Hardness of Water
- Created by: Jo Wells
- Created on: 10-04-13 15:10
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- Hardness of water
- hard water makes SCUM and SCALE
- whereas soft water makes a lather
- dissolved calcium & magnesium ions in the water react with the soap to make scum = insoluble
- to get a lather you need to use more soap
- when heated the water forms a scale (mostly calcium carbonate)
- on the inside of kettles, pipes & boilers
- reducing efficiency - can eventually block pipes
- scale is also a bit of a thermal insulator - e.g. a kettle will take longer to boil = less efficient
- on the inside of kettles, pipes & boilers
- hardness is caused Ca2+ & Mg2+ ions
- rain falling on some types of rocks (e.g. limestone, chalk & gypsum) can dissolve some compounds
- like magnesium sulfate (soluble) & calcium sulfate (a bit soluble)
- rain falling on some types of rocks (e.g. limestone, chalk & gypsum) can dissolve some compounds
- Ca2+ ions are good for healthy teeth and bones
- studies have found people who live in hard water areas are at less risk of developing heart disease than those who live in soft water areas
- removing the dissolved Ca2+ & Mg2+ ions makes water soft
- there are 2 kinds of hardness
- temporary
- caused by the hydrogen -carbonate ion (HCO3
- can be removed by boiling
- when heated the calcium hydrogen -carbonate decomposes to form insoluble calcium carbonate
- this is the 'limescale' formed in kettles
- as well as water & CO2
- when heated the calcium hydrogen -carbonate decomposes to form insoluble calcium carbonate
- permanent
- can't be removed by boiling
- both can be softened/ removed by =
- temporary
- caused by the hydrogen -carbonate ion (HCO3
- can be removed by boiling
- when heated the calcium hydrogen -carbonate decomposes to form insoluble calcium carbonate
- this is the 'limescale' formed in kettles
- as well as water & CO2
- when heated the calcium hydrogen -carbonate decomposes to form insoluble calcium carbonate
- both can be softened by adding washing soda (sodium carbonate, Na2CO3)
- the added carbonate ions react with the Ca2+ & Mg2+ ions to make an insoluble precipitate of calcium carbonate & magnesium carbonate
- the Ca2+ Mg2+ are no longer dissolved in the water so they can't make it hard
- the added carbonate ions react with the Ca2+ & Mg2+ ions to make an insoluble precipitate of calcium carbonate & magnesium carbonate
- both can be removed by running water through 'ion exchange columns'
- the columns contain sodium (or hydrogen) ions & they 'exchange' them for Ca or Mg ions in the water running through them
- temporary
- temporary
- there are 2 kinds of hardness
- titration can be used to compare the hardness of water samples
- method =
- 1. fill burette with 50cm3 of soap solution
- 2. put 50cm3 of 1st water sample in a flask
- 3. add 1cm3 of soap solution to flask using burette
- 4. put bung in flask & shake for 10 seconds
- 5. repeat 3 & 4 until a lather is formed
- 6. record how much soap was needed (in cm3)
- 7. repeat 1-6 with other samples
- 8. boil fresh samples of each type of water (10 mins) & repeat 1-7
- 7. repeat 1-6 with other samples
- where the bubbles cover the surface for at least 30 secs
- 6. record how much soap was needed (in cm3)
- 5. repeat 3 & 4 until a lather is formed
- 4. put bung in flask & shake for 10 seconds
- Untitled
- 3. add 1cm3 of soap solution to flask using burette
- 2. put 50cm3 of 1st water sample in a flask
- 1. fill burette with 50cm3 of soap solution
- results
- distilled water has little or no hardness
- should be able to tell whether temporary or permanent hardness
- method =
- hard water makes SCUM and SCALE
- the columns contain sodium (or hydrogen) ions & they 'exchange' them for Ca or Mg ions in the water running through them
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