mortar
  • Pestle
  • Propanone

Procedure

  • Grind in a mortar a few groundnuts (or cotton seeds) with a solvent e.g. Propanone for 2-3 minutes.
  • Filter and collect the extract.
  • Pour the filtrate in an evaporating dish and leave in a sunny place for 5-10minutes.
  • {The solvent evaporates off, leaving the liquid which is oil extract from the nuts}
  • Put a piece of plain paper in the liquid left in the evaporating dish. {The paper is used to test for oil-It becomes translucent after being dipped in oil.}

EFFECT OF HEAT ON SUBSTANCES

  • Matter exists in three physical states, namely;-
  1. Solid
  2. Liquid
  • Gas
  • The table below gives the main characteristics of the three states of matter;
Characteristics Solids Liquids Gases
SHAPE  definite  indefinite  indefinite
COMPRESSIBILITY  incompressible  incompressible  easy to compress
MOLECULAR MOVEMENT  Vibrate about fixed positions Free to move about randomly  Free to move about randomly independent of each other
INTER-MOLECULAR FORCE OF ATTRACTION.  strong  strong but not strong as those in solids  weaker than those in liquids
PACKING OF MOLECULES  closely packed üclosely packed  not closely packed

 

  • Those three states are interchangeable.

Exp: What happens when a solid is heated?

Aim

  • To investigate what happens when solid e.g. naphthalene is heated.

Apparatus and materials

  1. Spatula
  2. Boiling tube
  3. Thermometer
  4. Beaker
  5. Retort stand
  6. Stop watch
  7. Wire gauze
  8. Tripod stand
  9. Bunsen burner
  10. Naphthalene
  11. Water

Procedure

  1. Place a spatulaful of naphthalene into a boiling tube and note it temperature.
  2. Place the boiling tube in a beaker of water as shown below. [diagram pg 34,bk1]
  3. Heat the beaker.
  4. Record the temperature of naphthalene every half a minute through-out the experiment until boiling occurs. {boiling takes place when bubbling starts in the liquid}
  5. Continue heating for about two more minutes.
  6. Record the temperature readings in the table below.
  7. Plot a graph of temperature against time.

 

simple classification of substances notes free download

Results

Time (min) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Temp(oC)

Questions

  1. What happens to naphthalene when it is gently heated? Explain.

Its temperature rises steadily until it starts to melt where it remains constant for sometime before it rises again steadily until it starts to boil where it remain constant. This is because the heat absorbed increases the kinetic energy of particles and they vibrate more until the gain enough energy to break free from the intermolecular forces of attraction.

  1. Did the temperature change when the naphthalene was melting?

No, the temperature remained constant

  1. Did the temperature change when naphthalene was boiling?

No, the temperature remained constant

  1. List the state in which naphthalene exists
  • Solid
  • Liquid
  • Gas
  1. Why does heating cause melting and boiling of solids?

Heating provides the energy required to break lose the intermolecular forces of attraction in solids hence setting them free to move in a random manner in groups when they melt. During boiling the energy supplied by heat provides the necessary energy to set the molecule of the liquid free to move in random motion independent of each other.

  1. Explain how the changes observed in the experiment can be reversed.

The changes can be reverse by cooling the gaseous naphthalene.

Analysis

The following is a graphical representation of the heating curve of naphthalene.

 

simple classification of substances notes free download

Region AB;

  • The temperature increases steadily as the naphthalene absorbs heat energy.
  • The heat absorbed increases the kinetic energy of the particles and they vibrate more.

Region BC;

  • The temperature remains constant until all naphthalene melts.
  • The heat supplied is used to weaken the intermolecular forces of attraction holding the particles of naphthalene together.
  • The result of weakening the intermolecular forces of attraction of naphthalene solid changes to liquid naphthalene.

Region CD;

  • The temperature rises steadily as the liquid naphthalene absorbs heat energy.
  • The heat supplied increases further the kinetic energy of the particles causing them to move fast.
  • The rise in temperature stops when the liquid boils.

Region DE;

  • The temperature remains constant as boiling continues.
  • The heat supplied is used to break the intermolecular forces of attraction holding together the liquid particles.
  • The particles therefore break away from each other as a result of which naphthalene changes from liquid to gas.

NB: 1) The changes of state from solid to liquid to gas can be reversed by cooling. This changes can be summarizes in the flow diagram below.

 

2) Some solids sublime on heating i.e. they change from solid to gas without forming liquids e.g.          Solid Iodine   Iodine vapour

simple classification of substances notes free download

The kinetic theory of matter

  • According to the theory, matter is made up of particles which are in a continuous state of motion.
  • In solid state, the particles are closely packed together in fixed positions.
  • They do not move from one point to another because there are forces that hold the particle in these positions but vibrate in these fixed positions.
  • When a solid is heated, the kinetic energy of the particles increases and they begin to vibrate more vigorously.
  • At a certain temperature, which is fixed for a particular substance, the forces holding the particles are weakened and the solid changes into a liquid.
  • The constant TEMPARATURE at which a solid substance changes to liquid is known as the melting point.
  • In liquids state, the particles are not as close as they are in solid state i.e. they can move from one position to another.
  • The particles exert some attraction on one another and these attraction forces make them stay close together in groups.
  • When a liquid is heated, the particles move more rapidly as the attractive forces are further weakened.
  • The weakening continues until the particles gain enough energy to overcome the attractive forces between them at a point where the liquid changes to gas.
  • The constant TEMPERATURE at which a liquid changes to gas is known as the boiling point.
  • In the gaseous state, the particles are far apart and free to move randomly in all directions.
  • When gases are cooled, the particles lose the kinetic energy and hence slow down gradually attracting their neighbouring particles making them to move closer to form a liquid in a process known as Condensation.
  • On further cooling of the liquid, the kinetic energy of the particles continues to decrease and the particles take up fixed positions as the liquid solidifies in a process known as
  • The TEMPERATURE at which a liquid changes to solid is called the freezing point and takes place at the same temperature as melting.
  • The model below show the changes discussed above;

[Diagram klb bk1]

Effect of impurities on melting and boiling point of substances.

  1. Effect on the melting point;
  • Impurities lower the melting point e.g. impure naphthalene does not have a sharp melting.
  • The graph of temperature against time obtained for impure naphthalene when heated to melting point is as shown below;

 

Applications

  • Clearing of ice from roads in temperate countries by spreading common table salt on the ice. Addition of salt lowers the melting point of ice making it to melt.
  • Extraction of metals from their molten compounds. Impurities are added to lower the melting points of the compounds.
  1. Effect on boiling point
  • Impurities raise the boiling point of a liquid e.g. impure water boils at a temperature above 1000C at sea level as shown by the heating curve below.

 

 

NB:  Melting and boiling points can be used to determine the purity of a substance since pure substances melt or boil at specific temperatures unique to them.

Temporary and Permanent changes

  • Substances undergo various changes when subjected to different conditions of temperature.
  • When the change can be easily be reversed and in which no new substance are formed is called temporary physical
  • The following are characteristics of temporary physical changes;
  1. They are easily reversible
  2. No new substances are formed
  3. The mass of the substance does not change
  4. They are not accompanied by great heat changes
  • Examples of temporary physical changes include;
  1. Heating of zinc oxide
(Yellow)
(White)

Zinc Oxide        Zinc Oxide

  1. Heating of solid wax

Solid wax   Liquid wax

  • Heating of solid Iodine
(Purple)
(Dark)

Solid Iodine   Liquid Iodine

simple classification of substances notes free download

Exp: Are all reversible reaction temporary physical change?

Apparatus and material

  1. Spatula
  2. Boiling tube
  3. Retort stand
  4. Holed cork
  5. Delivery tube
  6. Test-tube
  7. Beaker
  8. Ice-cold water
  9. Hydrated copper (II) sulphate
  10. Bunsen burner

Procedure

  1. Put a spatulaful of hydrated copper (II) sulphate crystals in a dry boiling tube.
  2. Set up the apparatus as shown below.

[Diagram pg 45, klb bk 1]

  1. Heat the copper (II) sulphate until there is no further change.
  2. Record your observations.
  3. Leave the solid product to cool and divide it into two portions.
  4. Put one portion in a test tube and add a few drops of tap water.
  5. Take the temperature of the resultant mixture.
  6. To the other portion, add a few drops of the liquid collected during heating and observe what happens.
  7. Repeat the experiment using hydrated cobalt (II) chloride.

Questions.

  1. What is observe when
  2. Hydrated copper (II) sulphate is heated?

It changes colour from blue to white

  1. Hydrated cobalt (II) chloride is heated?

It changes colour from pink to blue

  1. What is observed
  2. When a few drops of tap water are added to the solid product in 1a) and 1b)?

1a) changed from white to blue

1b) changed from blue to pink

  1. The liquid collected in 1a) and 1b) is added to the residue in each case respectively?

1a) changed from white to blue

1b) changed from blue to pink

  1. Identify the liquid collected in the above experiment

Water

 

  1. How can these changes be classified?

Temporary chemical change

Conclusion

  • Heating hydrated copper (II) sulphate or cobalt (II) chloride results into a temporary chemical change.
  • The characteristic of a temporary chemical change are;
  1. The change is not easily reversible
  2. A new substance is formed
  3. Heat energy is evolved or absorbed
  4. There is an apparent change in mass.
  • The decomposition of copper(II) nitrate and potassium Manganate (VII) are examples of permanent chemical change;
Oxygen gas
(Blue-green)
(Colourless)
(Red-brown)
(Black)

Copper (II) nitrate   Copper (II) oxide + Nitrogen (IV) oxide + Oxygen

Potassium Manganate (VII)    Potassium Manganate (VII) + Manganese (IV) oxide +

KMnO4=>Potassium Manganate (VII) {Purple}

KMnO2=> Potassium Manganate (VI) {black}

O2      => Oxygen {colourless}

  • Permanent chemical change have the following characteristics;
  1. New substances are formed
  2. The change is irreversible
  3. The change is accompanied by apparent change in mass
  4. Heat energy is released or absorbed

Elements

  • Elements are pure substances which cannot be split into simple substances by chemical means e.g. oxygen, hydrogen, copper, Sulphur, Carbon, iron etc.

Atoms

  • The atom is the smallest particle of an element which can take part in a chemical change.

                   Chemical symbols

  • These are letters that represent element in chemistry.
  • The chemical symbol of an element is usually the first letter or the first and another letter of the element English or Latin name.
  • When the symbol is made up of two letter, the first must be capital and the second a small letter e.g.

 

English name Latin name Chemical symbol
Carbon —————– C
Nitrogen ——————— N
Oxygen ———————– O
Hydrogen H
Potassium Kalium K
Sodium Natrium Na
Aluminium …………………….. Al
Silver Argentum Ag
Gold Aurum Au
Iron Ferrum Fe
Lead Plumbum Pb
Mercury Hydragyrum Hg
Copper Cuprum Cu
Calcium ——————- Ca
Cobalt —————- Co
Chlorine ————– Cl
Magnesium —————- Mg
Manganese ——————- Mn

 

Compounds

  • A compound is a pure substance made up of two or more elements chemically combined e.g. sodium chloride which is a compound of sodium and chlorine; water is a compound of hydrogen and oxygen; copper (II) oxide is a compound of copper and oxygen etc.
  • The difference between compounds and mixtures can given as follows;
Compounds Mixture
1.      The elements are combined in definite proportions by mass 1. Substance can be present in any proportion by mass.
2.      The properties of a compound are different from those of the elements making it. 2. The properties of a mixture are the average of the properties of the substance in it e.g. colour.
3.      The elements in a compound cannot be separated by physical means. 3.Substances in a mixture can be separated by physical means
4.      During the formation of a compound, energy is given out or absorbed. 4.During the formation of a mixture energy is not given out or absorbed
5.      They have chemical formulae 5. They have no chemical formulae.

Molecules

  • This is the smallest particle of an element or compound which can exist separately e.g. water molecule, chlorine molecule etc.

Chemical equations

  • Chemical reactions are represented by the use of chemical equations using words or chemical symbols.
  • These equations show what the reactants and products are in a chemical reaction.
  • Reactants in a chemical equation are written on the left hand side while the products are written on the right hand side of the equation.
  • Instead of an = sign an arrow is or          are used.
  • Show a permanent change and proceed only in one direction while        is used where the reactions are reversible and can be made to proceed in either direction.

Examples of word equation

  1. Iron reacting with Sulphur;

Iron + Sulphur                Iron (II) oxide

  1. Sulphur reacting with oxygen;

Sulphur + Oxygen           Sulphur (IV) oxide

  1. Carbon reacting with oxygen;

Carbon + Oxygen         Carbon (IV) oxide

  1. Sublimation of Iodine;

Iodine              Iodine Vapour

 

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