1.2.2(b) use of appropriate instrumentation to record quantitative measurements, such as a colorimeter or potometer Flashcards
whenusing a coloprimeter what two pieces of equipment can you insert into the corimeter?
Some use cuvettes, some will accept test tubes
what must you ensure when using the curvette
In either case ensure the tube or cuvette is clean and not scratched.
cuvettes often have two clear walls for the lightpath – insert such cuvettes in the correct orientation
what should one do when measuring turbidity,
ensure the solid phase is fully suspended
notes
Calibration curves can be constructed from readings of a dilution series of a known solution
Ensure any solids or precipitate are not in the light path (e.g. by filtration or centrifugation)
Zeroing the colorimeter requires a moment of thought to choose an appropriate zero sample – it could be distilled water but it might not be.
Select the appropriate wavelength of light for measurements (follow instructions or do a trial run to find maximal absorbance).
measuring phusing a pH meter.
more precise, accurate and high-resolution information
how to calibrate a pH meter?
use by dipping into a buffer solution of known pH and adjusting the reading so that it is correct for that solution.
how to avoid contamination between samples
Meters should be rinsed with distilled water between each measurement
why happens when many people are sharing the meter?
This minimises the number of instruments required, but it does mean that great attention must be paid to cleaning the probe before each use.
what should use do to the joints when using a repsiometer
Ensure that all joints are sealed properly. Vaseline can be applied as necessary
what should you do to the sodalime before you start the experiment
If using soda lime make sure it is fresh and not exposed to the air before use
what should you do if using food dye in the capillary tube
add a little ethanol for it to flow more smoothly. Trial before use.
If using small invertebrates e.g. woodlice or maggots, it is essential to ensure that the animals do not come into contact with the soda lime. how to so prevent this
Place the soda lime in the bottom of the boiling tube, cover with a little cotton wool and then put in the metal gauze ‘basket’ which will hold the animals.
what should you do before timing and measuring movement of dye up the capillary tube
Allow time for organisms to equilibrate to the environment
what type of plant should I use for better results for the potometer experiment?
the shoot should have a number of leaves
what should you ensure when setting up the photometer?
When setting up a potometer to measure the rate of uptake of water from a leafy shoot it is important to minimise the contact between the air and the cut end of the stem. There should be no air bubble and all joints should be sealed with e.g. Vaseline
