Experiment 2
Determination of density
Aim
The aim of this experiment is to
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determine the density of water,
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determine the density of an aqueous sodium chloride solution and subsequently find the
mass percentage of sodium chloride in the solution.
Introduction
The concepts of density, mass and volume will be reviewed in this experiment. You will
determine the density of water and the density of a solution of sodium chloride. In addition,
you will also carry out a beginner's exercise in graphing, as it is often easier to discern
relationships between variables from a graph than from a table of data.
It is essential that you complete the exercises in the Pre-lab sheet before you do this
practical.
Procedure
You will work individually.
Note: Use the same top-pan balance throughout the experiment.
Part A.
Density of water
In the first part of this experiment, you will determine the densities of three different volumes
of water.
1.
Weigh an empty, dry 100 mL measuring cylinder.
2.
Add distilled water up to the 10 mL mark of the measuring cylinder. Remember, the
bottom of the meniscus should just be touching the 10 mL line. Weigh the cylinder +
the water on the top-pan balance.
3.
Add water up to the 30 mL mark of the cylinder and weigh.
4.
Add water up to the 50 mL mark and weigh.
5.
Calculate the densities of the three volumes of water.
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6.
Plot a graph of the mass of water on the vertical scale versus the volume of water on the
horizontal scale. Use the graph sheet provided in the Report sheet.
Part B.
Density of a solution of sodium chloride
1.
Weigh a 100 mL beaker to the nearest 0.01 gram (top-pan balance).
2.
Pipette 10 mL of your unknown sodium chloride solution into the beaker and weigh the
beaker and contents.
3.
Calculate the density of the salt solution.
4.
Use the graph you plotted in question 4 of the pre-lab to determine the mass percent of
sodium chloride in the salt solution.
Note: The densities of the sodium chloride solution presented in question 4 of the pre-lab
were measured at 20oC. Although densities are temperature dependent, the values are
accurate to three significant figures after the decimal between 18oC – 24oC. If your
solution temperature is not in this range, then there will be a slight error.)
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Surname: ___________________________ First names: ___________________________
Student No.:_____________________ Group:________________
___________________________________________________________________________
Experiment 2: Pre-lab sheet
Complete this sheet before you come to the practical; have it signed by the demonstrator.
1.
Write down the apparatus and chemicals required in this experiment.
Apparatus required
2.
Chemicals required
A 10.0 mL sample of mercury weighs 135.5 g. Calculate the density of the mercury
sample and express your answer in SI units for density.
3.
A supersonic transport (SST) airplane consumes about 18 000 L of kerosene per hour of
flight. Kerosene has a density of 0.965 g/mL. What mass of kerosene is consumed on a
flight of duration 3.0 h?
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4.
The density versus concentration (% m/v) of several aqueous sodium chloride solutions
is given below. Prepare a graph by plotting the percent by mass of sodium chloride on
the horizontal axis (x-axis) and the density on the vertical (y-axis). (Use the graph paper
on the next page.)
Note:
% m / v = mass over volume percentage
= (mass of NaCl in g / 100 mL solution) x 100%
NaCl (% m/v)
0.00
5.00
10.00
15.00
20.00
25.00
Density (g/mL)
0.998
1.034
1.071
1.108
1.148
1.189
Note: Choose a good scale to ensure that your graph covers most of the graph paper.
(Hint: The y-axis scale need not start from zero, but could start, for example, at
0.98 g/mL with 1 cm = 0.01 g/mL.)
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Graph for question 4 of the Pre-lab.
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Surname: ___________________________ First names: ___________________________
Student No.:_____________________ Group:________________
___________________________________________________________________________
Experiment 2: REPORT SHEET
This report is to be handed in when you come for the next lab
Part A.
Density of Water
1. Volume of water
10.0 mL
30.0 mL
50.0 mL
2. Mass of graduated cylinder + water (g)
3. Mass of empty graduated cylinder (g)
4. Mass of water (g)
5. Density of 10.0 mL sample of water (g/mL)
6. Density of 30.0 mL sample of water (g/mL)
7. Density of 50.0 mL sample of water (g/mL)
1.
Show your calculations for steps 5, 6 and 7.
Step 5 (density of 10.0 mL):
Step 6 (density of 30.0 mL):
Step 7 (density of 50.0 mL):
2.
Plot a graph of mass of water (on the y-axis) versus volume of water (on the x-axis).
(Start both axis from the origin (0,0) and choose a good – but also easy - scale such that
the graph covers most of the graph paper.
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Graph for question 2 of the Report sheet
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3.
a.
Determine the slope of your graph and show its units. (Show in the graph the ∆y and ∆x
sections used to find the slope.)
b.
What does the slope represent?
c.
Does the density of water change as its mass changes? Explain your answer.
Part B.
Density of a solution of sodium chloride
1.
Number of unknown:
______________
2.
Mass of beaker:
______________
3.
Mass of beaker + 10.00 mL of unknown:
______________
4.
Mass of 10.00 mL of unknown:
______________
5.
Density of unknown:
______________
6.
From the graph you plotted in question 4 of the pre-lab,
determine the percent by mass of sodium chloride in your
unknown: __________________
Show on the graph how you determined this value
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