Chapter 3

Seawater is composed of salt, sand, and water. Is seawater a heterogeneous or homogeneous mixture? Explain.

Iced Tea Use iced tea with and without ice cubes as examples to explain homogeneous and heterogeneous mixtures. If you allow all of the ice cubes to melt, what type of mixture remains?

Chromatography What is chromatography, and how does it work?

State the definition of element.

Correct the following statements. \begin{equation} \begin{array}{l}{\text { a. An element is a combination of two or more }} \\\ {\text { compounds. }} \\ {\text { b. When a small amount of sugar is completely dissolved }} \\ {\text { in water, a heterogeneous solution is formed. }}\end{array} \end{equation}

Name the elements contained in the following compounds. \begin{equation} \begin{array}{ll}{\text { a. sodium chloride }(\mathrm{NaCl})} & {\text { c. ethanol }\left(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\right)} \\ {\text { b. ammonia }\left(\mathrm{NH}_{3}\right)} & {\mathrm{d} \text { bromine }\left(\mathrm{Br}_{2}\right)}\end{array} \end{equation}

What was Dmitri Mendeleev's major contribution to the field of chemistry?

Is it possible to distinguish between an element and a compound? Explain.

How are the properties of a compound related to those of the elements that comprise it?

Which law states that a compound always contains the same elements in the same proportion by mass?

\begin{equation} \begin{array}{l}{\text { a. What is the percent by mass of carbon in } 44 \text { of }} \\ {\text { carbon dioxide }\left(\mathrm{CO}_{2}\right) ?} \\\ {\text { b. What is the percent by mass of oxygen in } 44 \mathrm{g} \text { of }} \\ {\text { carbon dioxide }\left(\mathrm{CO}_{2}\right) ?}\end{array} \end{equation}

A \(25.3-\mathrm{g}\) sample of an unknown compound contains 0.8 \(\mathrm{g}\) of oxygen. What is the percent by mass of oxygen in the compound?

Magnesium combines with oxygen to form magnesium oxide. If 10.57 g of magnesium reacts completely with 6.96 g of oxygen, what is the percent by mass of oxygen in magnesium oxide?

When mercury oxide is heated, it decomposes into mercury and oxygen. If 28.4 g of mercury oxide decom- poses, producing 2.0 \(\mathrm{g}\) of oxygen, what is the percent by mass of mercury in mercury oxide?

Carbon reacts with oxygen to form two different compounds. Compound I contains 4.82 g of carbon for every 6.44 g of oxygen. Compound II contains 20.13 \(\mathrm{g}\) of carbon for every 53.7 \(\mathrm{g}\) of oxygen. What is the ratio of carbon to a fixed mass of oxygen for the two compounds?

A 100 -g sample of an unknown salt contains 64 g of chlorine. What is the percent by mass of chlorine in the compound?

Which law would you use to compare \(\mathrm{CO}\) and \(\mathrm{CO}_{2}\) ? Explain. Without doing any calculations, determine which of the two compounds has the highest percent by mass of oxygen in the compound.

Which state(s) of matter are compressible? Which state(s) of matter are not compressible? Explain.

Classify each mixture as homogeneous or heterogeneous. \begin{equation} \begin{array}{l}{\text { a. brass (an alloy of zinc and copper) }} \\ {\text { b. a salad }} \\ {\text { c. blood }} \\ {\text { d. powdered drink mix dissolved in water }}\end{array} \end{equation}

Phosphorus combines with hydrogen to form phosphine. In this reaction, \(123.9 \mathrm{~g}\) of phosphorus combines with excess hydrogen to produce \(129.9 \mathrm{~g}\) of phosphine. After the reaction, \(310 \mathrm{~g}\) of hydrogen remains unreacted. What mass of hydrogen is used in the reaction? What was the initial mass of hydrogen before the reaction?

If you have 100 particles of hydrogen and 100 particles of oxygen, how many units of water can you form? Will you use all the particles of both elements? If not, what will remain?

Classify each substance as a pure substance, a homogeneous mixture, or a heterogeneous mixture. \begin{equation} \begin{array}{llll}{\text { a. air }} & {\text { c. soil }} & {\text { e. sediment }} \\ {\text { b. aerosol }} & {\text { d. water }} & {\text { f. muddy water }}\end{array} \end{equation}

Identify each as a homogenous mixture, a heterogeneous mixture, a compound, or an element. \begin{equation} \begin{array}{l}{\text { a. pure drinking water }} \\ {\text { b. salty water }} \\ {\text { c. helium }}\end{array} \end{equation} \begin{equation} \begin{array}{l}{\text { d. seawater }} \\ {\text { e. air }}\end{array} \end{equation}

Cooking List physical properties of eggs before and after they are cooked. Based on your observations, does a physical change or chemical change occur when eggs are cooked? Justify your answer.

Ice Cream You might have noticed that while eating ice cream on a hot day, some of the ice cream begins to melt. Is the observed change in the state of the ice cream a physical or a chemical change? Justify your answer.

Iced Tea Is a mixture of tea and ice homogeneous or heterogeneous? Does that change as the ice melts?

Sodium reacts chemically with chlorine to form sodium chloride. Is sodium chloride a mixture or a compound?

Is air a solution or a heterogeneous mixture? What technique can be used to separate air into its components?

Indicate whether combining the following elements yields a compound or a mixture, \begin{equation} \begin{array}{l}{\text { a. } \mathrm{H}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \text { water }} \\ {\text { b. } \mathrm{N}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \text { air }}\end{array} \end{equation}

Apply Air is a mixture of many gases, primarily nitrogen, oxygen, and argon. Could distillation be used to separate air into its component gases? Explain.

Analyze Is gas escaping from an opened soft drink an example of a chemical or a physical change? Explain.

Identify Lead Compounds A sample of a certain lead compound contains 6.46 g of lead for each gram of oxy- gen. A second sample has a mass of 68.54 \(\mathrm{g}\) and contains 28.76 \(\mathrm{g}\) of oxygen. Are the two samples the same? Explain.

What is chemistry? (Chapter 1\()\)

What is mass? Weight? (Chapter 1\()\)

Express the following numbers in scientific notation. (Chapter 2\()\) \begin{equation} \begin{array}{ll}{\text { a. } 34,500} & {\text { d. } 789} \\ {\text { b. } 2665} & {\text { e. } 75,600} \\ {\text { c. } 0.9640} & {\text { f. } 0.002189}\end{array} \end{equation}

Perform the following operations. (Chapter 2\()\) \begin{equation} \begin{array}{l}{\text { a. } 10^{7} \times 10^{3}} \\ {\text { b. }\left(1.4 \times 10^{-3}\right) \times\left(5.1 . \times 10^{-5}\right)} \\ {\text { c. }\left(2 \times 10^{-3}\right) \times\left(4 \times 10^{5}\right)}\end{array} \end{equation}

Convert \(65^{\circ} \mathrm{C}\) to kelvins. (Chapter 2\()\)

Synthetic Elements Select a synthetic element, and prepare a short written report on its development. Be sure to discuss recent discoveries, list major research centers that conduct this type of research, and describe the properties of the synthesized element.

Is the production of charcoal from the dry distillation of wood a chemical or a physical change? Explain.