PRACTICAL PAPER Flashcards
independent variable
the factor that changes in an investigation
dependent variable
the factor that changes as a result.
controlled experiment
experiment to ensure independent variable is causing results
standardizing temperature
Thermo-statically controlled water bath
standardizing pH
pH Buffer solution of known concentration
standardizing light
Heat-shielded lamp set at constant
standardizing intensity
Distance/power
standardizing wind speed
Fan set at constant distance & power
measuring temperature
Thermometer
measuring colour
Colorimeter
measuring pH
pH indicator / pH meter
measuring mass
balance
measuring length
Microscope with calibrated eyepiece graticule/Ruler.
measuring volume
Beaker/Measuring cylinder/Burette/Pipette.
measuring time
stopwatch
how to read measuring cylinders accurately
Read from bottom of meniscus, perpendicular to scale
accuracy
closeness to true value
improving accuracy
better instruments
precision
closeness to repeated readings
improving precision
control all variables
reliability
confidence in results
improving reliability
repeat readings and take mean
validity
agreement between hypothesis and investigation
improving validity
check relation between key and derived variables
systematic errors
result from uncertainties in measurements.
random errors
differ across investigation as they arise owing to difficulties in controlling standardised variables and measuring dependent variable.
common error sources
- Anomalous readings (owing to inadequate technique/replicates)
- Inadequate range and intervals.
- Uncontrolled variables.
state the actual error in measuring an increase in temperature of 6 degrees celsius using a thermometer
1 degrees celsius
you can read reading 0.5 degrees out for one recording and 0.5 degrees out for the other recording so error would be 1 degrees
measuring temperature from water in a beaker source of error and how to improve it?
1) energy may be transferred to the surroundings and won’t stay in the water
- Use insulation or lids
observable features of Xerophytes
many air spaces - for buoyancy - and relatively small amount of xylem as water diffusing through epidermis
counting bubbles sources of error and how to improve them?
1) Different sizes of bubbles released
- Use a gas syringe to measure volume of gas released in total
2) Too many bubbles so not all are counted
- Video in slow motion and count from the video so no bubbles are missed out
getting enzymes from a fruit or vegetable (like potatoes) source of error and how to improve it?
1) Species of potato have different enzyme catalase
- Use the same potato or same species of potato
describe how to standardise the position of the delivery tube in the test-tube of water
Make a mark on the delivery tube to standardise the position of delivery tube
judging end points source of error and how to improve it?
1) Difficult to judge when the colour has changed
- Use a colour chart for comparison or use a colorimeter
lack of precision or accuracy in measuring instruments
1) Measuring instrument (thermometer, colorimeter) is not properly calibrated (not accurate)
- Ensure calibration occurs or use alternate instruments that allow you to calibrate it
2) Using imprecise instruments / methods
- Use instruments that have smaller divisions E.g. using a graduated pipette instead of syringe
- Take measurements more often
when talking about modifications to experiment
- don’t forget to mention exactly how much of each sample. etc. like 5 different concentrations or 5 different sized cubes
- mention an exact concentration as well
using a grid to find area of a specimen - limitations and improvements
- count number of squares that cover more than half of the square
improvement : count using a grid with smaller squares
drops of milk sources of error + improvement
1) Different sizes of drop of milk
- Use a small syringe or graduated pipette
when talking about enzymes ALWAYS mention
- enzyme substrate complexes
- higher temp –> higher kinetic energy –> more collisions
- denaturing
reducing sugar test
- 80 degrees celsius in thermostatically controlled waterbath
- Use benedict’s solution
- reducing sugar present - turns from blue to brick red
non-reducing sugar test
sucrose is a non-reducing sugar made of glucose and fructose which are reducing sugars
- add HCL and heat gently to break down non-reducing sugar into reducing sugars (glycosidic bonds)
- neutralise the sample with sodium hydrogen carbonate solution
- add benedict’s reagent (80 degrees in water bath)
- observe colour change
protein test
- add sodium hydroxide and copper sulfate solution to sample (biuret solution)
- if protein present solution turns from blue to purple
