General and characteristic properties

In Physics and Chemistry class, you measured these properties of several materials: mass, volume, density, melting point, hardness, and electrical conductivity. Classify them into two groups: general properties (those that all matter possesses) and characteristic properties (those used to distinguish one substance from another). Briefly justify your classification.

You inflate a balloon and see that it takes up space that it did not occupy before; furthermore, on a very precise balance, the full balloon weighs a little more than the empty balloon, as shown in the diagram.

Which two general properties of matter does air demonstrate with this experiment? Name them and explain which observation corresponds to each.

At the greengrocer's, the shopkeeper places a melon on the scales and they read $2,5\ \text{kg}$.

1. a) Which property of the melon is being measured?
2. b) Is it a general or characteristic property? Justify your answer.
3. c) What is the unit of this quantity in the International System of Units?

Water always boils at $100\ \celsius$ (at sea level) and alcohol at $78\ \celsius$.

1. a) What is the property referred to by these data called?
2. b) Is it a general or characteristic property?
3. c) How would this property help you determine which of the two liquids is in a bottle that has lost its label?

With a coin, you can scratch the wood of a pencil, but no matter how much you rub the wood against the coin, you cannot scratch it.

1. a) Which characteristic property are you comparing with this test?
2. b) Which of the two materials has a higher value for it? Explain how you know.

Marcos has two marbles that weigh exactly $20\ \text{g}$ each: one is made of glass and the other of steel, but they are painted the same colour and have got mixed up.

1. a) Does knowing their mass help him tell which is which? Why?
2. b) Which characteristic property could he measure to distinguish them? Explain how he would do it.

In the laboratory, Lucía pours water into a measuring cylinder up to the $100\ \text{mL}$ mark, as shown in the diagram.

1. a) Which property of water is she measuring with the measuring cylinder?
2. b) Express this quantity in $\text{cm}^3$ (remember: $1\ \text{mL} = 1\ \text{cm}^3$).
3. c) Is it a general or characteristic property?

The teacher heats an unknown white substance and observes that it melts at exactly $80\ \celsius$. The laboratory table lists these melting points: sugar, $186\ \celsius$; naphthalene, $80\ \celsius$; table salt, $801\ \celsius$.

1. a) Which of the three substances is the unknown one?
2. b) Explain why the melting point helps to identify it, whereas the white colour does not.

A substance has a melting point of $-10\ \celsius$ and a boiling point of $60\ \celsius$, as shown in the diagram.

1. a) In which state of matter is it at $20\ \celsius$?
2. b) What about at $-20\ \celsius$?
3. c) What about at $80\ \celsius$?
4. d) Justify each answer by comparing the temperature with the two characteristic points, and explain why these points can be used to predict the state of the substance at any temperature.

Frying pans are made of metal because metal conducts heat from the stove very well to food, but the handle is usually made of wood or plastic, as shown in the diagram.

Explain, using the term 'thermal conductivity', why the frying pan and handle are not made from a single piece of metal.

In winter, walking barefoot on the marble bathroom floor feels much colder than walking on the hallway carpet, even though both are at the same temperature.

1. a) Which of the two materials has higher thermal conductivity?
2. b) Using that fact, explain what happens to the heat from your foot in each case and why the sensation is so different.

An unlabelled piece of shiny metal arrives at the laboratory. You perform three tests and obtain: density $7,9\ \text{g/cm}^3$; melting point $1535\ \celsius$; conducts electric current very well. The candidates are: aluminium ($2,7\ \text{g/cm}^3$, $660\ \celsius$), iron ($7,9\ \text{g/cm}^3$, $1535\ \celsius$) and lead ($11,3\ \text{g/cm}^3$, $327\ \celsius$).

1. a) Which metal is the piece?
2. b) Explain which candidates, if any, are ruled out by each of the three tests.
3. c) Reason why it is advisable to check several characteristic properties instead of settling for just one.

At a street market, a seller claims a bracelet is made of silver. Salma weighs it at home: $31\ \text{g}$. It turns out that a steel teaspoon from her kitchen also weighs $31\ \text{g}$.

1. a) Explain why the mass does not help Salma check whether the bracelet is made of silver.
2. b) The density of silver is $10,5\ \text{g/cm}^3$ and that of steel is $7,9\ \text{g/cm}^3$. Describe which two measurements Salma must take and what calculation she must perform to check this.

A laboratory bottle has lost its label and contains a colourless liquid. You heat it and it boils at $78\ \celsius$. The candidates are: water (boiling point $100\ \celsius$), alcohol ($78\ \celsius$) and acetone ($56\ \celsius$).

1. a) Which substance does it appear to be, based on its boiling point?
2. b) You measure its density and get $0,79\ \text{g/cm}^3$; that of alcohol is $0,79\ \text{g/cm}^3$ and that of acetone is $0,78\ \text{g/cm}^3$. Does this measurement resolve the doubt between alcohol and acetone? Justify your answer.
3. c) Which property turned out to be decisive in this case, and why is it advisable to measure more than one characteristic property to identify a substance?

Your young cousin claims that air 'is not matter, because it weighs nothing'.

1. a) Design an experiment using two balloons and a balance to show him that air has mass: describe what you would do and what he would observe.
2. b) Describe another simple experiment that demonstrates that air occupies volume (think, for example, of an upside-down glass submerged in a basin of water).
3. c) Conclude by explaining why air is matter, using the concept of general properties.