(A) to Determine the Melting Point of Ice

PRACTICAL EXPERIMENTS

EXPERIMENT NO.1

Aim: To determine the melting point of ice and the boiling point of water.

(a) To determine the melting point of ice.

MATERIALS REQUIRED: Beaker, wire gauze, tripod stand, burner, thermometer,

stirrer,ice cubes,thermometer,clamp stand etc..

THEORY: The constant temperature at which a solid changes into a liquid is called melting point of the solid.

When a solid is heated, its molecules absorb heat energy and their kinetic energy increases. This results in rise of temperature of the solid. During melting, the temperature remains the same till the entire solid melts even though we continue to supply the heat.

The quantity of heat required to completely change 1 kg of ice into water without any change in temperature is known as latent heat of fusion of ice.

PROCEDURE: Take some ice cubes in a beaker and place it over a wire gauze kept over a tripod stand. Suspend a thermometer with the help of a clamp stand so that its bulb is in contact with the ice. Start heating the beaker on a low flame and note the temperature when the ice starts melting. Finally note the temperature when all the ice has been converted into water.

OBSERVATION: The temperature remains constant till the ice has completely melted i.e 0o Celsius.

RESULT: The melting point of ice is 00 C .

PRECAUTIONS:

1. The bulb of the thermometer should be completely surrounded by ice.

2. Ice should be stirred regularly to keep a uniform temperature throughout.

3. Note temperature by keeping your eyes in line with the level of mercury.

(b) To determine the boiling point of water.

MATERIALS REQUIRED: Distilled water, boiling tube, rubber cork with two holes, delivery tube, clamp stand, thermometer, pumice stones etc.

THEORY: When heat energy is supplied to water, the particles start moving faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature the liquid starts changing into gas. The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

During the change of state from liquid to gas, the temperature of the system remains the same till the entire liquid is converted into vapours even though heat is continuously being supplied.

The amount of heat energy required to change 1 kg of liquid into vapours at atmospheric pressure at its boiling point is called latent heat of vapourisation.

PROCEDURE: Take some distilled water in a boiling tube and add few pieces of pumice stones to it. Fix a cork with two holes(one for thermometer and other for delivery tube) in the mouth of the boiling tube and clamp it with the stand. The thermometer should be introduced in such a way that the bulb of the thermometer is 3-4 cm above the surface of water. Heat the boiling tube and note the temperature when the boiling starts. Continue to heat till the temperature becomes constant and the water remains boiling. Note the constant temperature.

OBSERVATION: The temperature remains constant till all the water has been converted into vapour (i.e at 100oC.)

RESULT: The boiling point of water is 100oC

Plot a graph of Temperature vs Time (in minutes),

PRECAUTIONS:

1. The bulb of the thermometer should be kept 3-4 cm above the surface of water

2.|Pieces of pumice stone should be added to water before heating to avoid bumping.

3. Heating of water should be done by rotating the flame.

4. Note temperature by keeping your eyes in line with the level of mercury.

EXPERIMENT NO.2

Aim:To separate the components of a mixture of sand, common salt and ammonium chloride (or camphor) by sublimation.

Requirement: Common salt, sand and ammonium chloride, distilled water, china dish, funnel and tripod stand.

Principle:

Constituents of a mixture can be separated by simple physical methods.
Sublimation: It is the conversion of a solid directly into the vapour phase without changing to a liquid.
Sublimation can be used to separate a volatile solid and a non-volatile solid in a mixture.
The water-soluble solid/substance can be separated from non- water-soluble substance by filtration.

Experimental steps:

Mix the salt, sand and ammonium chloride thoroughly to get a mixture.
Take some amount of the mixture in a china dish; place it on a tripod stand for heating.
Cover the china dish with an inverted funnel with some cotton plugged in its stem to prevent vapours escaping out.
Continue heating for sometime until no more vapours of ammonium chloride are seen to be rising up.
Remove the funnel carefully so that the ammonium chloride deposited does not fall.
The mixture of sand and common salt remains in the china dish.

Cool the contents of the china dish and dissolve in a minimum amount of water and filter.
Sand remains as residue; the filtrate is concentrated by evaporation and left undisturbed for salt to crystallize out.

Conclusions:

Ammonium chloride is a sublimable substance, which is first separated by subliming the mixture.
Common salt readily dissolves in water and is separated from sand by dissolving in water and filtering the mixture.
Residue obtained is only sand.
Constituents of the given mixture could be separated by simple physical methods.

Precautions:

While heating the mixture the china dish should be very stable on the wire gauze over the tripod stand.
The funnel should not be very big otherwise vapours will escape out.
The stem of the funnel should be plugged with cotton to prevent loss of ammonium chloride vapours.
Water should not be added to the contents of the china dish unless it has cooled down.
Ammonium chloride should be gently scraped off from the funnel once it has cooled to room temperature.

Experiment No. 3

To prepare

a) a true solution of common salt, sugar and alum

b) a suspension of soil, chalk powder and fine sand in water

c) a colloidal of starch in water and egg albumin in water and distinguish between these on the basis of

i) Transparency

ii) Filtration criterion

iii) Stability

Requirements:common salt, sugar, alum, soil, chalk powder, fine sand, starch, distilled water egg albumin, test tubes, funnel, filter paper, test tube stand, glass rod, beakers.

Theory:

Solution is a homogeneous material formed by mixing of two substances, one in large amount (solvent) and the other in small amount (solute) . The particle size is smaller than 10-7 cm.

The solution in which no more solute is soluble in the solvent at a given temperature and pressure conditions is said to be a saturated solution.

A suspension is a heterogeneous material in which the solid particles can be seen by naked eye and magnifying glass. The suspended particles can be separated by filtration or by sedimentation as the particles settle down on standing. The particle size is of the order of 10-5 cm or larger.

A colloid is a heterogeneous material. The particles of a colloidal system can be seen by a powerful microscope. A colloidal system is stable; its components do not settle down under gravity and components cannot be separated by filtration. The particle size is generally in between 10-7 to 10-5 cm.

Procedure:

a) Preparation of a true solution of common salt, sugar and alum:

Take three beakers marked A, B and C containing 90ml of water in each. Add 10g of fine powder of each common salt, sugar and alum in beakers A, B and C respectively. Stir the solution of each beaker thoroughly with the help of a glass rod.

b) Preparation of a suspension of soil, chalk powder and fine sand in water :

Take three beakers marked D, E and F each containing 90ml of water. Add 10g of fine soil, fine chalk powder and fine sand in each of the beakers respectively. Stir the contents of each beaker well with a glass rod.

c) Preparation of a colloidal solution:

i) a colloidal of starch in water: Mix 1% dry cornstarch with 3ml of distilled water. To this add 97ml of boiling distilled water and stir it well. Cook it for two minutes stirring the solution continuously. Cool it and store in a test tube marked G.

ii) a colloidal of egg albumin in water :

Take 1g of egg albumin and 5ml of distilled water in a beaker and mix it well. Slowly add 95ml of distilled water while stirring constantly. After mixing add a few drops of dil.HCl or dil.H2SO4 and stir well. The clear solution of albumin and water will become turbid. Store this in a test-tube marked H.

Property to be tested / Experiment / Observation / Inference
1.Transparency / Paste small strips of same coloured cellophane paper on one side of each test-tube (A, B, C, D, E, F, G and H).
Arrange test-tubes in groups according to solution, suspension and colloid. Now observe the coloured paper of each test-tube from the other side of the test-tube through the liquid one by one. / Colour spot is clearly sen from the other side of the test-tubes A, B and C / A true solution is transparent while colloids and suspensions are not.
2. Filtration / Filter the contents of test-tubes A, B and C separately.
Filter the contents of test-tube D, E and F separately.
Filter the contents of test-tubes G and H separately. / No residue is left on the filter paper. A clear filtrate is obtained.
Particulate suspension is seen on the filter paper in each case but filtrate is a clear liquid.
No residue left on the filter paper in both the cases. But the filtrate obtained is translucent. / Solid particles cannot be separated from true solution by filtration.
Suspended components of a suspension can be separated by filtration.
Components of a colloid cannot be separated by filtration.
3. Stability / Leave the test-tubes A, B, C, D, E, F and G for sometime. / No change in test tubes A, B and C. the solution remains as it is without any settlement.
In test tubes D, E, F there is a gradual settlement of solid particles at the bottom.
No change is observed in test-tubes G and H / The true solutions are stable and do not show deposition of components.
Suspensions are unstable and show settlement of heavier particles.
Colloids are stable. Their solute particles do not settle down after sometime.

Result: (a) Colloidal solutions are somewhat translucent and their particles can pass through filter paper to give translucent filtrate. No particles are left as residue on the filter paper.

(b) True solutions are transparent; they pass through filter paper leaving no residue on the filter paper. The filtrate is also transparent.

(b)Suspension is opaque or dull. They leave residue particles over filter paper on filtration. The filtrate is more or less clear and transparent.

EXPERIMENT NO.4

Aim To prepare a) a mixture b) a compound using iron filings and sulphur powder and distinguish between these on the basis of :

i) Appearance i.e., homogeneity and heterogeneity

ii) Behavior towards a magnet

iii) Behavior towards carbon disulphide a solvent.

iv) Effect of heat.

Apparatus required:

A hard glass tube; test tube holder; pestle and mortar, two watch glasses, a hand lens, a magnet, a rack full of clean test tubes, burner.

Chemicals required:

Iron filings (10g), sulphur powder (5g), carbon disulphide

Theory: Physical Change-Changes in which original components do not change their properties and no new substances are formed.

Chemical Change- Changes in which original components undergo change to form new substances with entirely different properties.

Procedure:

a)Preparation of a mixture of iron and sulphur

Take the entire amount of iron filings and sulphur powder and put them in pestle and mortar. Grind the constituents thoroughly. The product so formed is a mixture of iron and sulphur. Divide the mixture into two halves and place them on two watch glasses.

b)Preparation of the compound of iron and sulphur (iron sulphide)

Transfer half of the mixture from one of the watch glasses to a hard glass

test tube. Hold the test tube with the test tube holder and heat the mixture strongly on a Bunsen burner till its contents start glowing with a reddish glow. Stop heating, the test tube will continue glowing for sometime because iron reacts with sulphur to form its compound iron sulphide with the release of heat energy. When the contents of the test tube cool, break the tube and gently remove the pieces of broken glass. Transfer the compound formed in the pestle and mortar and grind well. Now transfer the powdered compound onto the watch glass.

Fe + S FeS

Procedure:

Experiment / Observations / Inference
1.Action with bar magnet:
Roll the bar magnet in the mixture as well as its compound. / a) In case of mixture, iron particles cling to the magnet.
b) In case of its compound The black particles do not cling to the magnet. / a) Constituents of a mixture retain their properties and can be separated by physical means.
b) But constituents of a compound can not be separated by physical means
2. Appearance:
Observe the mixture as well as its compound under magnifying glass by spreading them thinly on a paper. / a) In case of mixture the grey particles of iron can be seen clearly in yellow particles of sulphur and they are not uniform throughout.
b) In case of the compound, uniform black particles are seen. / a) Mixtures are heterogeneous in nature
b) Compounds are homogeneous in nature.
3. Action with carbon disulphide:
Place a small amount of the mixture and its compound in separate test tubes and add 5 ml of carbon disulphide and shake them well. / a) In the case of mixture the yellow particles of sulphur dissolve and black particles of iron settle down.
b) In the case of compound no change occurs. / a) Sulphur retains its properties in the mixture.
b) Sulphur does not retain its properties in the compound.
4. Action of heat: Take small amount of mixture and compound in different test tubes respectively and heat them on the Bunsen flame. / a) In case of mixture the test tube starts glowing with a reddish glow. When the heating is stopped the reddish glow will continue for sometime. A grey solid mass is formed.
b) In case of compound no visible change occurs / a) On heating, mixture of iron and sulphur reacts and forms iron suphide.
b) No reaction takes place on heating iron sulphide

Result:

i) When iron filings and sulphur powder are mixed, both retain their properties. It means they have not undergone any chemical reaction. Thus it is a physical change.

ii) When iron filings and sulphur powder are mixed and heated, they undergo a chemical reaction. A new substance iron sulphide is formed which has properties entirely different from iron and sulphur. Thus it is a chemical change.

PRECAUTIONS:

Heat the mixture of iron and sulphur in a hard glass tube only.
Remove the pieces of broken glass with forceps only. Do not use bare hands as you are likely to injure your fingers.
Carbon disulphide should be kept away from the flame (It is volatile and can catch fire).
Hydrogen sulphide should not be inhaled. It can cause a headache.

Experiment No. 5

Aim: To carry out the following chemical reactions and record observations. Also to identify the type of reaction involved in each case.

i) Burning of Magnesium in air.

ii) Zinc with dilute sulphuric acid

iii) Iron with copper sulphate solution in water.

iv) Heating of Lead Nitrate.

v) Sodium sulphate with Barium chloride in the form of their solutions in water.

EXPERIMENT NO.5A

Aim: Burning of Magnesium in air.

Requirements: a) A strip of magnesium ribbon, tongs, china dish, burner.

Theory: Magnesium is a reactive metal; it combines with oxygen to form an oxide.

Combination reaction: It is a reaction in which two elements combine to give a compound e.g.

2 Mg + O22 MgO

magnesium oxide

Magnesium forms a basic oxide as it dissolves in water to form magnesium hydroxide.

MgO + H2O Mg(OH)2

Magnesium hydroxide

Magnesium hydroxide turns red litmus blue.

S.No. / Experiment / Observations / Inference
1 / Take a clean strip of magnesium ribbon and hold it with the tongs. Burn it the flame of burner. / It burns with a dazzling flame forming a white powder. / Magnesium combines with oxygen to form
Magnesium oxide.
2. / Collect the white powder in the china dish and dissolve it in distilled water and dip a red litmus paper in it. / Red litmus paper turns blue. / Magnesium oxide is basic in nature.

Precautions:

The magnesium ribbon should be cleaned before the experiment because it is a reactive metal; it combines with oxygen in air to form an oxide.
The dazzling flame should not be seen directly for long time.
The strip of magnesium ribbon should be held with a tongs to protect our hands from burning.
The white magnesium oxide powder should not be touched by hand.

EXPERIMENT NO.5B

Aim: Reaction of Zinc with dilute sulphuric acid

Requirements: Piece of zinc metal, dilute sulphuric acid, test tubes.

Theory: Zinc is very reactive metal and can displace hydrogen from dilute acids.

Displacement reaction: When metals like Zn, Mg, Fe, more reactive than hydrogen, react with dilute acid hydrogen gas is liberated e.g.

Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)

This is also an example of a Redox reaction ie reaction in which oxidation and reduction are taking place simultaneously.

S.No. / Experiment / Observations / Inference
1. / Take a few pieces of zinc in the test tube and add about 20ml of dil. H2SO4 to it. / Bubbles are formed immediately showing gas being evolved / Hydrogen gas is evolved.
2. / Bring wet red and blue litmus papers near the mouth of the test tube. / No colour change is observed on either red or blue litmus papers. / Hydrogen gas is neither acidic nor basic.
3. / Close the mouth of the test tube with your hand to prevent the gas from going out and then bring a burning matchstick near the mouth of the test tube. / The matchstick goes off with a ‘pop’ sound but the gas burns with a blue flame. / Hydrogen gas does not support combustion but is combustible.

Precautions: