Chemistry Water

• Water makes up of 70% of earth's surface. Water found from rivers , lakes , oceans , etc or in its natural form is called natural water , which is important for pant and human life. The purest form of water is rain water , while water found in oceans , lakes , etc are impure as they contain soluble sodium chloride.
• Henry Cavendish in 1781 found water to be a compound for hydrogen and oxygen.
• What is potable water and its characteristics?

  • It should be clear , colourless and odourless.
  • It should not have suspended impurities , cyanides , urea and should be free from harmful bacteria and germs.
  • It should have dissolved minerals and gases which give it a good taste while dissolved salts like sodium , calcium , magnesium also help with metabolic activities of the body.
• Water unfit for human consumption:

  • Saline and sea water: It has a high percentage of dissolved salts especially sodium chloride which makes it unfit for drinking and agricultural purposes.
  • Distilled water : Since it is free from certain dissolved salts , it tends to dissolve essential salts in the human body needed for metabolic activities , leading to their deficiency.
• Contaminants in water:

  1. Dissolved salts like calcium and sodium
  2. Dissolved gases like carbon dioxide
  3. Suspended particles like clay , sand and decaying matter
  4. Germs causing water borne diseases such as typhoid and jaundice.
• Why is water called a universal solvent?

  Water can dissolve a large number of substances (sugar , salts) and gases (hydrogen chloride , ammonia).

  Since water can dissolve almost every common substance , it is called universal solvent.
• 1. Solute: A substance that dissolves or disappears in the solvent or the liquid so as to form a solution is called a solute.
  2. Solvent: A liquid or medium of dissolution for the solute to dissolve in it so as to form a solution is called solvent.
  3. Solution: A homogenous mixture of a solute in a solvent is called a solution.
• Conditions affecting formation of a solution:

  1. Solubility
  2. Temperature
  3. Proportion
  4. Particle size
  5. Proper mixing
• Solubility of a solute is the maximum amount of solute in grams that will dissolve in a 100 gm water at t degree celsius
• Miscible liquids are some liquids that can dissolve in water.(alcohol)

  Immiscible liquids are liquids that are insoluble in water(kerosene).
• Solubility of gases in water with respect to temperature is indirectly proportional . (tap water when heated increases the temperature but decreases the solubility of gases , escaping out and making the water taste flat.)

  Solubility of gases in water with respect to pressure is directly proportional.(soda contains carbon dioxide in water under pressure.)
• On the basis of size of dissolved or dispersed particles in a medium, there are 3 solutions:

  1. True
  2. Colloidal
  3. Suspensions
• TRUE SOLUTION:

  • It is a homogenous mixture , clear and transparent in nature
  • It is not visible to naked eye
  • Do not settle down
  • Can pass through filter paper and semi permeable membrane
  • Cannot be seen under ultra microscope
  • Can be separated by physical means only.
  • Ex: Potassium chloride
• Colloidal solutions are a heterogeneous mixture and turbid in nature.

  Colloidal particles are in an intermediate state between the molecules or ions of true solutions and that of suspensions
• Colloidal solutions cannot be seen by the naked eye

  Colloidal solutions can be seen under an ultra microscope
• Colloidal solutions can pass through filter paper but not through a semi-permeable membrane.

  Colloidal solutions exhibit Brownian motion, which is the random movement of particles in a dispersed medium due to continuous bombardment of molecules
• Colloidal solutions show the Tyndall effect, which is the scattering of a beam of light by colloidal particles in the solution due to its heterogeneous nature.An example of a colloidal solution is shaving foam
• SUSPENSIONS:

  • Heterogenous in nature(undissolved particles in a dispersion medium)
  • Can be seen by naked eye
  • Can be seen under ultra microscope
  • Can settle down after sometime
  • Cannot pass through filter paper nor through a semi permeable membrane.
  • Ex: Sand
• An unsaturated solution is a solution which can dissolve more of the solute at a given temperature while a saturated solution cannot dissolve any more of the solute at a given temperature.

  A saturated solution can be turned into an unsaturated one by heating the solution or by adding more solvent.
• Super saturated solution is when a solution holds more of the solute at a given temperature then a saturated solution

  It is prepared in boiling water. If this is cooled , excess salt is separated from the hot saturated solution , since it contains excess salt , it is called a super saturated solution.
• Crystals are solids having definite regular shapes with symmetrical arrangement and sharp edges.
• What is crystallization?

  Crystallization is the process of separation or deposition of crystals from a hot saturated on gentle cooling.
• When a crystal is separated or deposited from a hot saturated solution on gentle cooling , it unites with a definite number of water molecules in a loose chemical combination with them. These definite number of water molecules are called water of crystallization and is responsible for the geometric shape and colour of the crystal.
• There are two types of crystals:

  1. Hydrated (It contains a definite number of water molecules and is in a loose chemical combination with the crystal.)
  2. Anhydrous (It contains any definite number of water molecules and is in a loose chemical combination with the crystal.)
• EFFLORESCENT CRYTALS:

  -Crystalline hydrated

  -Loses moisture partly or wholly to the atmosphere

  -Changes into powdery substance
• DELIQUESCENT CRYSTALS:

  -Crystalline water soluble

  -Absorbs moisture from the air

  -Changes into a saturated solution.
• HYGROSCOPIC CRYSTALS:

  -Amorphous liquids or solids

  -Absorbs moisture from the atmosphere

  -No change
• • Drying agents(absorbs moisture from substances)
  • Desiccating agents(drying agents in desiccators)
  • Dehydrating agents(to remove water chemically combined with compounds due to their strong affinity with water)
• Hard water does not lather readily with soap and waste soap. It consist of calcium and magnesium sulphates , chlorides and bicarbonates. It is from river water and spring water. It has temporary and permanent hard water.
• Soft water lathers easily with soap and doesn't waste soap. It doesn't consist of salts of calcium and magnesium. Found in distilled water and rain water.
• Temporary hard water can be removed by boiling and consists of magnesium and calcium bicarbonates . It is formed when rain water consisting of carbon dioxide falls on lime stone and magnesite ,while permanent hard water cannot be removed by boiling and consists of magnesium and calcium sulphates and chlorides and is formed when natural ground water dissolves chlorides and sulphates of calcium and magnesium in it.
• Hard water is not suitable for industrial purposes as it causes a crusty boiler scale or fur in boilers.
• Removal of temporary hard water by boiling . On boiling water containing of calcium and magnesium bicarbonates , it results in the formation of insoluble carbonates , water and carbon dioxide which escapes out. The resulting water is rendered soft.
• Removal of permanent and temporary hard water can be removed by adding of Na2SO4(washing soda) , this results in calcium and magnesium chlorides , sulphates and bicarbonates which creates an insoluble calcium or magnesium carbonates precipitate being formed and filtered out. The result is with soluble sodium salts which does not affect the hardness of water , therefore being rendered soft.