Experiment 2 - Physical Properties
Objectives
1. To determine the density of water, alcohol and hexane.
2. To determine the melting point of an unknown compound and then use this melting point
as an aid in its identification. The unknown compound will be one of the following:
o Acetanilide (m.p. = 113-115oC)
o Benzoic acid (m.p. = 122oC)
o Cinnamic acid (m.p. = 133oC)
o Adipic acid (m.p. = 152oC)
o Salicylic acid (m.p. = 159oC)
3. To compare the solubility of various solid substances in water and in hexane. Various
liquids will also be mixed to determine which combinations are miscible and immiscible.
Introduction
Density is a physical property which can be used to identify substances. Density is defined as the
mass per unit of volume (Review Unit 1.8 – Density).
Density = mass/volume
Mass is a measure of the quantity of matter contained in an object. Volume is a measure of the
space occupied by an object.
The melting point and boiling point of a substance are also characteristic physical properties,
which can be used to identify a substance. The melting point is defined as the temperature at
which the liquid and solid phase of a substance co-exist at equilibrium. Pure compounds melt at a
sharp temperature. Impure compounds melt at a lower temperature and over a wider temperature
range. The boiling point of a substance depends on the air pressure. The greater the air pressure
the higher the boiling point.
A solution has two components, a solute and solvent (Review Unit 9.1 – What is a Solution?).
When sugar dissolves in water the sugar is the solute and the water is the solvent. Whether a
solute dissolves in a solvent to form a solution depends on the nature of the solute and solvent.
Substances which dissolve in water (e.g. sugar) are described as being soluble while other
substances (e.g. sand), which do not dissolve in water are described as insoluble.
If two liquids are soluble in each other (e.g. alcohol and water) they are described as being
miscible. Two liquids, which are insoluble in each other (e.g. oil and water) are said to be
immiscible.
Apparatus:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
50 mL Erlenmeyer flask and stopper *
10 mL graduated cylinder *
Balance *
Melting point apparatus *
Watch glass
Melting point tubes
Three large test tubes and stoppers
Test tube rack
Spatula
Waste hexane container *
Liquids:
1. Ethyl alcohol *
2. Hexane *
Solids:
1. Potassium chloride
2. Naphthalene
* View photos on course website
Part A: Density
1. Weigh a clean 50 mL Erlenmeyer flask and rubber stopper.
2. Measure about 10 mL of distilled water with a 10 mL graduated cylinder. Record the
volume accurately with the proper number of significant figures.
3. Transfer the water into the Erlenmeyer flask. Stopper the flask to prevent losses due to
evaporation.
4. Weigh the flask, water and stopper.
5. Repeat the above steps 1 to 4 for ethyl alcohol and hexane. Avoid inhaling hexane
vapour. It is toxic. Pour the hexane into the waste container provided when you are
finished.
Part B: Melting Point
Use the melting point apparatus provided to determine the melting point of the unknown
compound. Your instructor will demonstrate how to use the melting point apparatus.
Part C: Solubility
1. Use a spatula and scoop a spatula tip of potassium chloride and naphthalene into
separate test tubes containing about 5 mL of distilled water.
2. Stopper each test tube and shake.
3. Repeat steps 1 and 2 using hexane as the solvent.
4. Record the solubility (i.e. soluble, slightly soluble or insoluble) for each solid in each of
the two solvents.
5. In separate test tubes: mix:
o 20 drops of alcohol and 2 mL of water
o 20 drops of hexane and 2 mL of water
o 20 drops of hexane and 2 mL of alcohol
6. Record which combinations are miscible and which are immiscible. When you have
finished pour any remaining hexane or any mixture, which contains hexane, into the
waste container provided.
Datasheet:
Part A: Density
Mass of Empty
Flask + stopper
(g)
Water
Ethanol
Hexane
Sample Density Calculation:
Show work here for Ethanol:
Mass of Flask +
stopper +
Liquid
(g)
Mass of Liquid
(g)
Volume of
Liquid
(mL)
Density of Liquid
(g/mL)
% Error Calculation
The percent error is defined mathematically by equation:
% Error = |accepted value - experimental value| / accepted value * 100
Given that the accepted value for the density of ethanol is 0.79 g/mL, calculate the % error in your result.
Show work here and report your answer with proper number of significant figures.
Datasheet:
Part B: Melting Points
Unknown compound ID
Melting point range of
unknown compound
Identity of
unknown compound
Suggest another two physical properties which could be measured to confirm the identity of the
unknown compound.
1. ________________________________________________________________
2. ________________________________________________________________
Datasheet
Part C: Solubility
Describe whether potassium chloride and naphthalene are soluble or insoluble in water
and hexane:
Solvents
Potassium Chloride
Naphthalene
Water
Hexane
Describe whether the following mixtures are miscible or immiscible:
1. Ethanol and water __________________________________________
2. Hexane and water __________________________________________
3. Hexane and alcohol _________________________________________