C3.2 - Everything in the Specification

[blank_start]Soft[blank_end] water forms a [blank_start]lather[blank_end] with soap; [blank_start]hard[blank_end] water reacts to form [blank_start]scum[blank_end] with soap and so more soap is needed to form a [blank_start]lather[blank_end]. This makes using [blank_start]hard[blank_end] water moves [blank_start]expensive[blank_end].

What are the two ions in hard water that react with soap to form scum?

[blank_start]Hard[blank_end] water, when [blank_start]heated[blank_end], also forms [blank_start]scale[blank_end] on the insides of pipes, boilers and [blank_start]kettles[blank_end]. A build-up of scale reduces the [blank_start]efficiency[blank_end] of heating systems, and so using [blank_start]hard[blank_end] water is more [blank_start]expensive[blank_end].

[blank_start]Hard[blank_end] water, when [blank_start]heated[blank_end], also forms [blank_start]scale[blank_end] on the insides of pipes, boilers and [blank_start]kettles[blank_end]. A build-up of [blank_start]scale[blank_end] reduces the efficiency of [blank_start]heating[blank_end] systems because the [blank_start]scale[blank_end] is a [blank_start]thermal[blank_end] insulator. For example, a kettle with [blank_start]scale[blank_end] on the heating element takes longer to boil, and so using [blank_start]hard[blank_end] water is more [blank_start]expensive[blank_end].

What is the main compound that forms scale?

Give two benefits of hard water.

There are two kinds of water hardness - [blank_start]temporary[blank_end] and [blank_start]permanent[blank_end]. [blank_start]Temporary[blank_end] hardness is caused by the [blank_start]hydrogencarbonate[blank_end] ion, HCO₃. [blank_start]Permanent[blank_end] hardness is caused by dissolved [blank_start]calcium[blank_end] [blank_start]sulphate[blank_end], CaSO₄.

Which of the following water softening methods only apply to temporary hard water?

Fill in the blanks to complete the following passages about how hard water can be made soft. METHOD 1 - [blank_start]Temporary[blank_end] hardness can be removed by [blank_start]boiling[blank_end]. When heated, the calcium [blank_start]hydrogencarbonate[blank_end] decomposes to form calcium [blank_start]carbonate[blank_end], which is the [blank_start]scale[blank_end] that affects heating systems. This method does not apply to [blank_start]permanent[blank_end] hard water. METHOD 2 - Both types of hardness can be removed by adding [blank_start]washing[blank_end] [blank_start]soda[blank_end] ([blank_start]sodium[blank_end] [blank_start]carbonate[blank_end], or Na₂CO₃) to the water. The [blank_start]carbonate[blank_end] reacts with the calcium and [blank_start]magnesium[blank_end] ions to form an [blank_start]insoluble[blank_end] precipitate of calcium [blank_start]carbonate[blank_end] and magnesium [blank_start]carbonate[blank_end]. The ions are no longer [blank_start]dissolved[blank_end] in the water, so they are unable to make it hard. METHOD 3 - Both types of hardness can be removed by running the hard water through '[blank_start]ion[blank_end] [blank_start]exchange[blank_end]' columns. The columns have lots of [blank_start]sodium[blank_end] (or hydrogen) ions, and '[blank_start]exchange[blank_end]' them for calcium or [blank_start]magnesium[blank_end] ions in the water.