Unit 3 - Chemical Analysis Flashcards
What is chromatography?
A technique used to separate and identify components in a mixture using their polarity and molecular size.
What is the stationary phase?
The medium (absorbant material)
The ____ the forces between the component and medium the ___ it takes for the component to travel.
- stronger
- longer
What is the mobile phase?
A gas or liquid used to carry the mixture through the absorbent stationary phase.
How does chromatography work?
It exploits the fact that different molecules experience different strengths of intermolecular forces as the mobile phase carries them through the stationary phase.
How do you calculate the Rf value?
Distance travelled by substance divided by distance traveller by solvent front
Will larger or smaller molecules take longer to move up the paper?
Larger
What is the setup of gas liquid chromatography?
A coiled column and the mobile phase in an inert gas. (eg helium)
How does gas liquid chromatography identify substances?
Through retention time.
How do you identify concentration of a substance using chromatography?
The height of peak.
What is retention time?
The time it takes the component to travel through the column from the injector point to the detector.
What does a long retention time mean?
Big molecule
Greater affinity for stationary phase
What does a short retention time mean?
Small molecule
Greater affinity for mobile phase.
The ___ the area under the curve the ___ the concentration.
- larger
- higher
What happens if you use a non polar solvent in chromatography?
• Polar molecules are not attracted to the solvent.
•Polar molecules will have a longer retention time.
What happens if you use a polar solvent in chromatography?
•Polar molecules in the mixture are attracted to the solvent.
• Polar molecules will have a shorter retention time.
What happens if you use a non polar column?
• Polar molecules are not attracted to the column.
• Polar molecules will have a shorter retention time.
What happens if you use a polar column?
• Polar molecules will be attracted to the column.
• Polar molecules will have a longer retention time.
If the stationary phase in gas chromatography column is non polar, explain how the retention times of polar and non polar samples in the column compare to each other?
•Non polar sample will have a greater affinity for it than the polar sample will.
•Therefore, the non polar sample will take longer to travel through the column than the polar sample.
•Therefore, the non polar sample will have a longer retention time than the polar sample.
What is a standard solution?
A solution of accurately known concentration.
How do you make a standard solution?
- Dissolve an accurately calculated and weighed mass of solute in the minimum volume of distilled water. Add to the standard flask.
- Rinse the beaker with distilled water and add the washings/rinsings to the flask.
- Add distilled water to the flask, use a dropper as the meniscus reaches and rests on the graduation mark.
- Place the stopper on the flask and mix. (invert several times)
Do you need to use an indicator for a reaction involving a coloured reactant or product (eg. permanganate)?
No. It’s self indicating
What is a concordant result?
2 results within 0.2cm3 of each other. Cannot include rough.
What are 6 points of good practice when carrying out titrations?
- Rinse burette and pipette with the liquid that has to go in them before use.
- Remove filter funnel from burette before titration begins.
- Add liquid drop by drop as you approach end point.
- Fill burette past zero line and run liquid out until the meniscus rests on the zero line.
- Continuously swirl contents of flask gently.
- White tile to see color change clearer.
How can you measure mass?
Weigh in a beaker/flask with electronic balance
OR
weigh by difference with electronic balance
When shouldn’t you use a bunsen burner?
When heating a flammable substance.
When shouldn’t you collect gas with a water trough?
When collecting a soluble gas (eg. CO2)
If i’m doubt, use gas syringe
Rank the measuring devices from most to least accurate.
- Pipette
- Burette
- Measuring cylinder
- Beaker
What are reproducible results?
Results close together
What are poor reproducible results?
Results far apart.
What type of best fit line should you use for temperature?
Curve - rate ≠ directly proportional to temp
What is a locating agent?
A type of indicator, used in chromatography, that is sprayed.
