Water Flashcards
What two elements makes up the compound water?
Hydrogen and oxygen
Why is it difficult to find pure water?
Water is an excellent solvent
Give six properties of water
Freezing point 0°C Boiling point 100°C Excellent solvent Colourless and odourless liquid Turns copper sulphate from white to blue Turns cobalt chloride paper from blue to pink
Name four stages in the water cycle
Evaporation
Condensation
Precipitation
Run down back to the sea after relief rainfall
What are typhoid and cholera
Diseases resulting from untreated water
Name the five stages of water treatment
Screening Settling Filtration Chlorination Fluoridation
Give a rhyme to remeber the five stages of screening
Silly Shane Follows Chelsea Football
Explain what happens during screening
Passing water through a wire/screen to remove floating material from water
Explain what happens during settling
Aluminium sulphate is added and gathers smaller insoluble solids to the bottom of the tank
Explain what happens during filtration
Water passes through sand to remove remaining insoluble particles
Explain what happens during chlorination
Chlorine is added and kills any bacteria present
Explain what happens during fluoridation
Fluorine is added (only in certain countries) to prevent tooth decay from drinking water
Explain electrolysis
The splitting up of a compound by passing electricity through it
What is the tubing used for electrolysis called
Hoffman Voltameter
How much oxygen compared to hydrogen is produced when water is split
H2O releases 2 hydrogen atoms for every oxygen atom so there is twice as much hydrogen
Give the chemical formula for the splitting of water
2H20 —–> 2H2+O2
Why do water pipes burst in the cold
Water expands after it is cooled past 4°C
Explain miniscus
Curved surface of a liquid when in an object or vessel
Explain desalination
Process where water is obtained from sea water
Why would soap be added to water
For washing, to help it to dissolve tougher substances such as grease and oil
Explain hard water
Water that does not lather easily with soap
Explain soft water
Water that lathers easily with soap
Give a word equation for the forming of scum
Calcium ions + soap = scum
What causes water hardness?
Caused by presence of magnesium and calcium ions in the water
Explain how limescale forms
When hard water is heated it deposits white insoluble solid called limescale on pipes
Three ways which water can be softened
Ion exchange
Distillation
Boiling
Give the advantages to hard water
Good source of calcium
Most people prefer the taste
Good for brewing/tanning
Disadvantages to hard water
Limescale blocks pipes of ex. Kettle
Wastes soap
Produces scum with soap.
