Module 5 Pag Flashcards
How to use colorimeter to find conc for Co ti out monitoring
We only care about reactants for the orders
1)identify the reactant that’s causing the colour
2) get standard solutions if the reactant with known conc
3) and do colorimeter test with them to give values for absorbance or transmittance
- do this by selecting a wavelength of opposite light
- zero using distilled water and check
4) now plot a calibration curve of absrobsnce vs conc
- now whatever absorabance you find yiu csn get conc
5) so now take frequent samples against time and check your conc
How to do iodine clock reaction (the thinking behind it)
Big assumption ?
1) iodine is produced in one reaction but is used up by thisulfste straight away
2) once thisukfste used up then it will show as orange brown , but in presence of starch blue black. Else colourless
3) we use thisulfste to delay the time such that we can actually measure time taken show colour. If the thisulfste and everything else kept constsnt then this is proptinal to rate
Assumption is = that less than 15% of the reaction has happened when this colour change is first seen, as now the rate found is very similar to INITAL rate . ( not all reaction has happened, this is why we can’t use do much thisukfste, but a bit so we can add measure the time else it will be impossible)
So now we can do the iodine clock, how to use ir to find the different rates and thus rate equation?
Change each of the conc of the reactants and keep rest same, and find times. Then plot this vs conc to get shape
Do this for all the reactants, can now write down the rate equation
However to find the k constsnt we need a real rate first. So we need to plot orignal conc time graph for that first … (can’t use 1/t as rate)
How can you use a pH probe to monitor pH continously as acid / alklai added
PH probe consists of an electrode that’s dipped into a solution and then it measures the pH
- for ease, use a pH probe connected to a datalogger, and a MAGNETIC STIRRER
- then slowly add solution and the data logger will be able to automatically plot a pH against volume graph
Id using pH probe manually and adding manually, what to do when pH starts to decrease / increase slowly
If it does that, you’re nearing equivalence point, so now add the solution DROP BY DROP SLOWLY
Make sure to swirl flask mix as you go!
How to do MNO4- titration
Colour changes?
What MUST you afd
1) in burette add manganite solution of known conc
2) in conical flask add your resvtnat. Ass manganite reduced, this must be something that will be OXIDISED
3) NOW ADD SOME SULFUIRC ACID IN CONICAL FLASK TO PROVIDE ACIDIC CONDITIOMS (h+ ions) needed
4) run titration. Each time manganite reacts it becomes colourless
5) when the solution is all used up, the solution with the next drop of manganite will remain PERMANENT PALE PINK, this is end point (self indicating )
How does thisulfste iodine titration work
How to do it, what colour changes and when is end point
1) basically we in the conical flask mix a solution with EXCESS KI. The solution should oxidise the iodine ions to become pure Iodine.
= This gives the solution an orange brown colour
- we have a certain amount of iodine now. Thus all of the iodine reacting is equivalent to our solution that oxidised iodine ions reacting. We can use this to work out concs
2) in a burette add a known conc of thiosulfste. When this reacts with iodine, it makes it back into Iodine ions so the colour becomes less yellow
3) run the titration. When the colour of the solution is now left as a PALE STRAW COLOUR, we can add starch as an indicator
- the starch will make the solution Blue black.
- once all the iodine is reacted , this colour will become colourless.
This is the END point.
What to ensure to include in conical flask like last time
Not only excess KI, your solution but also some HCL to provide acidic conditions (always remember if equation has H+ must be acidic )
How to now use thisukfste resvtion to determine concentration of anything
Use volume and conc of thio to find moles
- use the reactions to find moles of solution thus reacted
- scale up if needed
And now divide by volume of solution you out in in the first place
Why MUST WE ADD STARCH NEAR THE END POINT ONLH q
Must add near when a PALE STRAW COLOUR is seen as starch iodine complex is very strong, so if we added it in the start, there is a chance some will stick with the starch forger and miss out on titration
As a result we add it near the end when conc of iodine is low, to minimise this IRREVERSIBLE STICK
