the science of chemistry - mrs. neill's...

CHAPTER 1

The Scienceof Chemistry

1.1 What Chemistry

Is About

2 1.1 What Chemistry Is About

Measurements

Using clear standards of measurements,

we can communicate more effectively

in answering simple questions.


MassHow heavy is an egg?

VolumeHow much space does an egg occupy?

DensityDoes an egg size piece of steel or

wood have the same mass?

PressureHow hard is it to crush an egg by squeezing

evenly from all sides?

Measurements








Measurements


Mass

The size (or volume) does not tell us how much matter there is.


Mass

1,000 g = 1 kg

Remember: Size (volume) does not tell us how much matter there is.


Measurements








Volume indicates an amount of space.

The milliliter (mL) is a unit of volume.

Volume


You can measure the volume of a

liquid using a graduated cylinder.

75 mL

Volume


Volume

1 mL = 1 cm3

You can measure the volume of a

liquid using a graduated cylinder.


Measurements








3 blocks of equal volume

3 different mass values

plastic glass iron

Density


density: a property of a substance that describes how

much matter the substance contains per unit volume;

typical units are grams per cubic centimeter (g/cm3).

Relationship between

mass and volume


Density

If 45 g of titanium are added to a graduated

cylinder containing 50 mL of water, what will

the cylinder read after the titanium has been

added?


If 45 g of titanium are added to a graduated cylinder containing 50 mL

of water, what will the cylinder read after the titanium has been added?

Density

Asked: Volume of graduated cylinder after adding 45 g of titanium

Given: 45 g of titanium, density of titanium d = 4.5 g/cm3, 50 mL of water

Relationships: mdV


If 45 g of titanium are added to a graduated cylinder containing 50 mL

of water, what will the cylinder read after the titanium has been added?

Density

Asked: Volume of graduated cylinder after adding 45 g of titanium

Given: 45 g of titanium, density of titanium d = 4.5 g/cm3, 50 mL of water

Relationships:

Solve:

The titanium adds 10 mL to the cylinder, which now reads 60 mL.

Answer: 60 mL

Discussion: This is an example of measurement using the displacement

method.

mdV

3 3

45 1.0

40

.51

m g mLV

d g cm cmmL








Measurements


Is the mass exactly 10.0 g?

We don’t know since any mass between 9.95 g and 10.05 g

would round off to 10.0 g

Accuracy and precision

Could it be 9.96 g?

10.04 g?


Accuracy and precision

Measurements that are not

accurate could lead you to the wrong conclusion.

If a measurement is not

precise, you may not be able to tell the difference

between agreement and

disagreement.


Accuracy how close a measurement is to the true

(correct) value.

Precision, how close the measured values are to

each other. These values

may be incorrect or correct.


Significant figures

Do you record 10 g or 10.0 g?

Does it make a difference?


Significant figures

Yes, it makes a difference in precision

Do you record 10 g or 10.0 g?

Does it make a difference?


109 11

If you record “10 g”

If you record “10.0 g”


Precision and accuracy

What value should be recorded for the volume

measurement in the picture?





Asked: The value with the correct number

of significant figures

Given: You can estimate to a tenth of the

graduation of a cylinder or ruler

Relationships: The last digit on the right is assumed to be plus or minus

one-tenth.



Asked: The value with the correct number

of significant figures

Given: You can estimate to a tenth of the

graduation of a cylinder or ruler

Relationships: The last digit on the right is assumed to be plus or minus

one-tenth.

Solve: The meniscus is right on 18, so estimate 18.0 mL.

Answer: 18.0 mL

Discussion: The real value is confidently known to be between 17.9

and 18.1 mL.




1 sigfig 3 sigfigs 1 sigfig


Science encompasses very large and very small objects.

The scientific notation is a shorthand system to write very large and very small numbers

Large Small


Scientific notation

1,500 = 15 x 100

mantissa

power of 10


1,500 = 15 x 100

mantissa

= 102

100 = 10 x 10 = 102 exponent

Scientific notation


1,500 = 15 x 100

mantissa

= 102

1,500 = 1.5 x 1,000

= 103

mantissa

Scientific notation


1,500 in scientific notation: 1.5 x 103

1,500 = 1.5 x 1,000

= 103

mantissa

Scientific notation


40,000,000

= 4 x 107

3,600

= 3.6 x 103

83,100

= 8.31 x 104

Scientific notation


0.0015 = 1.5 x 0.001

mantissa

power of 10

Scientific notation


0.0015 = 1.5 x 0.001

mantissa

= 10–3

A negative exponent

means: the number is smaller than 1

does not mean: the whole number is negative

Scientific notation


0.0015 in scientific notation: 1.5 x 10–3

0.0015 = 1.5 x 0.001

mantissa

Scientific notation

= 10–3


0.000 000 4

= 4 x 10–7

0.003 6

= 3.6 x 10–3

0.000 083 1

= 8.31 x 10–5

Scientific notation


Convert 0.00065 to scientific notation.

Scientific notation

Asked: The number in scientific notation

Given: 0.00065 as a decimal number

Relationships: 40.0001 10


Convert 0.00065 to scientific notation.

Scientific notation

Asked: The number in scientific notation

Given: 0.00065 as a decimal number

Relationships:

Answer:

40.0001 10

46.5 10


Using scientific notation on a calculator

Scientific notation


Measuring physical properties

Mass grams

Volume liters

Density grams per liter

Pressure atmospheres, psi

Precision vs. accuracy

Scientific notation

40,000,000

= 4 x 107

0.000 000 4

= 4 x 10–7

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