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Do Now:

• Who is your tallest teacher?• Who is your shortest teacher?• Approximate their heights.

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• Qualitative measurement -

• Quantitative measurement -

Descriptive, nonnumerical form

Definite form, with numbers and units

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Let’s Measure!

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When taking a measurement…take advantage of the scale

• Each measurement contains -

all the certain digits of the measuring device + 1 estimated digit

• Together this makes up the

Significant Digits

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The uncertainty in the measurement must be carried throughout the calculation

• Provided with a measurement, you must be able to tell how many significant digits it has.

Rules1. Digits other than zero are always

significant.2. Zeros between two other significant digits

is also significant.3. Zeros that are placeholders are not

significant digits. 85.6 19 505 1.60058 20.05 5000 0.5 0.005 0.0050

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A chain is only as strong as its weakest link• A value can only be as accurate as the numbers

used to produce it.• When adding and subtracting, answer will have as

many decimal places as the value with the smallest number of decimal places.

3.0056 m

2.52 m

3.1 m

8.6256 m

8.6 m

• When multiplying and dividing, answer will have as many significant digits as the value with the smallest number of significant digits

V = l w h = 2.06 cm x 0.058 cm x 10.0 cm =

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Scientific Notation• Used to easily describe small or large

numbers• Sometimes the only way to express

your answer with the correct number of significant digits

• 5.046 x 10-7

• 2.4 x 104

• Significant digits must be constant between scientific notation and expanded notation

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Change

1. 50000 to scientific notation

2. 25.03 to scientific notation

3. 0.00740 to scientific notation

4. 1.34 x 10-3 to expanded notation

5. 4.506 x 102 to expanded notation

6. 2.0 x 103 to expanded notation

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What is an exact number?• Numbers that are exact by definition, such as

1 inch = 2.54 cm    100 cm = 1 m

1 foot = 12 inches

or• Things you count… 10 pencils, 23 students• Numbers in formulas… radius = diameter/2

Exact numbers are ignored when determining significant digits in your final answer.

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Which are exact numbers?

• Mass of a 32-oz can of coffee• Surface area of a dime• Pages in your chemistry book• Number of seconds in an hour

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In this class and most places on the EARTH! the metric system is

used. WHY?

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Metric SystemSI (International System of Units)

Base Units

Quantity Unit

Length meter, m

Mass kilogram, kg

Time second, s

Sometimes these units will not be the best way for us to express a measurement

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Derived unit• Combination of base units• Examples

Area m2

Density g/cm3

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Use prefixesPrefix Symbol

Mega M

Kilo k

Deci d

Centi c

Milli m

Micro mNano n

Pico p

Meaning (based on g)

1 x106 g = 1 Mg

1000 g = 1 kg

1 dg = 0.1 g

1 cg = 0.01 g

1 mg = 0.001 g

1 mg = 1x10-6 g

1 ng = 1 x10-9g

1 pg = 1 x10-12g

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What is volume?

• Amount of space occupied by a sample of matter

• Units: mL, L or cm3, m3, mm3

• Find the volume of my tissue box in cm3

• Find the volume of this object

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What are precision and accuracy?

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Percent Error% Error = (Experimental Value – Accepted Value) x 100

Accepted Value

• A student measures the volume of an object to be 225 mL. The accepted value is 249 mL. Determine the percent error.

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What is density?• Ratio of an object’s mass to its volume• More closely packed the atoms or molecules are,

the greater the density• Typically, solid density>liquid density>gas density• Water is an exception, solid density<liquid density

D = m

V

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0011 0010 1010 1101 0001 0100 10111.Find the density of a metal sample with a mass of 45.3 grams and a volume of 5.99 mL.

2.What are units for density?

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1. Determine the volume of a 25.0 g sample of metal whose density is 5.67 g/cm3

2. Determine the mass of a 250 mL sample of liquid whose density is 1.45 g/mL.

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Dimensional Analysis• Method in problem solving to convert units• You are following a recipe on the cooking

channel prepared by a British chef. The recipe requires 1.25 L of apple cider. The only volume measuring equipment you have is in cups. You go online and find that:

1 L = 4.22675 cup (US) How many cups do you need?

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Let’s try another

• You need 32.0 inches of material to complete your project. The supplier sells the material by the meter. You find out that 1 inch = 2.54 cm. How many meters will you need?

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A piece of wood is measured to be 1.25 ft x 3.5 ft

• What is the area of the wood in ft2?• If one foot = 12 inches, convert from

ft2 to in2

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0011 0010 1010 1101 0001 0100 1011The denisty of alcohol is 0.754 g/cm3. Convert this to

g/m3.

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How fast can you pitch?