Download Understanding Temperature Scales and Significant Figures in Chemistry and more Lecture notes Dimensional Analysis in PDF only on Docsity!
1.7 The statement "that is just a theory" is generally taken to mean that there is no scientific proof behind the statement. This statement is the opposite of the meaning in the context of the scientific theory, where theo- ries are tested again and again.
1.8 Matter can be classified according to its state—solid, liquid, or gas—and according to its composition.
1.9 In solid matter, atoms or molecules pack close to each other in fixed locations. Although the atoms and mol- ecules in a solid vibrate, they do not move around or past each other. Consequently, a solid has a fixed vol- ume and rigid shape.
In liquid matter, atoms or molecules pack about as closely as they do in solid matter, but they are free to move relative to each other, giving liquids a fixed volume but not a fixed shape. Liquids assume the shape of their container.
In gaseous matter, atoms or molecules have a lot of space between them and are free to move relative to one another, making gases compressible. Gases always assume the shape and volume of their container.
1.10 Solid matter may be crystalline, in which case its atoms or molecules are arranged in patterns with long-range, repeating order, or it may be amorphous, in which case its atoms or molecules do not have any long-range order.
1.11 A pure substance is composed of only one type of atom or molecule. In contrast, a mixture is a substance com- posed of two or more different types of atoms or molecules that can be combined in variable proportions.
1.12 An element is a pure substance which cannot be decomposed into simpler substances. A compound is com- posed of two or more elements in fixed proportions.
1.13 A homogeneous mixture has the same composition throughout, while a heterogeneous mixture has differ- ent compositions in different regions.
1.14 If a mixture is composed of an insoluble solid and a liquid, the two can be separated by filtration, in which the mixture is poured through filter paper (usually held in a funnel).
1.15 Mixtures of miscible liquids (substances that easily mix) can usually be separated by distillation, a process in which the mixture is heated to boil off the more volatile (easily vaporizable) liquid. The volatile liquid is then recondensed in a condenser and collected in a separate flask. I 1.16 A physical property is one that a substance displays without changing its composition, whereas a chemical property is one that a substance displays only by changing its composition via a chemical change.
r 1.17 \ Changes that alter only state or appearance, but not composition, are called physical changes. The atoms or
V / molecules that compose a substance do not change their identity during a physical change. For example, when water boils, it changes its state from a liquid to a gas, but the gas remains composed of water mole- cules, so this a physical change. When sugar dissolves in water, the sugar molecules are separated from each other, but the molecules of sugar and water remain intact.
In contrast, changes that alter the composition of matter are called chemical changes. During a chemical change, atoms rearrange, transforming the original substances into different substances. For example, the rusting of iron, the combustion of natural gas to form carbon dioxide and water, and the denaturing of pro- teins when an egg is cooked are examples of chemical changes.
1.18 In chemical and physical changes, matter often exchanges energy with its surroundings. In these exchanges, the total energy is always conserved; energy is neither created nor destroyed. Systems with high potential energy tend to change in the direction of lower potential energy, releasing energy into the surroundings.
1.19 Chemical energy is potential energy. It is the energy that is contained in the bonds that hold the molecules together. This energy arises primarily from electrostatic forces between the electrically charged particles (pro- tons and electrons) that compose atoms and molecules. Some of these arrangements—such as the one within the molecules that compose gasoline—have a much higher potential energy than others. When gasoline
undergoes combustion the arrangement of these particles changes, creating molecules with much lower potential energy and transferring a great deal of energy (mostly in the form of heat) to the surroundings. A raised weight has a certain amount of potential energy (dependent on the height the weight is raised) that can be converted to kinetic energy when the weight is released.
1.20 The SI base units include the meter (m) for length, the kilogram (kg) for mass, the second (s) for time, and the Kelvin (K) for temperature.
1.21 The three different temperature scales are Kelvin (K), Celsius (°C), and Fahrenheit (°F). The size of the degree is the same in the Kelvin and the Celsius scales, and they are 1.8 times larger than the degree size for the Fahrenheit scale.
1.22 Prefix multipliers are used with the standard units of measurement to change the value of the unit by pow- ers of 10.
For example, the kilometer has the prefix "kilo," meaning 1000 or 10^3. Therefore:
1 kilometer = 1000 meters = 10^3 meter
Similarly, the millimeter has the prefix "milli," meaning 0.001 or 10~^3.
1 millimeter = 0.001 meters = 10~^3 meters
1.23 A derived unit is a combination of other units. Examples of derived units include: speed in meters per second (m/s), volume in meters cubed (m^3 ), and density in grams per cubic centimeter (g/cm^3 ).
1.24 The density (d) of a substance is the ratio of its mass (m) to its volume (V): mass m Density = — - or d = — Volume The density of a substance is an example of an intensive property, one that is independent of the amount of the substance. Mass is one of the properties used to calculate the density of a substance. Mass, in contrast, is an extensive property, one that depends on the amount of the substance.
1.25 An intensive property is a property that is independent of the amount of the substance. An extensive property is a property that depends on the amount of the substance.
1.26 Measured quantities are reported so that the number of digits reflects the uncertainty in the measurement. The non-place-holding digits in a reported number are called significant figures.
In multiplication or division, the result carries the same number of significant figures as the factor with the fewest significant figures.
In addition or subtraction, the result carries the same number of decimal places as the quantity with the fewest decimal places.
When rounding to the correct number of significant figures, round down if the last (or left-most) digit dropped is four or less; and round up if the last (or left-most) digit dropped is five or more.
1.30 Accuracy refers to how close the measured value is to the actual value. Precision refers to how close a series of measurements are to one another or how reproducible they are. A series of measurements can be precise (close to one another in value and reproducible) but not accurate (not close to the true value).
1.31 Random error is error that has equal probability of being too high or too low. Almost all measurements have some degree of random error. Random error can, with enough trials, average itself out. Systematic error is error that tends towards being either too high or too low. Systematic error does not average out with repeated trials.
1.32 Using units as a guide to solving problems is often called dimensional analysis. Units should always be included in calculations; they are multiplied, divided, and canceled like any other algebraic quantity.
substance pure or mixture Type (element or compound)
water pure compound
coffee mixture neither - mixture
ice pure compound
carbon pure element
1.41 (a) pure substance that is a compound (one type of molecule that contains two different elements)
(b) heterogeneous mixture (two different molecules that are segregated into regions)
(c) homogeneous mixture (two different molecules that are randomly mixed)
(d) pure substance that is an element (individual atoms of one type)
1.42 (a) pure substance that is an element (individual atoms of one type)
(b) homogeneous mixture (two different molecules that are randomly mixed)
(c) pure substance that is a compound (one type of molecule that contains two different elements)
(d) pure substance that is a compound (one type of molecule that contains two different elements)
1.43 (a) physical property (color can be observed without making or breaking chemical bonds)
(b) chemical property (must observe by making or breaking chemical bonds)
(c) physical property (the phase can be observed without making or breaking chemical bonds)
(d) physical property (density can be observed without making or breaking chemical bonds)
(e) physical property (mixing does not involve making or breaking chemical bonds, so this can be observed without making or breaking chemical bonds)
1.44 (a) physical property (color can be observed without making or breaking chemical bonds)
(b) physical property (odor can be observed without making or breaking chemical bonds)
(c) chemical property (must observe by making or breaking chemical bonds)
(d) chemical property (decomposition involves breaking bonds, so bonds must be broken to observe this property)
physical property (the phase of a substance can be observed without making or breaking chemical bonds)
chemical property (burning involves breaking and making bonds, so bonds must be broken and made to observe this property)
physical property (shininess is a physical property and so can be observed without making or break- ing chemical bonds)
(c) physical property (odor can be observed without making or breaking chemical bonds)
(d) chemical property (burning involves breaking and making bonds, so bonds must be broken and made to observe this property)
\ L4~6\ (a) physical property (vaporization is a phase change and so can be observed without making or break- ing chemical bonds)
(b) physical property (sublimation is a phase change and so can be observed without making or break- ing chemical bonds)
(c) chemical property (rusting involves the reaction of iron with oxygen to form iron oxide; observing this process involves making and breaking chemical bonds)
(d) physical property (color can be observed without making or breaking chemical bonds)
chemical change (new compounds are formed as methane and oxygen react to form carbon dioxide and water)
physical change (vaporization is a phase change and does not involve the making or breaking of chemical bonds)
chemical change (new compounds are formed as propane and oxygen react to form carbon dioxide and water)
chemical change (new compounds are formed as the metal in the frame is converted to oxides)
chemical change (new compounds are formed as the sugar burns)
physical change (dissolution is a phase change and does not involve the making or breaking of chem- ical bonds)
physical change (this is simply the rearrangement of the atoms)
chemical change (new compounds are formed as the silver converts to an oxide)
(d)
(a)
(b)
(c)
(a) physical change (vaporization is a phase change and does not involve the making or breaking of chemical bonds)
chemical change (new compounds are formed)
physical change (vaporization is a phase change and does not involve the making or breaking of chemical bonds)
physical change (vaporization of butane is a phase change and does not involve the making or break- ing of chemical bonds)
chemical change (new compounds are formed as the butane combusts)
physical change (vaporization of water is a phase change and does not involve the making or break- ing of chemical bonds)
in Measurement
(a)
op _ 32 To convert from °F to °C, first find the equation that relates these two quantities. °C = - — Now
substitute °F into the equation and compute the answer. Note: The number of digits reported in this °F — 32 0 answer follow significant figure conventions, covered in Section 1.6. °C = - - = — '- = 0.°C 1.8 1.
(b) To convert from K to °F, first find the equations that relate these two quantities. °F - 32 K = °C + 273.15 and °C = -
Since these equations do not directly express K in terms of °F, you must combine the equations and then solve the equation for °F. Substituting for °C: °F - 32 °F — 32 K = —- + 273.15 rearrange K - 273.15 = (^) l g rearrange 1.8 (K - 273.15) = (°F - 32) finally °F = 1.8 (K - 273.15) + 32 Now substitute K into the equa- tion and compute the answer. °F = 1.8 (77 - 273.15) + 32 = 1.8 (-196) + 32 = -353 + 32 = -321 °F
The Reliability of a Measurement and Significant Figures
1.73 In order to obtain the readings, look to see where the bottom of the meniscus lies. Estimate the distance between two markings on the device.
(a) 73.0 mL - the meniscus appears to be sitting on the 73 mL mark.
(b) 88.2 °C - the mercury is between the 84 °C mark and the 85 °C mark, but it is closer to the lower number.
(c) 645 mL - the meniscus appears to be just above the 640 mL mark.
1.74 (^) In order to obtain the readings, look to see where the bottom of the meniscus lies. Estimate the distance between two markings on the device. Use all digits on a digital device.
(a) 4.50 mL - the meniscus appears to be on the 4.5 mL mark.
(b) 27.43 °C - the mercury is just above the 27.4 °C mark. Note that the 10s digit is only labeled every 10 °C.
(c) 0.873 g - read all the places on the digital display.
Remember that
interior zeroes (zeroes between two numbers) are significant.
leading zeroes (zeroes to the left of the first non-zero number) are not significant. They only serve to locate the decimal point.
trailing zeroes (zeroes at the end of a number) are categorized as follows:
- Trailing zeroes after a decimal point are always significant.
Trailing zeroes before an implied decimal point are ambiguous and should be avoided by using scientific notation or by inserting a decimal point at the end of the number.
(a)
(b)
(c)
(d)
1,050,501 km
8.8820m
8.881090cm
Remember that
- interior zeroes (zeroes between two numbers) are significant.
- leading zeroes (zeroes to the left of the first non-zero number) are not significant. They only serve to locate the decimal point.
- trailing zeroes (zeroes at the end of a number) are categorized as follows:
- Trailing zeroes after a decimal point are always significant.
- Trailing zeroes before an implied decimal point are ambiguous and should be avoided by using scientific notation or by inserting a decimal point at the end of the number.
(a)
(b)
(c)
(d)
180,701 mi
8.881040m
8.885710km
9Q,2Q1 m
/^^^x
1.77 ) Remember all of the rules from Section 1.7.
(a) Three significant figures. The 3,1, and the 2 are significant (rule 1). The leading zeroes only mark the decimal place and are therefore not significant (rule 3).
(b) Ambiguous. The 3, 1, and the 2 are significant (rule 1). The trailing zeroes occur before an implied decimal point and are therefore ambiguous (rule 4). Without more information, we would assume 3 significant figures. It is better to write this as 3.12 x 105 to indicate three significant figures or as 3.12000 __ 105 to indicate six (rule 4).
(c) Three significant figures. The 3,1, and the 2 are significant (rule 1).
(d) Five significant figures. The Is, 3,2, and 7 are significant (rule 1).
(e) Ambiguous. The 2 is significant (rule 1). The trailing zeroes occur before an implied decimal point and are therefore ambiguous (rule 4). Without more information, we would assume one significant figure. It is better to write this as2x 103 to indicate one significant figure or as 2.000 x 103 to indicate four (rule 4).
1.78 Remember all of the rules from Section 1.7.
(a) Four significant figures. The Is are significant (rule 1). The leading zeroes only mark the decimal place and are therefore not significant (rule 3).
(b) One significant figure. The 7 is significant (rule 1). The leading zeroes only mark the decimal place and are therefore not significant (rule 3).
(c) Ambiguous. The 1, 8, and the 7 are significant (rule 1). The first 0 is significant, since it is an interior 0 (rule 2). The trailing zeroes occur before an implied decimal point and are therefore ambiguous (rule 4). Without more information, we would assume 4 significant figures. It is better to write this as 1.087 x 105 to indicate 4 significant figures or as 1.08700 x 105 to indicate six (rule 4).
(d) Seven significant figures. The I , 5,6, and 3s are significant (rule 1). The trailing zeros are significant because they are to the right of the decimal point and non-zero numbers (rule 4).
(e) Ambiguous. The 3 and 8 are significant (rule 1). The first 0 is significant because the first one is an interior zero. The trailing zeroes occur before an implied decimal point and are therefore ambiguous (rule 4). Without more information, we would assume three significant figures. It is better to write this as 3.08 x 104 to indicate three significant figures or as 3.0800 x 104 to indicate five (rule 4).
1.79 (a) This is not exact because IT is an irrational number. The number 3.14 only shows three of the infinite number of significant figures that TT has.
(b) This is an exact conversion because it comes from a definition of the units, and so has an unlimited number of significant figures.
(c) This is a measured number and so it is not an exact number. There are two significant figures.
(d) This is an exact conversion because it comes from a definition of the units, and so has an unlimited number of significant figures.
1.80 (a) This is a measured number and so it is not an exact number. There are nine significant figures.
(b) This is a an exact conversion, so it has an unlimited number of significant figures.
(c) This is a measured number and so it is not an exact number. There are three significant figures.
(d) This is an exact conversion because it comes from a definition of the units and so has an unlimited number of significant figures.
Round the intermediate answer to one decimal place to reflect the quantity with the fewest decimal places (2.3). Truncate non-significant digits since the first non-significant digit is 0.
(c) 19.
72.956 = 73.
Round the intermediate answer to one decimal place to reflect the quantity with the fewest decimal places (19.6). Round the last digit up since the first non-significant digit is 5.
(d) 5.
Round the intermediate answer to two decimal places to reflect the quantity with the fewest decimal places (5.99). Round the last digit up since the first non-significant digit is 8.
(a) 0.
0.10279 = 0.
Round the intermediate answer to three decimal places to reflect the quantity with the fewest deci- mal places (0.004). Round the last digit up since the first non-significant digit is 9.
(b) 1239.
1252.45 = 1252.
(c)
Round the intermediate answer to one decimal place to reflect the quantity with the fewest decimal places (1239.3). Round the last digit up since the first non-significant digit is 5.
0.623 = 0.
Round the intermediate answer to one decimal place to reflect the quantity with the fewest decimal places (2.4). Truncate non-significant digits since the first non-significant digit is 2.
(d)
Round the intermediate answer to zero decimal places to reflect the quantity with the fewest decimal places (532). Round the last digit up since the first non-significant digit is 7.
Perform operations in parentheses first. Keep track of significant figures in each step, by noting which is the last significant digit in an intermediate result.
(a) (24.6681 x 2.38) + 332.58 = 58.Z
391.290078 = 391.
The first intermediate answer has one significant digit to the right of the decimal, because it is allowed three significant figures (reflecting the quantity with the fewest significant figures (2.38)). Underline the most significant digit in this answer. Round the next intermediate answer to one decimal place to reflect the quantity with the fewest decimal places (58.7). Round the last digit up since the first non- significant digit is 9.
(b)
= 1.081542 xlO^4 = l.lxlO^4 0.0059 0. The first intermediate answer has one significant digit to the right of the decimal, to reflect the quan- tity with the fewest decimal places (85.3). Underline the most significant digit in this answer. Round the next intermediate answer to two significant figures to reflect the quantity with the fewest signifi- cant figures (0.0059). Round the last digit up since the first non-significant digit is 8.
(c) (512 + 986.7) + 5.44 = 0.
5.9589014 = 5.
The first intermediate answer has three significant figures and three significant digits to the right of the decimal, reflecting the quantity with the fewest significant figures (512). Underline the most significant digit in this answer. Round the next intermediate answer to two decimal places to reflect the quantity with the fewest decimal places (5.44). Round the last digit up since the first non-significant digit is 8.
(d) [(28.7xlO^5 ) * 48.533] + 144.99 = 59135.
59280.01 = 59300 = 5.93 x 10^4
The first intermediate answer has three significant figures, reflecting the quantity with the fewest sig- nificant figures (28.7 x 10^5 ). Underline the most significant digit in this answer. Since the number is so large this means that when the addition is performed, the most significant digit is the 100's place. Round the next intermediate answer to the 100's places and put in scientific notation to remove any ambiguity. Note that the last digit is rounded up since the first non-significant digit is 8.
Perform operations in parentheses first. Keep track of significant figures in each step, by noting which is the last significant digit in an intermediate result.
(a) [(1.7 xlO^6 ) *• [(2.63 x 10^5 )] + 7.33 = 6.
13.793878 = 13.
The first intermediate answer has one significant digit to the right of the decimal, because it is allowed two significant figures (reflecting the quantity with the fewest significant figures (1.7 x 10^6 )). Underline the most significant digit in this answer. Round the next intermediate answer to one deci- mal place to reflect the quantity with the fewest decimal places (6.5). Round the last digit up since the first non-significant digit is 9.
(b) (568.99 - 232.1) * 5.3 = 336.89 * 5.3 = 63.564151 = 64
The first intermediate answer has one significant digit to the right of the decimal, to reflect the quan- tity with the fewest decimal places (232.1). Underline the most significant digit in this answer. Round the next intermediate answer to two significant figures to reflect the quantity with the fewest signifi- cant figures (5.3). Round the last digit up since the first non-significant digit is 5.
(c) (9443 + 45 - 9.9) x 8.1 x 10^6 = = 9478.1 x 8.1x 10^6 = 7.67726 x 10^10 = 7.7 x 10,
The first intermediate answer only has significant digits to the left of the decimal, reflecting the quan- tity with the fewest significant figures (9443 and 45). Underline the most significant digit in this answer. Round the next intermediate answer to two significant figures to reflect the quantity with the fewest significant figures (8.1 x 10^6 ). Round the last digit up since the first non-significant digit is 7.
(d) (3.14 x 2.4367) -2.34 = 7. -2. 5.311238 = 5.
The first intermediate answer has three significant figures, reflecting the quantity with the fewest sig- nificant figures (3.14). Underline the most significant digit in this answer. This number has two signif- icant digits to the right of the decimal point. Round the next intermediate answer to two significant
