Unit 4 Questions MEGATHREAD!

[Zebra]

h2so4

[h+] = 2 x [h2so4]? (eventhough the second ionisation reaction is not complete.)

[kensan]

In unit 1/2 i think you make that assumption, but because we know the Ka is so small for the second ionisation I don't think we include it, but I'm not 100% sure

[LachieEvans]

no we wouldn't assume that [H+] = 2 x [H2SO4].. as we dont have this acidity constant in the data book, we would be given it if we had to use it to calculate say the mol of HSO4-.

[Asx4Life]

How come increasing the surface area of reactants wont increase the rate of a chemical reaction?

Where'd you get this from?

Insight 2008 MC Q3.

Also, Question 3C of SA, I don't get why addition of FeCl3 makes the solution go Darker red in colour. The answer says it will Increase Fe3+ ions so system shifts right to decrease conc Fe3+ ions, and hence produces more FeSCN3+ ions which are red in colour. But I thought adding FeCl3 will increase the amount of Fe3+ ions which are yellow in colour makes solution go yellower?

[Graphite]

no we wouldn't assume that [H+] = 2 x [H2SO4].. as we dont have this acidity constant in the data book, we would be given it if we had to use it to calculate say the mol of HSO4-.

Yes you do ASSUME this....We UNDERSTAND it is not what happens in REALITY but we DO assume this in VCE

[Zebra]

okay so we just assumes its a strong diprotic acid i see.

another question!

in an alkaline battery.... (involving zn and mn02)

HOW THE HECK ARE YOU SUPPOSE TO DEDUCE HALF EQS OCCURING @ THE ELECTRODES?

someone please take me thru the steps


EDIT: ONE MORE QUESTION, can you say that the ignition wire in bomb calorimeter provides activation energy to initiate the reaction?

[david10d]

How come increasing the surface area of reactants wont increase the rate of a chemical reaction?

Where'd you get this from?

solutions fmo insight 2008

[generalkorn12]

For VCAA 2008, Question 7b iii. How come they wrote a half-equation for Cadmium, and used OH rather than something like Water (which is what I figured you would use for balancing half equations), or even the Cd from Electrochemical series.

[HenryP]

How come increasing the surface area of reactants wont increase the rate of a chemical reaction?

Where'd you get this from?

solutions fmo insight 2008

If you actually read the solutions, you can see that its not properly worded. I think the last option of that question should be adding more reactant instead of increasing the surface area. Therefore the answers would be correct in saying that by adding more reactants, the rate of reaction does not always increase

[Asx4Life]

How come increasing the surface area of reactants wont increase the rate of a chemical reaction?

Where'd you get this from?

solutions fmo insight 2008

If you actually read the solutions, you can see that its not properly worded. I think the last option of that question should be adding more reactant instead of increasing the surface area. Therefore the answers would be correct in saying that by adding more reactants, the rate of reaction does not always increase the rate of reaction

wut?

[Zebra]

no we wouldn't assume that [H+] = 2 x [H2SO4].. as we dont have this acidity constant in the data book, we would be given it if we had to use it to calculate say the mol of HSO4-.

Yes you do ASSUME this....We UNDERSTAND it is not what happens in REALITY but we DO assume this in VCE

apparently not.

[HarveyD]

Consider the following buffer equilibrium system:
HCN (aq) + H2O (l)  H3O+ (aq) + CN- (aq)
What is the net result of adding a small amount of HNO3 ?
A. The pH increases slightly.
B. The pH decreases slightly.
C. The [CN-] increases slightly.
D. The [HCN] decreases slightly.

[yjml77]

okay so we just assumes its a strong diprotic acid i see.

another question!

in an alkaline battery.... (involving zn and mn02)

HOW THE HECK ARE YOU SUPPOSE TO DEDUCE HALF EQS OCCURING @ THE ELECTRODES?

someone please take me thru the steps


EDIT: ONE MORE QUESTION, can you say that the ignition wire in bomb calorimeter provides activation energy to initiate the reaction?

OMG YES SOMEONE PLEASE ANSWER THE ALKALINE QUESTIONS!!! absolutely no clue how to work em out

[DavidSheena]

Do we need to know the diagrams of the Hall-Hero...something cell and the molten NaCl and the diaphram cell? The systems are easy to understand, it's just whether we need to know specific details of the process and diagram. Eg; operating voltages, catalysts etc.

[HenryP]

How come increasing the surface area of reactants wont increase the rate of a chemical reaction?

Where'd you get this from?

solutions fmo insight 2008

If you actually read the solutions, you can see that its not properly worded. I think the last option of that question should be adding more reactant instead of increasing the surface area. Therefore the answers would be correct in saying that by adding more reactants, the rate of reaction does not always increase the rate of reaction

wut?

Fixed it. Sorry about that