PAG Knowleege AS Flashcards
What is a standard solution
How to make one
Standard solution is a solution of KNOWN conc
1) measure out EXACT mass of solute needed in weighing boat
2) add into BEAKER, then rinse boat with solvent
3) add solvent until it dissolves use stirring rod.
4) now add to VOLUMETRIC FLASK, and again rinse everything
5) add solvent until almost reach graduation mark, then drop by drop until bottom of meniscus coincides with mark.
DONT GO OVER or will ruin
6) add stopper invert flask several times before use to make it even!
What is room temp compared to standard chem temp
Chem temp = 25
Room temp = 20
3 reasons to why percentage yield not 100%
1) some of the product lost during transferring product / purification
2) side reactions may have occurred
3) not gone to completion (if it’s reversible reaction)
What are the benefits of having high atom economies (2)
ONE WAY to increase atom economy?
- less natural resources are wasted
- reduces waste altogether
2: increase atom economy by finding a use for the WASTE PRODUCT
Atom economy only provided part of the picture for efficiency. What are some of the reasons why?
- can have high atom economy but low percentage yields
- can have high atom economy but need a lot of energy for the reaction to even take place
- materials really hard to get so technique is not favoured
The undeserved product is a harmful one, could be bad
2 ways to measure gas
Which way do we use if the gas DISSOLVES in a liquid
- easiest way is gas SYRINGE
- however we use upturned flask as more attainable
But if the gas dissolved in water we should use gas syringe, or the DIFFERENCE IN MASS as a proportion !
How to reduce energy loss to surroundings / errors in combustion enthlapy experiment
1) DRAUGHT SCREENS TO STOP BREEZES (energy loss)
2) use OXYGEN canister and give oxygen so no incomplete combustion
When reacting two mixtures etc , how to reduce error in finding enthalpy change
Reduce heat loss = polystyrene cup, lid with TEMPERTAURE hole, insulated gel in between too
Heating something for longer, and burning more mass would lead to more or less accurate value?
When talking about accuracy in chem what always to refer too
Accuracy about uncertainty really
If you burn for longer, this means HIGHER TEMO CHANGE and HIGHER MASS CHANGE
This means ther percentage uncertisnty in these both is less, and therefore more accurate
Good lag stuf!
How to do upturned cylinder gas monitoring
Whars much easier way
As soon as resctsnt in , close thr bung
- delivery tube connected to the upturned cylinder full of liquid
- as gas is deleibered it displaces liquid away
- so read the measurements for thr amoutn if gas collected
2) easier to use a gas syringe that’s it , that pushed the syringe as gas enterd
How to improve results for these bung expeidemfs where you need to bung asap to not let any air escape
Attach string hanging off bung with reactant so as it closes it reavts, effeicnt
