Lab O

Question 1

equilibrium

Answer 1

rate of forward reaction equals rate of backwards reaction

Question 2

equilibrium constant

Answer 2

ratio of product concentrations : reactant concentrations

Question 3

How does changing the initial reactant concentrations affect K

Answer 3

K is a ratio and therefore remains the same as long as the temperature remains constant

Question 4

How does changing the temperature affect K

Answer 4

increasing temp. increases the rate of reaction, increasing K

decreasing temp. decreases the rate of reaction, decreasing K

Question 5

What is the mainchemical reaction of experiment O

Answer 5

Fe ^3+ + SCN ^1- = FeSCN ^2+

Question 6

What colour is FeSCN ^2+

Answer 6

orange - red

Question 7

what are the parts of the equation
A = εbc

Answer 7

A = absorbance
ε = proportionality constant/molar absorptivity
b = path length of light through sample
c = concentration of sample in M

Question 8

What wavelength is the absorbance measured at and why

Answer 8

447nm
it is deep blue which is opposite to the orange-red colour of FeSCN ^2+

Question 9

In Lab O, is Fe ^3+ or SCN- in excess and why

Answer 9

Fe ^3+ is in excess so that the reaction can go to completion. All SCN- is used up

Question 10

Why do all solutions of FeSCN ^2+ include a high concentration of H+

Answer 10

does not interfere with reaction but prevents Fe ^3+ from reacting with water to form compounds

Question 11

Experiment O Process Timeline (8)

Answer 11

1. 4 erlenmeyer flasks are prepared.
   - Constant volume and higher M of Fe ^3+
   - Varied vols of SCN- and H2O but constant total volume
2. flasks are stirred to reach equilibrium
3. spectrometer used on blank cuvette at 447nm
4. flask 1 temp is measured, then scanned by spectrometer in a cuvette at 447nm
5. steps 1-4 repeated for each flask
6. 4 new flasks are prepared
   - constant volume and lower M of Fe ^3+
   - varied vols of SCN- and H2O (adds up to 10)
7. spectrometer absorbance test repeated for 4 new flasks