Environmental Chemistry - Hardness in water

Complete the following sentence "Hard water is water that

• forms a lather easily with water.

• does not form a lather easily with water

Which of the following compounds are responsible for causing temporary hardness in water?

• CaCl₂

• Ca(HCO₃₎₂

• CaSO₄

• Mg(HCO₃)₂

_________ hardness can be removed by boiling while __________ hardness cannot by removed by boiling.

Which of the following would be considered to be caused by temporary hardness in water?

• Blocking of pipes with limescale

• Furring of kettles

• Scum formation when using soap

• Coating of heating element of dishwasher, shower, washing machine with limescale

Which of the following are methods used to remove permanent hardness in water?

• Distillation

• Adding washing soda crystals

• Boiling the water

• Using an ion exchange resin

The removal of temporary hardness in water that is heated, is represented by which of the following equations?

• H₂O + CO₂ ➡️ H₂CO₃

• H₂CO₃ + CaCO₃ ➡️ Ca(HCO₃)₂

• Ca(HCO₃)₂ ➡️ CaCO₃ + CO₂ + H₂O

When carbon dioxide reacts with water in the air, a weak acid called carbonic acid is produced. What is the formula of carbonic acid?

Carbonic acid falls as rainwater that is slightly acidic. This reacts with calcium carbonate, which is limestone rock, producing a soluble chemical that causes temporary hardness in water. What is the correct formula for this soluble compound?

When cold water containing temporary hardness is heated, an insoluble substance precipitates out of the water. What is the formula for this insoluble precipitate?

• CaCO₃

• CaCO3

• CO₂

• H₂O