1 Measurement in Chemistry In chemistry we do experiments measure quantities use numbers to...

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1 Measurement in Chemistry In chemistry we do experiments measure quantities use numbers to report measurements

Transcript of 1 Measurement in Chemistry In chemistry we do experiments measure quantities use numbers to...

Page 1: 1 Measurement in Chemistry In chemistry we  do experiments  measure quantities  use numbers to report measurements.

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Measurement in Chemistry

In chemistry we

do experiments

measure quantities

use numbers to report measurements

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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?

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Standards of Measurement

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

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Some Tools for Measurement

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Learning Check M1

From the previous slide, state the tool (s) you would use to measure

A. temperature ____________________

B. volume ____________________

____________________

C. time ____________________

D. weight ____________________

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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

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Stating a Measurement

In a measurement there is a

Number

and a

Unit from measuring device

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Learning Check M2

What is the unit of measurement in each of the

following examples?

A. The patient’s temperature is 102°F.

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.

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Solution M2

A. °F (degrees Fahrenheit)

B. lbs (pounds)

C. miles

D. L (liters)

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Exact Numbers

Do not involve a measuring toolAre obtained when you count objects

4 tennis rackets

1 watch

2 pizzas

Or use a definition1 foot = 12 inches

1 meters = 100 cm

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Learning Check M3

Classify each of the following as an exact (1) or a measured(2) number.

A. ___Gold melts at 1947°F

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

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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

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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.

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Accuracy

Is how close a measurement is to the actual or true value

good accuracy

true value

poor accuracy

true value

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Precision

How well several measurements agree with each other

good precision

poor precision

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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

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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?

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Pizza Precision

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

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

The next four pizzas.

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Accuracy is improving.

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

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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?

Learning Check M4

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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.

Solution M4

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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.

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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.

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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

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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

11

2

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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

Learning Check M7

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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

Solution M7

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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

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Solution M8

A. Exact numbers are obtained by

2. counting

3. definition

B. Measured numbers are obtained by

1. Using a measuring tool

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Worksheet M2: M&M’s Statistics

Obtain the M&M’s Statistics worksheets and a package of M&M’s 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.