Chapter 2 Measurements and Calculations

Chapter 2 Table of Contents Return to TOC Copyright © Cengage Learning. All rights reserved 2.1 Scientific Notation 2.2 Units 2.3 Measurements of Length, Volume, and Mass 2.4 Uncertainty in Measurement 2.5 Significant Figures 2.6Problem Solving and Dimensional Analysis 2.7Temperature Conversions: An Approach to Problem Solving 2.8Density

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Measurement Quantitative observation. Has 2 parts – number and unit.  Number tells comparison.  Unit tells scale.

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Technique used to express very large or very small numbers. Expresses a number as a product of a number between 1 and 10 and the appropriate power of 10.

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Using Scientific Notation Any number can be represented as the product of a number between 1 and 10 and a power of 10 (either positive or negative). The power of 10 depends on the number of places the decimal point is moved and in which direction.

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Using Scientific Notation The number of places the decimal point is moved determines the power of 10. The direction of the move determines whether the power of 10 is positive or negative.

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Using Scientific Notation If the decimal point is moved to the left, the power of 10 is positive. 345 = 3.45 × 10 2 If the decimal point is moved to the right, the power of 10 is negative = 6.71 × 10 –2

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Concept Check Which of the following correctly expresses 7,882 in scientific notation? a)7.882 × 10 4 b)788.2 × 10 3 c)7.882 × 10 3 d)7.882 × 10 –3

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Concept Check Which of the following correctly expresses in scientific notation? a)4.96 × 10 –5 b)4.96 × 10 –6 c)4.96 × 10 –7 d)496 × 10 7

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Precision vs. Accuracy good precision poor precision good precision poor accuracy good accuracy good accuracy

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Measurement Accuracy How long is this line? There is no such thing as a totally accurate measurement!

Section 2.2 Units Return to TOC Copyright © Cengage Learning. All rights reserved Quantitative observation consisting of two parts.  number  scale (unit) Nature of Measurement Measurement Examples  20 grams  6.63 × 10 –34 joule·seconds If a CHP asks you what do you have and you answer I have 3 kilos, you may go to jail. You should have said I have 3 kg of doughnuts (or cream cheese danish) for my chemistry instructor.

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved Length MassVolumeTime metergramLitersecond SI System Km=1000m Kg=1000gKL=1000L1min=60sec 100cm=1m1000mg=1 g1000mL=1L60min=1hr 1000mm=1m British 12in=1ft16oz=1 lb4qt=1gal(same) 3ft=1yd2000 lb=1 ton2pts=1qt 5280ft=1mile Footpoundgallonsecond lll Measurement in Chemistry

Section 2.1 Scientific Notation Return to TOC Copyright © Cengage Learning. All rights reserved 2.54 cm = 1 in 1.06 qt = 1 L 454 g = 1 lb 1 (cm) 3 = 1 cc = 1 ml = 1 g water Conversion between British and SI Units

Section 2.2 Units Return to TOC Copyright © Cengage Learning. All rights reserved Prefixes are used to change the size of the unit. Prefixes Used in the SI System

Section 2.3 Measurements of Length, Volume, and Mass Return to TOC Copyright © Cengage Learning. All rights reserved Fundamental SI unit of length is the meter. Length

Section 2.3 Measurements of Length, Volume, and Mass Return to TOC Copyright © Cengage Learning. All rights reserved Volume Measure of the amount of 3-D space occupied by a substance. SI unit = cubic meter (m 3 ) Commonly measure solid volume in cm 3. 1 mL = 1 cm 3 1 L = 1 dm 3

Section 2.3 Measurements of Length, Volume, and Mass Return to TOC Copyright © Cengage Learning. All rights reserved Mass Measure of the amount of matter present in an object. SI unit = kilogram (kg) 1 kg = lbs 1 lb = g

Section 2.3 Measurements of Length, Volume, and Mass Return to TOC Copyright © Cengage Learning. All rights reserved Concept Check Choose the statement(s) that contain improper use(s) of commonly used units (doesn’t make sense)?  A gallon of milk is equal to about 4 L of milk.  A 200-lb man has a mass of about 90 kg.  A basketball player has a height of 7 m tall.  A nickel is 6.5 cm thick.

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty. Record the certain digits and the first uncertain digit (the estimated number).

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Measurement of Length Using a Ruler The length of the pin occurs at about 2.85 cm.  Certain digits: 2.85  Uncertain digit: 2.85 Estimate between smallest division!

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Significant Figures Numbers that measure or contribute to our accuracy. The more significant figures we have the more accurate our measurement. Significant figures are determined by our measurement device or technique.

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Rules of Determining the Number of Significant Figures 1. All non-zero digits are significant. 203 = 3 sig figs = 4 sig figs 1,030.2 = 5 sig figs 2. All zeros between non-zero digits are significant. 234 = 3 sig figs = 4 sig figs 1,234.2 = 5 sig figs

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Rules of Determining the Number of Significant Figures 3. All zeros to the right of the decimal and to the right of the last non-zero digit are significant = 3 sig figs = 4 sig figs = 5 sig figs 4. All zeros to the left of the first non-zero digit are NOT significant = 3 sig figs = 4 sig figs = 5 sig figs

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Rules of Determining the Number of Significant Figures 5.Zeros to the right of the first non-zero digit and to the left of the decimal may or may not be significant. They must be written in scientific notation = 2.3 x 10 3 or 2.30 x 10 3 or x sig figs 3 sig figs 4 sig figs

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Rules of Determining the Number of Significant Figures 6. Some numbers have infinite significant figures or are exact numbers. 233 people 14 cats (unless in biology lab) 7 cars on the highway 36 schools in town

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved How many significant figures are in each of the following? 1) ) significant figures 3) ) 210 5) 200 students 6) significant figures 2 or 3 significant figures infinite significant figures 1, 2, 3, or 4 significant figures

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Using Significant Figures in Calculations Addition and Subtraction 1.Line up the decimals. 2.Add or subtract. 3.Round off to first full column = ? = 38.4 or three significant figures

Section 2.4 Uncertainty in Measurement Return to TOC Copyright © Cengage Learning. All rights reserved Using Significant Figures in Calculations Multiplication and Division 1.Do the multiplication or division. 2.Round answer off to the same number of significant figures as the least number in the data. (23.345)(14.5)(0.523) = ? = 177 or three significant figures

Section 2.5 Significant Figures Return to TOC Copyright © Cengage Learning. All rights reserved 1.If the digit to be removed is less than 5, the preceding digit stays the same.  5.64 rounds to 5.6 (if final result to 2 sig figs) Rules for Rounding Off

Section 2.5 Significant Figures Return to TOC Copyright © Cengage Learning. All rights reserved 1.If the digit to be removed is equal to or greater than 5, the preceding digit is increased by 1.  5.68 rounds to 5.7 (if final result to 2 sig figs)  rounds to 3.9 (if final result to 2 sig figs) Rules for Rounding Off

Section 2.5 Significant Figures Return to TOC Copyright © Cengage Learning. All rights reserved 2.In a series of calculations, carry the extra digits through to the final result and then round off. This means that you should carry all of the digits that show on your calculator until you arrive at the final number (the answer) and then round off, using the procedures in Rule 1. Rules for Rounding Off

Section 2.5 Significant Figures Return to TOC Copyright © Cengage Learning. All rights reserved Concept Check You have water in each graduated cylinder shown. You then add both samples to a beaker (assume that all of the liquid is transferred). How would you write the number describing the total volume? 3.1 mL What limits the precision of the total volume? 1 st graduated cylinder

Section 2.6 Problem Solving and Dimensional Analysis Return to TOC Copyright © Cengage Learning. All rights reserved Example #1 To convert from one unit to another, use the equivalence statement that relates the two units. 1 ft = 12 in The two unit factors are: A golfer putted a golf ball 6.8 ft across a green. How many inches does this represent?

Section 2.6 Problem Solving and Dimensional Analysis Return to TOC Copyright © Cengage Learning. All rights reserved Choose the appropriate conversion factor by looking at the direction of the required change (make sure the unwanted units cancel). Example #1 A golfer putted a golf ball 6.8 ft across a green. How many inches does this represent?

Section 2.6 Problem Solving and Dimensional Analysis Return to TOC Copyright © Cengage Learning. All rights reserved Multiply the quantity to be converted by the conversion factor to give the quantity with the desired units. Correct sig figs? Does my answer make sense? Example #1 A golfer putted a golf ball 6.8 ft across a green. How many inches does this represent?

Section 2.6 Problem Solving and Dimensional Analysis Return to TOC Copyright © Cengage Learning. All rights reserved Example #2 An iron sample has a mass of 4.50 lb. What is the mass of this sample in grams? (1 kg = lbs; 1 kg = 1000 g)

Section 2.6 Problem Solving and Dimensional Analysis Return to TOC Copyright © Cengage Learning. All rights reserved Concept Check What data would you need to estimate the money you would spend on gasoline to drive your car from New York to Los Angeles? Provide estimates of values and a sample calculation. Sample Answer: Distance between New York and Los Angeles: 2500 miles Average gas mileage: 25 miles per gallon Average cost of gasoline: $3.25 per gallon

Section 2.7 Temperature Conversions: An Approach to Problem Solving Return to TOC Copyright © Cengage Learning. All rights reserved Fahrenheit Celsius Kelvin Three Systems for Measuring Temperature

Section 2.7 Temperature Conversions: An Approach to Problem Solving Return to TOC Copyright © Cengage Learning. All rights reserved The Three Major Temperature Scales F = 1.8C + 32 C = (F-32)/1.8 K = C What is 35 o C in o F?95 o F What is 90 o F in o C?32 o C What is 100K in o C?-173 o C

Section 2.7 Temperature Conversions: An Approach to Problem Solving Return to TOC Copyright © Cengage Learning. All rights reserved Converting Between Scales

Section 2.7 Temperature Conversions: An Approach to Problem Solving Return to TOC Copyright © Cengage Learning. All rights reserved Exercise The normal body temperature for a dog is approximately 102 o F. What is this equivalent to on the Kelvin temperature scale? a)373 K b)312 K c)289 K d)202 K

Section 2.7 Temperature Conversions: An Approach to Problem Solving Return to TOC Copyright © Cengage Learning. All rights reserved Exercise At what temperature does  C =  F?

Section 2.7 Temperature Conversions: An Approach to Problem Solving Return to TOC Copyright © Cengage Learning. All rights reserved Since °C equals °F, they both should be the same value (designated as variable x). Use one of the conversion equations such as: Substitute in the value of x for both T °C and T °F. Solve for x. Solution

Section 2.7 Temperature Conversions: An Approach to Problem Solving Return to TOC Copyright © Cengage Learning. All rights reserved Solution So –40°C = –40°F

Section 2.8 Density Return to TOC Copyright © Cengage Learning. All rights reserved Mass of substance per unit volume of the substance. Common units are g/cm 3 or g/mL.

Section 2.8 Density Return to TOC Copyright © Cengage Learning. All rights reserved Measuring the Volume of a Solid Object by Water Displacement

Section 2.8 Density Return to TOC Copyright © Cengage Learning. All rights reserved Example #1 A certain mineral has a mass of 17.8 g and a volume of 2.35 cm 3. What is the density of this mineral?

Section 2.8 Density Return to TOC Copyright © Cengage Learning. All rights reserved Example #2 What is the mass of a 49.6 mL sample of a liquid, which has a density of 0.85 g/mL?

Section 2.8 Density Return to TOC Copyright © Cengage Learning. All rights reserved Exercise If an object has a mass of g and occupies a volume of L, what is the density of this object in g/cm 3 ? a)0.513 b)1.95 c)30.5 d)1950

Section 2.8 Density Return to TOC Copyright © Cengage Learning. All rights reserved Using Density as a Conversion Factor How many lbs of sugar is in 945 gallons of 60.0 Brix (% sugar) orange concentrate if the density of the concentrate is g/mL? 945 gal 4 qt 1 gal 1 L 1.06qt 1000 mL 1 L g T 1 mL 60.0 g S 100 g T 1 lb s 454g S = lbs= 6.06 x 10 3 lbs sugar lbs of what?Coffee? Cocaine?

Section 2.8 Density Return to TOC Copyright © Cengage Learning. All rights reserved Using Density as a Conversion Factor Using the Formula How many lbs of sugar is in 256 L of 60.0 Brix (% sugar) orange concentrate if the density of the concentrate is g/mL? DV = M = 3.29 x 10 5 g T ( g/mL)(256,000 mL) = g T Solve for Mass M D = V 3.29 x 10 5 g T 1 lb T 454 g T 60.0 lbs S 100 lbs T = lbs S = 4.35 x 10 2 lbs S = 435 lbs S

Section 2.8 Density Return to TOC Copyright © Cengage Learning. All rights reserved Concept Check Copper has a density of 8.96 g/cm 3. If 75.0 g of copper is added to 50.0 mL of water in a graduated cylinder, to what volume reading will the water level in the cylinder rise? a)8.4 mL b)41.6 mL c)58.4 mL d)83.7 mL