Hard and Soft Water

Temporary hardness-

• Temporary hard water contains dissolved hydrogen carbonate ions, HCO_3–
• When heated these ions decompose to form CO₃^2–
• The carbonate ions in the bolied water react with the dissolved Mg and Ca ions to form insoluable precipitates
• Temporary hardness can reduce the effieciency of kettles and heating systems this is because of the build up of limescale (a solid containg calcium carbonate produced when the water is heated), it coats the insides of pipes meaning more energy is needed to heat the water which increases the cost

Testing for hardness-

• One way to measure the hardness in water is to perform a titration (A titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution) with soap solution:

• A known volume of water is put into a conical flask. Soap solution is added to it from a burette or pipette. The mixture is swirled to help it form lather. The volume of soap solution that needs to be added to form permanent lather is recorded. The harder the water, the greater the volume of soap solution needed.

Benefits of hard water-

The calcium:

• improves the taste
• helps develope and mantain healthy bones and teeth
• can reduce the risk of heart disease

Disadvantages of hard water-

• more soap is needed to form a lather which increases the cost
• scum is produced which is unsighlty
• temporary hardness produces limescale which coats pipes and decreases efficiency

Hard water- 

• Hard water is formed when water flows over limestone and chalk and picks ups calcium and magnesium ions
• Water slightly acidic and this reacts with the calcium carbonate to form                           carbonic acid + calcium carbonate → calcium hydrogencarbonate                             H₂CO₃(aq) + CaCO₃(s) → Ca(HCO₃)₂(aq)
• The dissolved calcium ions and magnesium ions in hard water make it difficult to form a lather, instead it reacts with soap to form a scum

Fixing hardness-

Adding Sodium Carbonate/ Washing soda/ Na₂CO₃:

• The carbonate ions from sodium carbonate react with the calcium and magnesium ions in the water to produce insoluable precipitates: Ca²⁺(aq) + Na₂CO₃(aq) → CaCO₃(s) + 2Na+(aq) calcium ions + sodium carbonate → calcium carbonate + sodium ions (but this forms limescale)
• The water is softened because it no longer contains dissolved calcium and magnesium ions

Ion exchange columns:

• These have ion exchange resins packed into colomns
• These resin beads have sodium (or hyrdrogen) ions attached to them, as hard water goes through the column, the calcium and magnesium ions swap places with the sodium ions.The calcium and magnesium ions are left attached to the beads, while the water leaving the column contains more sodium ions.
• Once the resin beads are saturated with Ca and Mg ions salt add salt to regenerate them