Some Questions!! (1 Viewer)

[Premus]

These are questions from the 2004 independent paper

q24)
a bottle of vinegar is labelled 4.0% w/v (4.0g per 100mL of solution) acetic acid(ethanoic acid)
a) Describe the lab procedure you would use to verify this concentration.
b) calculate the volume of 0.118 mol/L NaOH required to neutralise the acid in 5.0mL of this vinegar.

q27) partb) .....its from a graph, so i cant type it out.( idont have a scanner)

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other random questions..

1. in the reaction btw Br and cyclohexane/ene ........ how come both decolourise in the presense of UV light? do we need to know why?

2. what would be the differences in terms of turbidity, dissolved oxygen, pH, BOD, dissolved solids when you compare sea water , tap water and fresh water?

Thank you sooo much in advance!

 

[lucyinthehole]

for q24, that'd be a titration, wouldn't it?


1. yes, you need to know why. they both discolourise because the UV light gives energy to the reaction with cyclohexAne, and the cyclohexene just does it in normal conditions

 

[Steven12]

i am not good at this so, if anybody can tell me if i am wrong

for q24 (b)

first we work out the concentration of acetic acid. 4/100ml is 40/(litere)
40 g per 1 litre of vinegar. since molar mass of ethanoic acid is (60g)

40/60=2/3 mol per litre

naoh+ch3cooh=Nach3coo+h2o

ratio is 1:1

so we balance

0.118* volume=5*(2/3)
volume=28.25 (ml)

i think i did it right

 

[Paroissien]

These are questions from the 2004 independent paper
1. in the reaction btw Br and cyclohexane/ene ........ how come both decolourise in the presense of UV light? do we need to know why?

2. what would be the differences in terms of turbidity, dissolved oxygen, pH, BOD, dissolved solids when you compare sea water , tap water and fresh water?

Thank you sooo much in advance!

1. You don't need to know why.

 

[Tommy_Lamp]

q24a) You would do a titration. Titrate the vinegar with sodium hydroxide. This is weak acid + strong base hence equivalence point would be basic, hence Phenolphthlein indicator.
q24b) Using your value of the acetic acid concentration in a), you just do a basic calculation.
c1v1 = c2v2
v1 = (c2v2)/c1

27b) You would graph the Nickel Concentration vs. Absorbance. Concentration, being the independant variable, would be on the x-axis. Absorbance, being the dependant variable, would go on the y-axis.


1. The whole idea is that the reaction between cyclohexene and bromine water occurs much faster then the reaction between cyclohexane and bromine water. All the UV light does is speed it up.
2.
Turbidity: Salt water>Freshwater>Tap Water
DO: No idea
pH: Saltwater = ~8, Tap Water = ~8 Freshwater = No idea, probably around 6-7 since rainwater is generally slightly acidic
BOD: Freshwater/Saltwater > Tap Water
DO: Saltwater>Freshwater>Tap Water

Hope that helps.

 

[Premus]

Hey

For q 27 from the paper...i get the graph....but i dont get the calculation??
Using the graph, determine the concentration of nickel in the original sample of river water

Thanks!!