Preparation of a true solution, a suspension and a colloidal solution and distinguish between these on the basis of transparency, filtration criterion and stability

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Experiment 1(A)

Aim

To prepare true Solutions of (i) common salt (ii) sugar and (iii) alum in water and study their properties like (a) transparency (b) filtration criterion and (c) stability.

Materials Required

Beakers, test tubes, test tube stand, glass rod, filter paper, funnel, funnel stand, pestle and mortar, common salt, sugar, alum, conc. H₂SO₄ etc.

Theory

All the three given substances are freely soluble in water. To make the process of dissolution easier and quicker, powder each substance and dissolve them in warm water. A true solution is obtained in all the three cases.

A true solution is always transparent. It may be coloured or colourless.

In case of a true solution, the size of the solute particles is so small (less than 1nm) that they can easily pass through the pores of a filter paper. Therefore, a solute cannot be separated from a solution by filtration.

Further, a true solution is always stable i.e, the solute particles never settle down (provided temperature remains constant and the solution is either unsaturated or at the most saturated).

Procedure

• Take nearly 50 ml of distilled water in a 250 ml beaker. Warm it, if needed.
• Add to it nearly 10 g of common salt, finely powdered and stir it well with a glass rod till it dissolves completely. This is a true solution of common salt in water.
• In a similar manner prepare a solution of nearly 10 g of sugar in 50 ml of distilled water in another beaker.
• Prepare a solution of potash alum in water ina similar manner but add a few drops of conc. H₂SO₄ in the end to made the solution clear and transparent.
• Put all the three solutions in three clean test tubes separately and view through them. Note down your observation.
• Filter the three solutions through three filter paper separately. Note if any residue is left on the filter paper in each page.
• Again take the three solutions in three clean test tubes and keep them undisturbed for same time. Note if any solid settels down.

Observations

S.No.	Test	Solution of common salt in water	Solution of sugar in water	Solution of potash alum in water
1.	Test for transparency	Transparent	Transparent	Transparent
2.	Filtration criterion	No residue on filter paper	No residue on filter paper	No residue on filter paper
3.	Stability	Stable	Stable	Stable

Results and Discussion

• Common salts in water, sugar in water and potash alum in water form true solutions.
• True solutions are transparent in nature.
• On filtering a true solution through a filter paper, no residue is obtained on the filter paper.
• A true solution is stable in nature i.e., no solute be settle down if the temperature remains constant.

Precautions

• In case of a solution of potash alum in water, add 1 to 2 drops of conc. H₂SO₄ to make it clear.
• Powder the solids by using pestle and mortar, if needed.
• Warm water, if it is very cold only.
• Use only distilled water to make the solutions.

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Experiment 1(B)

Aim

To make suspensions of a (i) soil (ii) chalk powder and (iii) fine sand in water and study their properties like (a) transparency (b) filtration criterion and (c) stability.

Materials Required

Beakers, test tubes, test tube stand, glass rod, filter paper, funnel stand, pestle and mortar, soil, chalk powder, fine sand etc.

Theory

All the three given substances (soil, chalk powder and fine sand) are insoluble in water. When finely powdered and mixed with water, these give suspensions. A suspension in thin sections (say in a test tube) may be translucent. However, in a thicker section (say muddy water in a deep pond) a suspension is obaque. When filtered, the suspended particles are retained on the filter paper. When left undisturbed for some time, a suspension settles down i.e., a suspension is unstable.

Materials Required

Beakers, test tubes, test tube stand, glass rod, filter paper, funnel stand, pestle and mortar, soil, chalk powder, fine sand etc.

Procedure

• Take nearly 50 ml of water in a 250 ml beaker.
• Add to it nearly 10 g of finely powdered soil and stir it well with a glass rod. This is a suspension of soil in water.
• In a similar manner prepare suspensions of chalk powder and fine sand in water.
• Take nearly 10 ml of suspension of soil in water after shaking it throughly. Immediately view through tthe test tube. Note down your obsrevations in a note book. In a similar manner test for the transparency of other two suspensions.
• Filter the three suspensions through three filter papers separately. Note the appearance of fiterate (is it same or different from the original suspension) and residue (if any) on the filter paper. Note down your observations.
• Put the three suspensions in three test tubes after through shaking. Keep these test tubes undisturbed in a test tube stand for some time (say 2-5 minutes). Note down, if any solid has settled down, in each case.

Observations

S. No.	Test	Suspension of soil in water	Suspension of fine sand in water	Suspension of chalk powder in water
1.	Test for transparency	Opaque or translucent	Opaque or translucent	Opaque or translucent
2.	Filtration criterion	Soil particles are retained by the filter paper. Filtrate is transparent.	Soil particles are retained by the filter paper. Filtrate is transparent.	Soil particles are retained by the filter paper. Filtrate is transparent.
3.	Stability	Unstable. Soil particles settle down and the supernatant liquid is transparent.	Unstable. Fine sand particles settle down and the supernatant liquid is transparent.	Unstable. Particles of chalk powder settle down and the supernatant liquid is transparent.

Result and Discussion

• Soil in water, fine sand in water and chalk powder in water form suspensions.
• Suspensions are opaque in nature.
• On filtering a suspension through a filter paper, the suspended particles are retained by the filter paper. The filtrate obtained is transparent.
• Suspensions are unstable in nature. If left undisturbed forsome time, the suspended particles settle down. The supernatant liquid is transparent.

Precautions

• Powder the solids, if needed, by using a pestle and mortar.
• As a suspension is unstable in nature, stir the suspension thoroughly before each test.
• If any foreign article, like a stone, detected in the given sample, remove it before grinding.

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Experiment 1(C)

Aim

To make colloidal solutions of (i) starch and (ii) albumin (say egg albumin) in water and study their properties like (a) transparency (b) filtration criterition and (c) stability.

Theory

To obtain a colloidal solution of starch in water, make a thin paste of ordinary starch (maida or corn flour) in cold water. Add this paste to boiling water, with constant stirring, to get colloidal solution of starch in water.
Egg albumin is the scientific name for white of an egg. Dissolve nearly a spoonful of egg white in 100 ml of cold water. Use only cold water to get a colloidal egg solution of albumin in water. This is because hot water will coagulate the egg white.
A colloidal solution is generally translucent i.e., it appears milky or cloudy.
When filtered through an ordinary filter paper, a colloidal solution passes through the filter paper unchanged i.e., no residue is obtained on the filter paper and the filtrate is translucent as the original solution. This is because the size of the colloidal particles is between 1-1000 nm, Which is less than the size of pores of an ordinary filter paper.
A colloidal solution is stable i.e., colloidal particles do not settle down if a colloidal solution is left undisturbed for sometime.

Apparatus

Beakers, test tubes, test tube stand, glass rod, filter paper, funnel, stand, burner, starch (maida) or corn flour, egg albumin (egg white), distilled water etc.

Procedure

• Take nearly 2 g of ordinary starch. Make a thin paste of this starch with nearly 10 ml of cold water. Heat nearly 100 ml of water in a 250 ml beaker to boiling. Add the paste of starch in water to boiling water, in a thin stream, with constant stirring. Boil this solution for 2-3 minutes and let it cool. Label it as colloidal solution of starch in water.
• Break an egg carefully so that the whites of the egg and egg yolk do not mix. Carefully separate the two. Dissolve a spoonful of the egg whites in nearly 100 ml of water in a 250 ml beaker. Label it as a colloidal solution of egg albumin in water.
• Put these two colloidal solutions in clean test tubes and view through them. Note down your observations in the note book.
• Filter the two colloidal solutions through ordinary filter paper. Note if any residue is obtained on the filter paper. Note the appearance of the filtrate. Note down your observations in the note book.
• Again, take the two colloidal sotions in two clean test tubes. Pur these test tubes in a test tube-stand undisturbed for some time. Note down if any solid settle down or if there is any change in the appearance of the two solutions. Note down your observations in the note book.

Observations

S. No.	Test	Colloidal solution of starch in water	Colloidal solution of albumin in water
1.	Test for transparency	Translucent	Translucent
2.	Filtration criterion	Passes through an ordinary filter paper unchanged.	Passes through an ordinary filter paper unchanged.
3.	Stability	Stable as no solid settles down.	Stable as no solid settles down.

Result and Discussion

• A suspension of starch in water, when boiled for some time forms a colloidal solution.
• Egg albumin in cold water forms a colloidal solution.
• Colloidal solutions are translucent in nature.
• Colloidal solutions pass through an ordinary filter paper unchanged.
• Colloidal solutions are stable as no solids settle down with time.

Precautions

• Use only cold water to get colloidal solution of egg albumin in water.
• Starch with cold water forms a suspension. Boil it to get a colloidal solution.
• Use only distilled water to make colloidal water to make colloidal solutions. This is because presence of ions generally destabilies colloidal solutions.

Experiment 1(D)

Aim

To distinguish between a true solution, a suspension and a colloidal solution on the basis of
(i) transparency
(ii) filtration criterion
(iii) stability.

Theory

A true solution, a suspension and a colloidal solution can be differentiated on the basis of transparency, filterability and stability.

A true solution is always transparent. A suspension is opaque while a colloidal solution is translucent. To check transparency, take the three mixtures (i.e., true solution, colloidal solution and suspension) in three identical test tubes and veiw through them.

On filtration through an ordinary filter paper, a true solution and a colloidal solution pass through the filter paper unchanged. However, when a suspension is filtered througha filter paper, the suspended particles are retained on the filter paper. This is because the size of these particles is more than the pore size of filter paper.

In terms of stability, a true solution and a colloidal solution are stable i.e., they do not settle down. On the other hand, a suspension settles down, if left undisturbed.

Material Required

100 ml beakers (3 nos.), test tubes, test tube stand, glass rod, funnel, funnel stand, burner, filter paper, common salt, soil (or chalk powder or fine sand), starch (or egg albumin), distilled water.

Procedure

• Take 100 ml beaker, half full of water. Add some powered common salt (or sugar) to it. Stir well with a glass rod till whole of the salt dissolves. This is true solution of salt in water. Alternatively prepare a true solution of alum in water but add a few drops of conc. H₂SO₄ to make it clear.
• Take another 100 ml beaker, half full of water. Add to it some fine stand (or chalk powder or soil). Stir it well with a glass rod. A suspension of fine sand inn water is obtained.
• Take another 100 ml beaker half full of water. Heat the water till it starts boiling. Now add a suspension of starch in water to it with constant stirring. Boil it for 2-3 minutes. This is a colloidal solution of egg albumin in water, shake some egg albumin with cold water.
• Test for transparency : Take the true solution in a test tube and label it as A. Take the suspension in another similar test tube. Shake it will and label it as B. In another similar test tube take the colloidal solution and label it as C. Put the three test tubes in a test tubes stand and view through them. Recoed your observations (transparent, opaque or translucent) in your note book.
• Filtration Criterion : Filter the true solution through a filter paper. Note if there is any residue on the filter paper. Also check, if there is any change in appearance of the filtrate. Note your observations in the note book. In a similar manner filtrate the suspension through a filter paper and note your observations in the note book. Similarly filter the colloidal solution through a filter paper and record your observations in the note book.
• Stability : Take 100 ml of each of the three mixtures in three different test tubes. Leave them undisturbed for a few minutes (5-10 minutes). Is the mixtures stable or do the particles begin to settle down after some time ? Record your observations in the note book.

Observations

S. No.	Test	Solution of common salt in water (Test tube A)	Suspension of fine sand in water (Test tube B)	Colloidal solution of starch in water (Test tube C)
1.	Test for transparency	Transparent	Opaque	Translucent
2.	Filtration criterion	Passes through a filter paper unchanged	Fine sand particles are retained by the filter paper while the filtrate is clear water.	Passes through a filter paper unchanged
3.	Stability	Stable	Unstable fine sand particles settle down with time	stable

Results and Discussion

• Common salt (or sugar, or alum) and water forms a true solution. A true solution is transparent, passes through a filter paper unchanged and is stable in nature.
• Fine stand (or chalk, or soil) and water forms a suspension. A suspension is opaque, when passed through a filter paper, the stand particles are retained by the filter paper. A suspension is unstable in nature.
• starch (or albumin) and water form a colloidal solution. A colloidal solution is translucent, passes through a filter paper unchanged and is stable in nature.

Precautions

• Use only distilled water.
• Use only cold water to prepare colloidal solution of albumin in water.
• To obtain colloidal solution of starch in water, boil a suspension of starch in water.
• Shake the suspension vigorously before checking it for transparency.