Water Flashcards
What does water naturally contain?
Microorganisms and dissolved salts, which should be of sufficiently low levels to be safe for humans to drink.
How is water that is good quality and safe to drink produced?
- The water is passed through a filter bed to remove any solid particles.
- Chlorine gas is then added to kill any harmful microorganisms.
- Fluoride is added to drinking water in order to reduce tooth decay.
- By choosing an appropriate source.
What is the problem with consuming too much fluoride?
It can cause discolouration of teeth.
What can be done to improve the taste and quality of tap water?
More dissolved substances can be removed by passing the water through a filter containing carbon, silver and ion exchange resins.
Why is water distilled?
To produce pure water.
What water can be distilled?
Any water.
How is water distilled?
- The water is boiled to produce steam.
2. The steam is condensed by cooling to produce pure liquid water.
What are the disadvantages of distilling water?
The process uses a lot of energy, which makes distillation an expensive process.
What determines whether water is described as hard or soft?
The amount of compounds present.
Why does soft water readily form a lather with soap?
Because it doesn’t contain many dissolved compounds.
What happens when permanently hard ward is boiled?
It remains hard.
What happens when temporary hard water is boiled?
It is softened.
What ions does temporary hard water contain?
Hydrogencarbonate ions (HCO3-)
What happens to hydrogencarbonate ions upon heating?
They decompose to produce carbonate (CO3^2-) ions.
How do carbonate ions form precipitates?
By reacting with calcium and/or magnesium ions.
What do calcium and magnesium compounds dissolved in water react with soap to form?
Scum.
When do calcium or magnesium compounds dissolve in natural water?
As it flows over ground or rocks containing compounds of these elements.
What does scum do?
It makes it harder to form a lather.
Why are soapless detergents used?
As they don’t form scum.
What is an advantage of hard water?
The dissolved compounds in water are good for your health. For example, calcium compounds help the development of strong bones and teeth, and also help to reduce the risk of heart disease.
What are two disadvantages of hard water?
- More soap is needed to form a lather, which increases cost.
- Using hard water often leads to deposits (called scale) forming in heating systems and appliances like kettles, which reduces their efficiency.
How can hard water be made soft?
The dissolved calcium and magnesium need to be removed. This can be done by either adding sodium carbonate solution or passing the hard water through an ion-exchange column.
How does adding sodium carbonate solution to hard water soften it?
The carbonate ions react with the calcium and magnesium ions to form calcium carbonate and magnesium carbonate (respectively), which precipitate out of solution as they are both insoluble.
How does passing the hard water through an ion-exchange column soften it?
The ion-exchange column contains a resin that supplies hydrogen ions or sodium ions. As the hard water passes through the resin, the calcium and magnesium ions contained in it are replaced by hydrogen or sodium ions from the resin.
