Researching Chemistry 2 - Techniques Used In the Analysis of Compounds and Practical Skills and Techniques Flashcards
How can dilutions of a coloured standard solution can be used in colorimetry?
they are used to plot a graph with a calibration curve/line
Colorimetry uses the relationship between ___ and ___ of coloured solutions.
absorbance, concentration
In colorimetry, a colorimeter is used to measure…
This allows a ___ ___ to be plotted, which can tell you the ___ of an unknown solution, once you’ve measured its ___.
the absorbance of light of a series of coloured standard solutions.
calibration graph, concentration, absorbance
What do colorimeters do?
measure the absorbance of light of a sample by shining light through it.
Which two things must you do to the colorimeter before colorimetry?
- select an appropriate filter (must be complementary to the colour of the solution)
- calibrate it with a blank solvent
Why must a colorimeter’s filter be complementary to the sample?
it provides maximum absorbance
What is the melting point of a substance?
the range of temperatures over which it starts to melt to when it has completely melted
The identify of a ___, unknown compound can be determined by comparing its melting point to ___ ___.
pure, known values
How does the presence of impurities in a sample affect its melting point?
it will be lower, and the range of temperatures will be wider
(the range from when it starts to melt to when it has completely melted)
Why is the melting point range for a sample with impurities wider?
disruptions in the intermolecular bonding of the crystal lattice
Determination of a mixed melting point involves…
What do the results tell us?
mixing a small quantity of a known compound with the product to be tested.
The purity of product - the closer its MP to the known compound, the higher its purity
What does Thin Layer Chromatography (TLC) do?
What does it use?
separates components of a mixture.
a thin layer of silica gel or aluminium oxide spread over a non-reactive backing
How do you set up TLC, and how does it work?
A small sample of the substance to be separated is placed in a dot or line near the bottom of the chromatogram. The solvent dissolves the components of the mixture and carries them up the chromatogram.
What determines the rate at which components of a mixture are carried up a chromatogram?
their relative solubilities in the solvent and how well they adhere to the plate
How can you visualise the different spots at the end of TLC?
a developing agent or UV light
