AT- b Flashcards
(5 cards)
What are two practical equipment’s used to make quantitative measurements?
colorimeter and potometer
What is a potometer used for?
practical apparatus used to measure the rate of water uptake in plants and therefore represents rate of transpiration.
What is a colorimeter used for?
used to quantify and measure the light absorbance of a sample.
How is a potometer set up?
A sample of a plant must be cut from a plant underwater, this is to prevent any air from entering the xylem and breaking the water column.
The potometer is filled with water and all air bubbles are removed.
The cut leafy plant is then attached to the potometer, using rubber seals and petroleum jelly to make the equipment air tight.
One air bubble is then introduced into the equipment and the distance that this air bubble has moved towards the plant is recorded.
Volume of water/ time taken for bubble to move across
volume of cylinder =PIr*2
How is a colorimeter used to find concentration of an unknown?
- Prepare Known Concentrations (Calibration Curve)
Make a series of solutions of known concentrations
Usually done by serial dilution.
2. Add Indicator (if needed)
Add a reagent that produces a color
3. Filter/Remove Precipitate
If a precipitate forms, filter or centrifuge the solutions to get a clear sample for testing.
- Calibrate the Colorimeter
Use distilled water (or blank) to zero the colorimeter.
5. Measure Absorbance/Transmission
Place each known concentration solution into a cuvette.
Measure absorbance or % transmission using a colorimeter with the correct filter (usually a red filter for blue solutions).
6. Plot Calibration Curve
Plot a graph of absorbance vs concentration.
Draw a line of best fit.
7. Test Unknown Sample
Prepare your unknown in the same way.
Measure its absorbance using the colorimeter.
8. Determine Unknown Concentration
Use the calibration curve to read off the concentration that matches the absorbance of the unknown.
