Vitamin C practical Flashcards
what is the independent variable
type of juice
how do you vary the independent variable
have different types of vitamin c juice
grapefruit
orange
what is the dependent variable
vitamin c concentration in the juices
how do you measure the dependent variable
use a graduated pipet (5cm3 0.05% concentration)
titrate the juice into DCPIP
use calibration curve to find vitamin c concentration
what organism (fruit) variables should be controlled
same brand of juice
other brands could have different recipes
what environmental variables should be controlled
temperature of juices
either room temp or refrigerated
what procedural variables should be controlled
volume of DCPIP
use graduated pipet to measure accurately 5cm3 at 0.05% concentration
what repeats should be carried out
repeat 5 times then calculate mean average
how is the investigation made reliable
identify anomalies
repeat 5x
do not change method during repeats
how is the investigation made valid
use control variables
same volume of DCPIP
use a wider range of vitamin c samples
what are the safety hazards and what precautions can you take
DCPIP or juice getting into eyes
wear goggles
what is the method
extract juice from the fruit and measure 5cm3 of DCPIP
titrate juice into DCPIP
swirl beaker constantly and look for colour change (blue to colourless)
record volume of juice used
repeat 3-5 more ties and calculate mean volume of juice used
use calibration curve to determine vitamin c concentration
why is DCPIP used
DCPIP is a free radical which is oxidised
antioxidants in vitamin c reduces DCPIP ( gives it an electron)
DCPIP becomes stable
creates colour change blue - colourless/ pink
more vitamin c in juice = more electrons given so less juice is needed to make colour change (less juice needed to reduce DCPIP)
