Chemical Analysis Flashcards
(16 cards)
What is chromatography?
A technique used to separate the components present within a mixture
How does chromatography separate substances?
By making use of differences in their polarity or molecular size(different speeds depending on size/polarity)
When are the substances separated?
As they travel in a mobile phase which passes through a stationary phase
What is the relationship between the size of the molecule and the time it takes to get through the stationary phase?
The larger the molecule the longer it takes to move through the stationary phase
If a polar solvent was used would a polar molecule move further?
Yes as they’ll be more attracted to polar solvents so would move further if a polar solvent was the stationary or mobile phase
What is the mobile phase?
What affects the solubility of the molecules in the mobile phase?
A liquid or gas which carries the sample through the material
Size of molecules and polarity affect how soluble they are in the mobile phase(how far they travel)
What is the stationary phase?
May be paper, silica gel or an inert(unreactive) packing material in a column
Size and polarity affect their affinity for the stationary phase(how little they travel in the mobile phase)
How is the Rf value for the substances in a mixture using chromatography calculated?
Rf=distance moved by solute/distance moved by solvent
What is retention time?
How long it takes for the compound to pass though the column
What does volumetric analysis involve?
Using a solution of accurately known concentration in a quantitive reaction to determine the concentration of another substance(normally done using titrations)
What is a titration used to do?
Determine, accurately, the volumes of solution required to reach the end point of a chemical reaction
What is an indicator normally used for?
To show when the end point of a chemical reaction is reached
What are titre volumes within 0.2cm3 considered as?
Concordant results(ignore rough titration)
What are standard solutions?
Solutions with an accurately known concentration
What are redox titrations based on?
Redox reactions
Do titrations using acidified permanganate solution need an indicator?
No an indicator isn’t required as purple permanganate solution turns colourless when reduced
