Introduction to Chemistry Unit Recap

Introduction to Chemistry Unit Recap

Purpose

Revisit transferable skills from previous unit that will be continuously used in future concepts

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• Measurement: a type of observation

• Qualitative measurements: descriptive

– Ex: hot, cold, heavy, light, big, blue,

furry

• Quantitative measurement: observation

made with a measuring instrument and
includes both a number and a unit
– Ex: ruler, balance, thermometer,

graduated cylinder, 13.5°C, 25kg, 17L

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• Accuracy: How close a

measurement is to the true or
accepted value
–Ex: Weighing a 50g mass

50.00g – accurate
32.18g – not accurate
49.99g – accurate

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• Precision: How close multiple measurements

are to each other
– Ex: Take the weight of a 50g mass

Accurate, precise:

Accurate, precise:

50.00g

50.00g

50.00g

49.99g

50.00g

50.00g

Not accurate, precise:

32.18g
32.18g
32.18g

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An easy way to remember…

ACcurate = Correct

PRecision = Reproducibility

Multiple Choice

This bullseye demonstrates...

• High Accuracy & High Precision
• High Accuracy & Low Precision
• Low Accuracy & High Precision
• Low Accuracy & Low Precision

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Scientific Notation

• Short hand for writing very large or small

numbers

• Two parts: Coefficient and Power of 10

A number between 1
and 10 (can include
1 but not 10).

Exponent:

>1, positive exponent
<1, negative exponent

Multiple Choice

Change from standard form to scientific notation: 12,000,000

• 12.0  x  10⁷
• 0.12  x  10⁷
• 1.2  x  10⁶
• 1.2  x  10⁷

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• There is uncertaintyin all measurements.

• The “certain” digits include all numbers

read directly off of the measuring device
PLUS one extra estimated digit.

• Ex:

This device is a graduated

cylinder. The units are mL.

The

proper reading should

be:

56.0mL (estimated digit)

Multiple Choice

Looking at the image, what is the correct measurement?

• 36 mL

• 35 mL

• 36.5 mL

• 36.5

• 37

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• The amount of definite digits depends on the

measuring device.

• An exact number has no uncertainty, and

therefore has an infinite number of significant
figures

– Example: 25 people, 25.0000000000000000000….

• Defined quantities are considered to be exact.

Example: 12 in=1ft, 100cm=1m

Multiple Choice

Which of the following is an exact measurement?

• 12.1 s

• 2.54 cm

• 12 people

• 100 grams

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Rules for Sig Figs!!

1. All non-zero digits are significant
Example: 2.17 - 3 s.f.

3894.6 – 5 s.f.

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2. Leading zeros are never significant

(zeros to the left)

Example: 0.003 - 1 s.f.

0.04 – 1 s.f.

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3. Captive zeros are always significant

(zeros in the middle)

Example: 205 – 3 s.f.

20005 – 5 s.f.

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4. Trailing zeros are sometimes

significant (zeros at the end)
a) They are significant if the number
contains a decimal point

Example: 155.0 – 4 s.f.

0.450 – 3 s.f.

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4. Trailing zeros (cont.)

b) They are not sig. if the number does
not contain a decimal point

Example: 1550 – 3 s.f.

45000 – 2 s.f.

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Summary

0.000424000600

(Leading)

NEVER

significant

(Captive)
ALWAYS

significant

(Trailing)

SOMETIMES
significant

(decimal=sig.)

Multiple Choice

How many significant figures does the following number have: 0.002040

• 6
• 4
• 3
• 2

Multiple Choice

How many significant figures does the following number have: 0.002040

• 6
• 4
• 3
• 2

Multiple Choice

How many significant figures does the following number have: 0.998005

• 9
• 10
• 6
• 5

Multiple Choice

How many significant figures does the following number have: 100.00210

• 7
• 5
• 10
• 8

Multiple Choice

How many significant figures does the following number have: 100.3

• 4
• 3
• 5
• 2

Multiple Choice

How many significant figures does the following number have: 2001800.

• 1
• 4
• 6
• 7

Multiple Choice

How many significant figures does the following number have: 56.040

• 2
• 3
• 4
• 5

Multiple Choice

Round 0.010229 to four sig figs

• 1022
• 1023
• 0.01023
• 0.01022

Multiple Choice

Round 1047.78 to three sig figs

• 104
• 105
• 1050
• 1050.00

Multiple Choice

How many Significant Figures in the number below?
0.456

• 3
• 4
• 2
• 1

Multiple Choice

How many significant figures does the following number have: 0.002040

• 6
• 4
• 3
• 2

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Sig Figs in Calculations

Addition and Subtraction:
LOOK at the decimal places!
The answer is rounded to the same number of
decimal places as the number used in the calculation
with the least decimal places.

Multiplication and Division:
LOOK at the total number of sig figs!
The answer is rounded to the same number of sig.
figs. as the number used in the calculation with the
least significant figures.

Multiple Choice

What is the result of adding 5.7 m and 2.11 m?

• 7.81 m

• 7.12 m

• 5.775 m

• 7.8 m

Multiple Choice

How many significant figures are in the number 9983?

• 1

• 2

• 3

• 4

Multiple Choice

What is the result of adding 5.7 m and 2.11 m?

• 7.81 m

• 7.12 m

• 5.775 m

• 7.8 m

Multiple Choice

What is the result of subtracting 1.345 g from 7.12 g?

• 8.304.2 g

• 5.67 g

• 5.667 g

• 7.8 g

Multiple Choice

What is the result of the division 17.85 g / 2.13 mL?

• 8.3803 g/mL

• 8.38028 g/mL

• 8.38 g

• 8.38028 mL

Multiple Choice

What is the result of the division 5.0 g / 7.77 L?

• 0.6435 g/L

• 0.64 g/L

• 0.009225 g/L

• 0.0092 g/L

Multiple Choice

What is the result of subtracting 2.0 mL from 100.45 mL?

• 98.45 mL

• 98.5 mL

• 98.45 mL²

• 98.5 mL²

Multiple Choice

What is the result of multiplying 0.0045 mL by 2.05 mL?

• 0.0092 mL²

• 0.009225 mL²

• 0.00922 mL²

• 0.009 mL²

Multiple Choice

What is the result of the multiplication 11.7 cm * 3.522 cm * 0.013 cm?

• 0.5356 cm³

• 0.54 cm³

• 0.535 cm³

• 0.54 cm

Multiple Choice

Calculate 5.50 cm + 5.50 cm and give your answer with the appropriate number of significant figures.

• 11 cm

• 11.0 cm

• 11.00 cm

• 11.000 cm

Multiple Choice

Calculate 12.34 + 1.234 + 0.1234 and provide your answer with the appropriate number of significant figures.

• 13.6974

• 13.697

• 13.70

• 13.7

Multiple Choice

Calculate 345.009 g - 23.009 g and give your answer with the appropriate number of significant figures.

• 322.00 g

• 322 g

• 322.000 g

• 322

Multiple Choice

Calculate 7.987 m - 0.54 m and give your answer with the appropriate number of significant figures.

• 7.45 m

• 7.447 m

• 7.4 m

• 7.5 m

Multiple Choice

Solve and round to the correct number of significant figures:

791.6 x 52

• 41000

• 41

• 41160

• 41200

Multiple Choice

Solve and round to the correct number of significant figures.

730 / 1.89

• 390

• 386.243

• 386

• 386.24

Multiple Choice

Solve and round to the correct number of significant figures.

23.7 x 3.8

• 90.06

• 90.1

• 91

• 90

Multiple Choice

Solve and round to the correct number of significant figures:

1.678 / 0.42

• 4.0

• 3.99

• 3.9

• 4