UNITS OF MEASUREMEN

TThe metric system

CHEMISTRYYou will be studying chemistryChemistry is defines as “the study of matter and its reactions”

Chemistry is a physical science so we need to discuss how we measure things

WHAT ARE UNITS OF MEASUREMENT?

Units describe what aspect of matter is being measured Qualitative: something that is described Quantitative: something that is measured

Examples: Unit of distance – mileUnit of volume – gallonUnit of time – hourUnit of weight - pound

SI UNITS OF MEASUREMENT

SI – Standards InternationalSet of units that are recognized by

the scientific community In science (unlike math), you need

a unit for EVERY NUMBERThese are the units we will be using

in this class – not English units

BASE UNIT Metric system is a base 10 system

A base unit is a unit that measures some sort of physical/chemical data

Distance – meter (m) Mass – gram (g) Volume – liter (L) Time – second (s) Temperature – degrees Celsius (°C) Energy – Joules (J)

MASS – A QUICK EXPLANATION

Mass and weight are different Weight can change. It is not an absolute

value Weight depends upon the force of gravity You weigh more on Earth than on the

Moon Mass cannot change. It is an absolute value

Mass depends on the amount of matter in a substance

Mass does not change with gravity

PREFIXES (GET HANDOUT) Look at the name of the prefixes and the

abbreviation on the sheet These prefixes work for all base units The prefix tells you how the base unit can be

changed Example:

If you have a cg (centigrams), this means that the centigram is 1/100 of a gram.

If you have a cL (centiliter), this means that the centiliter is 1/100 of a liter.

HOW DO WE CHANGE THE BASE UNIT?

How big the measurement is depends on the prefix from the metric system

You increase or decrease the size of the number by changing the prefix in front of the base unit

IMPORTANT NOTE: When you go DOWN the chart, the number

gets BIGGER When you go UP the chart, the number gets

SMALLER

STEPS TO CONVERT : EXAMPLE: 100mm = _?_cm

Step 1: Find the conversion on the last column of the handout (Look at the prefixes)

100mm = _____ cm m (milli): 1 meter = 1000 mm c (centi): 1 meter =100 cm

Step 2: Use the conversion from the last column to convert to the base unit. (We will use ratios)

We start with 100millimiters (mm) and we want to make it the base unit meters (m) The base unit DOES NOT have a prefix

Therefore: 100 mm = ??? m

MATH FOR THE STEP 2 We look at the prefix conversion from

the first step 1m = 1000mm We start with 100mm So the equation is:

1m____ = (x) m____1000mm 100mm

Solve for x to find the number of meters NOTE: The meters(m) are both on top and

the millimeters(mm)are both on bottom

ANSWER FOR STEP 2 When you cross-multiply, you get the

following:

x = 0.1m

STEPS TO CONVERTStep 3: Use the answer that you got from step 2, to calculate into the unit you are looking for (cm)

We have our answer from step 2 (0.1m) We want to convert it to our second unit

(cm) Therefore, we want to turn 0.1m into

centimeters (cm) We will use the other conversion from

the first step 1meter (m) = 100 centimeters (cm)

MATH FOR STEP 3 1m = 100cm We start with 0.1m So the equation is:

1m____ = 0.1 m____100cm (x) cm

Solve for x to find the number of centimeters

NOTE: The meters(m) are both on top and the centimeters (cm) are both on bottom

ANSWER FOR STEP 3 When you cross-multiply, you get the

following:

x = 10 cm

NOTE: I know most of you know how to move the decimal to get the answer. YOU have to do it this way for the homework and quizzes. THERE IS A REASON.

ONE FINAL THING The example we just did showed how to

go from to numbers with prefixes in their units mm to cm This process involved 2 math steps

If your problem only has 1 number with a prefix, you will only need 1 math step Example: 250 cm = ??? m

MATH FOR EXAMPLE100 cm = ??? m

Find the value in the final column for centimeters (cm)

1meter (m) = 100 centimeters (cm)Set up the ratio:

1m__ = (x) m__100 cm 250 cm

x = 2.5m

PRACTICE Try the following 3 conversions IN

YOUR NOTES:1. 1500 g = __?__ kg

2. 63.3 hL = __?__ mL

3. 1.22 km = __?__ nm

ANSWERS

1. 1.500 g

2. 6,330,000 mL

3. 1,220,000,000,000 nm

TRY THESE IN ON YOUR OWN1. 0.25 hg = ________ g2. 3200 cm = ________ m3. 0.0036 kL = ________ mL4. 33400nJ = _______ kJ5. 225 dkg = ________ dg6. 880 hm = ________ um7. 1 nL = ________ kL

SCIENTIFIC NOTATION Some numbers are so big or small that

you have to write too many numbers Scientists have a short hand way to

abbreviate these number called scientific notation

Let’s look at the current national debt13,600,000,000,000 dollars

FORMAT In scientific notation we use exponents

to tell us how to move the decimal1. Write the number (without any zeroes

before or after it) 136

2. Put a decimal after the first digit 1.36

FORMAT3. Count how many spaces before

or after the decimal that you need to move the decimal to get to your original number

1.36 13,600,000,000,000. You have to move the decimal 13

spaces to the right

FORMAT4. Use the following convention

that shows you moved the decimal 13 spaces

x 1013

5. Put the original number from step 2 with step 4

1.36 x 1013

This tells you to move the decimal 13 places to the right

QUESTIONHow do you show that we

move the decimal to the left?For example:

0.00122

ANSWER Same method except you use a

negative (-) number in the exponent to show that the decimal goes to the left

1.22 x 10-3

The (-)3 says to move the decimal 3 spots to the left in the number 1.22

TRY THESE1. What are the following numbers in

scientific notation?

1. 356,000,0002. 0.0000125

2. What are the following numbers written out as a numeral?

1. 2.50 x 102

2. 7.77 x 10-3

ANSWER1. What are the following numbers

in scientific notation?1. 3.56 x 108

2. 1.25 x 10-5

2. What are the following numbers written out as a numeral?

1. 2502. 0.00777

PRACTICE WITH CALCULATORS

You will need to know how to read and enter scientific notation on calculators

After receiving a calculator, we will practice some on the board.