Chapter 02 Post-Lecture

9/7/22, 2:49 PM Chapter 02 Post-Lecture Chapter 02 Post-Lecture Due: 11:59pm on Monday, September 12, 2022 . Problem 2.21 - Enhanced - with Feedback - Clinical Applications Part A Identify the following as measured or exact. Drag the appropriate statements to their respective bins. ANSWER: Reset The Daily Value (DV) for magnesium for an adult is 420 . Help The mass of a medication is 160.5 . In November, 23 babies were born in a hospital. There are white blood cells in a milliliter of blood. Correct The mass of a medication or a dietary supplement is determined with a measuring device such as a scale or balance. Therefore, these are measured numbers. The amount of white blood cells in a blood sample is not manually counted; it is measured using a laboratory instrument. However, counting the number of births does not require a measuring device. Therefore, the number of babies born in November is an exact number. Part B Give the number of significant figures (SFs) in each measured number. Drag the appropriate statements to their respective bins. ANSWER: 1/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture Reset The Daily Value (DV) for magnesium for an adult is 420 . There are white blood cells in a milliliter of blood. Help The mass of a medication is 160.5 . All attempts used; correct answer displayed All nonzero digits are significant and a zero between two nonzero digits is counted as significant, so the mass of the medication has 4 SFs. A zero is not significant if it is used as a placeholder at the end of a number without a decimal point. Therefore, the Daily Value of magnesium has 2 SFs. The measurement of white blood cells is written in scientific notation. Since all digits are significant in the coefficient of a number in scientific notation, the measurement of white blood cells has 3 SFs. Problem 2.26 Round off or add zeros to each of the following to two significant figures: Part A 2.2805 Express your answer using two significant figures. ANSWER: 2.3 Correct Part B ANSWER: 2/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture Correct Part C 0.004412 Express your answer using two significant figures as a decimal. ANSWER: 0.0044 All attempts used; correct answer displayed Part D 8 Express your answer using two significant figures. ANSWER: 8.0 Correct Core Chemistry Skill: Counting Significant Figures When we report a measurement in science, we are careful to report only digits known with certainty, plus a final digit that is recognized to be uncertain. It is important to know how to count significant figures correctly, including in numbers containing zeros. Number Significant figures Explanation 23.56 4 All nonzero digits are significant. 23.560 5 Trailing zeros are significant when a decimal point is shown. 1000 1 Trailing zeros are not considered significant when no decimal point is shown. 1000. 4 Showing the decimal point indicates that the preceding zeros are significant. 500.01 5 Zeros between nonzero digits are significant. 0.0078 2 Leading zeros are not significant. Part A Determine the number of significant figures in the measurement 6.07 . Express your answer numerically as an integer. Hint 1. How many nonzero digits are in the number? How many nonzero digits are in the measurement 6.07 ? Express your answer numerically as an integer. ANSWER: 2 Hint 2. Classify the zero 3/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture What is the rule regarding zeros found in between two nonzero digits? ANSWER: They are always significant. They are never significant. They are significant if to the right of the decimal. They are significant if to the left of the decimal. ANSWER: 3 Correct Part B Determine the number of significant figures in the measurement 0.0030 . Express your answer numerically as an integer. Hint 1. How many nonzero digits are in the number? How many nonzero digits are in the measurement 0.0030 ? Express your answer numerically as an integer. ANSWER: 1 Hint 2. Classify the leading zeros What is the rule regarding zeros at the beginning of a number? ANSWER: They are always significant. They are never significant. They are significant if to the left of the decimal. They are significant if to the right of the decimal. Hint 3. Classify the trailing zeros What is the rule regarding zeros at the end of a number? ANSWER: They are always significant. They are never significant. They are significant only if there is a decimal point shown in the number. ANSWER: 4/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture 2 Correct Leading zeros are not significant. Trailing zeros are significant if there is a decimal point shown in the number. Part C Round the value 44.981 to three significant figures. Express your answer numerically using three significant figures. Hint 1. How to perform rounding Imagine that you want to round the value 0.08206 to three significant figures. First, identify which digits should be dropped to leave just three significant figures: 0.08206. Next, look at the first digit to be dropped, in this case 6. Because this digit is 5 or greater, we round the previous digit up, giving us 0.0821. Hence the number 0.08206 is closer to 0.0821 than it is to 0.0820. Hint 2. Identify the digits to be dropped When rounding 44.981 to three significant figures, which digits should be dropped? Choose the option that has the dropped digits underlined. ANSWER: 44.981 44.981 44.981 44.981 ANSWER: 45.0 Correct The number 44.981 is closer to 45.0 than it is to 44.9. Core Chemistry Skill: Using Significant Figures in Calculations Imagine that your friend steps on a digital scale that then reads 175 something like 175.2 , or 174.9 . . You know that this is not an exact number, and that your friend's actual weight could be You then hand your friend a golf ball that weighs 0.1 . What will the combined weight of your friend and the golf ball be? If you were to report 175.1 combined weight, you would be implying that you know the value to the tenths place, when really you only know that it's about 175 . as the In mathematics, . In science, however, we tend to deal with measurements rather than exact numbers, and so to a scientist, . Keeping track of the significant figures in measurements will prevent you from reporting calculated answers with more precision than you can truthfully claim. Part A Evaluate and round the answer appropriately. Express your answer numerically using the appropriate number of significant figures. 5/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture Hint 1. How to approach the problem In multiplication or division, the result carries the same number of significant figures, s.f., as the factor with the fewest significant figures. For example: The intermediate result ( figures. ) is rounded to two significant figures to reflect the least precisely known number ( ), which has two significant Hint 2. Calculate the unrounded answer Evaluate Do not round the answer. Express the unrounded answer numerically. ANSWER: 9.324 All attempts used; correct answer displayed Hint 3. Determine the number of significant figures in the answer Based on the factors given in , to how many significant figures should the final answer be rounded? Express your answer numerically as an integer. Hint 1. Determine the number of significant figures in each factor The factors , , and have ______, ______, and ______ significant figure(s), respectively. Express your answers numerically, separated by commas. ANSWER: significant figure(s) 1,3,2 ANSWER: significant figure(s) 1 Incorrect; Try Again; 2 attempts remaining ANSWER: 9 All attempts used; correct answer displayed In multiplication or division, the result carries the same number of significant figures, s.f., as the factor with the fewest significant figures. In this case, The intermediate result ( ) is rounded to one significant figure to reflect the least precisely known number ( ), which has one significant figure. Part B Evaluate and round the answer appropriately. Express your answer numerically using the appropriate number of decimal places. 6/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture Hint 1. How to approach the problem In addition or subtraction, the result carries the same number of decimal places as the quantity carrying the fewest decimal places. For example: We round the intermediate answer ( ) to two decimal places because the quantity with the fewest decimal places ( ) has two decimal places. Hint 2. Calculate the unrounded answer Evaluate Do not round the answer. Express the unrounded answer numerically. ANSWER: 11.111 Hint 3. Determine the number of decimal places in the answer When is evaluated and rounded appropriately, how many digits should appear after the decimal point? Express your answer numerically as an integer. Hint 1. Determine the number of decimal places in each quantity The quantities , , and have ______, ______, and ______ digit(s) after the decimal point, respectively. Express your answers numerically, separated by commas. ANSWER: 3,1,1 digit(s) after the decimal point ANSWER: 1 digit(s) after the decimal point ANSWER: 11.1 Correct Part C Evaluate and round the answer appropriately. Express your answer numerically using the appropriate number of significant figures or decimal places. Hint 1. How to approach the problem In calculations involving both multiplication/division and addition/subtraction, do the steps according to order of operations. Determine the number of significant figures in each intermediate answer, but don't round until the end. For example: 7/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture We do the subtraction step first: We use the subtraction rule to determine that the intermediate answer ( ) has only one significant decimal place. To avoid small errors, it is best not to round at this point; instead, underline the least significant figure as a reminder: We use the multiplication rule to determine that the intermediate answer ( significant figures in . ) rounds to two significant figures ( ) because it is limited by the two Hint 2. Calculate the unrounded answer Evaluate Do not round the answer. Express the unrounded answer numerically. ANSWER: 0.662 Hint 3. Identify the precision of the intermediate answer The first step of this calculation has the following unrounded answer: Which choice shows the least significant figure, that is, to which digit would we round if this were the final answer? ANSWER: ANSWER: 0.7 Correct Core Chemistry Skill: Using Prefixes The most convenient system for science measurements is based on the metric system and is called the International System of units, or SI units. SI units are a set of standard units agreed on by scientists throughout the world. SI units can have prefix multipliers, which change the value of the unit by powers of 10. For example, a nanosecond ( ) has the prefix nano, meaning . Therefore, . Part A What are the abbreviations for a teragram, a nanosecond, and a kiloliter, respectively? Enter the abbreviations, separated by commas. Hint 1. Determine the symbol for tera What is the symbol for the SI prefix tera ? ANSWER: 8/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture T Hint 2. Determine the symbol for nano What is the symbol for the SI prefix nano ? ANSWER: n Hint 3. Determine the symbol for kilo What is the symbol for the SI prefix kilo ? ANSWER: k Hint 4. Determine the symbol for gram What is the symbol for the unit gram? ANSWER: g Hint 5. Determine the symbol for second What is the symbol for the SI unit second? ANSWER: s Hint 6. Determine the symbol for liter What is the symbol for the SI unit liter? ANSWER: L ANSWER: Tg,ns,kL All attempts used; correct answer displayed Even though all SI prefix3unit combinations are possible, not all of them are commonly used. The prefix centi, for example, is commonly used with meters, but not so commonly with grams, which is why you have probably heard of a centimeter, but not a centigram. The prefix mega, while commonly used with non-SI units such as pixels and bytes, is not often used for meters. Part B Rank the following quantities in order of decreasing mass. Rank from highest to lowest mass. To rank items as equivalent, overlap them. Hint 1. How to approach the problem 9/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture First, determine the meanings of the SI prefixes. Use the prefix meanings to convert the units to grams. Once all the masses are in the same unit (grams), you can compare the values. Hint 2. Identify the meanings of SI prefixes Match the name and symbol of each prefix to its meaning. Drag each item to the appropriate bin. Hint 1. SI prefixes and conversions The following table gives some SI prefixes and their values. Prefix tera Value (decimal) 1000000000000 giga 1000000000 mega 1000000 kilo Value (scientific notation) 1000 hecto 100 deca 10 deci 0.1 centi 0.01 milli 0.001 micro 0.000001 nano 0.000000001 pico 0.000000000001 femto 0.000000000000001 For example, one nanometer (1 ) is equal to 0.000000001, or , . ANSWER: Reset giga mega kilo centi milli micro nano Help pico Hint 3. Convert an SI unit to grams Convert 50 million (50 ) to grams. You can convert by replacing the prefix with its meaning. For example, the prefix (deci) means . Thus, . 10/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture Express your answer numerically in grams. ANSWER: 50 million = 5.00×10−2 Hint 4. Convert all quantities to grams Convert each of the following to its equivalent mass in grams. Match the values in the left-hand column with the appropriate blank in the sentences in the right-hand column. ANSWER: Reset Help 1. A mass of 50 million (50,000,000) ng = 0.05 g. 2. A mass of 1 cg = 0.01 g. 50 3. A mass of 1 dg = 0.1 g. 4. A mass of 1 Gg = 1000000000 g. 5. A mass of 50 cg = 0.5 g. 100 6. A mass of 1 kg = 1000 g. ANSWER: Reset 1 Gg 1 kg 100 g 50 cg 1 dg 50 million ng Help 1 cg The correct ranking cannot be determined. Correct 11/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture ± Core Chemistry Skill: Using Conversion Factors Learning Goal: To understand the process of unit analysis and to solve unit conversion problems using this method. Unit analysis can be summarized in a three-step technique that makes use of conversion factors (also called unit factors) between two units: one that is asked for in the question and one that is given in the question. The steps to the unit analysis method are as follows: 1. Determine the unit asked for in the answer. 2. Find the given value in the question that is related to the answer. 3. Use the related unit factors or conversion factors. A unit factor is the ratio of two equivalent quantities with different units. For example, there are 24 hours in a day, so the two associated unit factors are: or A 20.00 milk chocolate bar is found to contain 12.00 of sugar. Part A How many milligrams of sugar does the milk chocolate bar contain? Express your answer in milligrams to four significant figures. Hint 1. Identify the unit asked for in the answer The first step of the unit analysis method is to determine the unit asked for in the answer. In the given problem, the amount of sugar is to be determined in _____. ANSWER: Hint 2. Identify the given value in the question related to the answer The second step of the unit analysis method is to identify the given value in the question that is related to the answer. In the given problem, the amount of sugar to be converted to milligrams is _____. ANSWER: 20.00 12.00 Hint 3. How to choose a unit factor To choose the unit factor, consider that the numerator of the unit factor should have the same unit as the unit asked for in the answer. The denominator of the unit factor should have the same unit as the unit of the given value. The unit of the given value and the unit of the term in the denominator of the unit factor will cancel each other out, giving you the unit asked for in the answer. For example, if you are calculating the number of hours in 2 days, the unit asked for is hours and the given value is in days. The unit equation is . The possible unit factors are or . Since you want to calculate the number of hours and the given value is in days, you will need to choose the unit factor that cancels the unit days and gives the answer in hours. Therefore, the complete unit analysis would be: 12/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture Hint 4. Complete the unit analysis The unit asked for in the answer is milligrams ( gram, the two unit factors are ). The unit of the given value related to the answer is grams ( ). Since there are 1000 milligrams in a or . Apply the relevant unit factor to convert the given amount in grams to the required amount in milligrams. Drag the appropriate labels to their respective targets. ANSWER: Reset 20.00 Help 1000 mg g 12.00 g 1g ANSWER: 1.200×104 Correct The unit analysis method is used in everyday activities. This method is very useful in quantifying the terms and making conversions. In chemistry, it is used frequently in the analysis of different substances. Part B What will be the amount of sugar in milligrams if the size of the milk chocolate bar is reduced from 20.00 to 4.000 ? Express your answer in milligrams to four significant figures. Hint 1. How to approach the problem First, determine the unit asked for in the answer. Next, determine the given value in the question as it relates to the answer. Consider that the size of the milk chocolate bar is reduced from 20.00 to 4.000 , so the amount of sugar in 4.000 of milk chocolate bar will be reduced as well. You must find the amount of sugar in grams for the reduced milk chocolate bar and then make use of the relevant unit factor. To find the grams of sugar in the 4.000 milk chocolate bar, first find the amount of sugar per gram of milk chocolate bar . Hint 2. Identify the unit asked for in the answer The first step of the unit analysis method is to determine the unit asked for in the answer. In the given problem, the amount of sugar is to be determined in _____. ANSWER: 13/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture Hint 3. Identify the given value in the question The second step of the unit analysis method is to identify the given value in the question. Consider that the size of the milk chocolate bar has been reduced to 4.000 . In the given problem, the amount of sugar to be converted to milligrams is for a _____ milk chocolate bar. ANSWER: 20.00 12.00 4.000 Hint 4. Identify the formula to calculate the amount of sugar per gram of milk chocolate bar Consider that the original 20.00 milk chocolate bar was found to contain 12.00 sugar per gram of milk chocolate bar? sugar. Which of the following formulas gives the correct amount of ANSWER: Hint 5. Complete the unit analysis The unit asked for in the answer is milligrams ( ). The unit of the given value related to the answer is in grams ( ). The unit equation that illustrates the relationship between grams and milligrams is 1 = 1000 . Therefore, the two unit factors are or its reciprocal . Choose the unit factor in which the denominator has the same unit as the unit of the given value so that the units will cancel. Consider that the amount of sugar in milligrams is to be determined for 4.000 of milk chocolate bar, so you need to consider the amount of sugar per gram of milk chocolate bar. Drag the appropriate labels to their respective targets. ANSWER: 14/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture Reset 4.000 12.00 g 20.00 g Help 1000 mg g 1g ANSWER: 2400 Correct Percent as a conversion factor The term percent is Latin, and it means "for every hundred." Thus, a percentage can be referred to as parts per 100 parts. For example, consider that 70 of water is present in 100 of cytoplasm. You can say that 70 of cytoplasm is water. This demonstrates that the percentage of a substance is the amount of the substance present for every one hundred parts of its sample. Part C Given that a 20.00 milk chocolate bar contains 12.00 of sugar, calculate the percentage of sugar present in 20.00 that the answer should have four significant figures (two decimal places). of milk chocolate bar keeping in mind Express your answer numerically to four significant figures. Hint 1. How to approach the problem To determine the percentage of sugar in the given milk chocolate bar, you need to divide the amount of sugar by the amount of milk chocolate bar and multiply that ratio by 100 . Hint 2. Identify the formula to determine percentage Which of the following is the correct formula to determine the percentage of sugar in the milk chocolate bar? Remember that a 20.00 bar contains 12.00 of sugar. milk chocolate ANSWER: 15/26 9/7/22, 2:49 PM Chapter 02 Post-Lecture ANSWER: 60.00 Correct Percentage calculations are most common in day-to-day activities and are also very useful when comparing two substances. For example, air contains 78.09 nitrogen ( ) and 20.95 oxygen ( ). Thus, we can conclude that the nitrogen content of the air is higher than that of the oxygen. Interactive Simulation4Density Determination of a Metal The density of a substance is independent of the amount of substance present. It is often used to identify a substance. Select the image to explore the simulation, which demonstrates density calculations for metals using water displacement to calculate volume and a scale to calculate mass. You may need to click and hold some of the buttons to complete the specified step. The calculation of the density of a metal using water displacement Density is equal to the mass of a substance divided by its volume: Water displacement can be used to find the volume of a solid by placing the object in a known volume of water. When the object is added to water, the measured total volume increases. This final volume is equal to the volume of the initial water plus the volume of the solid object added. To determine the volume of the water that is displaced by the object, subtract the initial volume from the final volume. The volume of water displaced is equal to the volume of the solid object. Using a scale to measure the mass of the object, you can now calculate the density of the object as its mass divided by its volume. Use the simulation to explore this method. Part A Follow the steps provided in the simulation to add water to the graduated cylinder, select one of the three samples (copper, silver, or gold), set its mass to the values given in the statements below, find its volume, and calculate its density. To save time, you can approximate the initial mass of the solid to the nearest and 15 . . For example, if you are asked to add 14.3 of copper, add between 13 Which of the following sets include two samples with an equal density? Check all that apply. Hint 1. How to use the simulation To begin, add the indicated volume of water to the measuring cylinder. To add water, click and hold until the desired volume has been added. Do not release the button until you have added the amount of water as indicated in the problem statement. Then, select a metal from the dropdown menu and add the metal to the weighing pan by clicking on . Do not release the button until you have added the amount of metal indicated in the problem statement. Next, add the metal to the water and calculate the density by clicking on . Hint 2. Calculate the density of copper Click on Weigh out between 14 and 16 to add any amount of water to the cylinder, and then select