Leeming SHS Yr 11 Chemistry
STAWA Exp 21
Student’s Name:
Date:
Preparation and properties of sulfur dioxide - SO2 (g)
Background
Sulfur dioxide is a poisonous gas with a pungent suffocating odour. It is used as a
preservative in many foods and has gained notoriety as a major contributor to acid
rain in industrial areas.
In this experiment sulfur dioxide will be prepared and its properties investigated.
Because of the poisonous nature of the gas the experiment should be carried out in a
fume cupboard.
Equipment and chemicals
250 mL conical flask with flexible gas
delivery tube fitted into a rubber stopper
3 large test tubes with stoppers
sodium sulfite – Na2SO3 - 2g
3 medium test tube
(to test solutions)
test tube rack
0.1M potassium dichromate solution –
K2Cr2O7 – 5 mL
0.01 M potassium permanganate
solution – KMnO4 – 5mL
0.1 M sodium sulfide solution – Na2S 5 mL
red and blue litmus paper
hot plate
retort stand and clamp
(to stabilize the reaction flask)
wax taper (or wooden splint)
2 M sulfuric acid – H2SO4 - 25 mL
Safety
• Sulfur dioxide is a poisonous gas that must be handled with care.
• Avoid inhaling the sulfur dioxide gas.
• Prepare and test sulfur dioxide gas in the fume cupboard.
International safety card information
sodium sulfite - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc12/icsc1200.htm
sulfuric acid - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc03/icsc0362.htm
potassium dichromate - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc13/icsc1371.htm
potassium permanganate - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc04/icsc0414.htm
sodium sulfide – http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc10/icsc1047.htm
sulfur dioxide - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0074.htm
harmful – KMnO4
STAWA21.DOC
H2SO4 , Na2S ,
KMnO4
Adapted from STAWA Exp 21
K2Cr2O7 , Na2S
SO2 K2Cr2O7
KMnO4
Page 1
Leeming SHS Yr 11 Chemistry
STAWA Exp 21
Procedure
Gas production
1.
Set up the gas generating equipment to collect the sulfur dioxide by the
upward displacement of air as shown in the diagram below.
upward displacement of air
(forced out by the denser SO 2 gas)
sulfur
dioxide
2g sodium sulfite
2 M sulfuric acid
Low heat
Hot Plate
2.
Clamp the reaction flask (to prevent accidental spillage)
3.
Place about 2 g of sodium sulfite – Na2SO3 and 2 mol L-1 sulfuric acid – H2SO4
to about 2 cm depth. The reaction should begin. Replace the gas collection
stopper and tubing.
4.
Use a hotplate to gently heat the reaction flask. Collect three test tubes of
sulfur dioxide gas. You can tell when the test tube is full by holding a piece of
moist blue litmus paper at the mouth. It turns red when the test tube is full.
Stopper each test tube and place in a test tube rack.
STAWA21.DOC
Adapted from STAWA Exp 21
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Leeming SHS Yr 11 Chemistry
STAWA Exp 21
Gas testing
5.
Continue to heat the reaction flask gently and pass some sulfur dioxide gas
into about 3 mL of 0.1 mol L-1 potassium dichromate solution – K2Cr2O7 .
Watch closely to prevent the solution being sucked back into the reaction flask
accidentally. Record you observations.
6.
In the same way pass some sulfur dioxide gas through 0.01 mol L-1 potassium
permanganate KMnO4 solution.
7.
In the same way pass some sulfur dioxide gas through 0.1 mol L-1 sodium
sulfide solution – Na2S.
8.
After the reaction flask has cooled down, flush the spent chemicals down the
sink and carefully wash it out with plenty of water.
9.
Use the first test tube of SO2 to observe its colour and carefully detect its
odour.
10.
Into the second test tube of SO2, place a lighted wax taper (or wooden splint).
11.
Remove the stopper from the third test tube, quickly add 1 mL of water and
replace the stopper. Shake the test tube, remove the stopper and add small
pieces of red and blue litmus paper. Record your observations.
12.
Dispose of used chemicals into waste bottles provided and clean the work
area for the next group.
Data Sheet
SO2 - Sulfur dioxide gas
observations
colour
odour
density
litmus paper
burning wax taper test
SO2 (g) + K2Cr2O7 (aq)
SO2 (g) + KMnO4 (aq)
SO2 (g) + Na2S (aq)
STAWA21.DOC
Adapted from STAWA Exp 21
Page 3
Leeming SHS Yr 11 Chemistry
STAWA Exp 21
Processing of Results
1.
Write a balanced equation for the preparation of sulfur dioxide - SO2
2.
List the following physical properties of sulfur dioxide – SO2
•
colour
•
odour
•
density
•
solubility in water
•
acidic or alkaline property
•
From your observations, what can you say about the solubility of sulfur dioxide
in water?
•
Write an equation to show the reaction that takes place when sulfur dioxide
dissolves in water.
3.
STAWA21.DOC
Adapted from STAWA Exp 21
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Leeming SHS Yr 11 Chemistry
STAWA Exp 21
4.
Could sulfur dioxide - SO2 gas be collected using the downward
displacement of water method? Explain.
5.
Does SO2 support combustion?
6.
Write equations for the reactions of SO2 (g) with –
•
Cr2O7 2- (aq)
•
MnO4- (aq)
•
S2- (aq)
STAWA21.DOC
Adapted from STAWA Exp 21
Page 5