CHE2: HYGROSCOPE SUBSTANCES

Is one which absorbs water vapor from the atmosphere but not enough to development dissolve it to become wet or form a solution examples are; cement, milk powder, cigarettes, biscuits, anhydrous copper (II) sulphate, calcium oxide, copper (II) oxide.

Hygroscopic substances do not undergo a change of state when the absorb water from the air.

Hygroscope:

This is the process by which a substance absorbs water vapor from the atmosphere but doesn’t become wet or form a solution

Deliquescent and hygroscopic substances are used as drying agents.

In the laboratory, some the hygroscopic and deliquescent substance are used to dry gases

Drying agent Suitable for drying
1.      Anhydrous calcium chloride or fused calcium chloride –          Oxygen carbon dioxide hydrogen-          It is not suitable for drying ammonia gases because it reacts with it
2.      Concentrated sulphiric acid –          Oxygen, carbon dioxide, hydrogen chloride, hydrogen, sulphur dioxide-          It is not suitable for drying ammonia and other alkaline gases because it reacts with them
3.      Calcium oxide (quick lime) –          Ammonia, hydrogen-          Not suitable for drying acidic gases like carbon dioxide sulphur dioxide, hydrogen chloride because it reacts with these agents

Efflorescence:

This is the giving up of water for crystal to the atmosphere

Efflorescent substance

This is one which gives up water of crystallization when it is exposed to air.

Example are:

Sodium carbonate crystals (Sodium carbonate -10- water crystals Na2O3. 10H2O, Sodium sulphate 10- water crystals (Na2SO4.10H2O, copper (II) sulphate crystals CuSO4.5H2O

Anhydrous copper (II) Sulphate is white (grey). It is used to taste for water. Any substance that is water or contains waters turns anhydrous copper (II) sulphate blue.

Iron rust is very important because:

  1. Iron is the most abundant and most used metal
  2. Iron rust is destructive

crystal liquid

Fractional cytilastation is the separating of a mixture of salts in which dissolve in the same solvent providing they have different solubility [calculations liters]

Silicon – Si

Kryplan – Kr

Argon –Ar

Berilium – Ba

Lithium –Li

Benyllium –Be

Cobolt – Co

Hellion – He

Deliquescent are solid that absorb water from the copper atmosphere until they dissolve in it example copper nitrate, anhydrous calcium chloride semi nitrate

Zinc oxide is yellow when hot and white when cold.

Crystals

A crystal is a solid that has solidified in a definite regular shape.

Solids that area in crystal is called crystalline solids and those in power form are a amorphous solids, (shapeless).

Saturated solution

Is none which cannot dissolve more solute at a given temperature in contact with un dissolved solute.

Solubility of substances depends on temperatures.

Temperature- the solubility of most substance increases with a rise in temperature

However, solubility of gases decreases with increase in temperature.

Nature of the solvent

Super saturated solution

It is one which contains more solute than it can hold at given temperature in presence of undisclosed solute.

 

ASSIGNMENT : CHE2: HYGROSCOPE SUBSTANCES Assignment MARKS : 10  DURATION : 1 week, 3 days

 

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