Question

mass and volume are both extensive properties; they change with the amount of substance, such as cola in the container. density, however, is an intensive property and is independent of the amount of a substance. melting points, boiling points, and conductivity are other intensive properties. two liters of water boil at the same temperature and have the same density as one liter of water does.
analyze classify each statement as an extensive or an intensive property.
extensive intensive
a pot of boiling water has more energy than a cup of boiling water.
a pot of water boils at the same temperature as a cup of water.
copper wire conducts electricity.
a block of ice takes longer to melt than does a small ice cube.
mixtures and pure substances
matter can be either a pure substance or a mixture. a pure substance has a fixed composition. a mixture is a blend of two or more kinds of matter, each of which retains its own identity and properties.
plan how could you determine whether an unknown clear liquid is pure water or salt water? remember that you should never taste any substance of unknown identity.

figure 5: classification of matter

Explanation:

• For "A pot of boiling water has more energy than a cup of boiling water": Energy depends on the amount of substance (volume/mass). More water (pot vs cup) means more energy. So it's an extensive property.
• For "A pot of water boils at the same temperature as a cup of water": Boiling point is a characteristic of the substance (water). It doesn't change with the amount. So it's an intensive property.
• For "Copper wire conducts electricity": Conductivity is a property of the material (copper). It's inherent and doesn't depend on the amount of copper wire. So it's an intensive property.
• For "A block of ice takes longer to melt than does a small ice cube": Melting time depends on the amount of ice (mass/volume). More ice (block vs small cube) takes longer. So it's an extensive property.

For determining if an unknown clear liquid is pure water or salt water:

• Measure boiling point: Pure water has a fixed boiling point (\(100^{\circ}C\) at standard pressure). Salt - water (a solution) has a higher boiling point. Heat the liquid and measure the temperature at which it boils. If it's \(100^{\circ}C\) (standard pressure), it could be pure water. If higher, it's likely salt - water.
• Measure freezing point: Pure water freezes at \(0^{\circ}C\) (standard pressure). Salt - water freezes at a lower temperature. Cool the liquid and measure the freezing point. If \(0^{\circ}C\) (standard pressure), it could be pure water. If lower, it's likely salt - water.
• Evaporate the liquid: Put a small amount of the liquid in an evaporating dish. If it's pure water, after evaporation, there will be no residue. If it's salt - water, a white residue (salt) will be left.

Answer:

• "A pot of boiling water has more energy than a cup of boiling water": extensive
• "A pot of water boils at the same temperature as a cup of water": intensive
• "Copper wire conducts electricity": intensive
• "A block of ice takes longer to melt than does a small ice cube": extensive

For the liquid identification:

• If boiling point is \(100^{\circ}C\) (standard pressure) and no residue after evaporation (or freezing point is \(0^{\circ}C\) (standard pressure)), it may be pure water.
• If boiling point is higher than \(100^{\circ}C\) (standard pressure) and there is a residue after evaporation (or freezing point is lower than \(0^{\circ}C\) (standard pressure)), it is likely salt - water.