Molecule of the WeekPolystyrene

(Styrofoam)

- A polymer with styrene repeat units (monomers)

C C

HH

H

n C

H

H

C

H

n

Monomer – “one unit”

Polymer – “many units”

A foaming agent, usually CO2, is used to make the Styrofoam form of polystyrene. This material is used for Styrofoam cups, insulation, packing “peanuts.”

Polystyrene is also used for: hard, transparent CD cases, plastic cutlery, some food packaging.

TODAY- How does water dissolve different

substances?- Electrolytes in water - Monitoring contaminants in water

- Legislation and limits- Being an informed consumer- How are contaminants detected?

- Treatment of municipal water supplies- Treating your own water at home

5.8

Substances that will dissociate into ions in an aqueous solution are called electrolytes.

Dissolution (dissolving) of NaCl in Water

The polar water molecules stabilize the ions as they break apart (dissociate).

Ions are simply charged particles-atoms or groups of atoms.

They may be positively charged – cations,

Or negatively charged- anions.

The electrostatic attraction between cations and anions in an ionic compound is an ionic bond or just an ionic attraction.

Notice: the # of protons doesn’t change! It’s the # of electrons that changes when ions are formed.

Hydrogen bonding with covalent molecules

Water dissolving ethanol

d -

d +d + d -

d +

Sucrose (sugar)

d + d -The many polar O-H groups on a sucrose molecule make it readily soluble in water.

H OH

(how does water dissolve a compound that isn’t ionic and doesn’t have ions?)

Nonpolar compounds with waterOils are hydrocarbons.

Hydrocarbons are nonpolar molecules.

Nonpolar molecules have nothing for water to be attracted to, i.e., no d+ or d- (no poles) and no ions.

Like dissolves like.

Typically, water will dissolve compounds that are either polar

like it is, or ionic.

How Soap Works

Soap molecules are able to mix with both grease/oil and water. How does that happen?

Soap molecules have both:

- an ionic part that is attracted to water

- a nonpolar part that is attracted to grease/oil

O

Ionic part- notice the ions

Long, nonpolar hydrocarbon part

5.12

A pipe with hard-water scale build up

Hard water contains high concentrations of dissolved calcium and magnesium ions.

Soft water contains few of these dissolved ions.

Only water that contains dissolved ions will conduct electricity. Pure water DOES NOT conduct electricity!

Testing Conductivity in Water

If electrolytes are present in solution, the solution will conduct electricity. This means that if none of the compounds in the solution are ionic, the solution WILL NOT conduct electricity.

5.7

When ions (charged particles) are in aqueous solutions, the solutions are able to conduct electricity.

(a) Pure distilled water (non-conducting): a nonelectrolyte

(b) Sugar dissolved in water (non-conducting): a nonelectrolyte

(c) NaCl dissolved in water (conducting): an electrolyte

Safe Drinking Water Act (SDWA)Where does your municipal drinking water come from? Is there anything harmful in it?

http://www.epa.gov/enviro/html/sdwis/sdwis_query.html

Visit the EPA’s Safe Drinking Water Information System at:

The Safe Drinking Water Act, established in 1974, aims to protect the health of people serviced by municipal drinking water. The EPA carries out the mandates of the SDWA by setting contaminant limits and coordinating the monitoring of municipal water systems.

The Clean Water Act, passed in 1972, regulates the pollution of surface waters (from industries and ships, for example).

Contaminants in Drinking Water

MCLG = Maximum Contaminant Level Goal; the goal is zero ppm for carcinogens (compounds known to cause cancer).

MCL = Maximum Contaminant Level; the legal limit for a contaminant; set by the EPA

Detection of Contaminants by Gas Chromatography

Flowing gas stream in

Sample containing THMs injected

A sample chromatogram

Exit

Gas Chromatography (GC)- Sample for testing is mixed with a solvent to make a sample solution.

- Sample solution is injected into a gas chromatograph. The solution is immediately vaporized (becomes a gas), and travels into a long, coiled tube called a column. An inert gas, usually helium, is used to move the vaporized sample through the column. This gas is called the mobile phase.

- The column contains a material that is fixed to its inner walls, called the stationary phase.

- The compounds in the sample have varied degrees of attraction for the stationary phase. Those that are more attracted to it take longer to move the whole way through the column.

Gas Chromatography- continued

-GC is also used for:• detecting trace amounts of drug metabolites in urine or saliva • contaminants in soil• alcohol content in blood• contaminants in pharmaceutical products• flavor and fragrance compounds in food and personal care products

- The detector sends the signal to a computer that generates a chromatogram.

- As compounds exit the column, their presence is noted by a detector.

Treatment of Municipal Water Supplies

1) Filter out large items

2) Remove suspended clay and dirt particles using aluminum hydroxide. This process is called flocculation. The globby gel that forms is called floc.

3) Filter through sand and gravel

4) Disinfect- Chlorine (chlorination); a residual amount remains- Ozone (ozonation)- UV light treatment

5) Possibly adjust the pH of the water by adding calcium oxide (lime)

6) Possibly treat with fluoride.

Fig05.28

Typical municipal water treatment facility