Chapter 1 ChemicalFoundations

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–2 QUESTION The difference between a scientific law and a scientific theory can, at times, be confusing. For example, we will refer to the “Atomic theory” or perhaps the “Law of Gravity.” Should the Law of Gravity be changed to the Theory of Gravity? 1.Yes, no one can see gravity, it is better described as a theory. 2. No, scientific laws are based on summaries of many observations and gravity observations are well known and predictable. 3.Yes, gravity is better described as a theory because gravity explains why masses attract each other and theories are about explaining observations. 4.No, keep it as a law, laws offer explanations and gravity explains why masses attract each other and laws are about explaining observations.

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–3 ANSWER Choice 2 follows the agreed-upon distinction between a theory and a law. Observations that consistently agree and provide the same result in a variety of systems become “Laws.” Theories are attempts to offer human interpretations and explanations about what was observed. Therefore, we should continue calling the summary about attractions the Law of Gravitation. Section 1.2: The Scientific Method

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–4 QUESTION Conveniently, a U.S. nickel has a mass of approximately 5 grams. If you had one dollar’s worth of nickels what would be the mass of the nickels in milligrams? milligrams 2.50 milligrams 3.1,000 milligrams 4.100,000 milligrams

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–5 ANSWER Choice 4 shows the correct conversion. After determining that 20 nickels make up one dollar, then one dollar’s worth of nickels would have a mass of 100 grams. Next, the conversion between grams and milligrams can be performed by multiplying by 1,000 (because there are 1,000 milligrams per gram.) Section 1.3: Units of Measurement

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–6 QUESTION Two chemistry students are each drinking a canned beverage. The volumes of both cans are listed as 300 milliliters. Steve remarks that the bottlers must be precise and hope to get pretty close to that in every can. Which would be a correct response from Susan? 1.If precision were the only goal, bottlers could claim any volume in the can as long as it was always very nearly the same volume. 2.If precision were the only goal, bottlers would have to get exactly 300 mL in every can. 3.If bottlers wanted to be precise, all can volumes would have to average 300 mL.

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–7 ANSWER Choice 1 best fits what scientists define as precise. High precision measurements may have closeness to a set goal (such as 300 mL in a can) but precision always means closeness within a set of measurements. If the volumes of 100 cans were all from 294 to 295 mL the volumes would be precise, but not accurately 300 mL. Section 1.4: Uncertainty in Measurement

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–8 QUESTION Which one of the following does NOT represent a result with four significant digits?

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–9 ANSWER Choice 4 only has three significant digits. Note that the lone zero in front of the decimal point is not based on any measurement and the next zero serves only as a place holder not as a measurement. Section 1.5: Significant Figures and Calculations

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–10 QUESTION If you were unloading a kg box of books from your car and a “friend” added two more 482 gram chemistry books, how much in kg and using the rules for significant digits, would you be lifting? kg kg kg kg

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–11 ANSWER Choice 3 provides both the conversion and proper number of significant digits. Consider that the 482 grams of mass must be doubled (to include both books) and that 482 grams is kg. When adding two measurements always report your answer to the same number of decimal places as the least precise measurement used in the calculation. In this case the answer should be reported to the hundredths place. Section 1.5: Significant Figures and Calculations

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–12 QUESTION The volume of a sample can be obtained from its density and mass. If the mass of a sample of acid from a battery were 5.00 grams and the density was 1.2 g/mL, what would you report in mL and with the proper number of significant digits, as the sample volume? mL mL mL mL

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–13 ANSWER Choice 3 shows the correct volume for 5.00 grams of this sample. First, be sure to use the correct solution for solving volume from mass and density (V = m/D). Then recall that the significant digit pattern for dividing measurements is to retain the same number of significant digits in the answer as the least number in any of the related measurements. Section 1.8: Density

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–14 QUESTION The average mass of a certain brand of vitamin C tablets is 253 mg. What is the mass of three such tablets rounded to the proper number of significant digits? grams grams grams grams

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–15 ANSWER Choice 2 provides three significant digits (and accurate math work). 3 tablets  253 milligrams = 759 milligrams, then dividing by 1,000 converts the milligrams to grams. Note the three is a count of the number of objects, not a measured quantity and 759 retains the same number of significant digits as the least found in related measurements. Section 1.5: Significant Figures and Calculations

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–16 QUESTION When converting temperatures between Celsius and Fahrenheit we use the equation: T F = (9°F/5°C)T C + 32°F. This indicates that: 1.Five degrees on the Celsius scale is actually the same change in temperature as nine degrees on the Fahrenheit scale. 2.A change of 1°C is smaller than a change of 1°F. 3.Zero degrees Fahrenheit would then correspond to 1.8 degrees Celsius. 4.I do not know how to convert from Celsius to Fahrenheit (will I need to?)

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–17 ANSWER Choice 1 provides the correct relationship between Celsius and Fahrenheit temperature readings. There are 180 degrees between freezing and boiling of water on the Fahrenheit scale and only 100 for the separation on the Celsius scale. 180/100 is the same as 9/5. Section 1.7: Temperature

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–18 QUESTION Suppose your chemistry professor walks into class and claims, “It is really cold in here today. It feels like only 242 K.” If that were the temperature, would you agree that it would feel cold? What would that be in Celsius degrees? 1.I agree, that would be 31°C. 2.I agree, that would be – 31°C. 3.I do not agree, that would be 31°C. 4.I agree, that would be –31.15°C.

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–19 ANSWER Choice 2 provides a correct (very) cold temperature. The formula to use is K = °C However this must be rearranged slightly to yield K – = °C. Since this is a subtraction, the correct value would have no numbers beyond the decimal point because 242 does not have numbers beyond the decimal point. Section 1.7: Temperature

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–20 QUESTION Which would provide more grams of NaCl, sample one with a mass of 2,350 mg, or sample two, a solid with a volume of 2.00 cm 3 ? (The density of solid salt is 2.16 g/cm 3.) Report your choice and report the grams of the more massive sample. 1.Sample two; 1.08 grams 2.Sample two; 4.32 grams 3.Sample one; 2.35 grams 4.Sample one; grams

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–21 ANSWER Choice 2 provides the accurate mass for 2.00 cm 3 of salt. This mass is larger than the 2.35 gram sample. Be sure to solve for the mass of a sample from its density and volume by multiplying 2.00 cm 3 × 2.16 g/cm 3. Section 1.8: Density

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–22 QUESTION Would the coffee in a cup of coffee be classified as a solution or a compound? Which of the following agrees with your reasoning? 1.The coffee in the cup is a solution because it contains the same components throughout, but there are many compounds dissolved to make coffee. 2. The coffee in the cup is a compound because it has a set ratio of components that make it the same throughout. 3.The coffee in the cup is both a compound and a solution. It looks the same throughout like a true solution, yet it always has the same amount of each component.

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–23 ANSWER Choice 1 provides the best reasoning. The coffee in the cup is a homogeneous mixture of components, making it a solution. The amount of each component can vary greatly from coffee bean to coffee bean. Compounds do not have a variable composition like solutions. Section 1.9: Classification of Matter

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–24 QUESTION In the diagram of a simple distillation apparatus the condenser is important because…

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–25 QUESTION (continued) 1.That is where the main separation of components in the mixture takes place. 2.It allows water to be recycled during cooling. 3.It allows separated samples to be collected as the vapor physically changes to a liquid. 4.Mixtures that are distilled need to have their vapors mingled - the condenser does this.

Copyright © Houghton Mifflin Company. All rights reserved.CRS Question, 1–26 ANSWER Choice 3 properly explains the function of a condenser in distillation. The vapor has been separated from the nonvolatile component of the mixture before it reaches the condenser. As the vapor is cooled by the cool circulating water in the condenser, it can be collected as a liquid. Section 1.9: Classification of Matter