Flashcards in Module 1 Deck (32)
When choosing apparatus for experiments, what must we think about?
The SIZE of apparatus - Is it big enough to collect all of X?
The SENSITIVITY of our apparatus - use to smallest uncertainty to have the most accurate results.
After carrying out an experiment, list some questions you could ask yourself to evaluate your experimental technique
- Have I collected the most appropriate type of data?
- Have I controlled my variables?
- Have I set up my experiment's equipment correctly?
- Have I completed a risk assessment?
- How will I collect my data?
- Is this the best type of data to collect
What is a variable?
A quantity that has the potential to change e.g. mass
What is an independent variable?
The variable that you change in an experiment
What is a dependent variable?
The variable that you measure in an experiment
What is meant by reflux?
A technique used to keep volatile chemicals within a reaction mixture, ensuring that there is no lost of any volatile organic substances
What is meant by distillation?
A technique used to separate substances with different boiling points
Outline the process of distillation
The mixture is gently heated. The substances in the mixture will evaporate out in order of increasing BP. Therefore, if you know the BP of your pure product, you can use a thermometer to know when it will evaporate.
Give the method of filtration under reduced pressure
1) Connect some thick - walled rubber tubing to a vacuum source
2) Place a buchner or Hirsch funnel on top of a filter flask
3) Connect the tubing with the vacuum source to the side arm of the filter flask and start the suction
4) Put a piece of filter paper in the Buchner funnel, just enough to cover the walls
5) Using the solvent (likely to be distilled water), wet the paper so it sticks over all holes
6) Pour the reaction mixture into the centre of the funnel
7) Wash out the piece of equipment that contained the reaction mixture over the funnel using the solvent (Allows us to collect as much product as possible)
8) Rinse the solid on the filter paper with more solvent
9) Wait for some time and then turn off the suction by removing the tubing from the side arm of the flask
10) Tip the contents of the funnel onto a watch glass
Outline the process of re-crystallisation (Benzoic acid PAG)
1) Dissolve the impure solid in a minimum amount of hot solvent as possible
2) Place the filtrate in an ice bath
3) Collect the purified product using a vacuum filtrate
4) Wash with cold solvent and dry (dry agent is Magnesium sulphate)
Outline how we can test for purity by measuring melting points
1) Put a few grains of the organic product to be tested in a capillary tube
2) Insert the tub into a melting point machine with a thermometer with a suitable range
3) Turn on the machine and set the dial to 4
4) Note the temperature when the crystals stat to melt and when they are fully liquidised.
5) Compare to a trusted data base of melting points (sharp, very close MP = relatively pure) , (exact value = 100% pure)
What must our results be?
What does reproducible mean?
Others can use the same/similar equipment and the same method as us and get similar results
What does repeatable mean?
If I can repeat the experiment and get the same/similar results
How do we measure temperature?
Using a temperature probe or thermometer
1) Make sure the bulb of your thermometer/probe is COMPLETELY SUBMERGED in any mixture your measuring
2) Wait for the temperature to stabilise
3) If using a thermometer, read-off your measurement at EYE-LEVEL
Give a problem about qualitative tests
Hard to reproduce as they are often subjective (depends on opinion of individual)
How can we reduce the problem caused by qualitative tests?
- Use a white tile in the background (colour change reactions)
- Mark an X on a piece of paper and place it UNDER the reaction container. Your solutions is 'cloudy' when you can no longer see it.
How do we get from m^3 to dm^3 ?
Times by 1000
How do we get from dm^3 to cm^3 ?
Times by 1000
How do we get from cm^3 to dm^3 ?
Divide by 1000
How do we get from dm^3 to m^3 ?
Divide by 1000
When dealing with results table, do we include outliers in calculations?
How do we calculate the mean ?
Add all the results / Number of results obtained (not including outliers obviously)
Give the formula for percentage yield
(Actual yield / Theoretical yield) x 100
Give the formula of atom economy
(Mr of useful product / Sum of the Mr of all products) x 100
When dealing with calculations, what do we round to sig figures or decimal places?
Usually sig figures, unless stated otherwise
What is a sig figure?
The first digit that ISN'T zero
How do you find the gradient of a graph?
Draw a tangent, then do change in y / change in x
Give the formula for % error
(Uncertainty / Reading ) x 100