EXAMPLE EXERCISE 4.1 Change of Physical State

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EXAMPLE EXERCISE 4.1 Change of Physical State State the term that applies to each of the following changes of physical state: (a) Snow changes from a solid to a liquid. (b) Gasoline changes from a liquid to a gas. (c) Dry ice changes from a solid to a gas.

Solution Refer to Figure 4.1 for the changes of physical state. (a) The change from solid to liquid is called melting. (b) The change from liquid to gas is called vaporizing. (c) The change from solid to gas is called sublimation.

Practice Exercise State the term that applies to each of the following changes of physical state: (a) A refrigerant changes from a gas to a liquid. (b) Water changes from a liquid to a solid. (c) Iodine vapor changes from a gas to a solid.

Answers: (a) condensing; (b) freezing; (c) deposition Figure 4.1 Changes in Physical State As temperature increases, a solid melts to a liquid and then vaporizes into a gas. As temperature decreases, a gas condenses to a liquid and then freezes to a solid.

Concept Exercise Identify the physical state (solid, liquid, gas) that corresponds to each of the following pictorial representations:

Answer: See Appendix G.

Introductory Chemistry: Concepts and Critical Thinking, 6th Edition © 2011 Pearson Education, Inc. Charles H. Corwin EXAMPLE EXERCISE 4.2 Element, Compound, or Mixture Consider the following properties of the element copper: (a) Copper metal cannot be broken down by a chemical change. (b) Copper reacts with oxygen in air to give copper oxide. (c) Copper, in the form of malachite ore, is found worldwide. (d) Copper and tin compose bronze alloy.

Classify each of the following copper samples as an element, a compound, a homogeneous mixture, or a heterogeneous mixture: (a) copper wire (b) copper oxide (c) malachite ore (d) bronze alloy

Solution Refer to Figure 4.2 to classify each sample. (a) Copper wire is a metallic element. (b) Copper oxide is a compound of the elements copper and oxygen. Figure 4.2 Classification of Matter Matter may be either (c) Malachite ore is a heterogeneous mixture of a mixture or a pure substance. The properties of a copper and other substances. heterogeneous mixture vary within the sample (oil and (d) Bronze alloy is a homogeneous mixture of copper water). The properties of a homogeneous mixture are and tin. constant (salt solution). A pure substance may be either a compound (water) or an element (gold). Left to right: oil and water; NaCl solution; H2O; and gold nugget.

Practice Exercise Consider the following properties of the element mercury: (a) Mercury liquid cannot be broken down by a chemical change. (b) Mercury oxide can be heated to give mercury and oxygen gas. (c) Mercury, in the form of cinnabar ore, is found in Spain and Italy. (d) Mercury and silver compose the alloy used for dental fillings.

Classify each of the following mercury samples as an element, a compound, a homogeneous mixture, or a heterogeneous mixture: (a) mercury liquid (b) mercury oxide (c) cinnabar ore (d) dental alloy Answers: (a) element; (b) compound; (c) heterogeneous mixture; (d) homogeneous mixture

Concept Exercise Classify each of the following as an element, a compound, or a mixture as shown in the illustration:

Answer: See Appendix G.

Introductory Chemistry: Concepts and Critical Thinking, 6th Edition © 2011 Pearson Education, Inc. Charles H. Corwin EXAMPLE EXERCISE 4.3 Properties of Metals Which of the following properties is not characteristic of a metal? (a) good conductor of heat (b) malleable (c) high melting point (d) reacts with other metals

Solution Refer to Table 4.4 to classify each of the following properties: (a) Metals are good conductors of heat. (b) Metals are malleable. (c) Metals usually have high melting points. (d) Metals do not react with other metals; they mix to form alloys.

Which of the following properties is not characteristic of a nonmetal? (a) insulator of electricity (b) ductile (c) low density (d) reacts with nonmetals

Answer: (b) Nonmetals crush to a powder and are not malleable or ductile.

Concept Exercise Which of the following is a solid metal under normal conditions: calcium, phosphorus, mercury, or silicon? (Refer to Figure 4.7.) Answer: See Appendix G.

Figure 4.7 Pictorial Periodic Table of the Elements The natural abundance is the percent by mass of an element in Earth’s crust, oceans, and atmosphere. The natural abundance of an element listed as rare is less than 1 mg per metric ton (1000 kg). An element listed as synthetic is made artificially and does not occur naturally. An element listed as unstable often disintegrates in a fraction of a second.

Introductory Chemistry: Concepts and Critical Thinking, 6th Edition © 2011 Pearson Education, Inc. Charles H. Corwin EXAMPLE EXERCISE 4.4 Physical States of the Elements Indicate the physical state for each of the following elements at 25 °C and normal pressure; classify each element as a metal, nonmetal, or semimetal: (a) barium (b) boron (c) bismuth (d) bromine

Solution Referring to Figures 4.5 and 4.6, we observe the following: (a) Barium (Ba) is on the left side of the periodic table; it is a solid metal under normal conditions. (b) Boron (B) is in the middle of the periodic table; it is a solid semimetal. (c) Bismuth (Bi) is to the right, but below the semimetals in the periodic table, it is a solid metal. (d) Bromine (Br) is on the right side of the periodic table; it is a liquid nonmetal at normal conditions.

Figure 4.5 Metals, Nonmetals, and Semimetals The symbols of elements having metallic properties are on the left side of the periodic table, nonmetallic are on the right side, and semimetallic are midway between. Notice the special placement of hydrogen, a nonmetallic element.

Figure 4.6 Physical States of the Elements At 25 °C and normal atmospheric pressure, all metals are in the solid state except Hg. Most nonmetals are gases except C, P, S, Se, and I, which are solids. The only elements in the liquid state at normal conditions are Hg and Br.

Practice Exercise Indicate the physical state for each of the following elements at 25 °C and normal pressure; classify each element as a metal, nonmetal, or semimetal: (a) aluminum (b) hydrogen (c) helium (d) radium

Answers: (a) solid metal; (b) gaseous nonmetal; (c) gaseous nonmetal; (d) solid metal

Concept Exercise Which of the following is a liquid nonmetal under normal conditions: sodium, mercury, bromine, or sulfur? (Refer back to Figure 4.7.) Answer: See Appendix G.

State the total number of atoms in a molecule of vitamin B3, C6H6N2O.

Solution

The chemical formula for vitamin B3 indicates 6 carbon atoms, 6 hydrogen atoms, 2 nitrogen atoms, and 1 oxygen atom. Thus C6H6N2O has a total of 15 atoms.

Practice Exercise

Write the chemical formula for vitamin B6, if a molecule is composed of 8 carbon atoms, 11 hydrogen atoms, 1 nitrogen atom, and 3 oxygen atoms.

Answer: C8H11NO3 (total of 23 atoms) Concept Exercise Examine the model for vitamin C and determine the molecular formula. In the model shown, the black sphere = C atom, white = H atom, and red = O atom.

Answer: See Appendix G.

State the total number of atoms in a molecule of glycerin, C3H5(OH)3.

Solution The chemical formula for glycerin indicates 3 carbon atoms, 5 hydrogen atoms, and 3 OH units. Thus,

C3H5(OH)3 has a total of 14 atoms.

Practice Exercise Write the chemical formula for nitroglycerin if a molecule is composed of 3 carbon atoms,

5 hydrogen atoms, 3 oxygen atoms, and 3 NO2 units.

Answer: C3H5O3(NO2)3 Concept Exercise

State the total number of atoms in a molecule of nitroglycerin, C3H5O3(NO2)3.

Answer: See Appendix G.

Introductory Chemistry: Concepts and Critical Thinking, 6th Edition © 2011 Pearson Education, Inc. Charles H. Corwin EXAMPLE EXERCISE 4.7 Physical and Chemical Properties Classify each of the following properties as physical or chemical: (a) Water appears colorless and odorless at 20 °C. (b) Water dissolves sugar crystals. (c) Water produces a gas with calcium metal. (d) Water exists as ice at –10 °C. Solution If a reaction occurs, there is a change in composition and the property is chemical. Otherwise, the property is physical. (a) Color and odor are physical properties. (b) Solubility is a physical property. (c) A chemical reaction is a chemical property. (d) A physical state is a physical property. Practice Exercise Classify each of the following properties as physical or chemical: (a) Water appears hard and crystalline at 0 °C. (b) Water is insoluble in gasoline. (c) Water is a very weak conductor of electricity. (d) Water produces a gas with sodium metal. Answers: (a) physical; (b) physical; (c) physical; (d) chemical Concept Exercise Copper melts at 1083 °C, has a density of 8.92 g/mL, is a good conductor of electricity, and turns black when heated. Which of these is an example of a chemical property? Answer: See Appendix G.

Introductory Chemistry: Concepts and Critical Thinking, 6th Edition © 2011 Pearson Education, Inc. Charles H. Corwin EXAMPLE EXERCISE 4.8 Physical and Chemical Changes Classify each of the following observations as a physical or a chemical change: (a) Touching a lit candle to hydrogen soap bubbles gives an explosion. (b) Heating water in a flask produces moisture on the glass. (c) Combining two colorless solutions gives a yellow solid. (d) Pouring vinegar on baking soda produces gas bubbles.

Solution An observation that indicates a physical change is a change of physical state. The observations that suggest a chemical change include burning, fizzing, changing color, or forming an insoluble substance in solution. (a) Hydrogen explodes; thus, it is a chemical change. (b) Water is boiled; thus, it is a physical change. (c) Two solutions give an insoluble substance; thus, it is a chemical change. (d) Baking soda fizzes; thus, it is a chemical change. Practice Exercise Classify each of the following observations as a physical or a chemical change: (a) Freezing water in a refrigerator makes cubes of ice. (b) Adding silver nitrate to tap water gives a cloudy solution. (c) Burning sulfur gives a light blue flame. (d) Grinding aspirin tablets produces a powder.

Answers: (a) physical; (b) chemical; (c) chemical; (d) physical

Concept Exercise An Alka-Seltzer tablet dissolves in water and produces gas bubbles. Is this an example of a physical change or a chemical change? Answer: See Appendix G.

Alka-Seltzer An Alka-Seltzer tablet in water releases carbon dioxide gas bubbles.

Introductory Chemistry: Concepts and Critical Thinking, 6th Edition © 2011 Pearson Education, Inc. Charles H. Corwin EXAMPLE EXERCISE 4.9 Conservation of Mass Law In an experiment, 2.430 g of magnesium metal was ignited and burned with oxygen in the air. If 4.030 g of white magnesium oxide powder, MgO, was collected, what was the mass of oxygen gas that reacted?

Solution Applying the conservation of mass law, we find that the mass of the magnesium metal plus the mass of the oxygen gas equals the mass of the magnesium oxide powder. That is, 2.430 g Mg + mass of oxygen = 4.030 g MgO mass of oxygen = 4.030 g MgO – 2.430 g Mg mass of oxygen = 1.600 g Practice Exercise

If 0.654 g of zinc metal reacts with 0.321 g of yellow powdered sulfur, what is the mass of the zinc sulfide produced? Answer: 0.975 g Concept Exercise Heating 1.000 g copper metal with yellow sulfur produces 1.252 g of black copper sulfide. What is the mass of sulfur that reacted with the copper metal?

Answer: See Appendix G.

Introductory Chemistry: Concepts and Critical Thinking, 6th Edition © 2011 Pearson Education, Inc. Charles H. Corwin EXAMPLE EXERCISE 4.10 Kinetic Energy and Molecular Motion A balloon filled with helium gas is cooled from 25 °C to –25 °C. State the change in each of the following: (a) kinetic energy of the gas (b) motion of helium atoms

Solution Temperature, kinetic energy, and velocity are related as follows: (a) As the temperature cools from 25 °C to –25 °C, the kinetic energy of helium atoms decreases. (b) Since a drop in temperature produces a decrease in kinetic energy, the motion of helium atoms decreases.

Practice Exercise A steel cylinder containing air is heated from 25 °C to 50 °C. State the change in each of the following: (a) kinetic energy of the gas (b) motion of air molecules Answers: (a) increases; (b) increases Concept Exercise What happens to the kinetic energy and velocity of air molecules when the temperature increases? Answer: See Appendix G.

Introductory Chemistry: Concepts and Critical Thinking, 6th Edition © 2011 Pearson Education, Inc. Charles H. Corwin EXAMPLE EXERCISE 4.11 Forms of Energy Identify two forms of energy that are involved in each of the following conversions: (a) Radioactive emissions vaporize water to steam. (b) Steam drives a turbine. (c) A turbine spins and drives an electrical generator.

Solution We can refer to the six forms of energy listed above. It follows that (a) Nuclear energy is converted to heat energy. (b) Heat energy is converted to mechanical energy. (c) Mechanical energy is converted to electrical energy. Practice Exercise Identify two forms of energy that are involved in each of the following devices: (a) flashlight (b) solar calculator (c) lead–acid battery

Answers: (a) chemical and light; (b) light and electrical; (c) chemical and electrical Concept Exercise Which of the following is not a basic form of energy: chemical, electrical, heat, light, mechanical, nuclear, solar? Answer: See Appendix G.