Chemistry 2

Water that lathers easily is called soft water. Hard water does not lather easily. This is because hard water contains dissolved compounds of calcium/magnesium which react with soap to form scum. 

When temporary hard water is heated it produces a solid called scale which causes blockages and can be deposited in kettles, boilers and pipes.

Hard water can be made soft by removing the dissolved calcium and magnesium ions. There are two methods to remove these from permenant hard water:

- precipitation where you add sodium carbonate to the water. This reacts with the calcium and magnesium ions to form solid calcium carbonate and magnesium carbonate.

- ion exchange column which has a resin containing sodium or hydrogen ions. When hard water is passed through this resin, calcium and magnesium swap with sodium or hydrogen ions.

Drinking water needs to be made safe before you drink it. To do this water is treated by sedimentation and filtration to remove solids. This is followed by disinfection using chlorine to kill microbes in the water.

Advantages of water treatment:

- uses less soap

- doesn't produce scum which reduces effects on heating systems 

Dis-advantages of water treatment:

- reduces health benefits

- costs alot of money

Different amounts of energy are released by different fuels and foods. The amount of energy released is measured in Joules. We can use a calorimeter to measure the amount of energy released when substances burn. A simple calorimeter is water in a glass beaker which is heated when a substance burns. The temperature rise of the water depends on the amount of energy released. To measure the energy released we use the equation:

Energy released= mass of water (g) x specific heat capacity of water (J/g'c) x temp change

When reactions take place in solutions, energy is transferred to or from the solution. We can use the same equation.