End Of Unit Questions Flashcards
What is produced when temporary hard water is heated?
Scale (insoluble salts of calcium and magnesium carbonates)
Give one advantage of drinking hard water
- stronger teeth or bones
* reduced risk of heart attacks
Explain the difference between temporary and permanent hard water
Temporary hard water is softened by boiling it, permanent hard water is not softened or does not produce scale when heated
How does washing soda soften hard water?
Washing soda is sodium carbonate, which is soluble. Calcium or magnesium ions react with carbonate ions to produce precipitates/insoluble calcium carbonate/magnesium carbonate, thus removing the ions so they cannot react with soap
Give one disadvantage of using a sodium ion exchange resin to soften hard water
Replaces calcium ions with sodium ions that can have negative health effects
What type of substance is removed from water at a treatment works by filtration?
Insoluble solids
Why is chlorine used in water treatment?
To kill bacteria in the water
Why is it not necessary to distil water used for drinking?
No need for drinking water to be pure, just free from harmful chemicals
Why are fluorides added to drinking water?
To reduce amount of tooth decay
Explain what happens when temporary hard water is boiled. Include two balanced symbol equations in your answer
Hydrogen carbonate ions decompose when heated to produce carbonate ions, water and carbon dioxide
2HCO3-(aq) –> CO2 3-(aq) + H2O(l) + CO2(g)
Carbonate ions react with calcium and magnesium ions in the water to produce precipitates of calcium or magnesium carbonate that are deposited as scale
Ca2+(aq) + CO3 2-(aq) –> CaCO3(s)
(Same for magnesium)
Why does hard water produce scum?
Soap reacts with calcium or magnesium ions to produce insoluble salts
