Handling Data & Dealing with Units
Aims
The major aim of this session is to familiarise you with best practice in the treatment of units when
working with physical data. As a secondary aim, it will also introduce you to the learning methods
that will be used throughout the Foundations of Chemistry module.
Reading
Before attempting the following exercises you should read through the following material.
Essential Reading
Read through the web pages found at
http://www.warwick.ac.uk/fac/sci/Chemistry/pmrodger/pmr/teaching/found/handling_data.htm
These pages can also be found from www.warwick.ac.uk/fac/sci/Chemistry/pmrodger/pmr.html by
following the link to teaching material, then the link for the Foundations Course.
Recommended Reading
(1) ch 1 & 7, “Quantities, Units and Symbols in Physical Chemistry”, Mills, Cvitas, Kallay,
Homann & Kuchitsu, Blackwell, 1988 (this is the IUPAC green book)
(2) pp 3–6 in Housecroft & Constable, “Chemistry” (but note the corrections in the essential
reading — especially in the section on “quantity calculus”.
(3) pp 28–50 in Kotz & Treichel, “Chemistry & Chemical Reactivity”
Tutorial Work
You should first attempt the exercises given below on your own. You should then meet with your
self-help group to prepare a single set of answers for the group. This set of answers should left in
my mailbox (P.M. Rodger, 4th floor of Chemistry, beside the lift and stairwell) by 10 am Friday
morning. These questions will then be discussed in the workshop on Friday afternoon.
Office Hours
Thursday October 3, 2–4 pm, room B510
Exercises
(1)
Convert:
(2)
1 dm3
to
m3
1 cm–1
to
m–1
1 g cm–3 to
kg m–3
2 km s–1 to
Å ps–1 (this is the average speed of an H2 molecule at 300 K)
Write out the following in SI base units, and replacing the prefix by the appropriate power
of 10.
3 picosecond
5 terawatt
6 gigahertz
7 nanometer
(3)
Convert the following into appropriate SI units (conversion factors can be found in the
essential and recommended reading)
36.2 kcal mol–1
13.6 eV (the ionisation energy of an H atom)
30 miles per hour
25 mTorr
35.5 u (u is the unified atomic mass unit, also sometimes called the dalton)
(4)
A typical plant producing ammonia by the Haber process operates at 2.1 × 104 kN m–2 and
852 K (using a catalyst). How many moles of gas are there, under these conditions, in a
vessel of volume 125 m3 containing the equilibrium mixture?
(5)
The osmotic pressure, η, of a solution is related to the concentration (molarity), c, by the
expression
η = cRT
where T is the temperature and R is the gas constant. The concentration may further be
related to the mass concentration (mass per volume), m, of the solution and molar mass, M,
of the solute:
c = m/M
If a 3.87 g dm–3 solution of polyvinyl chloride (pvc) in dioxan gives an osmotic pressure of
63.1 Pa at 19°C, calculate the molar mass of the pvc.
(6)
Draw axes and label them appropriately for a plot of concentration against time. Assume
that the data has been given in mol dm–3 and min–1.
(7)
Imagine you have carried out an experiment to measure the pressure of a sample of gas as a
function of temperature. What would be the column headings in a table of your results?