Researching Chemistry Flashcards
What is a stoichiometric equation
A balanced equation
When is a reaction described as being quantative
When the substances react completely according to the mole ratios in balanced equation
When can gravimetric analyse be used
- when a reaction goes to completion
- when an insoluble product (precipitate) is formed
What are the key properties of product formed from gravimetric analyse
- low solubility
- easy to filter
- product must be stable at -105 c
Why might there be differences between theory and experiment
- mass transfer losses
- purity of reactant is less than 100%
- reaction was incomplete
What is gravimetric analysis
The use of accurate measurements of mass to determine something about an unknown
Describe the technique of drying to constant mass
- repeatedly heat a sample and cool in desiccator
- until successive weighings are +/- 0.01g
Why is a desiccator used
To prevent the sample absorbing moisture from the air whilst cooling
What is volumetric analysis
Uses accurate measurements of volumes to determine the concentration (composition) of a solution
What is a standard solution
A solution of accurately known concentration
What are the key properties of a primary standard
- very high purity
- stable in air and solution
- high relative formula mass
- soluble in water
What are the three main types of titration
- acid base
- redox
- complexometric (EDTA)
Why is the choice of indicator important in an acid base titration
The pH range in which it changed is critical
What type of titration is used to analyse solutions of transition metal ions
Complexometric
What is a back titration
Titration method where the concentration of an analyte is determined by reacting it with a known amount of excess reagent
It is undesirable to accept titre values which are ?
Very low (less than 6cm^3)
What is an accurate measurement
One that is in close agreement with the true or accepted value
When is a measurement precise
When they are in close agreement with each other
What does the phrase - weighing approximately 6.0g accurately mean
- the mass should be close to 6.0g
- but must be measured accurately (eg 5.890)
What is colorimetry
An analytical technique used to determine the concentration of coloured substances in solution
What is an empirical formula
The simplest ratio of atoms present in a substance found by experiment
What technique is used to purify chemicals
Recrystallisation
What is TLC (thin layer chromatography) used for
Used to separate non-volatile mixtures
How would the Rf value be calculated
Distance moved by compound / distance moved by solvent
