Unit 2

Evaluation(d) Are there any flaws or possible improvements in the

Experimental Design? Describe briefly.

(e) Suggest some improvements to the Materials andProcedure.

(f) How certain are you about the evidence obtained?Include possible sources of error or uncertainty.

Quantitative Paramagnetism

In Investigation 3.5.1, you obtained some preliminary evi-dence for a possible connection between unpaired electrons(as determined by the electron configuration) and paramag-netism. The purpose of this lab exercise is to test this hypoth-esis with a quantitative experiment.

QuestionWhat effect does the number of unpaired electrons have onthe strength of the paramagnetism of metal salts?

Prediction/Hypothesis(a) Write a prediction and provide your reasoning

based on electron configurations.

Experimental DesignA sensitive electronic balance is used to measure the attrac-tion between a powerful magnet and a test tube containinga metal salt. The balance is tared (zeroed) before the testtube is lowered (Figure 4). The mass reading is taken justbefore contact of the test tube with the magnet. Several ionic

Questioning Planning Analyzing

Hypothesizing Conducting Evaluating

Predicting Recording Communicating

LAB EXERCISE 3.6.1 Inquiry Skills

INVESTIGATION 3.5.1 continued

electronic balance

wooden block

neodymium magnets

paramagnetic substance

test tube

clamp

paper

Figure 4A strong magnet or magnets (such as

neodymium magnets) and a paramagnetic

substance attract each other. This means that

the magnet and block are slightly lifted toward

the fixed test tube.

compounds containing different metal ions are individuallytested using the same mass of each compound.

(b) Identify the independent, dependent, and controlledvariables.

EvidenceTable 1: Change in Mass in a Strong Magnetic Field

Ionic compound Mass reading, �m (g)

CaSO4(s) 0.00

Al2(SO4)3(s) 0.00

CuCl(s) 0.00

CuSO4�5H2O(s) �0.09

NiSO4�7H2O(s) �0.22

CoCl2�6H2O(s) �0.47

FeSO4�7H2O(s) �0.51

MnSO4�H2O(s) �1.26

FeCl3�6H2O(s) �0.95

mass of each compound in test tube � 3.00 g

Analysis(c) What is the significance of a zero-mass reading for

some substances and negative-mass readings forother substances?

Atomic Theories 215NEL

(d) How does this change in mass relate to the paramag-netic strength of the substance? (Each of the com-pounds has a different molar mass and therefore adifferent amount in moles in the controlled mass of3.00 g. In order to make a valid comparison, you needto know the change in mass per mole of the sub-stance.)

(e) Create a table with headings ionic compound, molarmass, number of moles. Create and complete anothertable with the following headings: metal ion, electronconfiguration, number of unpaired electrons, massdecrease per mole.

(f) Plot a graph of the number of unpaired electrons (x-axis) and mass decrease per mole (y-axis). Draw abest-fit line.

A mechanical model of Schrödinger’s standing waves asso-ciated with electrons can be made using a thin, stiff, loop ofwire which is vibrated with a variable frequency mechanicaloscillator. The mechanical oscillator is like a heavy-dutyspeaker cone with a rod attached to its centre. As the coneand rod move up and down, whatever is attached to the rodoscillates up and down.Vibrating one point in the loop sets upwaves in the wire. This is like holding the edge of a long spring,oscillating one end back and forth, and generating waves thatmove along the spring. When returning waves meet theyinterfere with each other, either constructively (increasingthe amplitude) or destructively (decreasing the amplitude).Standing waves are a special case of wave interference thatresults in apparently stationary nodes (zero amplitude points)and antinodes (maximum amplitude points).

• Secure the oscillator on a sturdy stand. Attach the plugcontaining the loop of wire and adjust so that theplane of the loop is horizontal.

• Set the frequency to its lowest setting. Plug in theoscillator and turn it on.

(g) Answer the Question asked at the beginning of thisinvestigation.

Evaluation(h) Evaluate the Experimental Design. Are there any

obvious flaws? Any improvements?

(i) Suggest some improvements to the materials and pro-cedure that would improve the quality and quantityof the evidence collected.

(j) How confident are you with the experimental answerto the question?

(k) Evaluate the Prediction (verified, falsified, or incon-clusive). State your reasons.

(l) Does the hypothesis appear to be acceptable based onyour evaluation of the prediction?

• Slowly increase the frequency and observe the results.

• Continue increasing the frequency until no furtherobservations are possible because the nodes and antin-odes are no longer visible.

• Slowly decrease the frequency back down to its lowestsetting and view the changes in reverse order.

• Repeat this procedure, if necessary, to complete yourobservations.(a) Describe, in general, the appearance of the nodes

and antinodes.(b) Do all frequencies produce standing wave pat-

terns? Discuss briefly.(c) List the number of antinodes from the lowest pos-

sible to as many as you were able to observe.(d) How does this physical model relate to the wave

mechanics model of the atom? What are somelimitations of this model?

LAB EXERCISE 3.6.1 continued

ACTIVITY 3.7.1

Modelling Standing Electron Waves

216 Chapter 3 NEL