Procedure

 Examine the following chemicals at their various stations:

NaCl        Ethanol                  CuSO4           NH4NO3                  Kerosene       Sulfur      CaSO4

Ca(NO3)2  Sucrose                  Unknown      O2                          K3Fe(CN)6

Record your observations in a table with the following headings:

Name, Formula, Ionic or Molecular, State at RT, Solubility, Colour of Solution, Conductivity of Solution, Melting Point, Boiling Point

Analysis Questions

Make a generalization about ionic and covalent substances by filling in the following table

ClassificationState at RTSolubility in H2OColour of solutionConductivity of solutionMelting PointBoiling Point
Ionicsolidyescolourlessyeshighhigh
Molecularliquidyescolourlessnolowlow

 

Determine whether the unknown is ionic or molecular. Give reasoning.

The unknown is ionic because its state at RT is solid, it is soluble in water, it is colourless and has conductivity in water. According to my lab results, all the ionic chemicals had the same chemical properties as the unknown chemical; therefore the unknown must be ionic.

Use the generalizations from above to classify the following substances as ionic, molecular or classification not possible with information given.

Properties of the Pure SubstanceIonic, molecular or?
A solid with dissolves in water to form a colourless, non-conducting solutionIonic
A liquid which dissolves in water to form a colourless solutionMolecular
A solid which dissolves in water to form a colourless solutionNot enough info
A solid which dissolves in water to form a coloured solutionIonic
A solid which does not dissolve in waterMolecular
A gas at room temperatureMolecular
A white solid which has a melting point of 800oCIonic
A substance which forms a conducting solutionIonic

 

A solid ionic substance like sodium chloride will not conduct electricity unless it is dissolved in water or melted (fused)

Why is water needed for electrical conduction?

Free ions in water conduct electricity. Water quits being an excellent insulator once it starts dissolving substances around it. Salts, such as common table salt (NaCl) is the one we know best. In chemical terms, salts are ionic compounds composed of cations (positively charged ions) and anions (negatively charged ions). In solution, these ions essentially cancel each other out so that the solution is electrically neutral (without a net charge). Even a small amount of ions in a water solution makes it able to conduct electricity. Once water contains these ions it will conduct electricity, such as from a lightning bolt or a wire from the wall socket, as the electricity from the source will seek out oppositely-charged ions in the water. Too bad if there is a human body in the way.

Why must an ionic solid be melted before it will conduct electricity?

Current is carried by the movement of ions, not by the movement of electrons. If it is solid the ions cannot move.

Define the terms electrolyte and non-electrolyte. Give an example of each.

The term electrolyte means that this ion is electrically-charged and moves to either a negative (cathode) or positive (anode) electrode: ions that move to the cathode (cations) are positively charged and ions that move to the anode (anions) are negatively charged.

E.g. (Na+) – cation (Cl-) – anion

A nonelectrolyte does not dissociate at all in solution and therefore does not produce any ions. Nonelectrolytes are typically polar covalent substances that do dissolve in water as molecules instead of ions. Sugar (C12H22O11) is a good example of a nonelectrolyte.

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