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In this high school Chemistry quiz we look at some of the factors which affect how well substances are dissolved in water. We also examine ions dissolved in impure water, hard water and limescale.
Water, Earth's most abundant natural resource, is vital for all life. The first life on Earth began in the water and remained there for millions of years until the Earth had an ozone layer and plants and animals had evolved sufficiently to colonize the land. Elsewhere in the Solar System, space probes have been looking for signs of water. On Mars, there are sedimentary rocks that seem to have been formed under water along with valleys that seem to have been carved by running water. Enceladus, one of the moons of the planet Saturn, has water geysers at the south pole and further research has confirmed that there is a liquid water ocean beneath an icy outer crust. Scientists also believe that an ocean, also beneath an icy crust, exists on one of the moons of Jupiter - Europa. It is possible that another of Jupiter's moons has an ocean underneath its icy outer crust.
Water itself is a covalently bonded molecule made from one oxygen atom sharing electrons with two hydrogen atoms. Pure water therefore does not conduct electricity to any great degree. When ionically bonded chemicals are dissolved in water, there is a ready supply of ions that can transfer the electrical current throughout the solution. That is why water and electricity in the home are so dangerous - tap water is free from microbes but is far from pure. Even after using a water filter, there are still sufficient ions in the water to allow it to conduct electricity.
Our water supplies come from the ground, either from boreholes or reservoirs. When they are in contact with soil and rock, any soluble compound will dissolve into the water. Soluble calcium and magnesium compounds form hard water. These can be deposited on the inside of pipes, kettles, boilers, irons and on taps as limescale (sometimes referred to more simply as 'scale'). This clogs up pipes and makes heating appliances less efficient. Limescale can completely wreck dishwashers and washing machines as it blocks up their internal pipework. Soap does not work as well in hard water as it does in soft water because it forms scum. The ions that cause hard water can be removed in several ways. However, hard water does perhaps have a couple of advantages: firstly, some people say that it tastes better whilst medical research has found that the minerals in hard water could be beneficial to your heart.