MOLES Flashcards
burette measurement is 17.65 - uncertainty of burette is +/-0.05cm^3
Calculate the percentage uncertainty
(0.05 x 2 / 17.65) x 100 = 0.57%
pipette measurement is 25 - uncertainty of pipette is +/-0.06cm^3
Calculate the percentage uncertainty
(0.06 / 25) x 100 = 0.24%
Which types of measurements should you multiply by two when calculating percentage uncertainty?
Whenever you are taking two readings of something!
- taking the mass of something (zeroing measurement and then the actual measurement)
- titration (initial - final)
- temperature measurements (initial - final)
Say you got this number as your answer to an ideal gas equation question, how would you round it?
5.53446 x 10^-3
YOU WOULDN’T
Keep it as: 5.53446 x 10^-3
how to convert mol dm^-3 to g dm^-3
x RFM
Equation for % of an alcohol that has been oxidised from a carboxylic acid?
(moles of carboxylic acid / moles of alcohol) x 100 = % alcohol oxidised
What is the non-official-equation that worked for me in a question that I could use as a last resort just in case it works?
concentration/density = volume
Equation for concentration of stuff after adding water?
(ie. experiment where it says like they have 2 moles of HCl which they transfer to a conical flask and add a bunch of water)
concentration x dilution factor
How to calculate a dilution factor
Hint: imagine the following scenario…
Conical flask filled with 10cm^3 HCl, 250cm^3 H20 is added. You now have 250cm^3 dilute HCl
How do you work out the DF factor?
volume of whole thing/volume of undiluted thing = dilution factor
Eg. 250/10 = 25
concentration of the original undiluted thing (HCl before water was added) x 25 = concentrated of dilute acid
What numbers are significant figures?
numbers, including 0, that come AFTER the decimal point
equation involving 24
moles = volume/24dm^3
another weird equation that worked for me (involves moles, mass and rfm)
mass of A/(moles of A + water) = RFM of A + water
In a water of crystallisation question, if you work out the moles of the metal salt without water, what can you do with this?
transfer it across as the moles of the metal salt WITH water
who knows why but I did it and got full marks on the question so…
If a conical flask contains 12cm^3 of DILUTED acid which is 0.05 moles, how do you work out the moles of the same dilute acid that is in a beaker of 120cm^3 of the dilute acid?
12 = 0.05 120 = 0.5 moles [(120/12) x 0.05]
if you aren’t given the mass of something, if in doubt what can you use instead?
molar mass = rfm
eg. density = mass/volume (can use rfm as mass sometimes)
