Techniques Flashcards
What is stoichometry?
The ratio of things
What are the different types of analyses?
Quantitative analysis
Gravimetric analysis
Volumetric analysis
What does volumetric analysis involve?
Volumes
What does gravimetric analysis involve?
Masses
What happens in volumetric analysis?
Volumetric analysis uses a solution of exact concentration to determine the volume
What is a standard solution?
One of exact concentration
What is a standard solution prepared from?
A primary standard
What should a good primary standard be?
Should be stable when solid/ solution
Should be readily soluble
Should have a reasonably high formula mass
Why should a primary standard have a reasonably high G fm?
So that errors in weighing molar quantities are reduced
Why can’t sodium hydroxide be used as a primary standard?
Because it absorbs water and carbon dioxide
What are some common primary standards?
Oxalic acid
EDTA
potassium iodate
When are results said to be concordant?
When the results are within 0.1 of each other
What is meant by ‘weigh accurately approximately’?
The exact mass should be known/measured and should be close to the given value
What is gravimetric analysis?
Analytical determination of composition of a substances mass by chemically changing the substance
What is weighing by difference?
Weigh the empty weighing boat
weigh substance and weighing boat
Mass of substance=B-A
What is ‘heated to a constant mass’?
Weigh hydrated substance in crucible Heat crucible strongly Cool in desiccator chamber Weigh substance in crucible Repeat until mass is constant
What is volumetric analysis?
Appreciation of the characteristics of substances that can be used as a primary standard
What must a primary standard have?
High state of purity
Stability in air and in solution
Solubility
Reasonably high gram formula mass.
How can results be improved?
If titre is less than 5ml, these are not acceptable
A larger volume of solution can be used or lower concentration of the known solution to improve accuracy
What does a control do?
A control validates a technique and may consist of carrying out a determination on a solution of known concentration
What is back titration?
Back titration is used to find the number of moles of a substance by reacting it with an excess volume of reactant of known concentration.
When is back titration useful?
When trying to work out the quantity of a substance in an insoluble solid.
What is distillation used for?
Distillation is used to purify a compound by separating it from a non-volatile or less volatile material
What is refluxing?
A technique used to apply heat energy to a chemical reaction mixture over an extended period of time
