Chemistry

Purifying Water



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INTRODUCTION

Water purification is an important technology. It has applications around the globe, for every person needs and deserves clean water to drink, be it on a camping excursion, recovering from a natural disaster, or simple daily living.

There are many ways by which water can be purified. Some are available in pocket-sized kits while others can require factory-sized housing. Some methods you can afford on a weekly allowance while others may require an investment of thousands or even millions of dollars.

This project offers you the opportunity to experiment to discover which techniques are most effective at purifying water, and to do some background research into cost and implementation on a practical scale.

THEORY

There are numerous ways to purify water, and they achieve varying degrees of purity. Before you can discuss purification, you need to understand the various contaminants that may be present in water.

1. Particles

Sand, mud, gold dust, rust - chances are that you really don't want to be drinking any of this. Some particulate material may be toxic, some abrasive, and all of it is certainly gritty and unpleasant. One aspect of water purification is to remove particles.

2. Microorganisms

Water and life go together, and that includes bacterial life. Not all microorganisms will make you sick, but there are plenty that will, and if your purification technique doesn't yield sterile - bacteria-free water, then you might be faced with any number of diseases, or even diarrhea and death.

3. Salts and other dissolved chemicals

Water is sometimes called the "universal solvent". While it doesn't actually dissolve everything (thank goodness), it sure can pick up a lot. Salt in particular is a concern, since most of the Earth's water contains salt. A person can't drink too much salt water without getting severely dehydrated - not to mention that salt water just doesn't taste very good.

Other chemicals (like pesticides and fertilizers) can also be dissolved in a water supply. Acids and bases may even be present, changing the pH of the water enough to be harmful. All such chemicals need to be removed before consumption.

4. Other contaminants

If you can imagine it, it's gotten into the water somewhere. Oil spills, radioactive fallout, smelly feet...and that's just for starters.

To remove the different contaminants, many different techniques can be employed. There is simple filtration, of course, which traps and removes anything larger than the pores of the filter. There is reverse osmosis, which uses pressure to force water through a membrane while leaving behind many dissolved impurities.

There is forward osmosis as well, which uses a membrane but draws the water through in order to dissolve a mixture akin to an instant sports drink. There is distillation, a chemistry classic that leaves anything non-volatile behind.

There are chemical techniques that kill microorganisms or precipitate toxic impurities. Boiling is another route that kills microorganisms. This is hardly a comprehensive list, but it is enough to get you started.

MATERIALS

Your first step will be to choose which purification techniques you want to test. You'll want to look at both cost and safety. Your local outdoor sporting goods store will likely have a selection of water purification gear available. If not, a similar online sporting goods store like www.rei.com will have a wide selection of gadgets and tablets.

Consider other options as well, anything ranging from as simple a method as a bandana or the addition of a little bleach to full blown distillation in the chemistry lab - or your kitchen if you're creative, and have your Mom's permission. (It can be done, but won't be very efficient.)

Once you have your line-up of purifiers, you're ready to get to work. Here's a mix of materials for you to round up.

* Distilled water - buy it buy the gallon at the grocery store for less than a dollar.

* Sports drink - Gatorade or similar - you can buy it pre-made or make it from a powder yourself.

* A mix of sand, dirt, mud, and other general muck - your back yard should have an ample supply.

* Pond water - or other source of stagnant water that is likely to be rich in microorganisms. If you have an aquarium that you haven't cleaned lately, it might do the trick as well.

* Oil - any type should work, but it's best if you can see it easily when it's mixed with water. Motor oil, corn oil...

* Agar plates, or small clean bowls of tomato soup covered with plastic wrap OR a microscope and slides.

* Test tubes - or other clean, clear, water holding containers.

* Pitchers or buckets for mixing and pouring.

* Spoons, spatulas, or other utensils for mixing with.

* Gloves, apron (or lab coat), and goggles - always be safe.


PROCEDURE

NOTE: Remember to clean your purification equipment between tests, according to directions, so that you don't have any cross-contamination.

#1 The Particulates Test

In a pitcher/bucket, make a mixture of your sand/dirt/mud/muck with distilled water. Divide it into portions - one portion for each of your purification techniques, plus one extra portion that will be your control sample.

Purify each sample using a different purification technique. Collect the "purified" water into a clean test tube (or whatever clear containers you will use for comparison), one for each technique. (Remember to label them!)

Compare the purified water visually to the unfiltered control sample.

Compare the purified water visually to a sample of distilled water.

Record all your observations for later.

#2 The Microorganisms Test

Take your pond water and divide it into portions, again keeping one sample aside for use as the control sample.

Purify each sample using a different purification technique. Collect the "purified" water into a clean test tube (or whatever clear containers you will use for comparison), one for each technique. (Remember to label them!)

If you have a microscope, examine each sample in turn beneath the microscope. Count the number of microorganisms you can see, and note whether they are alive (moving) or dead.

Compare your counts to the control sample, and to a sample of distilled water.

If you are using agar plates or tomato soup, you are going to try to grow your microorganisms. For each sample, take a drop of your purified water and place it in a container of the agar or soup. Cover it and leave it to sit at room temperature undisturbed for a few days. Prepare a separate dish for each sample, and for the control, and for distilled water.

Check the plates daily, but do not disturb them or uncover them. Watch for signs of growth where you placed the drop.

Compare amount and type of growth to the control sample and to distilled water.

Record all your observations for later.

#3 The Dissolved Chemicals Test

Distribute your sports drink into portions; one for each technique plus one control sample.

Purify each sample using a different purification technique. Collect the "purified" water into a clean test tube (or whatever clear containers you will use for comparison), one for each technique. (Remember to label them!)

Compare the color of each purified sample to the control sample.

Compare the color of each purified sample to distilled water.

Now taste them!

Compare the flavor (how fruity? how salty? how sweet?) of each purified sample to the control sample.

Compare the flavor (how fruity? how salty? how sweet?) of each purified sample to distilled water.

Record all your observations for later.

#4 The Oil Test

Oil and water don't mix well, so instead prepare each of your samples separately - one for each purification technique plus one control sample. Measure out your samples so that you have one part oil to ten parts water. (You can use any ratio you like, just be consistent.)

Purify each sample using a different purification technique. Collect the "purified" water into a clean test tube (or whatever clear containers you will use for comparison), one for each technique. (Remember to label them!)

Observe the amount of oil left floating on top of each sample.

Compare the amount of oil in each purified sample to the control sample.

Compare the amount of oil in each purified sample to distilled water.

Record all your observations for later.

RESULTS

Now you can compile your data. Using all your observations, make a chart that shows how well each technique worked to remove each impurity. Use this to assess which purification techniques are the best in different situations. To make your results more meaningful, you can also evaluate cost, time, and effort involved in each technique.

To follow up and impress the judges, you can discuss how the better techniques can be used to help people in developing nations who struggle for lack of clean water. Consider especially the initial expense versus the long term expense, and how much water can be purified daily, as it would be needed for whole villages, not simply individuals.

Good luck!


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