Water Flashcards
What does hard water contain?
dissolved calcium and magnesium ions
What type of water require little soap to form a lather?
soft
Describe the formation of hard water
water with dissolved CO2 = acidic water
rain water flows over carbonated rocks and reacts with them so compounds from rocks dissolve into water
What is scum?
insoluble precipitate
How does scum form?
dissolved calcium and magnesium ions in hard water react with soap to form scum.
Why is more soap needed to form a lather in hard water?
in order for lather to form all ions must have reacted with soap. Hard water has higher concentration of ions so require more soap
Why are soap less detergents used?
they don’t form scum with hard water so can be used to wash clothes to prevent scum sticking to clothes
What is scale?
insoluble solid
How is scale produced?
when temporary hard water is heated
Why is scale bad?
reduced efficiency of heating element because energy wasted heating up scale
Give positive evaluation points of hard water
calcium ions are good for bones and teeth
calcium ions linked to preventing heart disease
give negative evaluation points of hard water
more soap needed to form lather
produced scale which reduced efficiency
Give two methods of softening hard water
Add sodium carbonate
ion exchange columns
What is washing soda
sodium carbonate
Which types of hardness does adding sodium carbonate soften?
both permanent and temporary
How does adding sodium carbonate softening hard water?
sodium carbonate reacts with calcium ions/magnesium ions to form solid calcium/magnesium carbonate which is insoluble and can’t react with soap.
However these precipitates form lime scale
How do ion exchange columns soften hard water?
cylinder packed with resin beads.
resins beads have sodium or hydrogen ions attached
As hard water passes through column the calcium and magnesium ions swap places with sodium or hydrogen ions.
How can temporary hard water be softened?
heating it.
Temporary hard water contains hydrogencarbonate ions which, when heated, decompose to form carbonate ions, water and CO2.
Carbonate ions react with calcium and magnesium ions in water to form insoluble precipitates (calcium/magnesium carbonate = limescale)
What are the steps involved in treating water to make it safe to drink?
Sedimentation and filtration - remove solids
disinfection - kill microbes
What can chlorine be used for?
kill microbes in drinking water
How can the taste of water be improved?
Water filters.
Contain silver to kill bacteria
Carbon to absorb impurities
Ion exchange resin too often water and remove heavy metal ions
How can pure water be made and what are the drawbacks of it?
distillation:
Heat water so it evaporates
Water vapour passes through tubes
cooled down so condenses back into water
requires large amount of energy to boil water so expensive on large scale
Evaluate adding fluoride to water
+ reduces tooth decay
+ only added in tiny amounts
- unethical
- linked to tooth staining
What happens if ion exchange column runs out of sodium?
add sodium chloride ( dishwasher salt)
