U 4-2 - Composition Determination Flashcards
Colorimetry measures how intense the colour of a solution is. The _________ the concentration, the more intense the colour.
Colorimetry measures how intense the colour of a solution is. The higher the concentration, the more intense the colour.
What measurement is taken during colorimetry?
Absorbance of visible light
(or transmittance)
How do you decide which colour filter/light to use in colorimetry?
Must be complimentary to the colour of the solution.
(e.g. solution is green = use purple filter/light)
What must be done to the colorimeter before the absorbance of a solution can be measured?
Must be calibrated using a blank (only solvent in cuvette, usually deionised water)
What is a complimentary colour?
Opposite on the colour wheel
Name this piece of equipment
Cuvette
The absorbance measured for a solution gave a concentration higher than any of the standard solutions used to prepare the calibration graph.
What can be done to make the results more accurate?
Dilute the sample
OR
prepare new standard solutions of greater concentration.
Heating to constant mass
Heating until the mass of a solid no longer changes
Why is heating to constant mass typically used?
To remove moisture (e.g. from primary standards)
Name this piece of equipment
Desiccator
What is the purpose of a desiccator?
Prevents reabsorption of water
The formula for a compound is BaCl2·3H2O.
What is meant by ·3H2O?
The compound forms a complex with 3 water molecules
(molar ratio BaCl2 : 3H2O of is 1: 3)
How can filtration be carried out quickly?
Vacuum filtration
Name this piece of equipment
Buchner funnel (used for vacuum filtration)
During gravimetric analysis, a precipitate is formed and collected by filtration.
What must be done to the filtrate before moving on and why?
Filtrate must be tested by adding more reactant.
This is to ensure that no more precipitate is formed.
