Download Student`s Name: Date : Precipitation and gravimetric analysis of lead

Leeming SHS Yr 11 Chemistry
STAWA Exp 8
Student’s Name:
Date :
Precipitation and gravimetric analysis of lead Iodide
Background
In this experiment, you will obtain quantitative results for the reaction between
lead (II) nitrate and sodium iodide solutions. This reaction produces a bright
yellow precipitate of lead (II) iodide, PbI2.
This experiment is designed as a whole class activity. You will be assigned group
numbers. Each group will use different sets of masses. In each set the mass of
lead (II) nitrate will be the same but sodium iodide masses will be different. The
masses of lead (II) iodide produced will be determined by weighing after drying.
Ultimately, you will individually produce a table with the class results then
calculate the moles of reactants and the precipitated product.
Equipment and chemicals
lead (II) nitrate Pb(NO3)2
sodium iodide (NaI)
2 x glass rods (one fitted
with rubber policeman)
analytical balance
filter funnel
oven set to 70 oC
retort stand and ring
clamp
filter paper (Whatman No 1
- one 12.5 cm piece)
ethanol (5 mL approx)
distilled or reverse
osmosis (RO) water
Safety
• Lead salts are poisonous and must be handled with care.
• Make sure that the lead (II) nitrate does not come into contact with your
skin.
International safety card information
lead (II) nitrate - http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc10/icsc1000.htm
sodium iodide - http://ptcl.chem.ox.ac.uk/MSDS/SO/sodium_iodide.html
STAWA8.DOC
Rob Namestnik
Page 1
Leeming SHS Yr 11 Chemistry
STAWA Exp 8
Procedure
1.
Get your group number from the teacher and write it down here:
2.
Weigh out the amounts of Pb(NO3) and NaI required into separate 100 mL
beakers using the masses designated for your group number on page 3.
3.
Add about 35 mL of RO water to both beakers and stir with a stirring rod to
aid help them dissolve. Do NOT take the rods out. You might have to heat
the solutions on the hotplate to help them dissolve.
4.
Carefully add the lead (II) nitrate solution to the sodium iodide solution.
Rinse the empty beaker 3 times into the sodium iodide beaker with about
5 mL of RO water to make sure all the lead (II) nitrate is transferred.
5.
Stir the mixture and allow it to stand for 5 to 10 minutes. Leave the glass
rod in the beaker.
6.
Weigh a filter paper and record its mass using the analytical balance.
Write the mass on the data sheet on page 3.
7.
Fold the filter paper and place it in a filter funnel supported by a retort
stand and ring clamp. Moisten the filter paper with a few drops of RO
water to help it sit in the funnel.
8.
Carefully filter the solution containing the precipitate, ensuring you make a
quantitative transfer (without spilling a drop) to the filter paper. Use the
glass rod to direct the precipitate into the paper as in the diagram below:
9.
Rinse the walls of the beaker with about 5 mL of RO water and add the
rinsings to the filter paper. If the precipitate adheres (sticks) to the sides of
the beaker, use a glass rod with a “rubber policeman” to scrape the lead
(II) iodide.
Repeat the rinsing procedure with two more 5 mL volumes of distilled
water.
STAWA8.DOC
Rob Namestnik
Page 2
Leeming SHS Yr 11 Chemistry
STAWA Exp 8
10.
After draining, wash the precipitate with about 5 mL of ethanol and allow
this to drain away.
11.
Carefully remove the filter paper and place it in a labelled 100 mL beaker.
12.
Place the beaker in a drying oven at 110 oC and leave it for about one
hour.
13.
Re-weigh the filter paper and precipitate and record the mass.
Enter the mass in the data sheet.
13.
Wash all glassware and place in the drying rack.
14.
Dispose of the precipitate in the bin and wipe your work area bench clean.
Add your weighing results to the table (on the white board or over head
projector)
Return to your seat and begin processing the results.
Data Sheet
Group _______ Mass Pb(NO3)2 __________ Mass NaI ___________
MASS
Analytical Balance
ERROR
Mass of filter paper + PbI2 (s)
±
g
Mass of filter paper
±
g
Mass of PbI2 (s)
±
g
Results Table
Group
Number
1
Mass (g)
Pb(NO3)2
1.66
Mass (g)
NaI
0.75
2
1.66
0.90
3
1.66
1.05
4
1.66
1.20
5
1.66
1.35
6
1.66
1.50
7
1.66
1.65
8
1.66
1.80
9
1.66
1.95
10
1.66
2.10
STAWA8.DOC
Mass (g)
PbI2
Rob Namestnik
Moles
Pb(NO3)2
5.0 x 10-3
Moles
NaI
5.0 x 10-3
Moles
PbI2
Page 3
Leeming SHS Yr 11 Chemistry
STAWA Exp 8
Processing of Results
1.
Write a balanced equation for the reaction.
2.
Calculate the mass of PbI2 produced and enter this into your results table.
Write the other groups’ results into your table.
You may use a computer to produce an MS Excel spreadsheet for Question 3
(Enter formulas to allow the spreadsheet to calculate moles where needed)
3.
Convert the masses given in the table into moles and write them in the
results table.
You may use a computer to produce an MS Excel spreadsheet for Question 4
4.
Plot a graph in which the number of moles of potassium iodide is plotted
along the x-axis and the number of moles of lead (II) iodide is plotted
along the y-axis.
5.
Look at the graph closely and describe the shape.
Why is it this shape?
6.
For group numbers 1 to 5
a)
which reactant is present in excess?
b)
which is the limiting reactant?
(Explain this in terms of the equation)
7.
For groups 7 to 10
a)
which reactant is present in excess?
b)
which is the limiting reactant?
(Explain this in terms of the equation)
STAWA8.DOC
Rob Namestnik
Page 4
Leeming SHS Yr 11 Chemistry
8.
STAWA Exp 8
What is the mole ratio of Pb(NO3)2 to KI for group number 6?
Comment on how important this ratio is in relation to your graph and the
reaction equation.
9.
Use the website links provided under the safety notes on page 1 to find
safety information for the following:
a)
Describe in your own words, the dangers associated with using
lead (II) nitrate.
b)
How should lead (II) nitrate be safely disposed in the laboratory?
c)
Describe in your own words, the dangers associated with using
sodium iodide.
STAWA8.DOC
Rob Namestnik
Page 5
Leeming SHS Yr 11 Chemistry
STAWA Exp 8
As an option there is an excel spreadsheet at the www.chemed.biz website in the
Leeming SHS link for STAWA Experiment 8 that will allow you to input data from
the PbI2 weighings.
After recording the results from all the groups, type them into the correct column
in the spreadsheet and compare the moles of PbI2 produced.
Mole of reactants and product calculator
Group
Number
Mass (g)
Pb(NO3)2
Mass (g)
NaI
1
2
3
4
5
6
7
8
9
10
1.66
1.66
1.66
1.66
1.66
1.66
1.66
1.66
1.66
1.66
0.75
0.90
1.05
1.20
1.35
1.50
1.65
1.80
1.95
2.10
M Pb(NO3)2
=
M NaI =
M PbI2
Mass (g)
PbI2
Moles
Pb(NO3)2
Moles
NaI
Moles
PbI2
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.005
0.006
0.007
0.008
0.009
0.010
0.011
0.012
0.013
0.014
0.000
331 g/mol
150 g/mol
460.8 g/mol
=
n(Pb(NO3)2) = m(Pb(NO3)2) /M(Pb(NO3)2)
n(NaI) = m(NaI)/M(NaI)
n(PbI2) = m(PbI2)/M(PbI2)
STAWA8.DOC
Rob Namestnik
Page 6