Chapter 2 Lecture

Basic ChemistryFourth Edition

Chapter 2 Measurements2.1 Units of Measurement

Learning Goal Write the names and abbreviations for the metric or SI units used in measurements of length, volume, mass, temperature, and time.

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Key Math Skills

•Identifying Place Values (1.4A)

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Chapter 2 Readiness

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• Chemists use the metric system and the International System of Units (SI) for measurement when they

• measure quantities

• do experiments

• solve problems

The International System of Units (SI)

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Units of Measurement and Their Abbreviations

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Length is measured in

•units of meters (m) in both the metric and SI systems

•units of centimeters (cm) by chemists

Length

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Useful relationships between units of length include:

1 m = 1.094 yd

1 m = 39.37 in.

1 m = 100 cm

2.54 cm = 1 in.

Length

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Volume, the space occupied by a substance,

• is measured using units of m3 in the SI system

• is commonly measured in liters (L) and milliliters (mL) by chemists

Volume

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Useful relationships between units of volume include:

1 m3 = 1000 L

1 L = 1000 mL

1 mL = 1 cm3

1 L = 1.057 qt

946.3 mL = 1 qt

Volume

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The mass of an object, a measure of the quantity of material it contains,

•is measured on an electronic balance

•has the SI unit of kilogram (kg)

•is often measured by chemists in grams (g)

Mass

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Useful relationships between units of mass include:

1 kg = 1000 g

1 kg = 2.205 lb

453.6 g = 1 lb

Mass

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Temperature, a measure of how hot or cold an object feels,•is measured on the Celsius (ºC) scale•is measured on the Kelvin (K) scale in the SI system •is 18 ºC or 64 ºF on this thermometer

Temperature

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Time is based on an atomic clock and is measured in units of seconds (s) in both the metric and SI systems.

Time

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For each of the following, indicate whether the unit describes

(1) length, (2) mass, or (3) volume

A. A bag of onions has a mass of 2.6 kg.

B. A person is 2.0 m tall.

C. A medication contains 0.50 g of aspirin.

D. A bottle contains 1.5 L of water.

Learning Check

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For each of the following, indicate whether the unit describes

(1) length, (2) mass, or (3) volume

A. A bag of onions has a mass of 2.6 kg. (2)

B. A person is 2.0 m tall. (1)

C. A medication contains 0.50 g of aspirin. (2)

D. A bottle contains 1.5 L of water. (3)

Solution

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Identify the measurement that has an SI unit.

A. John’s height is _____.

(1) 1.5 yd (2) 6 ft (3) 2.1 m

B. The mass of a lemon is _____.

(1) 12 oz (2) 0.145 kg (3) 0.6 lb

C. The temperature is _____.

(1) 85 ºC (2) 255 K (3) 45 ºF

Learning Check

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Identify the measurement that has an SI unit.

A. John’s height is______. (3) 2.1 m

B. The mass of a lemon is _____. (2) 0.145 kg

C. The temperature is _____. (2) 255 K

Solution