Climate in cities

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1. Air Pollution - more

Worksheet 1

Air pollutants from motor vehicle exhausts

This worksheet will help you to find out something about the composition of vehicle exhaust gases and how catalytic converters reduce the emissions of air pollutants from vehicles.

Exhaust gases are dangerous to your health and should not, therefore, be inhaled!

Use a fume hood or work outside.

You will need:

TAKE CARE: Some of the chemicals used in the experiment are harmful. Experiment carefully and use safety equipment!

	concentrated ammonia (25%) [C, N; R: 34-50; S: 26-36/37/39-45-61]
	aqueous solution of silver nitrate, AgNO3 (aq), (ca. 2%)
	aqueous solution of calcium hydroxide, CaOH (aq)
	N, (1-naphthyl)-ethylenediamine dihydrochloride [Xi; R: 36/38; S: 22]
	sulfanilic acid [Xi; R: 36/38-43; S: 2-24-37]
	acetic acid [C; R: 10-35; S: 1/2-23-26-45]
	distilled water

Preparation of the Saltzmann-Solution.

This solution is used to measure nitrous acid (HNO₂).  This is formed when nitrogen oxides react with water. 

Dissolve:
5 g sulfanilic acid
0.050 g N, (1-naphthyl)-ethylenediamine dihydrochloride
50 mL acetic acid
in 800 mL distilled water.
Then make the solution up to 1 litre in volume using distilled water.  In the absence of light and air the solution can be stored for months.

Basic materials needed for each group (you may also need other other materials, it depends on how you plan your experiment!):

3	gas-washing bottles or alternatively: test tubes with lateral tube with offset extension, gas-entry tube (bent glass tube) and suitable plug
2	cuvettes or small, clean test tubes of the same shape
2	glass syringes (with clip)
	retort stands, clamps, sockets
	flexible tube pieces as connectors
	bag for sample collection (see below)
	flexible tube which fits onto the gas-entry-tube and the glass stopcock

1. Preparation and collection of exhaust gas samples in freezer bags

You will need collection bags to collect and transport your exhaust gas samples.  The best bags to use are commercial freezer bags (without a fastener). Before using them as collection bags they have to be modified as follows:

Materials needed for each bag:

1	freezer bag (or a thick airtight and gas-impermeable plastic bag) with a volume of  3 to 10 liters
1	tube (glass, plastic or metal) length: 15-30 cm, diameter: 25- 50 mm
	broad plastic tape
1	rubber stopper (to connect the glass stopcock to the glass tube, see pictures 1-4)
1	glass stopcock (or glass tube with rubber hose and clamp)

Place the glass tube in the middle of the open side of the plastic bag.  Make sure it reaches well into the bag.  Seal the bag by applying tape to the open edges of the bag.  Then wrap these sealed edges around the glass tube and tape again tightly (see pictures 1-3 ).

Attach the glass stop cock to the end of the glass tube using the bored rubber bung.

2. Taking the sample

Try to avoid inhaling the exhaust gases or burning yourself on the exhaust pipe!

You can usually take the sample by removing the stopper, wrapping the end of the glass tube with a piece of cloth, removing all air inside the bag and placing the glass tube tightly at the end of the exhaust pipe (see picture no. 5).  "Flush" the bag once with the exhaust gas before you take the actual sample. As soon as the bag is filled with gas the second time, attach the closed stopper to the glass tube (see picture no. 4).

Take samples from different engine types, as soon as the engine has been switched on and once the engine has reached its operating temperature.

3. Qualitative analysis of exhaust gases (CO, CO2 and NOx) 

T 3	Read the information below . Take a sheet of paper and write down the missing reaction schemes!

Information on the identification methods:

1. Identification of carbon monoxide using an ammoniac solution of silver nitrate:

Properties of carbon monoxide: solubility in water 0.23 g L^-1 (20°C), boiling point: -191°C, reducing agent, highly toxic in concentrations w>5%.
Reaction involved in the identification of the gas:

2. Identification of carbon dioxide with lime water (aqueous solution of calcium hydroxide):

Properties of carbon dioxide: solubility in water 1.78 g L-1 (20°C), sublimes at: -79°C.
Reaction involved in the identification of the gas:

3. Identification of nitrogen oxides with Saltzmann solution:

Properties of nitrogen dioxide: reacts with water yielding HNO₂ and HNO₃, boiling point:21°C, vapour pressure: 1013 hPa at 20°C, highly toxic in concentrations w>1%.
Reaction involved in the identification of the gas:

8. The reaction scheme for nitrous acid identification using the Saltzmann  solution.

Exhaust gases contain substances which can damage your health:

Carry out the experiments in a fume hood or work outside !

T 4

Plan an experimental set-up and procedure which meets the following requirements: Each exhaust gas sample should be simultanuously tested for carbon monoxide, carbon dioxide and nitrogen oxides. The identification should be done in the order in which they do not falsify or interfere with each other.  Take into consideration the different solubilities, reactivities with water and reaction products. A semi-quanitative determination of the concentrations of the pollutants in the different exhaust gases should be made by controlling the volume of the exhaust gases under test.

T 5

Carry out your analysis of the exhaust gas samples and list your results in a table.

About this page:

authors: M. Seesing, M. Tausch - Universität Duisburg-Essen, Duisburg, Germany
last update: 2004-05-24