Experiment 2- Identification of Substances by Physical Properties

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1

Purpose of Experiment 2?

Familiarize w/ the procedures used in

evaluating physical properties and

the use of these properties to identify substances

2

What will you do in this experiment?

Use the following properties to identify an unknown substance:

solubility, density, melting point, boiling point

3

What are properties?

the characteristics of a substance that

enable us to identify it (distinguish it from all other substances)

4

How can substances be identified?

some can be identified by simple examination

(color, size, shape, texture, odor, etc)

others can also quantifiable examination

a specif combination of properties is unique to a given substance wh/ makes it possible to ID most by careful examination of their properties

5

What are physical properties?

can be observed w/o altering the composition of the substance

6

List 5 physical properties:

  1. Density
  2. Boiling point
  3. Melting point
  4. Solubility
  5. Viscosity
7

Give examples of physical properties that are not easily quantifiable

taste, color, odor, etc (more subjective and difficult to express precisely using numbers)

8

Give examples of physical properties that are more easily quantified.

Density (g/cm3)

Melting point (Celsius), boiling point (C)

Viscosity

Solubility, Refractive index

9

When water and toluene are mixed, two layers form. Is the bottom layer water or toluene?

When water and toluene mix, the water will stay on the bottom layer while the toluene floats. This is due to the difference in their density. Since toluene is less dense, it will rise above water and water will remain in the bottom layer.

Water density= 1.008 g/mL

Toluene density = 0.87 g/mL

10

What is solubility?

solubility of substance in a solvent (usu water)

the maximum weight of that substance that dissolves in a given volume

11

How is solubility expressed (units)?

g/100 mL

12

What is the formula for density?

d= m/v

13

What are melting/freezing points?

the temperature at which the liquid and solid states of a substance are in equilibrium

14

What is the term freezing point?

the equilibrium temperature when approached from the liquid phase (when the solid begins to appear in the fluid)

15

What is the melting point?

the equil temp when approached from the solid phase (when liquid begins to appear in the solid)