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Published byKerry Scott Modified over 5 years ago

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**Chapter 2 – Section 2 Suggested Reading Pages 33-42**

Units of Measurement Chapter 2 – Section 2 Suggested Reading Pages 33-42

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**Making Measurements Measurements must have a number and a unit.**

The unit depends on the quantity being measured.

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**SI Measurement Le Systeme International d’Unites**

See Table of SI Base units – Page 34 See Table of SI Prefixes – Page 35

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**Standard SI Units Length = meter (m) Mass = kilogram (kg)**

Time = second (s) Temperature = Kelvin (K) Amount of substance = mole (mol)

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**Derived SI Units Produced by multiplying or dividing standard units.**

Area = square meter (m2) Volume = cubic meter (m3) Density = kilograms per cubic meter (kg/m3)

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**Definitions Mass – a measure of the quantity of matter in an object.**

Weight – a measure of the gravitational pull on matter. Volume – the amount of space occupied by an object. Density – the ratio of mass to volume

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**The object with the lowest density will float.**

The density of an object is calculated by dividing the mass of the object by its volume. The object with the lowest density will float.

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**Density is a Derived Unit**

Combination of base units Mass (g or kg) Volume (m3 or cm3) length length length 1 cm3 = 1 mL 1 dm3 = 1 L Density (kg/m3 or g/cm3 or g/mL) mass per volume D = M V

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Density Mass (g) Volume (cm3)

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**Density V = 825 cm3 M = DV D = 13.6 g/cm3 M = (13.6 g/cm3)(825cm3)**

An object has a volume of 825 cm3 and a density of 13.6 g/cm3. Find its mass. GIVEN: V = 825 cm3 D = 13.6 g/cm3 M = ? WORK: M = DV M = (13.6 g/cm3)(825cm3) M = 11,200 g We will talk about how to round correctly soon!

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**Density D = 0.87 g/mL V = M V = ? M = 25 g V = 25 g 0.87 g/mL**

A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid? GIVEN: D = 0.87 g/mL V = ? M = 25 g WORK: V = M D V = g 0.87 g/mL V = 29 mL

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**Dimensional Analysis –**

The technique of converting between units.

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**Six Steps that May Help You:**

Write down the starting number with unit, draw a horizontal line under it, and a vertical line next to it.

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**Look at the unit and write down conversion factors that might work**

Look at the unit and write down conversion factors that might work. (You have to THINK of these.) 3. Write down UNITS for conversion factors ABOVE & BELOW the line so the unit you started with will CANCEL OUT.

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**4. Fill in the numbers that go with the conversion factors.**

5. Cancel out units as required. 6. Do the math & don’t forget to round correctly at the end & put the correct unit on your final answer.

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Example: Convert 14 cm to meters 14 cm 1. Write it down, draw the lines.

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Example: Convert 14 cm to meters 14 cm Our factor that we think will work is 100 cm = 1 meter Write down the factor.

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**Example: Convert 14 cm to meters m 14 cm cm**

Conversion Factor: 100 cm = 1 meter 3. Fill in the units from the factor so that the starting unit will cancel out.

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**4. Fill in the numbers from the conversion factor.**

Example: Convert 14 cm to meters 14 cm 1 m 100 cm Conversion Factor: 100 cm = 1 meter 4. Fill in the numbers from the conversion factor.

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**Example: Convert 14 cm to meters 14 cm 1 m 100 cm 5. Cancel out units.**

Conversion Factor: 100 cm = 1 meter 5. Cancel out units.

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** Example: Convert 14 cm to meters 14 cm 1 m = 14 x 1 100 100 cm m =**

Don’t forget units! m = 0.14 6. Do the math. Multiply all numbers across the top, divide by each number across the bottom.

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**Some Problems Require Many Steps …**

Just draw a longer line! Example: Convert 4.7 kg to pounds

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Example: Convert 4.7 kg to pounds 4.7 kg 1. Write it down, draw the lines.

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Example: Convert 4.7 kg to pounds 4.7 kg Our factors that we think will work are g = 1 lb 1000g = 1 kg Write down the factors.

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**Example: Convert 4.7 kg to pounds g lb 4.7 kg kg g**

Conversion Factors: 454 g = 1 lb and g = 1 kg 3. Fill in the units from the factors so that the starting unit will cancel out.

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**4. Fill in the numbers from the conversion factors.**

Example: Convert 4.7 kg to pounds g 1000 1 lb 4.7 kg 1 kg 454 g Conversion Factors: 454 g = 1 lb and g = 1 kg 4. Fill in the numbers from the conversion factors.

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**Example: Convert 4.7 kg to pounds g 1000 1 lb 4.7 kg 1 kg 454 g**

Conversion Factors: 454 g = 1 lb and g = 1 kg 5. Cancel out units.

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** 454 *Example: Convert 4.7 kg to pounds 4.7 kg 1000 g 1 lb = 1 454**

10. lb Don’t forget units! 6. Do the math. Multiply all numbers across the top, divide by each number across the bottom.

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**How to measure Mass – balance Weight – a spring scale**

Volume – volumetric flask

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