VCE CHEMISTRY EXAM MISTAKES

Which of the following reation types has the highest atom economy

Addition: Have 100% atom economy as there is a single product. Condensation, redox and acid base have multiple products

What is the name of the volume dispensed from a pipette

Aliquot

Burette with a resolution of 0.1ml, reading should be recorde too?

Two decimal places

18 mol

Adding more reactant

Predict structure of alanine in solution of pH 7

C-Zwitterion exsists at neutral pH

Statement II

Statement I, II and III

0.2 M

The concentration of the hydrochloric acid was increased from 0.1 M to 0.2 M - increase surface area doesn’t change finam mass lost just increases rate, Volume decrease of HCl decreases mols (HCl already limiting reactant) this would decrease product

Name 3 fossil fuels

Crude oil / petroleum, natural gas / coal seam gas, coal

Equation for fermentation of glucose

C₆H₁₂O₆(aq) > 2C₂H₅OH(aq) + 2CO₂(g)

Ethical and economic issue with growing crops to produce bioethanol

Ethical:Using food crops such as sugarcane for fuel can be seen as unethical if it reduces food availability Economic:Demand for crops for bioethanol may raise the price of these crops making the cost of foods also produced from the same crop more expensive or demand for crops for bioethanol may result in increased cost of farmland

Write a balanced equations using semi-structural formulas to represent the reaction of ethanol with propanoic acid                                           

CH₃CH₂COOH(l) + CH₃CH₂OH(l) > CH₃CH₂COOCH₂CH₃(l) + H₂O(l)

Identify catalyst used to make esters

H₂SO₄

Assign oxidation numbers and explain how this is redox reaction:C₆H₈O₆(aq) + I₂(aq) > 2I^-(aq) + C₆H₆O₆(aq) + 2H⁺(aq)

Increase in oxidation number of carbon (from +2/3 to +1)

Decrease in oxidation number of I₂ (from 0 to -1)

+2/3 +1 -2 0 -1  > +1+1-2       +1       

Equivalence point or redox reaction?

When neither reactant is in excess / reactants have been added in the ratio as indicated by the stoichiometric equation.

Name the 2 highlighted functional groups

Carboxyl, ether

What part of the electromagnetic spectrum is used in 13C NMR spectroscopy in the presence of a strong magnetic field?

Radio waves

What n+1 rule show?

How many (equivalent) hydrogen atoms are present on adjacent carbon atom(s)

Would you expect to observe any splitting (of peaks) on a high resolution 1H NMR spectrum for methoxyethanoic acid?  Justify your response 

No.None of the unique hydrogen environments has hydrogen neighbours on adjacent carbons.

name structure

3-hydroxypropanoic acid

Improvement for solution calorimetry experiment

Place a lid on container containing water

For solution calorimetry experiment student didn’t realise thermometer was incorrectly calibrated. What type of error introduced

No error - measures temperature change

Define resolution

Smallest change in the quantity being measured that causes a perceptible change in the value indicated on the measuring instrument

How could reproducibility of investigation be evaluated?

Have method followed by another researcher at a different time and lab

Halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is a medication with anaesthetic properties. It can be synthesised according to the following equation.1.500 kg of 2-chloro-1,1,1-trifluoroethane was used to produce halothane. Calculate the percentage yield if 842.7 g of halothane was synthesised.

n(C₂H₂F₃Cl) =

mole ratio C₂H₂F₃Cl: C₂HF₃ClBr = 1:1

n(C₂HF₃ClBr) = 12.66 mol

M(C₂HF₃ClBr) = (2 x 12.0) + (1 x 1.0) + (3 x 19.0) + (1 x 35.5) + (1 x 79.9) = 197.4 g mol^-1

m(C₂HF₃ClBr) = n x M = 12.66 x 197.4 = 2499 g

% yield =  x 100 = 33.73%

 

Write an equation using structural, semi-structural or skeletal formulas to show the synthesis of a triglyceride containing three linoleic acid residues. States are not required.

Molecular formula of reactant required to synthesise biodiesel from triglyceride

any alcohol

Type of reaction used to synthesis biodiesel from triglyceride

Transesterification

Strongest bonding in enzyme

Covalent bonds