SACE 2 Chemistry Practical
Analysing Copper Ore
using Atomic Absorption
Spectroscopy (AAS)
Purpose:
A good friend of mine owns a copper refinery. For years he has been reasonably satisfied with
the mining company he used to purchase the copper-containing ore (which just happened to
be owned by his father-in-law…). Recently, however, he was approached by a competitor
mining company that wants to secure his business. They’re claiming that their ore is far
superior, containing between 12 and 15% w/w copper, and they’re willing to sell to him for
the same price as what he is already paying. Now, if this claim is correct, then my friend will
save a bundle (the ore he currently gets contains between 3 and 8% copper on average). BUT,
it’s a big risk – ‘coz it’ll upset the in-laws, which in turn will upset his wife, and that prospect
terrifies him!
So, he’s asked if we can check out a sample of the ore (discreetly so the family doesn’t find
out!) to see if the ‘new’ company is legitimate, or whether they’re trying to pull one over
him…
Part A
Digestion (already done for you)
Extracting the copper from the ore by converting it into a soluble form.
Ten samples of ore (containing copper as water-insoluble copper oxide, CuO) were accurately
weighed out and heated for 3 hours in concentrated acid. The extracts were filtered and the
filtrates (and rinsings) were transferred into volumetric flasks, which were made up to the
mark using deionised water. Each solution was then diluted 100-fold into volumetric flasks
which were labelled A to J.
Question: By referring to the position of copper in the periodic table, describe why the above
digestion and extraction procedure was suitable. Include a balanced equation for the reaction
that occurred.
Part B
Further dilution
The AAS is a very sensitive instrument, used to analyse samples in the parts per million
(ppm) range. The sample, therefore needs to be diluted so that it will have a
concentration no higher than 25 ppm.
Select ONE sample (from A to J) and accurately pipette 10 mL of the unknown sample into a
200 mL volumetric flask. Make up to the mark with deionised water.
Question: The original sample can be assumed to contain anywhere between 3 and 15% w/w
copper. The digestion/extraction/dilution steps carried out in Part A yielded solutions with
potential concentrations ranging between 600 and 3000 ppm Cu2+. What is the possible
concentration range of Cu2+ in the solution following the dilution step you performed in this
section?
Part C
Constructing a Calibration Curve
To be performed as a class and written up individually.
Complete the following table of absorbance readings measured on the AAS for a series of
standard Cu2+ solutions.
ppm Cu2+ (standard solutions)
Absorbance reading from AAS
0
5
10
15
20
25
From this data construct a calibration curve below of Absorbance versus Concentration (Cu2+)
in ppm. For your graph, give it a suitable title and label each axis.
Part D
Finding the Concentration of your Sample
Record below both the sample number* and absorbance value of your sample provided
from the AAS reading.
Sample number__________ Absorbance reading___________________
Use your calibration curve to determine the concentration in ppm of your dilute Cu2+ solution
and record your answer below.
Concentration of Cu2+ ions in dilute solution:__________________
ppm
Part E
Finding the %w/w of copper in the Original Ore
Sample
Calculate the actual %w/w copper in the original ore sample.
Should my friend change suppliers (and risk his marriage!)?
Further work: Describe the principles of AAS.
Incorporate into your answer a sketch of the layout of a
typical AAS showing its main components, along with a
brief explanation of the purpose of each component and
how it operates.
*
The software program for the AAS will call for “Sample 1; Sample 2; etc.