Unit 1 Notes Section D

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Unit 1 NotesSection D

• p. 90 - 105

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D.4 Chlorination of Water

• 1. Why do we add chlorine to water?
• The chlorine with kill disease-causing organisms
• 2. How does chlorination occur by using chlorine
  gas?
• The gas is bubbled through the water. It reacts
  with the water to produce a water-soluble
  compound removing impurities.

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3. How does chlorination occur by using sodium
hypochlorite?

• The sodium hypochlorite (NaOCl), an ingredient in
  bleach, is added to the water.
• In the water, it releases free chlorine that will
  kill micro-organisms.

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4. How does chlorination occur by using calcium
hypochlorite?

• The compound is dissolved in water.
• It is a powder or pellet and is often used in
  swimming pools.
• Will also release free chlorine when dissovled.

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5. What are THMs? Give an example.

• THM stands for trihalomethanes.
• These are carcinogenic compounds that are formed
  sometimes when chlorine to water.
• Example chloroform
• EPA standard is only 80ppm or less.

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Section D.5 Chlorination and THMs

• 1. Describe the 3 ways that municipal plants can
  deal with risks associated with THMs.
• Pass water through activated charcoal filter to
  remove organic compounds.
• Disadvantage filters are expensive, disposal is
  a problem, filters need frequent replacing.

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2nd option

• Use ozone or UV light to disinfect water.
• Disadvantage only works while at the plant, once
  water leaves it can be contaminated again.
• Also, ozone can be dangerous if not handled
  carefully

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3rd option

• Eliminate pre-chlorination.
• Only add chlorine after filtering the water.
• Disadvantage still some risk of producing THMs
  (but not as much). Also, might allow more growth
  of bacteria.

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Section D.6 Bottled vs. Tap water

• 1. Name some sources of bottled water.
• Natural sources springs
• Bottling plant
• 2. Do questions 1 2, p.92.

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D.7 Water Softening p.92

• 1. What is hard water?
• Water that contains dissolved minerals such as
  calcium, magnesium or iron
• 2.Where do these minerals come from?
• Are dissolved from rocks/minerals as the water
  passes through the ground.
• Limestone, chalk, dolomite, gypsum

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3. What levels of CaCO3 are in the water where we
live?

• Use figure 1.56 on p.93
• 180-240
• ppm

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4. What are 3 ways you can soften your water?

• 1. sand filtration
• 2. treatment with Calgon
• 3. treatment with an ion-exchange resin

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5. Describe how Calgon an soften your water.

• Calgon will remove hard water cations such as
  calcium by forming larger anions.
• These anions bind to the Ca cations and make them
  insoluble in water.
• The insoluble compound precipitates out of the
  solution and are rinsed away with the dirty water.

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6. Describe how the ion-exchange process works.

• Hard water is passed through an ion-exchange
  resin.
• Resin is made of tiny beads that attract and bind
  Ca cations.
• Soft water ions are released into the water
  (exchanged)
• System must be re-charged periodically.