Chapter 1

Examination of "homogenized" milk under a microscope reveals suspended globules of fat. Is milk a heterogeneous mixture or a homogeneous mixture? Explain.

Fog is a suspension of tiny droplets of water in air. Is fog a heterogeneous mixture or a homogeneous mixture? Explain.

Which of the following are compounds? (a) iron oxide \(\left(\mathrm{Fe}_{2} \mathrm{O}_{3}\right)\) (b) ozone \(\left(\mathrm{O}_{3}\right)\) (c) iron (Fe) (d) carbon monoxide (CO) (e) propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) Answer: \((a),(d)\), and \((e)\) because each is made from more than one kind of element; (b) and (c) are elemental substances, not compounds, because each is made of only one element.

Which of the following are compounds? (a) sulfur \(\left(\mathrm{S}_{8}\right)\) (b) mixture of iron powder and aluminum powder (c) mixture of \(\mathrm{O}_{2}\) gas and \(\mathrm{N}_{2}\) gas (d) sulfur dioxide \(\left(\mathrm{SO}_{2}\right)\) (e) ammonia ( \(\mathrm{NH}_{3}\) )

True or false? A compound is a pure substance, but a pure substance need not be a compound. Give examples to prove your answer.

Ice cubes slowly vanishing while stored in a freezer is an example of (a) vaporization (b) condensation (c) melting (d) sublimation Answer: (d); the ice cubes "vanish" by going directly from the solid state to the gas state.

Molten iron cooling to solid iron is an example of (a) sublimation (b) condensation (c) freezing (d) melting

True or false? After being heated to above its boiling point, ethanol is no longer ethanol but something else. Explain.

You are presented with a block made of some pure metal and told the metal is gold, but you have your doubts. Using a thermometer, how can you determine whether the metal is gold?

Which of the following represent a chemical transformation? (a) \(4 \mathrm{P}(s)+5 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{P}_{2} \mathrm{O}_{5}(s)\) (b) \(\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)\) (c) \(3 \mathrm{O}_{2} \rightarrow 2 \mathrm{O}_{3}\) Answer: (a) and (c) because the products are different from the reactants; (b) is a physical change because we have water on both sides of the arrow.

Water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) and carbon dioxide \(\left(\mathrm{CO}_{2}\right)\) are produced in a chemical reaction when methane \(\left(\mathrm{CH}_{4}\right)\) and oxygen \(\left(\mathrm{O}_{2}\right)\) are combined and heated. Which are the reactants, and which are the products?

What is the relationship between a theory and a law? Answer: \(A\) theory attempts to explain why a law is correct.

What is the relationship between a law and experimental data?

The United States started to undergo electrification in the late \(1800 \mathrm{~s}\), with the first example of widespread electric lighting at the 1893 Chicago World's Fair by Nikola Tesla. In 1831 , Michael Faraday discovered electromagnetic induction, which uses magnets to produce electricity in a wire. Explain which is an example of science and which an example of technology.

Define chemistry.

Give an example (not from this book) of a piece of scientific information and cite both a positive and a negative result of its technological application.

In the United States, most basic chemical research (science) is funded by the government, but most of the money spent on applying scientific knowledge (technology) comes from industry. Why do you suppose industry is reluctant to fund basic research?

When is a mixture not a solution?

Is it possible to have a mixture of compounds? If yes, give an example.

How does a solution differ from a heterogeneous mixture?

Flour is mixed with powdered sugar, and then the combination is ground to a fine dust. Is the resulting product a solution or a heterogeneous mixture? Explain.

Brass is an alloy (a solid solution) of copper, Cu, and zinc, Zn. Given this fact, answer the following: (a) Copper powder and zinc powder are ground together. Is the resulting product a solution or a heterogeneous mixture? Explain. (b) The Cu and Zn powders are ground together, and then the mixture is heated until it is molten metal. Is the molten metal a solution or a heterogeneous mixture? Explain. (c) The molten metal from part (b) is allowed to cool and solidify. Is the resulting solid a solution or a heterogeneous mixture? Explain.

The air you breathe is properly called a solution. Explain why.

What is an element? How many elements are known today?

If \(\mathrm{H}\) is the symbol for the element hydrogen and O is the symbol for the element oxygen, why is the symbol for sodium Na rather than \(S\), and the symbol for iron Fe rather than I?

What is the smallest possible piece of an element called?

Refer to the list of elements that appears on the inside front cover. What are the symbols for the elements lead, molybdenum, tungsten, chromium, and mercury?

Refer to the list of elements that appears on the inside front cover. Give the element name that goes with each symbol: \(\mathrm{Ti}, \mathrm{Zn}, \mathrm{Sn}, \mathrm{He}, \mathrm{Xe}, \mathrm{Li}\).

Sulfur is known in many forms, including yellow sulfur (formula \(\mathrm{S}_{8}\) ) and orange-red sulfur (formula \(\mathrm{S}_{6}\) ). Heating either of these forms to very high temperatures can yield \(\mathrm{S}_{2}\). Also known is a substance with the formula \(\mathrm{SO}_{2}\). Since all of these substances are made of elements, are they all elemental substances? Explain.

Compounds have properties that are different from those of their constituent elements. Discuss a real example to support this statement.

Which of the following are elemental substances and which are compounds: \(\mathrm{F}_{2}, \mathrm{BrCl}_{3}, \mathrm{P}_{4}, \mathrm{C}_{2} \mathrm{H}_{2}, \mathrm{HCl}, \mathrm{Ar}, \mathrm{Al}_{2} \mathrm{O}_{3}, \mathrm{Al} ?\)

Which of the following are elemental substances and which are compounds: chlorine, \(\mathrm{Cl}_{2}\); octane, \(\mathrm{C}_{8} \mathrm{H}_{18} ;\) sulfur, \(\mathrm{S}_{8} ;\) neon, Ne?

The smallest possible piece of the compound hydrogen peroxide contains two hydrogen atoms and two oxygen atoms. Write the chemical formula for hydrogen peroxide, with hydrogen first.

The smallest possible piece of the compound nonane, a component of gasoline, contains 9 carbon atoms and 20 hydrogen atoms. Write the chemical formula for nonane, with carbon first.

The smallest possible piece of the sugar glucose has twice as many hydrogen atoms as oxygen atoms or carbon atoms. Given that glucose has six carbon atoms, write its chemical formula with carbon first, then hydrogen, then oxygen.

The air you breathe is made up mostly of nitrogen gas, \(\mathrm{N}_{2}\). (a) What can you say about the smallest possible piece of nitrogen gas? (b) Is nitrogen gas a compound? Explain.

What are the three most common states of matter?

What is the name of the process by which matter changes directly from the solid state to the gas state?

What is the name of the process that is the opposite of evaporation?

Propane has a boiling point below room temperature, and hexane has a boiling point above room temperature. In what physical state would you expect to find each substance at room temperature (which is usually about \(\left.20{ }^{\circ} \mathrm{C}\right) ?\)

At normal atmospheric pressure, the freezing point of ethanol is \(-114^{\circ} \mathrm{C}\) and its boiling point is \(78.4{ }^{\circ} \mathrm{C}\). What is the melting point of ethanol?

Solid mothballs work by filling a closet with a chemical vapor that is toxic to moths, and the balls shrink and disappear slowly with time. What is going on?

What are the melting point and boiling point of water in degrees Celsius and degrees Fahrenheit (at normal atmospheric pressure)?

Water, \(\mathrm{H}_{2} \mathrm{O}\), is a harmless liquid, but hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\), is a poison. How is this possible, given that both are compounds of hydrogen and oxygen?

When you eat sugar \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\), it is eventually converted into \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\), which you exhale. If you exhale onto a cold window, the window fogs up. (a) What chemical change is being mentioned here? (b) What physical change is being mentioned here? (c) \(\mathrm{CO}_{2}\) is a solid that sublimes at \(-78^{\circ} \mathrm{C}\). Temperatures on planet Earth almost never get this cold. What does that tell you about the fog on the window?

When a candle burns, the solid wax melts and burns. In the process, the wax is combined with oxygen from the atmosphere and converted into carbon dioxide and water vapor. Explain what is going on in terms of chemical change and physical change.

Gasoline can be thought of as having the formula \(\mathrm{C}_{8} \mathrm{H}_{18}\). When gasoline is used in a car's engine, it reacts with oxygen \(\left(\mathrm{O}_{2}\right)\). If you look closely at the exhaust pipe of a running car, you will see water dripping out of it. Where did this water come form (what kind of change is involved)?

When exposed to oxygen in the air, white phosphorus, \(\mathrm{P}_{4}\), catches fire and produces the compound \(\mathrm{P}_{4} \mathrm{O}_{10}\). Is this a description of a physical property or a chemical property of phosphorus? Explain.

Is the tarnishing of silver, Ag, a physical change or a chemical change? (The chemical formula for the tarnish on silver is \(\mathrm{Ag}_{2} \mathrm{~S}\).)

Nitrogen, \(\mathrm{N}_{2}\), combines with hydrogen, \(\mathrm{H}_{2}\), to give ammonia, \(\mathrm{NH}_{3}\). Nitrogen and hydrogen are odorless gases that are not very soluble in water. Ammonia is also a gas, but it has an extremely powerful odor and is very soluble in water. How can you explain this great difference in properties?