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Testing Water &
Soil
Experiment #9: Tap Water Testing
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The water we use at home is probably one of the most important
safety concerns we face. It's unfortunate, that polluted water can look
the same as pure water. Cloudy or muddy water may just contain harmless
sediment. (This image is from an article that talked about high levels
of arsenic in a town's drinking water)
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Your kit has all items needed for this
experiment.
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#1 &2: You will be using the plastic pipettes
and the 10milliliter graduated cylinder. These are in the pockets in the
lid of your kit.
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#3. You will be using the small 50 mL beaker for
holding the tap water.
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#4: You will be using
six of the test tubes that have test papers in them. They will be pH paper
4.5-7.0, pH paper 6.5-10, Hardness, Chlorine, Nitrate/nitrite, and later
Alkalinity. |
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#5: You will be using the Color Chart for Test
Papers and Test Strips.
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INSTRUCTIONS FOR EXPERIMENT
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Fill the small 50mL beaker to abou 40 mL.
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Get these test papers to test
the pH (acidity) of the tap water. Tap water is probably close to being
neutral (pH 7), so we will use the two test papers that include pH 7 in
their range. pH 4.0-7.0 will be good if the water is somewhat acidic. pH6.5-10
will be good if the water is very slightly acidic to somewhat alkaline. |
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Let's say we start off with the pH 6.5-10 paper. Dip the
paper into the beaker with the tap water for just a couple of seconds.
Then take it to the chart.
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For my water, it looks like the pH is between 6.8 and
7.1. So it's looks pretty much neutral. We can now try the other test
paper (pH 4.0-7.0) for confirmation.
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This is the pH paper for the 4.0-7.0 range. Dip in the
tap water for a couple of seconds and take it to the chart.
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The 4.0-7.0 pH paper turns dark
blue which indicates that it was close to the 7.0 pH reading. So it appears
that the two different pH test papers both point to a pH close to the neutral
pH of 7. This is usual for tap water unless there is something wrong with
the water supply. (Write
down your best estimate of the pH of your water) |
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Let's now do
the Nitrate/Nitrite and Chlorine tests. I want to save the Hardness and
Alkalinity tests for last. |
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Chlorine is
heavily used by water treatment plants to sterilize the water. Usually some
chlorine stays in the water so that the antimicrobial benefits of chlorine
is present in the water all the way to people's homes. |
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Take the chlorine
test strip and "swirl" it in the water 3 times. Swirling allows
it to contact more of the chlorine that may be in the water. Then take it
to the chart. Once you pull it out of the water, you are suppose to read
it at 10 seconds. My water shows that it has very little chlorine in it.
I'd feel a little more comfortable if it had maybe 0.5 to 3 parts per million
(ppm) chlorine. (Write down your best estimate
of the chlorine level in your water) |
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Nitrates and
nitrites can get into the water supply from contamination from sewers, cattle
yards, and agriculture fertilizers. For babies, this can be deadly. Babies'
stomachs are less acid than normal allowing bacteria in the stomach to convert
nitrate (NO3) into nitrite (NO2).
Nitrite gets into the blood system and prevents the hemoglobin in red blood
cells from absorbing oxygen. This results in the "blue" baby syndrome. |
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Now take the
Nitrate/Nitrite test paper and dip it in your tap water for 2 seconds. Take
it over to your chart and wait one minute before reading it. Hopefully,
there won't be much nitrate or nitrite levels. |
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Since there
are no pink or red colors on the test strips, I would say that thankfully
my tap water has no nitrate or nitrite. (Write
down your best estimate of the nitrate and nitrite levels in your water) |
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HARDNESS:
I saved Hardness and Alkalinity last because I know Mesa water, like Phoenix
water is very hard. By hardness they
mean that there's a lot of calcium and magnesium
dissolved in the water. When hard water dries, you see a lot of salts left
behind. When it dries on a window, it's all spotted. The salts are mostly
calcium carbonate (chalk), calcium chloride (deicing salt), and sodium chloride
(french-fries salt). |
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ALKALINITY:
The pH scale has 2 sides, acid and alkaline. The acid
side (below pH 7) has a higher concentration of hydrogen ions (H+). The
alkaline side has more hydroxide ions (OH-). When H+ and OH- are equal,
they create H2O (water) and is neutral. Alkalinity
in water testing has a more specific meaning. It measures how much the water
will resist becoming acidic. It resists this
by having dissolved carbonates. One carbonate is calcium carbonate (CaCO3),
which is chalk, another is washing soda (Na2CO3).
If a acid (H+) comes in contact with a carbonate, the carbonate absorbs
the acid by becoming bicarbonate (HCO3). Therefore
water with higher alkalinity can resist becoming acidic due to acid rain
or acid contamination. |
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Take the hardness test paper and dip in tap water. Remove
immediately and wait 15 seconds to read the value on the chart.
Warning: I've noticed that the alkalinity test strips
have changed color since they were packaged. There must be something in
the package label paper that has altered the test strip. So until you
receive new test strips, skip the test for alkalinity.
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This is the
result of the hardness test. The hue seems to match the 180 ppm, but the
water makes it brighter. The hardness might be over 180 but we don't know
because 180 is the highest level shown. One way around this is to dilute
the tap water with pure water. |
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Use the plastic
pipette and transfer the tap water to the smaller 10mL graduated cylinder.
You will only transfer 2 millilters. |
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The graduated
cylinder will get filled to the 2 mL mark with the tap water. You will now
use your Purified Water to bring the water up to the 6 mL mark. This will
make the hardness of the water three times less. Perhaps, the reading will
show up lower on the chart. |
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When you add
the purified water to the graduated cylinder, it's a good idea to hold it
up to eye level to see the water level more accurately. Again, fill the
graduated cylinder up to the 6 mL mark using your purified water.
 (Take a picture
of yourself at this point in the lab.) |
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We will want
to use the small beaker to hold our diluted tap water that's in the graduation
cylinder. So pour out the tap water (it's easy to get more of that). |
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Dry the beaker. |
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Pour the tap
water that has been diluted with pure water into the clean 50mL beaker. |
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Dip another
Hardness test strip into the diluted tap water quickly and take over to
the chart. At 15 seconds after dipping, check the colors. |
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The color of
the test strip has definitely changed after the tap water was diluted with
pure water. But I have to admit, it's a little hard to read. The hue of
the test strip seems to be between the 60 and 120 ppm levels. The water
on the strip makes it brighter than the colors on the chart, but the hue
(tint) can be compared. The 180 ppm is a bit more purplish than the test
strip and the 30 ppm is more turquoise than the test strip. So I would say
the hardness is between 60 and 120. Now since the tap water had been diluted
to three times its original volume (2 mL to 6 mL), the readings we get now
are 3 times less than they should be. So the calculated hardness is between
3x60 (180 ppm) and 3x120 (360 ppm). When using other brands of test kits,
I have seen the hardness around 360 ppm. (So do
your best estimate from the chart and then multiply by three and record
it.) |
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With hardness
this high, there will always be problems with salt (also called mineral/scale)
build up on faucets, showers, windows, and dishes. It isn't unhealthy because
hardness is mostly due to calcium, which is good for your teeth and bones.
It's just not good for cleaning. Here you see some of the cleaning products
I use because of the hard water. Lime-A-Way is made of phosphoric acid which
dissolves the calcium carbonate residue. Scrubbing Bubbles dissolves the
soap scum that calcium causes when mixed with soap. The two smaller bottles
are for the dishwasher. They contain phosphates which capture calcium ions
and keep them from combining with the detergent or forming calcium carbonate
(scale) |
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A water softener
helps, but as a later experiment shows, you still have the same amount of
dissolved salts. The calcium gets replaced by sodium, which works better
with soaps and doesn't form scale that is hard to wash away. The sodium,
however, is not that healthy to drink. So I use my water softener for a
week or two and then turn it off for a week or two. |
| For now we will hold off on the alkalinity
tests until new alkalinity strips have been delivered. |
| Be sure to clean up your graduated cylinder
and beaker with distilled water. |
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Email the results
you got to me along with the one picture.
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