UNIT: Chemistry and Measurement

Objectives: Lesson 3 of 4• You will understand the relationship that exists between mass and

volume • You will learn which units we use to measure mass, volume, and

length• You will learn what the Metric System is and the common prefixes

used in measurement• You will learn how to convert between two units of temperature;

degrees Celsius and Kelvin

TOPIC: Units and Unit Conversions

QuickwriteIn 1-2 sentences answer one of the questions below:• What are some units of measurement you’re familiar with?• In football, the field is measured in yards, is the yard part of

the metric system or the English (standards) system???• Analyze gold blocks A and B below, which block do you think

has more mass (more atoms)? • Which block do you think has a greater volume (takes up more

space)?

BA= Gold Atom

Mass and Volume Relationship • Mass is how much stuff or matter an

object is made of• Think of mass as how many atoms or

molecules make up an object • For example, consider two gold blocks,

Block A and Block B, both of which are naturally made up of gold atoms

• Which block has more mass, Block A or Block B?

= Gold Atom

B

A

90 grams

50 grams

• Because Block B contains more atoms or “stuff” it therefore has a greater mass

• We could verify this by putting both blocks on a scale

• The block with more mass, Block B contains more atoms and will consequently weigh more

• Notice, mass is measured in grams

Mass and Volume Relationship • If an object has Mass, it takes up

space• Volume measures how much space

an object takes up• It is measured in either milliliters

(mL) or centimeters cubed (cm3)• Once again, consider our two gold

blocks, Blocks A and B= Gold Atom

B

A

• Which Block has more Volume?• In other words, which block takes up

more space?• Because Block B has more Mass, it will

have a greater volume• We could verify this by submerging

both Blocks in equal amounts of water• Notice, Block B displaced more water,

therefore Block B has a greater volume

What is the relationship between Mass and Volume?

• Mass is a measure of how much stuff or matter an object is made of

• Mass is measured in grams (g)• If an object has Mass, it has Volume• Volume is a measure of how space an object takes up • Volume is measured in Liters (L) or milliliters (mL)

Metric System• In science, we use the metric

system • The metric system is a

measurement system based on mulitples or powers of ten

• Consider a meter stick, which we use to measure length

• 1 meter contains 10 decimeters (1 meter = 10 decimeters)

1 meter = 10 decimeters= 100 centimeters

= 1000 millimeters• 1 meter also contains

100 centimeters (1 meter = 100 centimeters)

• 1 meter also contains 1000 tiny millimeters (1 meter = 1000 millimeters

10 decimeters1 meter

100 centimeters1 meter

1000 millimeters1 meter

Metric System• Notice, as each UNIT

became 10 times smaller a different prefix (deci-, centi-, or milli-) was put in front of the base unit METER

• The same is true if Units become larger

• Each prefix tells us how large or small a Unit is

1 meter = 10 decimeters = 100 centimeters = 1000 millimeters

Meter

Metric System• In the metric system, we use the

meter(m) to measure length, the gram (g) to measure mass and the liter(L) to measure volume

• These are the base UNITS of the metric system

• Prefixes are placed in front of each base unit to indicate the size and scale of each unit (10 times bigger or 10 times smaller)

A

Gram

Met

er

Liter

What is the Metric System?• Measurement system based on

multiples of 10• The meter(m) is used to measure

length, the gram (g) to measure mass and the liter(L) or milliliter (mL) is used to measure volume

• Each prefix is either tens time larger or ten times smaller than the next

• Please write down the table for your notes:

Prefix NumberKilo- 1000Hecto- 100Decka- 10Base Unit:Meter, Gram, Liter

1

Deci- 0.1

Centi- 0.01

Milli- 0.001

Unit Conversions and Dimensional Analysis• Have you calculated your height in Inches or your age in

minutes?• If so, you have performed unit conversions• A unit conversion is a method of changing a measurement from

one unit to another• Unit conversions are done using dimensional analysis • In chemistry, many of the calculations will involve unit

conversions and dimensional analysis• Dimensional analysis is a mathematical system using

conversion factors to move from one unit of measurement to a different unit of measurement

Steps for Solving Dimensional Analysis ProblemsSuppose you have a guitar that is 1 meter in length and you want to know the guitars length in millimeters.Through a series of steps, we can solve this problem:

1 meter =

??? m

illimeters

1. Start with what the problem gives you4. Solve the problem2. What are the conversion factors?3. Set up the calculation so the units cancel

= 1000 millimeters1 meter

1000 millimeters1 meter

Steps for Solving Dimensional Analysis ProblemsA year is 365 days long. How many minutes are in 1 year? Through a series of steps, we can solve this problem:

1. Start with what the problem gives you4. Solve the problem2. What are the conversion factors?3. Set up the calculation so the units cancel

= 525,600 minutes365 days

24 hours1 day

60 minutes1 hour

What is Dimensional Analysis?• A mathematical system using conversion

factors to move from one unit of measurement to a different unit of measurement

• Steps to solve:1. Start with what you are given2. What are the conversion factors?3. Set up the problem so units cancel4. Solve the problem

Practice:• You walked 5 kilometers to school today. How many meters

did you walk?

1. Start with what the problem gives you2. What are the conversion factors?3. Set up the calculation so the units cancel

= 5000 meters5 kilometers

1 kilometer1000 meters

4. Solve the problem

Units of Temperature• When measuring temperature, two units

of temperature you will need to become familiar with is the Kelvin and degrees Celsius Scale

• On the Celsius scale water boils at 100oC and on the Kelvin scale water boils at 373 K

• As temperature cools, water freezes at 0oC and 273 K

• The lowest possible temperature, where all molecular motion stops occurs at -273oC and 0 K

0-273o

0o 273

100o 373

Celsius Kelvin

Units of Temperature• To convert bewteen the Units of

temperature we will use the following equation: oC + 273 = K

• For example, lets say we want to 100oC into Kelvin

• Substituting our value into the equation we get: oC + 273 = K

• We could verify this by checking our thermometers to the right, notice 100oC matches up and agrees with 373K

0-273o

0o 273

100o 373

Celsius Kelvin

100oC

373 K

Practice:• Convert 293 K into degrees

Celsius using the equation: oC + 273 = K oC = 293 K - 273 oC = 10oC

293 K

Celsius Kelvin293 K

10oC??? oC

Summary (you can always write your own summary)

• Explain the relationship between mass and volume in your own words:

• What do we use to measure mass, volume and length?• What do the following metric prefixes represent: centi-,

milli-, and kilo-• If you are 60 inches tall, how many centimeters tall are

you? Conversion factor:• Convert 310 Kelvin into degrees Celsius:

2.54 centimeters1 inch