Chapter 1_Keys to the Study of Chemistry

8/9/2019 Chapter 1_Keys to the Study of Chemistry

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Chemistry is!The study of matter, its properties, the changesthat

matter undergoes, and the energyassociated with

these changes.

anything that hasboth mass and

volume

characteristicsthat give each

substance a

unique identity

the ability to dowork

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Does notinvolve

a change incomposition

A property that:

Does involve a

change incomposition

Can be reversed bytemperature changes

Is not simplyreversed by

temperature changes3


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Slowly turns

green when

exposed to air.

Malleable

Dissolves in

liquid ammonia.Can be melted

Forms a brown

gas when added

to nitric acid.

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Select the TRUEstatement.Chemical changes!

a) !are easily reversed by altering the temperature of the

system.

b)

!always produce substances different from thestarting materials.

c) !are accompanied by changes in the total mass of the

substances involved.

d)

!

provide the only valid basis for identification of asubstance.

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Observation Hypothesis

Experiment(Test

Hypothesis)

Model(Theory)

Experiment(Test

Theory)

Established

Theory8


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Converts a value from one unit to another in!

Quantity withdesired units

=Quantity withgiven units

ConversionFactor

x

For example, how many cm is in 12 m?

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Gimli Glider(1983)

Fuel loading was miscalculated converting mass of fuel required

(22,300 kg) to volume required.

Conversion factor needed: 0.803 kg/L

Conversion factor used: 1.77 lb/L

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Within a cell, proteins are synthesized on particles called

ribosomes. Assuming ribosomes are spherical, what is the volume(in dm3and L) of a ribosome whose average diameter is 21.4 nm.

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Weight:

is variabledepends on the local gravitational field

that is acting on an object.

Mass:

is constantdepends on the object's quantity of matter

Measured relative to a standard

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An intravenous nutrient solution is delivered to a hospital patient at

a rate of 1.5 drops per second. If a drop of solution weighs 65 mg,on average, how many kilograms are delivered in 8.0 h?

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massvolume

density =- A physical property

-

Depends on pressure,

temperature

Can density explain this?

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A piece of galena has a volume of 4.6 cm3. If the density of

galena is 7.5 g/cm3, what is the mass (in kilograms) of thispiece of galena?

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A small cube of aluminum measures15.6 mm on a side and has a mass of

10.25 g. What is the density ofaluminum in g/cm3?

a) 2.70 x 10-3g/cm3

b) 0.657 g/cm3

c) 2.70 g/cm3

d) 6.57 g/cm3

e) 5.35 g/cm3

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All measurements have uncertainty

- the rightmost (last) digit is the uncertain digit

What are these 2 thermometer readings?

Which reading is more accurate?

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1) If the number has a decimal point in it:- all digits in the number are significant except any

zeros used only to position the decimal point

e.g. 5400. 54.00 0.00540

2) If there is no decimal point in the number:

- zeros at the end of the number are not significant

e.g. 5400

3) The number is an exact number.- These are values with nouncertainty

e.g. Conversion factors, trial numbers, counted items

3 Cases

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For the following numbers, write the number of significant

digits, and re-write the number in scientific notation:

a) 850 oC

b)

1400. mL

c) .00000051 g

d) 13 pennies

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The specifications for a 100 mL volumetric flask state

that it is guaranteed to contain the specified volume towithin 0.1 mL. How many significant figures should youuse to record the volume contained in the flask?

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a) 1

b)

2c) 3d) 4e) The measurement would be

an exact number because a

volumetric flask is used.

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A,B,etc' to (613) 699-8734


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Multiplication and Division:The answer contains the same number of significant

figures as there are in the measurement with the

fewest significant figures.

2.2 x 3.7845 = 8.32590

3.76 4.236 = 0.8876298

(2.27 x 7.324) 3.3 = 5.0380

Rounds to:

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Addition and Subtraction:The answer has the same number of decimal places as

there are in the measurement with the fewest decimal

places.

For example:16.06 mL

+ 1.2344 mL

2.06 mL

- 1.1 mL

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Natural (ln) and base 10 (log) logarithmsThe answer has the same number of significant figures

after the decimal place as there are in the number whose

logarithm was taken.

For example: log(31.376) = 1.49659757!

10-4.8 = 0.0000158489!.

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If the digitremoved is:

Then the preceedingnumber is:

Example

< 5 Unchanged 3.62

> 5 Increased by 1 3.66= 5 or= 5 followed

by zero(s)

Unchanged if 5

3.45

3.65

= 5 followedby non-zero

numbersIncreased by 1

3.53

3.58

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In calculations use the rounding rules for each type of

mathematical operation, but carry through one or twoextra significant digits.

For example: 25.65 mL + 37.4 mL

73.55 s1 min

60 s

!

"#

$

%&

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The result of (3.8621 x 1.5630) - 5.98 is properly written as:

a) 0.06 b) 0.056 c) 0.0565 d) 0.05646 e) 0.056462

Another example:

=63.05 mL/73.55 s (1 min/60 s)

=51.4 mL

Note: the 5 is repeating


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how close themeasurements in a

series are to each

other

how close eachmeasurement is

to the actual

value.

There are 2 types of error that can be seen in anexperimental measurement:

produces values thatare both higher and

lower than the actual

value.

produces values thatare either allhigher or

alllower than the

actual value.31


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Which results are accurate?

Which results suffer from systematic error? Random error?

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SYSTEMATIC RANDOMSYSTEMATIC

ACCURATEACCURATE


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Finish LearnSmart Module 1

Recommended Exercises:

1.44, 1.48, 1.58, 1.66, 1.76, 1.82, 1.86

Note:1st DGD

tomorrow on

dimensional

analysis

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Chapter 1_Keys to the Study of Chemistry