Course

A2 Chemistry: Planning, Analysis and Evaluation (9701)

Name: A2 Chemistry: Planning, Analysis and Evaluation (9701)
Price: 1499 BDT

Paper 5 is one skill in many costumes: plan on paper, straighten the law, take the gradient, and find the measurement that was limiting the result all along.

16 lessons1h 33mEnglish

What you'll learn

State an independent, a dependent and several control variables, each with a value an examiner can credit
Choose apparatus by the precision the measurement needs, and say how a reading becomes an amount in moles
Write a hazard statement that names the substance, its hazard and a precaution that follows
Rearrange a law into y = mx + c and decide what to plot against what
Decide whether a law needs logarithms on one axis or on both, from where the variable sits
Linearise the Arrhenius equation and obtain an activation energy from the gradient
Calculate an intercept algebraically when the origin is suppressed, rather than reading it off the axis
Combine uncertainties: percentages under multiplication and division, absolutes under addition and subtraction
Draw a worst acceptable line through every error bar and use it to find the gradient uncertainty
Quote a result to a precision its uncertainty supports, and say why more figures would be a claim
Identify an anomaly against its error bar, exclude it from the line and account for it
Find the measurement with the largest percentage uncertainty and propose an improvement that removes it

Requirements

AS chemistry: the mole, concentration, titration arithmetic and the ideal gas equation
A2 kinetics: rate equations, the rate constant and the Arrhenius equation
Comfortable with logarithms, rearranging equations, and reading a gradient off a graph

Course content

16 lessons · 1h 33m

Planning an experiment

Fifteen marks for an experiment nobody performs. Name the variables, fix the quantities, and make every hazard statement specific enough to score.

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Variables and the question

One variable changed, one measured, the rest held fixed and SAID to be. A control you do not name is a control you do not get.

Preview8m 2.

Quantities and apparatus

A chemistry plan lives on numbers: what concentration, what volume, in what apparatus, and how it becomes moles.

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Hazards and precautions

Four predictable marks, routinely thrown away. Name the substance, name its hazard, and give the precaution that follows.

Turning data into a straight line

Every Question 2 is the same task in a new costume: rearrange the law into y = mx + c, decide what to plot, and get the constant out of the gradient.

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Choosing what to plot

Rearrange the law until one bracket sits where x belongs. No logarithms yet, because the algebra is the part that goes wrong.

Preview8m 2.

Logarithms in chemistry

A power law needs logs on both axes; an exponential law needs one. Choosing wrongly is a decision, not an accident.

Preview8m

Reading a constant off the gradient

A gradient is not an answer. Ea needs R, a scaled axis needs its factor of 1000, and the intercept is often not on the graph at all.

Uncertainty in a result

Percentages add under multiplication, absolutes add under subtraction, and the gradient gets its uncertainty from the worst acceptable line.

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Combining uncertainties

Add percentages when multiplying, absolutes when subtracting. Getting that the wrong way round is where the marks go.

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The uncertainty in a gradient

Draw the steepest line that still passes through every error bar. The difference from the best line is Δm.

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Significant figures and the final answer

How many figures is not a convention. It is whatever the uncertainty can support, and anything beyond that is a claim.

Evaluation

Identify the point off the line, find the measurement that limits the result, and propose an improvement that removes a named limitation.

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Anomalies and what to do with them

Circle it, leave it out of the line, and say why it might have happened. Deleting it quietly is data selection.

Preview7m 2.

Improving the method

Find the measurement with the largest percentage uncertainty and fix that one. "Be more careful" is not an improvement.

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Paper 5: a full question

One structured question end to end: plan, linearise, take the gradient, propagate the uncertainty and evaluate.

About the creator

8bitlesson

Cambridge O Level, A Level and university courses, taught through interactive labs.

Mentora builds the sciences and mathematics as things you can move rather than videos you watch. Cambridge O Level and A Level mathematics, physics, chemistry and accounting, a primary mathematics track, and first-year university computer science. Every lesson works a real exam question end to end.