PACES Chemistry

Purposeful Academic Classes Excelling Students

Wednesday 15th April 2009Shenton College

Why are we here?

How can we benefit from these sessions?

What resources are available

to help us maximise ourperformance?

✴teacher generated revision materials (ie from your school

and my podcasts and our forum page).

✴syllabus statement✴examiner’s report

✴past papers and solutions✴revision books (eg Creelman,

Academic Associates etc)

✴teacher generated revision materials (ie from your school

and my podcasts and our forum page).

✴syllabus statement✴examiner’s report

✴past papers and solutions✴revision books (eg Creelman,

Academic Associates etc)

✴teacher generated revision materials (ie from your school

and my podcasts and our forum page).

✴syllabus statement✴examiner’s report

✴past papers and solutions✴revision books (eg Creelman,

Academic Associates etc)

•Name•School•favourite ….?•intended course and institution•etc

✴investigate effective strategies for multiple choice,

calculation and extended answer style exam questions.

My aims for today’s session:

✴look at effective use of the syllabus statement, and

examiner’s reports

✴electrochemistry

Your suggestions for today:

✴extended answer questions✴bonding

✴electron configuration✴calculation strategies

✴redox

✴extended answer questions

2008 examiner’s report

page 1 summarypage 2 structurepage 3 structure and general commentspage 4 specific comments (multi-choice)page 5 specific comments (part 2)page 6 specific comments (part 3)page 7 specific comments (part 4)pages 9 - 30 marking guidelines

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All nitrates, and potassium and sodium salts are soluble and colourless solutions result. Any soluble nickel salt produces a green solution.

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Calcium carbonate is insoluble.

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Cadmium carbonate is insoluble.

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Cadmium carbonate is insoluble.

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ie which would favour the forward reaction.

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(a) adding a catalyst speeds up both forward and reverse rates but doesn’t favour either reaction.

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(b) adding Ar(g) increases overall pressure, but does not alter any of the individual gas pressures (ie concentrations) and therefore has no effect on equilibrium.

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(c) increasing the pressure would increase the concentrations of all gases, but would have a greater impact on the product side and would therefore favour the reverse reaction.

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(d) increasing the temperature will alter the equilibrium and favour the forward reaction.

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(d) increasing the temperature will alter the equilibrium and favour the forward reaction.

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Text

Rate is decreased by decreasing pressure, temperature, surface area, and use of an inhibitor.

Only alternative (a) satisfies these criteria.

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2008 TEE multiple choice examples

part 2 questions 2008 TEE

TEE part 3

a standard procedure for attempting chemistry

calculations

calculations in chemistry often appear to be unique

and complex ….

They may appear to be something that you’ve not

encountered before, but every calculation type that you will see in high school chemistry

can be approached in the same way.

Step 1

I suggest that the first step in any chemistry calculation, after

balancing equations, is to determine the number of moles of any substance that you can.

Eg. Phosphoric acid can be made by the following reaction:

Ca3(PO4)2(s) + H2SO4(aq) -> CaSO4(s) + H3PO4(l)

Balance the equation

b) How many grams of phosphoric acid can be made by reaction of 155 g of Ca 3(PO4)2(s) with more than enough (excess) sulfuric acid?

Eg. Phosphoric acid can be made by the following reaction:

Ca3(PO4)2(s) + 3H2SO4(aq) ->3CaSO4(s) + 2H3PO4(l)

Balance the equation

b) How many grams of phosphoric acid can be made by reaction of 155 g of Ca 3(PO4)2(s) with more than enough (excess) sulfuric acid?

if you have the mass of a solid you would use:

number of moles = actual mass ÷ molar mass

ie n = m/M

if you have the volume of a solution you would use:

number of moles = concentration x volume

ie n = cv

if you have the volume of a gas you would use:

n = PV/RTor n = VSTP/22.41

Step 2

The second step you should employ is to use the ratio from the chemical equation for the

reaction to determine the number of moles of the

substance that you need to find out about.

Step 3

The third step is to use the value of the number of moles that you have just determined

to work out the substance’s mass, volume, concentration

etc.

Step 4

The fourth step is to use the substance’s mass, volume,

concentration etc. to answer the question. ie % composition,

empirical formula etc

mass

vol (gas)

conc &vol

current& time

moles ofknown

moles ofunknownmoles ofunknown

mass

conc &vol

current& time

vol (gas)

from equation ratio

use formulae to determine nuse formulae to determine m, v, etc

Empirical and molecular formulaeStep 1

DETERMINE THE NUMBER OF MOLESi. Start with an AMOUNT of each element. (ie % or g)

ii. Convert the amount to grams of the elementa.) if % convert to g in 100gb.) if g of compound, convert to g of an element. (eg C = 12.01g/44.01g in carbon dioxide and H = 2.016/18.016g in water)

iii. Convert grams to moles (molar masses)

Empirical and molecular formulaeStep 2

COMPARE THE NUMBER OF MOLES

i Look at the number of moles of each element and find a ratio that relates them.

(Hint: divide each number of moles by the smallest number to simplify the ratio.)

ii. Reduce to whole integers a.) round only 0.1 and 0.9 b.) multiply all others (eg. 1.3 x 3 = 3.9 & 2.5 x 2 = 5)

Empirical and molecular formulaeStep 3

ANSWER THE QUESTION

i. Determine the empirical formulaIf the compound is ionic then you have finished, but if it is a molecular compound, then …..

Is a molar mass given?

ii. If molar mass = empirical formula mass, then the empirical formula is the molecular formula

iii. If the empirical formula mass is some multiple (x) of the molar mass, then distribute the multiple (x) to the empirical formula, to determine the molecular formula.

Empirical and molecular formulaeStep 3

ANSWER THE QUESTION

iv. Is any information on the no. of atoms given?  IF NO INFORMATION GIVEN ASSUME EF=MF

Empirical and molecular formulaeHints:-- always proceed down the process NEVER go backwards -- do not round until the very end-- all percentages must add to 100-- the grams of all species present must total to the mass of the compound present-- make sure Ar not MW used in calculations (eg. Ar(O) = 16, not 32)-- make sure multiples of EF to MF distributed properly (ex. 5CH2O = C5H10O5)

Empirical and molecular formulae

Problems: A sample contains 71.65% Cl, 24.27% C and 4.07% H. The molecular weight is known to be 98.96 g/mol.

What are the empirical and molecular formulas?

Empirical and molecular formulae

Problems: A 0.1000 g sample of a compound composed of C, H and O undergoes combustion analysis. If 0.0928 g of water and 0.288 g of carbon dioxide are collected, what is the molecular formula for the compound?

Extended answer style questions

ie part 4 of your exam.

2007 TEE multiple choice examples

2007 TEE part 2 examples

2007 examiner’s report

page 1 summarypage 2 structurepage 3 structure and general commentspage 4 specific comments (multi-choice)page 5 specific comments (part 2)page 6 specific comments (part 3)page 7 specific comments (part 4)pages 9 - 30 marking guidelines

2007 TEE multiple choice examples

2007 TEE part 2 examples

2007 TEE part 3