Chapter 2 Introductory Chemistry Measurements and Calculations Objectives: 1) To define measurement 2)To show how very large or very small numbers can be expressed in scientific notation

Demonstration Number Line

Measurement Quantitative observation Every measurement -number -and a unit

Scientific Notation Scientific notation expresses a number as a product of a number between 1 and 10 and the appropriate power of 10. Example: 93,000,000= 9.3 x 107 0.0000167= 1.67 x 10-5

Scientific Notation 238,000 1,500,000 12,500 247 10 3,500,000 1430 2.38x 105 0.00043 0.089 0.135 0.0024 0.104 0.0306 0.00000072 4.3 x 10-3 1.5 x 106 8.9 x 10-2 1.25 x 104 1.35 x 10-1 2.4 x 10-3 2.47 x 102 1.04 x 10-1 1.0 x 101 3.06 x 10-2 3.5 x 106 1.43 x 103 7.2 x 10-7

Units Objectives: To learn the English, metric, and SI systems of measurement

Units Measure the following strings: Group A: mm Group B: cm Group C: m Group D: inches Group E: feet

Units Units: part of a measurement that tells us what scale or standard is being used. Two main systems are used: English system (United States) Metric system (used in most of the world) In 1960, INTERNATIONAL system(le Systeme Internationale) (SI) for scientists

Units Fundamental SI Units Physical Quantity Name of Unit Abbreviation mass kilogram kg length meter m time second s temperature kelvin K

Table 5.2

Measurements of Length, Volume, and Mass Objectives: To use the metric system to measure length, volume, and mass

Table 5.3

Length Figure 5.1: Comparison of English and metric units. 1 inch = 2.54 cm

Figure 5.2: Cube representations. Volume: the amount of 3D space occupied by a substance. Figure 5.2: Cube representations.

Figure 5.3: A 100 mL graduated cylinder. Volume ( in a laboratory) Beaker (inaccurate) Pipet Biuret Volumetric Flask Figure 5.3: A 100 mL graduated cylinder.

Mass Mass is the quantity of matter present in an object.

Uncertainty in Measurement Objectives: To learn how uncertainty in a measurement arises. To learn to indicate a measurement’s uncertainty by using significant figures. Homework: Self-check exercise 5.2 p. 126

Figure 5.5: Measuring a pin. Tell me the length of the pin. Estimate the last number

Uncertainty in Measurement The first 2 digits are certain. The third digit is estimated and can vary. (uncertain number) 2.8 A measurement always has some degree of uncertainty. Certain numbers Depends on the type of measuring device SIGNIFICANT FIGURES: all the certain numbers plus the first uncertain number

Significant Figures Rules for Counting Significant Figures All nonzero integers are significant. (1437) Zeroes Leading zeroes precede all nonzero are not significant (0.000025) Captive zeroes between all nonzero are significant (0.205) Trailing zeroes right end of number. Significant if number is written with a decimal point 100 (1 significant figure) 100. (3) 3) Exact numbers (determined by counting) have an unlimited number of significant figures in a calculation 1 inch=2.54 cm. Neither limits the number of significant figures

Significant Figures: Practice The mass of a single eyelash is 0.000304 The length of a skidmark is 1.270 x 102 A 125-g sample of chocolate chip Cookies contains 10g of chocolate. The volume of soda remaining in a can after a spill is 0.09020 L. A dose of antibiotic is 4.0 x 10-1 3 4 1 2

Significant Figures: Practice A sample of orange juice contains 0.0108 g of Vitamin C A forensic chemist in a lab weighs a single hair and records its mass as 0.0050060 The distance between 2 points was found to be 5.030 x 103 In yesterday’s race 110 riders started but only 60 finished. 3 5 4 unlimited

Rounding off Numbers When you use your calculator, you get more numbers than are significant so you must round off.

Rounding off Numbers Rules: If the digit to be removed Is less than 5, the digit remains the same If it’s = or > 5, the preceding digit increases. 2) In a series of calculations, carry the extra digits to the final calculation and then round off.

Rounding off If you round off to 2 significant digits 4.348= 4.3 4.348= 4.3 Use only the first number to the right of the last significant figure.

Determining Significant Figures in Calculations For multiplication/division: # of significant figures = the smallest number of significant figures (Measurement is limiting) Example: 4.56 x 1.4 = 6.384 6.4 8.315/298 = 0.0279027 0.0279 2 significant figures 3 significant figures

Determining Significant Figures in Calculations For addition and subtraction: limiting term is one with the smallest number of decimal places. 12.11 0.6875 18.0 -0.1 1.013 0.5875 0.6 31.123 31.1

Practice with Calculations 5.19 1081 2.3 x 3.14 1.9 - 7.25 3 boxes of candy 0.842 @$2.50 17.1 0.77 241 Do self-check exercise p.129 Homework: Focus Questions p. 129

Density Objective: To define density and its units Homework : Self-check exercise 5.4 p. 133 Self-check exercise 5.5 p. 134

Density Density can be defined as the amount of matter present in a given volume. Density = mass volume Specific gravity is the ratio of the density of a given liquid to the density of water at 4 C.

Problem Solving and Dimensional Analysis Objective: To learn how dimensional analysis can be used to solve various types of problems. Unit1 x conversion factor = Unit 2 Equivalence statement: 1 inch = 2.54 cm Converting from one unit to another is often called dimensional analysis.

Rules for Converting Step 1: Use the equivalence statement. Step 2: Choose the conversion factor by looking at the direction of the required change. Step 3: Multiply the quantity to be converted by the conversion factor Step 4: Check for significant figures Step 5: Ask whether your answer makes sense

Practice Problems A new baby weighs 7.8 lbs. What is its mass in kilograms? A piece of lumber is 88.4 cm long. What is its length in mm? in inches? A bottle of soda conains 2.0 L What is the volume in quarts? p.132

Chapter 2: Temperature Conversions Objectives: To learn the three temperature scales. 2) To learn to convert from one scale to another 3) To continue to develop problem-solving skills

Figure 5.6: The three major temperature scales. The size of each temperature unit is the same for the Celsius and Kelvin scale. The size of each unit Is < Celsius/Kelvin. Zero point is different on all 3 scales.

Converting from Celsius to Kelvin Temp oC + 273 = Temp oK Temp oK- 273= Temp oC The temperature is a balmy 28.5 oC. Convert it to the Kelvin scale. The freezing point of Nitrogen is -210 oC. What is the temperature on the Kelvin scale?

Figure 5.8: Comparison of the Celsius and Fahrenheit scales. Celsius to Fahrenheit Temp in Fahrenheit= 1.8 (Temp in Cel) +32 Fahrenheit to Celsius Temp in Celsius= Temp in Fahrenheit -32 1.8

Practice Problems Self check exercise 5.7 and 5.8 p. 140-141 Focus questions p.146 1-5 Complete for Homework

Figure 5.9: Tank of water.

Figure 5.9: Person submerged in the tank.