Last-Minute Tips for the VCE Chemistry Exam

exam-hall-empty
You’ll be sitting here tomorrow.

Only positively-charged fragments from mass spectrometers produce a peak on the spectrum. Uncharged free radical fragments are not detected because they lack a positive charge.

Weak acids with a lower Ka value are the weakest… this means that they ionise to a lesser extent when in aqueous solution, giving rise to a lower concentration of available H3O+(aq) and a higher pH.

The conversion of triglycerides (a type of ester) into biodiesel (another type of ester) is called transesterification.

The covalent bonds between deoxyribose and phosphate groups in DNA form a group of atoms called a phosphodiester group.

Ether bonds and glycosidc bonds are not the same. Ether bonds are C-O-C. Glycosidic bonds are a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.

Amide groups and peptide groups are not the same, either. Amide groups are CONH. Peptide groups are CONH between amino acid residues in a polypeptide chain. Nylon, for example, has amide groups (CONH) which aren’t called peptide groups.

Ether: C-O-C
Ester: COO
Amine: NH2
Amide: CONH

The molar mass of any amino acid without its Z-group is 74 gmol-1.

The molar mass of glucose, fructose and galactose (all monosaccharides) is 180 gmol-1. By coincidence, aspirin is also 180 gmol-1.

The molar mass of sucrose is 342 gmol-1 because (180*2)-18=342.

In general, energy is required to break bonds. Energy is released when bonds are formed.

Use the formula C-(H/2) to find how many C=C are present in a fatty acid (only works for fatty acids).

Use the shortcut formula (Ka/[acid])^0.5 to find % ionisation of a weak acid.

Use -log(Ka) to find the exact pH at the end point of an indicator.

Use the quick titration formula for rapid multi-choice titration questions: c1v1/ratio1 = c2v2/ratio2

A hydrogen bond is an intermolecular bond that forms between O-H groups. The covalent bond between the O and the H is not a hydrogen bond.

Can you write the half-equation for the reaction occurring at the anode in an ethanol-oxygen fuel cell with an alkaline electrolyte? Tip: start by writing the known reactants and products then use KOHES(OH) to balance your equation.

The products of a titration determine the pH at the equivalence point. For example, the the pH at the equivalence point in a titration between CH3COOH(aq) and NaOH(aq) is around 8.5 because at equivalence point, only products are present: Na+(aq) and CH3COO(aq). The ethanoate ion (CH3COO(aq)) is a weak base, which makes the solution produced slightly basic.

If you have absolutely no clue in the multiple choice sections, pick C. In the last 4 years of VCE Chemistry examinations, C has been correct 50% more of the time than B.

The multiple choice questions really do get harder towards the end. I’ve done the statistics.

Use your reading time wisely. During reading time, read all the questions with the following idea in mind: “how would I do this question?” without actually doing the question.

Bring sharp pencils.

Sleep early tonight (before 9pm). At this stage, getting enough sleep is far more important than revising those tiny details that may or may not come up in the examination.

All the best tomorrow.

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