11.2 Synoptic Data Handling & Graphical Skills

Outline the difference between a random error and a systematic error.

[2]

A student forgets to tare the balance while carrying out an experiment to find the empirical formula of magnesium oxide.

State what type of error this is, and deduce the impact on the student's mass readings.

[2]

Explain how random errors may be reduced in an experiment.

[1]

A student carries out a thermal decomposition of copper(II) carbonate. The copper(II) carbonate is placed in a pre-weighed crucible and the crucible is weighed again when cool. The reaction that takes place is:

CuCO₃ (s)  → CuO(s) + CO₂ (g)

The results are recorded in the table.

	Mass/ + 0.01 g
Mass of empty crucible	38.52 g
Mass of crucible + copper(II) carbonate	46.73 g
Mass of crucible + copper(II) oxide	43.61 g

Calculate the mass of copper(II) oxide formed and determine the percentage uncertainty in the calculated mass.

[2]

Determine the theoretical yield of copper(II) oxide in part a)

[3]

Determine the percentage error in the experiment.

[1]

The student forgets to turn the Bunsen burner, used to heat the crucible, to a blue flame. The yellow, sooty flame, soon coats the outside of the crucible with a black layer.

Identify the black layer and suggest whether the error will have a major or minor effect on their results.

[2]

Explain the difference between a dependent variable and independent variable on a graph.

[1]

A student analyses a set of results from the determination of the empirical formula of magnesium oxide by burning magnesium ribbon.
They plot a graph on the following grid:

Identify the dependent and independent variables.

[1]

The student plots the result an obtains the following graph.

Justify whether a best fit straight line on this graph can or cannot be considered.

[2]

The sketch graph below shows the variation of the mass of magnesium with the mass of oxygen, from the results of an empirical formula investigation.

Describe the relationship between the two variables.

[1]

Using the graph in part a), show how the gradient maybe calculated and explain it's significance for magnesium and oxygen.

[2]

The rate of reaction between magnesium and hydrochloric acid was investigated. The concentration of acid was varied and the results plotted on a graph.

Draw a best fit line and calculate the gradient.

[2]