temperature on equilibrium yield (observations/results)

[Mr Edwards]

Fe³⁺(aq) + SCN^-(aq) <==> Fe(SCN)²⁺(aq); exothermic
1) Half-fill two semi-micro test tubes with Fe(SCN)²⁺ solution.
2) Place one test-tube in ice-water. Carefully heat the other test tube until the solution almost boils.
3) Compare the colour of the mixtures in the two test-tubes. Recrod your observations.

H₃PO₄(aq) <==> H₂PO₄^-(aq) + H⁺(aq); exothermic
1) Pour 1 M phophoric acid into each of two semi-micro test-tubes, to a depth of about 3 cm. Add two drops of methyl violet indicator to each test-tube.
2) Place one test-tube in ice-water. Carefully heat the other test-tube until the solution almost boils. Record the colour of the indicator in the heated and cooled test tubes.
3) Note the acidity of each solution. Methyl biolet indicator is yellow in solutions with a high concentration of H⁺⁽aq). Its colour changes through green, blue violet as H⁺(aq) concentration reduces.

N2O4(g) <==> 2NO2(g); exothermic
1) Carefully place one of the stoppered test-tubes containing an N2O4/NO2 gas mixture in a beaker of hot water for about one minute, holding the stopper firmly in place. Place the other tube in a beaker of ice-water.
2) Remove the test tubes from the hot water and ice-water and immediately compare the intesities of the brown colour in the tubes. Record your observations.

My question is: Does anybody know what these observations are (the colour changes of solutions in each semi-micro test-tubes)? This practical was done whilst I was away from class and I must do a practical report on it. None of my classmates recorded the results (or remembered them) and my teacher does not have the results. I'm guessing at least some people would have done this experiment here. If anyone could help out it would be appreciated!

[jasoN-]

Well if you know Fe3+(aq) is pale yellow, SCN-(aq) is colourless and Fe(SCN)2+(aq) is red, you could determine the colours without actually having to do the experiment.
i.e. As the reaction is exothermic, heating it will make the solution less red [net back reaction]
cooling the solution will make the solution more intense red [net forward reaction]

Similarly with N2O4(g) and 2NO2(g), you know N2O4(g) is colourless and 2NO2(g) is brown.
If its exothermic, heating will make the solution more pale (ie. less brown)
Cooling will make the solution a more intense brown.

Given the information about the indicator, a forward rection of phosphoric acid forming hydronium ions and dihydrogen phosphate increases the concentration of H+, hence the colour becomes more yellow.
You could argue that reducing the temperature will decrease the concentration of H+, therefore the colour will become more violet (going through green and blue).

Of course all this is theoretical and according to Le Chatelier's principle. But the experiment shouldn't be flawed and little error would probably occur. Just remember to use comparative adjectives for the colours of the solution. (eg. less red, in comparison to the standard (room temp))

[helloworld123]

hey for your answer on this forum dont u mean that for an increase in temperature will decrease the concentration of H+, therefore the colour will become more violet (going through green and blue).??