Criteria for Purity of Substances

Which of the following is the best indicator of a substance's purity?

• Color

• Melting point

• Odor

• Taste

The boiling point of a pure substance is:

• Variable

• Lower than the boiling point of its mixture

• Higher than the boiling point of its mixture

• Constant at a given pressure

In chromatography, a pure substance will typically produce:

• A single spot

• Multiple spots

• No spots

• Undefined spots

Which property is least likely to be affected by impurities in a substance?

• Melting point

• Boiling point

• Density

• Color

The melting point of pure ice is:

• 0°C

• 100°C

• -5°C

• 25°C

In countries where temperature falls below 0 degrees celsius, salt in sprinkled on icy roads to;

• Increase the melting point of ice

• Increase the solubility of salt

• Decrease the melting point of ice

• Decrease the solubility of salt

A substance is said to be impure if

• It has difficulty dissolving in water

• It is colorless

• The melting point has a wide range

• It easily sublimes

The presence of impurities in a liquid typically causes the boiling point to:

• Decrease

• Remain unchanged

• Increase

• Vary randomly

What happens to the melting point of a substance when it contains impurities?

• It increases

• It becomes more defined

• It remains unchanged

• It decreases

Which of the following can be used to determine the purity of an unknown metal?

• Melting point determination

• Chromatography

• Density measurement

• Distillation