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C3 HardWater

Edexcel C3 Hard Water

What ions are in hard water? Ca+2 and Mg+2
What is the effect of hard water? Produces Scum and Scale
What is Scale? the deposit left behind after boiling the kettle in a hard-water area. It is Calcium Carbonate
What is Scum? The deposit made from soap reacting with the Ca+2 ions
Which type of water creates the most lather with soap: hard or soft water? Soft
What is temporary hardness? Caused by having bicarbonate ions dissolved in water
What is permanent hardness? Caused by having sulfate ions dissolved in water
How can you remove temporary hardness? Simply boiling
How can you remove permanent hardness? Ion exchange
How does ion exchange work? where Ca+2 ion are replacing Na+ on a resin; the Na+ ions are replacing the Ca+2 in water
Why should you treat your water if you live in a hard-water area? Overtime, limescale will build up in washing machine pipes and block them
Why does the water become hard again after having used an ion-exchange resin for a while? All the Na+ions have been replaced on the resin
How do you regenerate the resin? Pass a concentrated brine (NaCl solution) through the resin will force the Ca+2 out of the resin and the resin will carry Na+ ions again
What is the concentration of calcium ions in a sample of water that has: 0.4 g of calcium ions dissolved in 2 dm3 of the water 0.4/2=0.2 gdm−3
What is the concentration of calcium ions in a sample of water that has: 0.25 g of calcium ions dissolved in 5 dm3 of the water? 0.25/5=0.05 gdm−3
A sample of hard water has a concentration of calcium ions of 0.12 g dm-3. What mass of calcium ions would there be in a 200 cm3 glass of the water? 0.12 x 0.2dm3 = 0.024g
What is the formula to work out concentration? concentration ( = mass(g) / volume(dm3)
Created by: UrsulineChem



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