Chapter 3

Chromatography What is chromatography, and how does it work?

State the definition of element.

Name the elements contained in the following compounds. \(\begin{array}{ll}{\text { a. sodium chloride (NaCl) }} & {\text { c. ethanol }\left(C_{2} H_{6} O\right)} \\ {\text { b. ammonia ( } NH_{3} )} & {\text { d. bromine }\left(Br_{2}\right)}\end{array}\)

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

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

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

a. What is the percent by mass of carbon in 44 \(g\) of carbon dioxide \(\left(CO_{2}\right) ?\) b. What is the percent by mass of oxygen in 44 \(g\) of carbon dioxide \(\left(CO_{2}\right)\) ?

A 25.3-g sample of an unknown compound contains 0.8 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 decomposes, producing 2.0 g of oxygen, what is the percent by mass of mercury in mercury oxide?

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 \(CO\) and \(CO_{2} ?\) 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. a. brass (an alloy of zinc and copper) b. a salad c. blood d. powdered drink mix dissolved in water

Phosphorus combines with hydrogen to form phosphine. In this reaction, 123.9 g of phosphorus combines with excess hydrogen to produce 129.9 g of phosphine. After the reaction, 310 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. \(\begin{array}{lll}{\text { a. air }} & {\text { c. soil }} & {\text { e. sediment }} \\ {\text { b. aerosol }} & {\text { d. water }} & {\text { f. muddy water }}\end{array}\)

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, a. \(H_{2}(g)+O_{2}(g) \rightarrow \mathrm{water}\) b. \(N_{2}(g)+O_{2}(g) \rightarrow \mathrm{air}\)

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 oxygen. A second sample has a mass of 68.54 g and contains 28.76 g of oxygen. Are the two samples the same? Explain.

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

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

Convert \(65^{\circ} C\) 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.

a. Compare the mass percent of carbon in charcoal, indigo, and verdigris. b. Compare the mass percent of oxygen in iron oxide and Egyptian blue.

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