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minor address change
Support Document
2008 Chemistry Year 11 Term 2 SA
12.30-2.30pm
Wed 11th June
ppm = parts per million
this means mg per L, for example if a solution
has a concentration = 1g per L this is the same
as 1000ppm
Fresh water - less than 1,000 ppm
Slightly saline water - From 1,000 ppm to 3,000 ppm
Moderately saline water - From 3,000 ppm to 10,000 ppm
Highly saline water - From 10,000 ppm to 35,000 ppm
Bring along a calculator, your research (1 page) and a (1 page) partly
completed lab report (this can include all the procedure and your raw
titration results.
Part A - Stimulus: Research and Data collected for SA. 1 page typed text for
introduction I page for materials, methods and results.
Water quality is highly variable, and for any task an appropriate grade of water must be chosen. For example, tap
water is fine for washing dishes. It is not recommended for making solutions because the quality of such water is
unknown. Tap water typically contains sediments (suspended particles), metal and other ions, deliberately added
chemicals such as chlorine or fluoride, and/or traces of organic solvents. Although tap water is generally safe for
drinking and other personal uses, materials in tap water can be toxic to some cells or may interfere with assays or
biochemical reactions. It is recommended that glassware that has been washed and rinsed in tap water be thoroughly
rinsed with a higher quality water.
Distilled water, obtained from the condensation of steam, is of better quality because distillation eliminates all of the
sediment and most of the inorganic solutes. Organic contaminants and some of the inorganic contaminants remain.
Deionized water is produced by running tap water through a resin cartridge or series of them. A home deionizing
system might simply replace divalent cations with sodium ions, producing what is commonly known as “soft” water.
Laboratory deionized water is usually treated so as to remove both cations and anions, which are exchanged for
hydrogen and hydroxyl ions respectively. Deionized water is often of better quality than distilled water although on the
downside, the resins used in the cartridges may release organic contaminants into the water.
The highest grade of water is called 18 megohm water. Eighteen megohms is 18 million ohms, which are units
representing resistance to the flow of electricity. Eighteen meghoms is more than a million times the electrical
resistance of a typical household electric circuit. Very pure water does not conduct electricity well compared with
contaminated water because it contains no inorganic ions with which to carry electric current. Eighteen megohm water
is usually produced in multiple steps, including reverse osmosis and the passage of product through ion exchange
resins, activated carbon beds and filters.
Pure water is somewhat acidic, with pH close to 5. It is also what we call an aggressive reagent, meaning that it will
leech ions from plastic or glass containers. It does so because of the polar nature of water molecules. Ions dissolve
most readily in 18 megohm water because the system (water plus dissolved ions) is more stable than when pure water
is separated from soluble materials. Because very pure water accumulates contaminants during storage, it should be
freshly prepared. The use of plastic tubing, funnels, and especially metal containers, should be avoided.
http://www.ruf.rice.edu/~bioslabs/methods/solutions/water.html
carbon adsorption
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Adsorb/adsorb.htm
http://www.cee.vt.edu/ewr/environmental/teach/wtprimer/carbon/sketcarb.html#Adsorp
http://www.lenntech.com/deionised-demineralisedwater.htm
http://www.culliganmiami.com/pf5.html
WOW useful!
About deionizer resins
http://www.youtube.com/watch?v=UHYWIM8AbPE
watch at home!
http://www.geocities.com/setseng2004/ConductivityandSalinityofAqueousSolution.pdf
testing water quality by conductivity
Desalination + recycling in QLD
http://www.google.com.au/search?hl=en&q=recyling+water+Queensland&meta=cr%3DcountryAU
http://www.google.com.au/search?hl=en&q=desalination+Queensland&meta=cr%3DcountryAU
Salt titration
AgNO3 + NaCl ---------> AgCl + NaNO3
When all the salt
has been used up,
AgCl can no longer
form
2AgNO3 + K2CrO4 --------> 2KNO3 + Ag2CrO4(s)
K2CrO4 acts as the indicator
The first drop of excess AgNO3 reacts with the
chromate solution and it forms the red ppt
A typical calculation
AgNO3 + NaCl ---------> AgCl + NaNO3
1
:
1
M NaCl = 58.5g
0.1M / 26.07mL
25.00mL of C
C = 0.1042M
= 2.607 x 10-3 mole
25.00mL of salt
contains = 2.607 x 10-3 mole
mass of NaCl per L?
0.1042 x 58.5g = 6.0957g
or 6096mg per L this solution should fit
into the moderate range
Please collaborate (share ideas) and links etc
Please test yourself by answering the SA at home
the written section is two hours!
Check your calculation, and buy new calculator
batteries!