C3.2 Water Flashcards
What does soft water form with soap?
Lather
What does hard water form with soap?
Scum, so more soap is required to from lather
Do soapless detergents produce scum?
No
What are the two types of hard water?
Permanent hard water ad temporary hard water
How can temporary hard water be softened?
By boiling it
What happens when permanent hard water is boiled?
It remains hard
What does temporary hard water contain?
Hydrogencarbonate ions
What do the hydrogencarbonate ions in temporary hard water decompose on heating to form?
Calcium carbonate, this solid is ‘limescale’ on your kettle
What do the carbonate ions produced by the hydrogencarbonate ions decomposing react with and what do they form?
Calcium and Magnesium ions to form precipitates
Why can using hard water increase costs?
More soap is needed
Why can heating temporary hard water reduce efficiency?
It produces scale that reduces the efficiency of heating systems and kettles
What benefits does hard water have?
Calcium compounds are good for the development and maintenance of bones and teeth, they also help to reduce heart disease
How can hard water be made soft?
By removing the dissolved calcium and magnesium ions
How can sodium carbonate be used to make hard water soft?
Sodium carbonate reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate
How do commercial water softeners make hard water soft?
Ion exchange columns contain hydrogen ions or sodium ions, these ions replace calcium and magnesium ions when hard water passes through the column
What should drinking water have?
Low levels of dissolved salt and microbes
How is water cleaned / purified?
It passes through a mesh screen to remove big bits like twigs. Chemicals are then added which make solids and microbes stick together and fall to the bottom. The water is then filtered through beds to remove all the solids. Water is then chlorinated to kill any harmful microbes left
Water needs to come from an…
Appropriate source
What do water filters contain?
Carbon, silver and ion exchange resins which can remove some dissolved substances from tap water to improve taste and quality
Why may fluorine be added to drinking water?
To improve dental health
Why may chlorine be added to drinking water?
To reduce microbes and therefore diseases
How can pure water be produced?
By distillation
What are the arguments against adding fluorine to water?
It can cause cancer and bone problems in high doses, some believe if they want fluorine they can use fluoride toothpaste
Why is distillation expensive?
It requires a lot of energy
What are the arguments against adding chlorine to water?
It can increase certain cancers, it can react with other natural substances in the water to produce toxic-by products which could also cause cancer
