Molarity Practical Flashcards
Why are measurements important ?
Quality control
Accuracy and precision
Experimental results
Safety
What are common measurement units ?
1 Kg = 1000 g
1 g = 1000 mg
1 mg = 1000 µg
1 µg = 0.000001 g
What do suffixes micro and milli mean ?
Suffix milli =10-3
Suffix micro = 10-6
What steps should be carried out pre measuring ?
Plan and practice protocols
Check reagents are in date
Check reagents have been stored correctly
Don’t take shortcuts in equipment SOP’s or protocol methods
Maintain equipment and report faults or concerns
How would you avoid contamination ?
Keep area clean and tidy
Keep glassware clean, report if broken or unavailable
Do not pipette reagents from original bottle – decant approximate amounts into a beaker etc.
Do not return unused reagents to original bottle to avoid contamination
Return reagents to correct storage
What should be used and shouldn’t be used for accurate measurement ?
Should;
- measuring cylinders and Pasteur pipettes, designed to give closely approximate measurements
- volumetric flasks, used to prepare solutions of known volumes
- Pipettes (variable and fixed): give accurate volumes but must be used correctly and calibrated
Shouldn’t;
- Beakers and conical flasks: not for accurate measurement – mostly for transfer or making solutions up in
What is the difference between accuracy and precision ?
Accuracy - how close a measured value is to the true/ accepted value
Precision - how close multiple measurements of the same quantity are to each other regardless of accuracy
How do you achieve accuracy and precision ?
Calibrated equipment
Correct equipment
Correct use of equipment
Careful readings of measurements
Define the terms;
stock solution
standard solution
working solution
Stock solution - usually most concentrated solution
Standard solution - accurate known concentration
Working solution - actual concentration used in experiment
Define molarity;
Molarity is the no of moles of a solute dissolved in 1 litre and is a measure of concentration
