please read the material underneath is not clear to me how toaproach this am not a chem major so its kind of hard. thanks forthe help
In Part I, when the solution containing aluminum and sodiumhydroxide is heated under the hood, why should you wait until the“fizzing†stops?
In Part I, item #8, what is the purpose of the centrifuge?
To speed the process of settling thealuminum hydroxide gel.
Would it be safe for you to drink the water from today’sexperiment?
Why or Why not?
CLARIFICATION OFWATER
One of the steps that must beperformed on water to make it suitable for drinking is that anysuspended solid material must be removed from the water. Suspendedsolids are materials such as very fine dirt particles that arecarried along by, but not truly dissolved in the water. One way toremove suspended particles is to use a type of chemical called aflocculant that combines with the suspended solids to form a massor floc that is solid enough to be filtered out of the water. Watertreatment plants use several different flocculants to removesuspended solids. In this experiment, you will prepare onef1occulant, aluminum hydroxide [Al(OH) 3] from aluminummetal and then use the aluminum hydroxide to clarify (remove thesuspended solids from) some dirty water. Taking used aluminum cansand preparing aluminum hydroxide from them is one possible use forthe old cans, but turning the cans into new aluminum cans is a moreeconomical way to recycle the aluminum.
The reactions involved in thisexperiment are:
Dissolving aluminum metal with sodium hydroxide solution:
Al +     2 Na+       +     2 OH-    +   6 H2O→   2 Na+   +  2Al(OH)4-         +      3 H2 (g)
Converting the aluminum ion into aluminum sulfate (aluminum andsulfate ions in solution):
Al(OH)4- +     4H2SO4        →      2Al3+    +    4SO42-     +   8 H2O
Converting the aluminum sulfate solution into solid aluminumhydroxide:
Al3+ +   6 OH-     →      2 Al(OH)3 (s)
The hydroxide ions used in step 3come from the reaction of sodium hydrogen carbonate (also known assodium bicarbonate or baking soda) when it is dissolved inwater:
                               NaHCO3 (s) +          H2O →  Na+   +   OH-  +    CO2(g)  +    H2O
Another type of material thatsometimes must be removed from water before it can be used fordrinking is a dissolved chemical. If the dissolved molecules arelarge enough, they can be removed by passing the water over a formof carbon called activated charcoal. Activated charcoal has a verylarge surface area and this surface is able to latch onto (absorb)certain dissolved materials and hold onto them. The charcoal, alongwith the chemicals it has caught, can, then be filtered out of thewater. After the charcoal has been filtered from the water, it canbe made ready to be used again by heating it with steam (500- 1000°C). This causes the charcoal to release the absorbed chemicalsleave clean charcoal that can be used again.
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PROCEDURE:
PREPARATION AND USE OF ALUMINUM HYDROXIDE
Weigh out 0.20 g of aluminum foil and put it into a 250 mLbeaker.
Measure out 15 mL of 6 M sodium hydroxide (NaOH) solution andpour it over the aluminum foil in the beaker. Make sure that thefoil is completely covered by the solution.
Put the beaker on a hot plate in the fume hood and GENTLY heatthe mixture. Do not boil. Stir the mixture to keep it from foamingover.
Continue warming the solution until most of the fizzing stops(about five minutes). Remove the beaker from the hot plate andallow it to cool.
Add 20 mL of 3 M sulfuric acid (H2S04) to the beakerand stir the mixture well to dissolve as much of the gel-likematerial as possible.
Suction filter the mixture using a Büchner funnel as yourinstructor will demonstrate. Be sure that the filter paper liesflat on the bottom of the Büchner funnel. Wet the filter paperslightly with deionized water to help flatten the filter paper.Take the filtrate (the liquid that went through the filter paperinto the flask) and pour it into a 150 mL beaker.
Add 10 mL of the filtrate to 10 mL of the dirty water providedin a 100 mL beaker. Add solid sodium hydrogen carbonate slowly,with stirring; until the liquid is basic to litmus. Stir well andpour some of the slurry into a centrifuge tube and label it tube\"1.\"
The aluminum hydroxide gel will settle out over time with itstrapped \"dirt,\" but we can speed up the process by using acentrifuge. Using untreated dirty water, fill a second centrifugetest tube (tube \"2\") to the same level as tube \"1.\" Put the tubesin the centrifuge on opposite sides and centrifuge them for twominutes.
Decant the liquid from the centrifuge tubes intospectrophotometer tubes labeled “1†and “2â€. Fill a thirdspectrophotometer test tube (tube \"3\") with untreated dirty waterto the same height as the other two tubes. Compare the absorbanceat 500 nm of each solution using a spectrophotometer. Record theresults on the lab report form.
Put the waste from this part of theexperiment into the waste beaker provided.
USE OF ACTIVATED CHARCOAL
Take two Erlenmeyer flasks of the same size and add 50 mL ofdeionized water to each flask. Add five drops of methylene blue dyesolution to each flask.
Add about 0.5 g of activated charcoal to one of the flasks.Swirl the flask to mix the water and charcoal well.
Filter the charcoal from the water using the suction filtrationmethod used earlier and compare the appearance of the treated waterwith the untreated water that still has methylene blue in it.Record the results on the lab report form.
The liquid waste from this part ofthe experiment can be rinsed down the drain.
