Measurement in Chemistry

1
Measurement in Chemistry

• In chemistry we
• do experiments
• measure quantities
• use numbers to report measurements

2
Measurement

• You are making a measurement when you
• Check you weight
• Read your watch
• Take your temperature
• Weigh a cantaloupe
• What kinds of measurements did you make today?

3
Standards of Measurement

• When we measure, we use a measuring tool to
  compare some dimension of an object to a
  standard.

4
Some Tools for Measurement
5
Learning Check M1

• From the previous slide, state the tool (s) you
  would use to measure
• A. temperature ____________________
• B. volume ____________________
• ____________________
• C. time ____________________
• D. weight ____________________

6
Solution M1

• From the previous slide, state the tool (s) you
  would use to measure
• A. temperature _thermometer
• B. volume measuring cup graduated
  cylinder
• C. time _watch
• D. weight scale

7
Stating a Measurement

• In a measurement there is a
• Number
• and a
• Unit from measuring device

8
Learning Check M2

• What is the unit of measurement in each of the
  following examples?
• A. The patients temperature is 102F.
• B. The sack holds 5 lbs of potatoes.
• C. It is 8 miles from your house to school.
• D. The bottle holds 2 L of orange soda.

9
Solution M2

• A. F (degrees Fahrenheit)
• B. lbs (pounds)
• C. miles
• D. L (liters)

10
Exact Numbers

• Do not involve a measuring tool
• Are obtained when you count objects
• 4 tennis rackets
• 1 watch
• 2 pizzas
• Or use a definition
• 1 foot 12 inches
• 1 meters 100 cm

11
Learning Check M3

• Classify each of the following as an exact (1)
  or a measured(2) number.
• A. ___Gold melts at 1947F
• B. ___1 yard 3 feet
• C. ___A red blood cell is 6 x 10-4 cm in
  diameter
• D. ___There were 6 hats on the shelf
• E. ___A can of soda contains 355 mL of soda

12
Solution M3

• Classify each of the following as an exact (1)
  or a measured(2) number. Give reason.
• A. 2 Requires a thermometer(measuring tool)
• B. 1 From a definition in English system
• C. 2_ Need measuring tool to determine
• D. 1_ Counted the hats (no measuring tool
• E. 2 Measured

13
Worksheet M1 Types of Numbers

• Obtain the worksheet and a metric ruler.
• Work together in groups of 3-4 students.
• Complete the data.
• Compare your measurements with another group of
  students.
• Complete the questions.

14
Accuracy

• Is how close a measurement is to the actual or
  true value
• good accuracy
• true value
• poor accuracy
• true value

15
Precision

• How well several measurements agree with each
  other
• good precision
• poor precision

16
Accuracy and Precision

• What can you say about the accuracy and
  precision in each of the following
• Good precision, poor accuracy
• Good precision, good accuracy

17

• In your new job, you are to make the pizzas the
  size shown above. Your first four pizzas are
  shown below.
• What can you say about the accuracy and
  precision of your pizzas?

18
Pizza Precision

• You have very good precision, but poor accuracy.
  I think the customers will want the pizzas made
  larger.

19
The next four pizzas.

• What can you say about the accuracy and
  precision of the next four pizzas?

20
Accuracy is improving.

• The two pizzas in the center show good accuracy.
  However, the precision is poor.

21
Learning Check M4

• Match the following terms
• 1) Precision 2) Accuracy
• ___ Is how close a measurement is to the
• true value.
• ___ Is how close several measurements
• are to each other.
• Can you have data that are precise, but not
  accurate? Why or why not?

22
Solution M4

• Match the following terms
• 1) Accuracy 2) Precision
• _1_ Is how close a measurement is to the
• true value.
• _2_ Is how close several measurements
• are to each other.
• Yes. Data can be precise, but not close to
  the true value.

23
Learning Check M5

• How will each of the following affect accuracy
  and precision?
• 1. A meter stick that is missing the first
  centimeter.
• 2. A scale that has a zero point that is really
  five pounds above zero.

24
Solution M5

• How will each of the following affect accuracy
  and precision?
• 1. The cut off meter stick will produce
  measurements that have poor accuracy, but good
  precision is possible.
• 2. The poorly calibrated scale will give a
  weight that is not accurate, but good precision
  is possible.

25
Learning Check M6

• True(1) or false (2). Measurements can have
• poor accuracy and poor precision
• good accuracy and poor precision
• poor accuracy and good precision
• good accuracy and good precision

26
Solution M6

• True or false. Measurements can have
• poor accuracy and poor precision
• good accuracy and poor precision
• poor accuracy and good precision
• good accuracy and good precision

1
2
1
1
27
Learning Check M7

• True(1) or False(2)
• 1. ___All measuring tools have limitations
• 2. ___Some measurements can be exact
• 3. ___Every measurement has some error
• 4. ___Every measurement has uncertainty

28
Solution M7

• True(1) or False(2)
• 1. _1_All measuring tools have limitations
• 2. _2_Some measurements can be exact
• 3. _1_Every measurement has some error
• 4. _1_Every measurement has uncertainty

29
Learning Check M8

• A. Exact numbers are obtained by
• 1. measuring
• 2. counting
• 3. definition
• B. Measured numbers are obtained by
• 1. measuring
• 2. counting
• 3. definition

30
Solution M8

• A. Exact numbers are obtained by
• 2. counting
• 3. definition
• B. Measured numbers are obtained by
• 1. Using a measuring tool

31
Worksheet M2 MMs Statistics

• Obtain the MMs Statistics worksheets and a
  package of MMs for your group.
• 1) Part 1. Predict the items requested, then
  open the package and determine the actual number.
• 2) Complete the data requested in Part 1 .
• 3) Keep the paper and Part 2 for calculations at
  a later time.