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Leeming SHS Yr 11 Chemistry STAWA Exp 9

STAWA9.DOC Adapted from the STAWA Chemistry Lab Manual by Rob Namestnik Page 1

Students Name: Date:

Electrical conductivity of ionic & covalent molecular substances

Background

When elements join together to form compounds, ionic or covalent bonds canhold the atoms together. In ionic bonds the atoms achieve a noble gas electronconfiguration by transfer of electrons from one atom to another. The positive andnegative ions are held together by electrostatic forces to form an ionic lattice.When compounds are molten or dissolved in water the ions can move through theliquid and are therefore able to conduct an electric current.

In covalent bonds the atoms achieve a noble gas electron configuration bysharing electrons between atoms. When molten, covalent substances do notconduct an electric current, as there are no charge carriers to move through the

liquid. When dissolved in water, some covalent substances react to produce ionsand hence a conducting solution results. In this experiment the electricalconductivities of some substances in the molten state, liquid state and in aqueoussolution will be investigated. From this you should be able to draw someconclusions about the nature of the bonding in these substances.

Equipment and chemicals

D.C. power supply (0-12V) Bunsen burner

ammeter or globe ( 6V, 500 mA) clay pipe triangle

4 x electrical leads 2 withalligator clips

tripod

emery paper crucible & lid (at lest 2 required)

tongs paper towel to dry electrodes

wire electrode system(see diagram next page)

100 mL beaker

plate electrode system(see diagram next page)

kerosene (50 mL)

ethanol (50 mL) sodium hydroxide NaOH (5g)

deionised water (50 mL) silver nitrate Ag NO3 (5g)

sucrose solution C12H22O110.1 mol L

-1(50 mL)

candle wax (5g)

sodium chloride solution NaCl0.1 mol L

-1(50 mL)

naphthalene C10H8 (5g)

sodium hydroxide NaOH0.1 mol L-1 (50 mL)

sulfur S8 (5g)

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International safety card information

Use the website to find safety information for all the hazardous chemicals used in this experiment

http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/

Electrode construction details

Safety Information (Steps 1 - 6)

Sodium hydroxide - NaOH is very corrosive and must NOT be allowed tocome into contact with your skin or eyes.

Handle the NaOH pellets with a spatula

Handle the silver nitrate - AgNO3 carefully as it produces dark stains onskin.

Be extremely careful when handling the molten substances.

wire electrode system plate electrode system

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Part A Electrical conductivity of some molten substances

1. Connect a 6 V DC power supply, ammeter and or globe and wire electrodesystem in series as shown in the diagram below.

2. Place some sodium hydroxide pellets in a crucible to a depth of about

0.5 cm.

Place the crucible on a clay pipe triangle supported by a tripod.

3. Gently heat the crucible until the sodium hydroxide melts. Do NOT heatthe crucible excessively. Apply enough heat to keep the sodium hydroxidejust molten.

4. Place the electrode system into the molten sodium hydroxide (the melt)and note the conductivity in terms of the brightness of the globe or theammeter reading. It is necessary to continue gentle heating, as there will

be some solidification around the cool electrodes.

5. Remove the electrodes and clean them thoroughly with some emerypaper.

6. Repeat the procedure using silver nitrate instead of sodium hydroxide in aclean crucible.

Safety Information (Step 7)

Care must be taken when heating the candle wax, sulfur, andnaphthalene.

If they catch fire, use tongs to place a lid on the crucible. This willextinguish the fire - by starving it of oxygen

After the crucibles have cooled, wash out those containing the NaOH andAgNO3 and scrape out the others.

7. Repeat the procedure using, in turn, candle wax, sulfur and naphthalene.

Record your results in the Data Sheet supplied.

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Part B Electrical conductivity of some liquids and aqueous solutions

1. Connect a 6 V DC power supply, ammeter and/or globe, and plateelectrode system in series as shown on the previous page.

2. Place about 50 mL of kerosene into a 100 mL beaker. Place the plateelectrode system into the liquid and note the conductivity in terms of thebrightness of the globe or the ammeter reading. Record your results in theData Sheet.

3. Remove the electrodes and dry them with a paper towel.

4. Repeat the procedure using, in turn, ethanol, distilled water, 0.1 mol L-1sucrose, 0.1 mol L

-1NaCl, 0.1 mol L

-1NaOH and 0.1 mol L

-1HCl.

Record your results in the Data Sheet.

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Data Sheet

Part A

Molten compounds

tested

Ammeter reading or

globe brightness

Type of bonding

NaOH

AgNO3

candle wax

sulfur

naphthalene

Part B

Liquid samples tested Ammeter reading orglobe brightness

Type of bonding

kerosene

ethanol

distilled water

naphthalene

Aqueous compoundstested

Ammeter reading orglobe brightness

Type of bonding

0.1 M sucrose -

C12H22O110.1 M NaCl

0.1 M NaOH

0.1 M HCl

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Processing of results and questions

Question 1

a) Which of the pure substances (not the solutions) tested in parts A and Bconducted an electric current?

b) What can you say about the nature of the bonding present in thesesubstances?

c) List the species which were the charge carriers in each case.

Question 2

a) List the pure substances tested in the experiment that did not conduct anelectric current.

b) What can you say about the type of bonding present in these substances?

c) What species are present in each case?

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Question 3

a) Which of the solutions (sucrose, NaCl, NaOH, and HCl) conducted anelectric current?

b) List the species present in each case and state why the solutions areconducting or not.

Question 4

In the solid state, both NaCl and NaOH are ionic lattices. What happens tothese substances when they dissolve in water?

Question 5

Pure HCl is a covalent molecule. What happens to each HCl moleculewhen it is dissolved in water?

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Question 6

Use the website links provided under the safety notes on page 2 to findsafety information for the following:

a) Describe in your own words, the dangers associated with using

molten sodium hydroxide - NaOH

b) What is the main danger associated in using paraffin wax(candle wax) in the way you did in part B?

c) Is AgNO3 dangerous to handle? Explain?

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