Serial dilution Flashcards
Define volume
Volume is the space taken up by something (cm^3)
Define concentration
Concentration is the proportion of solute to solvent within a solution Usually measured in mol dm3 or g dm3
The more concentrated a solution is..
The greater the proportion of solute to solvent
The more dilute a solution is..
The greater the proportion of solvent to solute
What is serial dilution
Making a range of concentrations of a solution
Why do we do serial dilution
- Use as standards for comparison (e.g. colour change)
- To plot a line of best fit to work out an unknown concentration
- To make bacterial cultures easier to count
What steps are taken to calculate serial dilution
- Write concentration and volume
- Write the starting concentration and volume
- Write down the target concentration
- Work out how I got from the starting to target concentration by dividing the starting concentration by the target concentration
- Do the same calculation to the other side
- Minus this from the total volume to work out the volume of water we need to add
- Mix it thoroughly
Why do we set the water bath to 30 degrees
- To control the temperature
- Temperature changes affect the kinetic energy of the particles and thus the rate of osmosis
Why do we remove any peel on the potatoes
Potato peel is not permeable to water and so would prevent osmosis
Why do we cut all the potato chips to the same length
This controls the surface area - a larger surface area to volume ratio would increase the rate of osmosis
Why do we blot the potato chips dry
Without doing so, the potato chips will appear heavier than they are
Why do we leave the potato chips in the boiling tube for 20 minutes before removing them
The potatoes are left for this long so that they reach equilibrium with the solution and there is no further water movement
Why do we calculate the percentage change in mass
To enable comparisons between potato chips with different starting mass
