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Note on Solubility of Substance and Crystallization

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Solubility of a substance

The solubility of a substance (solute) at a given temperature is defined as the amount of substance (solute) dissolved in 100 gm. of solvent to make a saturated solution at that temperature.

Mathematically,

Solubility(s) =

Effect of heat on Solubility

The molecules of a solute in solid are compactly packed. But when we heat the solid, they start to vibrate about their mean position as they posses kinectic energy on them. When we increase the temperature their kinetic energy increases and they start to move with high speed. Similary, the molecules of solvent in liquid state are loosely packed as there is less intermolecular force of attraction between them. These molecules of liquid are constantly moving inside. When we heat the liquid, these molecules gain more and more kinectic energy and moves with very high speed. Also, b during shaking , the molecules moves with high speed as they gain kinectic energy during shaking too. As a result the molecules strike with eachother and are separated. This molecules then mixed with the molecules of solvent to make a solution.
More will be the surface area of solute (solid state), more it will mix with molecules of solvent at a faster rate. When we heat the molecules at high temperature, the intermolecular spaces between them increases as the intermolecular force become due to heat. It helps to adjust more molecules of solute in the increased space. So, solubility of the substances also increases with increase in temperature.

Solubility curve

A curve obtained by plotting the solubility of substances at different temperatures against these temperatures is known as solubility curve.

Temperature

0C

0 10 20 30 40 50 60 70
Solubility of copper sulphate 14 17 21 24 29 34 40 47
Fig : Solubility
Fig : Solubility
Information obtain from solubility curve
  • The solubility of substances at a particular temperature can be known.
  • The solubility curve helps us to compare the solubility of difference substances at same temperature.
  • It gives the idea that solubility changes with the temperature.
  • The solubility curve helps us to predict which substance will crystalize out first from hot solution containing two or more solutes.

Crystals

Crystals are the granular substances having sharp edges and smooth surface.

Characteristics of crystals

  • They are solid particles with definite or regular shapes.
  • They are pure substances with fixed melting point.
  • They are arranged in a three dimensional patterns.

Crystallization

The process in which crystals are formed by cooling a hot saturated solution of solid materials is called crystallization.

To obtain crystals from copper sulphate solution

Take a solution of copper sulphate in a porcelain basin. Make the solution hot saturated either by dissolving more copper sulphate or by evaporating solvent as shown in the figure. Continue heating until the small crystals are seen. Now cool the apparatus. After a while, the crystals are formed. Now, separate the crystals from the mother liquor and place them on filter paper to dry.

Amorphous solids

Those solid substances, which do not have any definite geometrical forms or shapes, are called amorphous solids.

Crystalline solids

Those solid substances, which have definite geometrical forms or shapes, along with definite and rigid morphology, are called crystalline solids.

  • The solubility of a substance (solute) at a given temperature is defined as the amount of substance (solute) dissolved in 100 gm. of solvent to make a saturated solution at that temperature.
  • A curve obtained by plotting the solubility of substances at different temperatures against these temperatures is known as solubility curve.
  • Crystals are the granular substances having sharp edges and smooth surface.
  • The process in which crystals are formed by cooling a hot saturated solution of solid materials is called crystallization.
  • Those solid substances, which do not have any definite geometrical forms or shapes, are called amorphous solids.
  • Those solid substances, which have definite geometrical forms or shapes, along with definite and rigid morphology, are called crystalline solids
.

Very Short Questions

The solubility of a substance at a particular is defined as the amount of solute dissolved in 100gm of solvent to a saturated solution at that temperature.
Mathematically,
Solubility = [Weight of solute(gm) / Weight of solvent (gm)] × 100

A curve obtained by plotting the solubility of a substance at different temperature is known as solubility curve. Solubility of a substance at different temperature can be known from the solubility curve.

Applications of a solubility curve are listed below:

  1. The solubility of a substance at a particular temperature can be found.
  2. The solubility's of two or more substances of the same temperature can be compared.
  3. The solubility curve shows how the solubility of substance varies with the rise in temperature.
  4. With the help of solubility curve, the amount of solute that precipitates out when a saturated solution at higher temperature is cooled to a lower temperature can be calculated.

Crystals are homogeneous solids bounded by plane surfaces, meeting in sharp edges and having regular and definite geometrical shape. When a saturated solution of a solid in a liquid at higher temperature is allowed to cool then crystals are formed.

When a saturated solution of a solid in a liquid at higher temperature is allowed to cool, a quantity of solid is deposited in the form of crystals. This process is known as crystallization.

Temperature is mentioned along with the solubility of a substance because solubility changes on changing the temperature.

It means 21 gm CuSO4 can dissolve in 100gm of water to make saturated solution of CuSO4 at 20°C.

0%
  • The unit of Solubility is

    No unit
    gm/ml
    gm/lt
    gm/gm
  • What is false about solubility?

    Solubility has no unit
    Solute which separates out from a saturated solution are called crystals
    Different chemicals have different solubility
    increasing temperature increases solubility
  • What is solubility of  X in water if maximum of 25 gm of X can be dissolved in 50g of water at 25 degree?

    5
    50
    10
    25
  • Calculate the amount of sugar required to saturate 20 gm of water, if the solubility of sugar at 20 degree is 204

    81.6
    61.2
    122.4
    40.8
  • Which salt solution does not increase in solubility when heated?

    Potassium Chloride
    Potassium Nitrate
    Sodium Chloride
    Lithium Carbonate
  • What information is not provided by the solubility curve?

    Compare solubility of different substance
    Calculate amount of precipitate obtained after cooling the solution from higher to lower temperature
    Find solubility of a substance at certain temperature
    know the transition temperature of hydrate salt
  • Which is not a crystal?

    Sodium Hydroxide
    Copper Sulphate
    Diamond
    Quatrz
  • Which is not a characteristic of crystals?

    They are pure substance
    They are homogenous solid particles
    The only way of getting crystals is by cooling supersaturated solution
    They have definite geometrical shape
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