Chemistry C3 - Water

Many substances dissolve in water -

Most ionic compounds dissolve in water

Some molecular compounds do

Most covalent compounds do not

Solubility is given in 100 grams of water (or solvent) at that given temperature

Soluble Salts -

• All nitrates
• Most sulphates
• Most chlorides, bromides and iodides
• Sodium carbonate and Potassium carbonate
• Sodium hydroxide and Potassium hydroxide

Insoluble Salts -

• lead and barium sulphate
• silver and lead bromide, chloride and iodide
• most other carbonates
• most other hydroxides

In Solids -

Increases as the temperature increases

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In Gases -

Decreases as the temperature increases

Increases as pressure increases

Carbon Dioxide

• Dissolving carbon dioxide in water under high pressure makes carbonated water.
• When the pressure is released, gas bubbles out of the solution
• Carbonated water is used to make fizzy drinks

Oxygen

• Dissolved oxygen is essential for aquatic life
• If the temperature of the water increases, the amount of oxygen dissolved decreases

Soft Water readily forms lather with soap

Hard water reacts with soap to form scum

Hard water contains dissolved ions - Mg2+ and Ca2+

The compounds become dissolved when water comes into contact with rocks

Using hard water increases costs because more soap is needed

When hard water is heated, it can produce scale that reduces the efficiency of heating systems and kettles

Hard water has some benefits because compounds are good for your teeth

Scum -

Stearates formed when Ca2+ and Mg2+ ions react with sodium stearate in soap

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Scale -

A limescale (CaCO3) deposit formed when Mg2+ and Ca2+ ions thermally decompose