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# Numbers in Science Chapter 2 - PowerPoint PPT Presentation

Numbers in Science Chapter 2. Measurement. What is measurement? Quantitative Observation Based on a comparison to an accepted scale. A measurement has 2 Parts – the Number and the Unit Number Tells Comparison Unit Tells Scale There are two common unit scales English Metric. The Unit.

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Chapter 2

• What is measurement?

• Quantitative Observation

• Based on a comparison to an accepted scale.

• A measurement has 2 Parts – the Number and the Unit

• Number Tells Comparison

• Unit Tells Scale

• There are two common unit scales

• English

• Metric

• English (US)

• Length – inches/feet

• Distance – mile

• Volume – gallon/quart

• Mass- pound

• Metric (rest of the world)

• Length – meter

• Distance – kilometer

• Volume – liter

• Mass - gram

• All units in the metric system are related to the fundamental unit by a power of 10

• The power of 10 is indicated by a prefix

• The prefixes are always the same, regardless of the fundamental unit

• Established in 1960 by an international agreement to standardize science units

• These units are in the metric system

• SI unit = meter (m)

• About 3½ inches longer than a yard

• 1 meter = distance between marks on standard metal rod in a Paris vault or distance covered by a certain number of wavelengths of a special color of light

• Commonly use centimeters (cm)

• 1 inch (English Units) = 2.54 cm (exactly)

Figure 2.1: Comparison of English and metric units for length on a ruler.

• Measure of the amount of three-dimensional space occupied by a substance

• SI unit = cubic meter (m3)

• Commonly measure solid volume in cubic centimeters (cm3)

• Commonly measure liquid or gas volume

in milliliters (mL)

• 1 L is slightly larger than 1 quart

• 1 mL = 1 cm3

• Measure of the amount of matter present in an object

• SI unit = kilogram (kg)

• Commonly measure mass in grams (g) or milligrams (mg)

• 1 kg = 2.2046 pounds, 1 lbs.. = 453.59 g

Any idea what the three most common temperature scales are?

• Fahrenheit Scale, °F

• Water’s freezing point = 32°F, boiling point = 212°F

• Celsius Scale, °C

• Temperature unit larger than the Fahrenheit

• Water’s freezing point = 0°C, boiling point = 100°C

• Kelvin Scale, K (SI unit)

• Temperature unit same size as Celsius

• Water’s freezing point = 273 K, boiling point = 373 K

Thermometers based on the three temperature scales in (a) ice water and (b) boiling water.

• Technique Used to Express Very Large or Very Small Numbers

• 135,000,000,000,000,000,000 meters

• 0.00000000000465 liters

• Based on Powers of 10

• What is power of 10 Big?

• 0,10, 100, 1000, 10,000

• 100, 101, 102, 103, 104

• What is the power of 10 Small?

• 0.1, 0.01, 0.001, 0.0001

• 10-1, 10-2, 10-3, 10-4

1. Locate the Decimal Point : 1,438.

2. Move the decimal point to the right of the non-zero digit in the largest place

- The new number is now between 1 and 10

- 1.438

3. Now, multiply this number by a power of 10 (10n), where n is the number of places you moved the decimal point

- In our case, we moved 3 spaces, so n = 3 (103)

4. Determine the sign on the exponent n

If the decimal point was moved left, n is +

If the decimal point was moved right, n is –

If the decimal point was not moved, n is 0

• We moved left, so 3 is positive

• 1.438 x 103

• Determine the sign of n of 10n

• If n is + the decimal point will move to the right

• If n is – the decimal point will move to the left

• Determine the value of the exponent of 10

• Tells the number of places to move the decimal point

• Move the decimal point and rewrite the number

Try it for these numbers: 2.687 x 106 and 9.8 x 10-2

• We reverse the process and go from a number in scientific notation to standard form…..

• Change these numbers to Scientific Notation:

• 1,340,000,000,000

• 697, 000

• 0.00000000000912

• Change these numbers to Standard Form:

• 3.76 x 10-5

• 8.2 x 108

• 1.0 x 101

1.34 x 1012

6.97 x 105

9.12 x 10-12

0.0000376

820,000,000

10

• A measurement always has some amount of uncertainty, you always seem to be guessing what the smallest division is…

• To indicate the uncertainty of a single measurement scientists use a system called significant figures

• The last digit written in a measurement is the number that is considered to be uncertain

cm

• We follow guidelines (i.e. rules) to determine what numbers are significant

• Nonzero integers are always significant

• 2753

• 89.659

• .281

• Zeros

• Captive zeros are always significant (zero sandwich)

• 1001.4

• 55.0702

• 4780.012

• Zeros

• Leading zeros never count as significant figures

• 0.00048

• 0.0037009

• 0.0000000802

• Trailing zeros are significant if the number has a decimal point

• 22,000

• 63,850.

• 0.00630100

• 2.70900

• 100,000

Scientific Notation

• All numbers before the “x” are significant. Don’t worry about any other rules.

• 7.0 x 10-4 g has 2 significant figures

• 2.010 x 108 m has 4 significant figures

• How many significant figures are in these numbers?

• 102,340 0.01796 92,017

• 1.0 x 107 1,200.00 0.1192

• 1,908,021.0 0.000002 8.01010 x 1014

• Exact Numbers are numbers known with certainty

• Unlimited number of significant figures

• They are either

• counting numbers

• number of sides on a square

• or defined

• 100 cm = 1 m, 12 in = 1 ft, 1 in = 2.54 cm

• 1 kg = 1000 g, 1 LB = 16 oz

• 1000 mL = 1 L; 1 gal = 4 qts.

• 1 minute = 60 seconds

• Exact numbers do not affect the number of significant figures in an answer

• Answers to calculations must be rounded to the proper number of significant figures

• round at the end of the calculation

• For addition and subtraction, the last digit to the right is the uncertain digit.

• Use the least number of decimal places

• For multiplication, count the number of sig figs in each number in the calculation, then go with the smallest number of sig figs

• Use the least number of significant figures

If the digit to be removed

• is less than 5, the preceding digit stays the same

• Round 87.482 to 4 sig figs.

• is equal to or greater than 5, the preceding digit is increased by 1

• Round 0.00649710 to 3 sig figs.

In a series of calculations, carry the extra digits to the final result and then round off

Don’t forget to add place-holding zeros if necessary to keep value the same!! Round 80,150,000 to 3 sig figs.

• 5.18 x 0.0208

• 21 + 13.8 + 130.36

• 116.8 – 0.33

Answers must be in the proper number of significant digits!!!

• 0.107744 round to proper # sig fig

• 5.18 has 3 sig figs, 0.0208 has 3 sig figs so answer is 0.108

• 165.47

• Limiting number of sig figs in addition is the smallest number of decimal places = 12 (no decimals) answer is 165

• 116.47

• Same rule as above so answer is 116.5

• Exact Numbers are numbers known with certainty

• They are either

• counting numbers

• number of sides on a square

• or defined

• 100 cm = 1 m, 12 in = 1 ft, 1 in = 2.54 cm

• 1 kg = 1000 g, 1 LB = 16 oz

• 1000 mL = 1 L; 1 gal = 4 qts.

• 1 minute = 60 seconds

Fundamental Unit 100

• In the metric system, it is easy it is to convert numbers to different units.

• Let’s convert 113 cm to meters

• Figure out what you have to begin with and where you need to go..

• How many cm in 1 meter?

• 100 cm in 1 meter

• Set up the math sentence, and check that the units cancel properly.

• 113 cm [1 m/100 cm] = 1.13 m

• 250 mL to Liters

• 0.250 mL

• 1.75 kg to grams

• 1,750 grams

• 88 µL to mL

• 0.088 mL

• 475 cg to kg

• 47,500,000 or

• 4.75 x 107

• 328 mm to dm

• 3.28 dm

• 0.00075 nL to µL

• 0.75 µL

• Many problems involve using equivalence statements to convert one unit of measurement to another

• Conversion factors are relationships between two units

• Conversion factors are generated from equivalence statements

• e.g. 1 inch = 2.54 cm can give or

• Arrange conversion factor so starting unit is on the bottom of the conversion factor

• Convert kilometers to miles

• You may string conversion factors together for problems that involve more than one conversion factor.

• Convert kilometers to inches

• Find the relationship(s) between the starting and final units.

• Write an equivalence statement and a conversion factor for each relationship.

• Arrange the conversion factor(s) to cancel starting unit and result in goal unit.

• Convert 1.89 km to miles

• Find equivalence statement 1mile = 1.609 km

• 1.89 km (1 mile/1.609 km)

• 1.17 miles

• Convert 5.6 lbs to grams

• Find equivalence statement 454 grams = 1 lb

• 5.6 lbs(454 grams/1 lb)

• 2500 grams

• Convert 2.3 L to pints

• Find equivalence statements: 1L = 1.06 qts, 1 qt = 2 pints

• 2.3 L(1.06 qts/1L)(2 pints/1 qt)

• 4.9 pints

• To find Celsius from Fahrenheit

• oC = (oF -32)/1.8

• To find Fahrenheit from Celsius

• oF = 1.8(oC) +32

• Celsius to Kelvin

• K = oC + 273

• Kelvin to Celsius

• oC = K – 273

• 180°C to Kelvin

• To convert Celsius to Kelvin add 273

• 180+ 273 = 453 K

• 23°C to Fahrenheit

• Use the conversion factor: F = (1.80)C + 32

• F = (1.80)23 + 32

• F=73.4 or 73°F

• 87°F to Celsius

• Use the conversion factor C=5/9(F-32)

• C = 5/9(87-32)

• C = 30.5555555… or 31°C

• 694 K to Celsius

• To convert K to C, subtract 273

• 694-273= 421°C

and

Calculations

• Density is a physical property of matter representing the mass per unit volume

• For equal volumes, denser object has larger mass

• For equal masses, denser object has small volume

• Solids = g/cm3

• Liquids = g/mL

• Gases = g/L

• Volume of a solid can be determined by water displacement

• Density : solids > liquids >>> gases

• In a heterogeneous mixture, denser object sinks

• What is the density of a metal with a mass of 11.76 g whose volume occupies 6.30 cm3?

• What volume of ethanol (density = 0.785 g/mL) has a mass of 2.04 lbs?

• What is the mass (in mg) of a gas that has a density of 0.0125 g/L in a 500. mL container?

• To determine the volume to insert into the density equation, you must find out the difference between the initial volume and the final volume.

• A student attempting to find the density of copper records a mass of 75.2 g. When the copper is inserted into a graduated cylinder, the volume of the cylinder increases from 50.0 mL to 58.5 mL. What is the density of the copper in g/mL?

• A student masses a piece of unusually shaped metal and determines the mass to be 187.7 grams. After placing the metal in a graduated cylinder, the water level rose from 50.0 mL to 60.2 mL. What is the density of the metal?

• A piece of lead (density = 11.34 g/cm3) has a mass of 162.4 g. If a student places the piece of lead in a graduated cylinder, what is the final volume of the graduated cylinder if the initial volume is 10.0 mL?

Percent Error determines the mass to be 187.7 grams. After placing the metal in a graduated cylinder, the water level rose from 50.0 mL to 60.2

• Percent error – absolute value of the error divided by the accepted value, multiplied by 100%.

% error = measured value – accepted value x 100%

accepted value

• Accepted value – correct value based on reliable sources.

• Experimental (measured) value – value physically measured in the lab.

Percent Error Example determines the mass to be 187.7 grams. After placing the metal in a graduated cylinder, the water level rose from 50.0 mL to 60.2

• In the lab, you determined the density of ethanol to be 1.04 g/mL. The accepted density of ethanol is 0.785 g/mL. What is the percent error?

• The accepted value for the density of lead is 11.34 g/cm3. When you experimentally determined the density of a sample of lead, you found that a 85.2 gram sample of lead displaced 7.35 mL of water. What is the percent error in this experiment?

• Joe measured the boiling point of hexane to be 66.9 determines the mass to be 187.7 grams. After placing the metal in a graduated cylinder, the water level rose from 50.0 mL to 60.2 °C. If the actual boiling point of hexane is 69 °C , what is the percent error?

• A student calculated the volume of a cube to be 68.98 cm3. If the true volume is 71.08 cm3, what is the student’s percent error?

• Tom used the density of copper and the volume of water displaced to measure the mass of a copper pipe to be 145.67 g. When he actually weighed the sample, he found a mass of 146.82 g. What was his percent error?