ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: lzxnl on October 01, 2013, 09:04:12 pm
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Just a few uncertainties I've come across in some chemistry exams.
2009 VCAA question 9. K for the reaction 1/2 H2 + 1/2 F2 => HF is given as 313 at 298 K. But let's use some common sense...is fluorine REALLY going to be more stable bonded to another large fluorine, meaning a larger atomic separation, or when bonded to a tiny hydrogen where it can grab more electron density and form more hydrogen bonds with other HF molecules? A quick search online gives the actual K value as more than e^100 for that reaction. Come on. The natural log of the actual K value is closer to the given K value.
Learning Materials Lisachem 2012 Unit 4 Exam, Multiple Choice Question 13
OK, so we have carbon electrodes, an aqueous solution of 1.0 M XY and we've added bromothymol blue indicator. When an electric current is passed through the cell at 298 K, the solution around the positive electrode changes from green to yellow (due to the indicator; implies solution is initially neutral). Now my only problem is...the given answer, potassium fluoride, is a weak base...unless there is something else in the solution to keep the solution neutral, we wouldn't have green bromothymol blue indicator. If you do the calculations, using the acidity constant for the conjugate acid HF given in the data booklet, you can work out that 1.0M KF has a pH f around 8.56, which is outside bromothymol blue's "neutral" zone. Is my interpretation incorrect or is there a problem with the question?
Insight 2012 Unit 3 Exam Extended Response question 5di
We're asked to find the average titre of HCl, and the answers use the three titres given, 10.12, 10.18 and 9.98 mL in the calculation of the average titre. I swear we're not meant to use non-concordant titres...
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Anyone who's done Chemology U3 2008:
please check question 1 of the short answer and tell me I'm not hallucinating. They screwed the answer/question up (see it as you will) I think.
They also gave the wrong answer to question 3 of the multiple choice. >:(