Water Hardness LO3

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Pure Water

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40 Terms

1

Pure Water

Water that is free from contaminants and other substances, possessing physical properties such as being odourless, tasteless, and colourless, boiling at 100°C and freezing at 0°C, and having a maximum density of 1 g/cm³ at 4°C.

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2

Hydrated Salts

Salts that contain water molecules in their structure, known as water of crystallisation, which can be removed by heating to form an anhydrous salt.

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3

Water of Crystallisation

Water molecules present in the structure of hydrated salts, influencing the shape of crystals and can be removed by heating the hydrated salt.

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4

Anhydrous Salt

A salt that has had the water of crystallisation removed, which can regain water molecules to become hydrated.

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5

Homogenous Mixture

A mixture where all parts are in the same state of matter, such as rock salt or air.

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6

Heterogeneous Mixture

A mixture where the parts are in different states of matter, like sand and water.

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7

Soluble Substances

Substances that can dissolve in a liquid to form a solution, with the dissolved solid called the solute and the liquid doing the dissolving called the solvent.

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8

Insoluble Substances

Substances that do not dissolve in a liquid, forming a suspension if present as a fine powder in the liquid.

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9

Factors that affect solubility are:

  1. Size of particles

  2. Stirring

  3. Amount of solute already dissolved

  4. Temperature

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10

Substances which are soluble:

  • All nitrates

  • All hydrogen carbonates

  • All group 1 metal salts

  • All ammonium salts

  • Halides except silver and lead halides

  • Sulfates except barium, calcium and lead sulfates

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Substances which are insoluble:

  • Carbonates except group 1 metal and ammonium carbonates

  • Metal oxides except group 1 and 2 metal oxides that react with water

  • Hydroxides except group 1 metal and ammonium hydroxides

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12

Filtration

A separation technique used to separate an insoluble solid from a liquid or aqueous solution based on particle size and density.

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13

Evaporation to dryness

A method used to obtain a soluble solid from a liquid solvent by evaporating the solvent until dry, affecting crystal size.

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14

Crystallisation

A process to obtain a soluble solid from a liquid solvent by cooling a saturated solution to form crystals, often used for obtaining hydrated salts.

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15

Ionic bond

A strong bond between metal and non-metal ions in salts, characterized by electrostatic forces of attraction in a crystal lattice structure.

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16

Solubility

The maximum quantity of solute that can dissolve in a certain quantity of solvent at a specified temperature.

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17

Solvent

The substance in which the solute dissolves to form a solution.

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Saturated Solution

A solution that cannot dissolve any more solute at a given temperature.

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19

Dilute Solution

A solution with a relatively small amount of solute dissolved in the solvent.

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Concentrated Solution

A solution with a relatively large amount of solute dissolved in the solvent.

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Solubility Curve

A graph showing how the solubility of a substance varies with temperature in a specific solvent.

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22

Solubility of a Substance

The ability of a substance to dissolve in a solvent, often influenced by factors like temperature and pressure.

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23

Hard water

Hard water is water that will not readily form a lather with soap, instead it forms a scum.

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24

Temporary hardness

Hardness in water caused by the presence of dissolved calcium hydrogen carbonate or magnesium hydrogen carbonate, which can be removed by boiling.

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Word equation for the reaction when water passes over hydrogen carbonate

calcium carbonate + hydrogen carbonate → calcium hydrogen carbonate

magnesium carbonate + hydrogen carbonate → magnesium hydrogen carbonate

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Word equation for when calcium hydrogen carbonate undergoes thermal decomposition

Calcium hydrogen carbonate → calcium carbonate + water + carbon dioxide

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Permanent hardness

Hardness in water caused by the presence of dissolved calcium or magnesium ions like calcium sulfate or magnesium sulfate, which cannot be removed by boiling.

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Boiling

A method of softening water by removing temporary hardness through the thermal decomposition of calcium and magnesium hydrogen carbonates.

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Distillation

A technique used to separate the solvent (water) from dissolved solutes, capable of removing both temporary and permanent hardness from water.

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30

Washing soda

Sodium carbonate decahydrate (Na₂CO₃.10H₂O) used to remove both temporary and permanent hardness from water by forming precipitates with calcium or magnesium ions.

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31

Reaction that occurs with washing soda and temporary hard water

sodium carbonate + calcium hydrogen carbonate → sodium hydrogen carbonate + calcium carbonate

Na₂CO₃(aq) + Ca(HCO₃)₂(aq) → 2NaHCO₃(aq) + CaCO₃(s)

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32

Reaction that occurs with washing soda and permanent hard water

sodium carbonate + calcium sulfate → sodium sulfate + calcium carbonate

Na₂CO₃(aq) + CaSO₄(aq) → 2NaSO₄(aq) + CaCO₃(s)

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33

Ion-exchange

Method of removing both types of water hardness by passing water through a resin containing sodium ions, which exchange with calcium or magnesium ions present in hard water.

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Reaction that happens in ion exchange

calcium ions + sodium resin → sodium ions + calcium resin

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35

Precipitation reaction

Chemical reaction where two soluble solutions react to form an insoluble precipitate, as seen in the removal of hardness from water using washing soda or ion-exchange resin.

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36

Scum

Solid material formed on the surface of water when soap reacts with dissolved calcium or magnesium ions in hard water, leading to the formation of insoluble calcium salts.

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37

Lather

Foam formed when soap dissolves in water, indicating the ability of water to form a lather with soap and distinguishing between hard and soft water.

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38

Chemical tests for water (Word equations)

anhydrous copper (II) sulfate + water → hydrated copper (II) sulfate

anhydrous cobalt (II) chloride + water → hydrated cobalt (II) chloride

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39

Chemical test for water (Balanced equations)

CuSO₄(s) + 5H₂O(l) → CuSO₄.5H₂O(s)

CoCl₂(s) + 6H₂O(l) → CoCl₂.6H₂O(l)

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40

Osmosis

Osmosis is the movement of water molecules across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration. It is used to purify water (remove the salts present in it)

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