PRINCIPLES OF CHEMISTRY I

CHEM 1211

CHAPTER 1 DR. AUGUSTINE OFORI AGYEMAN

Assistant professor of chemistryDepartment of natural sciences

Clayton state university

CHAPTER 1

MEASUREMENT

- Is the determination of the dimensions, capacity, quantity, or extent of something

- Is a quantitative observation and consists of two parts: a number and a scale (called a unit)

- Is the tool chemists use most

Examplesmass, volume, temperature, pressure, length, height, time

MEASUREMENT

SIGNIFICANT FIGURES

Precision - Provides information on how closely individual(repeated) measurements agree with one another

Accuracy - Refers to how closely individual measurements

agree with the true value (correct value)

Precise measurements may NOT be accurate

SIGNIFICANT FIGURES

Exact Numbers - Values with no uncertainties

- There are no uncertainties when counting objects or people(24 students, 4 chairs, 10 pencils)

- There are no uncertainties in simple fractions(1/4, 1/7, 4/7, 4/5)

Inexact Numbers - Associated with uncertainties

- Measurement has uncertainties (errors) associated with it- It is impossible to make exact measurements

SIGNIFICANT FIGURES

Measurements contain 2 types of information- Magnitude of the measurement- Uncertainty of the measurement

Only one uncertain or estimated digit should be reported

Significant Figures digits known with certainty + one uncertain digit

RULES FOR SIGNIFICANT FIGURES

1. Nonzero integers are always significant 4732 (4 sig. figs.) 875 (3 sig. figs.)

2. Leading zeros are not significant 0.0045 (2 sig. figs.) 0.00007895 (4 sig. figs.) The zeros simply indicate the position of the decimal point

3. Captive zeros (between nonzero digits) are always significant 1.0025 (5 sig figs.) 12000587 (8 sig figs)

RULES FOR SIGNIFICANT FIGURES

4. Trailing zeros (at the right end of a number) are significant only if the number contains a decimal point 2.3400 (5 sig figs) 23400 (3 sig figs)

5. Exact numbers (not obtained from measurements) are assumed to have infinite number of significant figures

RULES FOR SIGNIFICANT FIGURES

How many significant figures are present in each of the following?What is the uncertainty in each case?

significant figures uncertainty1.24 g 3 ± 0.01 g

0.0024 L 2 ± 0.0001 L0.39200 mL 5 ± 0.00001 mL3.0026 kg 5 ± 0.0001 kg

RULES FOR SIGNIFICANT FIGURES

Rounding off Numbers

1. In a series of calculations, carry the extra digits through to the final result before rounding off to the required significant figures

2. If the first digit to be removed is less than 5, the preceding digit remains the same (round down) Round to two significant figures 2.53 rounds to 2.5 and 1.24 rounds to 1.2

RULES FOR SIGNIFICANT FIGURES

Rounding off Numbers

3. If the first digit to be removed is greater than 5, the preceding digit increases by 1 (round up) (2.56 rounds to 2.6 and 1.27 rounds to 1.3)

4. If the digit to be removed is exactly 5 (round even)- The preceding number is increased by 1 if that results in an even number (2.55 rounds to 2.6 and 1.35000 rounds to 1.4)- The preceding number remains the same if that results in an odd number (2.45 rounds to 2.4 and 1.25000 rounds to 1.2)

RULES FOR SIGNIFICANT FIGURES

Multiplication and Division- The result contains the same number of significant figures as the

measurement with the least number of significant figures

2.0456 x 4.02 = 8.223312 = 8.22

3.20014 ÷ 1.2 = 2.6667833 = 2.7

- The certainty of the calculated quantity is limited by the least certain measurement, which determines the final number of

significant figures

RULES FOR SIGNIFICANT FIGURES

Addition and Subtraction- The result contains the same number of decimal places as the

measurement with the least number of decimal places

- The certainty of the calculated quantity is limited by the least certain measurement, which determines the final number of

significant figures

5.479

0.234

3.2

2.045

4.028

3.52

7.548

= 5.5 = 4.03 6.00

3.47

47.9

= 6.00 (not 6)

SCIENTIFIC NOTATION

- Used to express too large or too small numbers (with many zeros)in compact form

- The product of a decimal number between 1 and 10 (the coefficient)and 10 raised to a power (exponential term)

24,000,000,000,000 = 2.4 x 1013

coefficientexponential term

exponent (power)

0.000000458 = 4.58 x 10-7

SCIENTIFIC NOTATION

- Provides a convenient way of writing the required number of significant figures

6300000 to 4 significant figures = 6.300 x 106

2400 to 3 significant figures = 2.40 x 103

0.0003 to 2 significant figures = 3.0 x 10-4

SCIENTIFIC NOTATION

- Add exponents when multiplying exponential terms(5.4 x 104) x (1.23 x 102)

= (5.4 x 1.23) x 10 4+2

= 6.6 x 106

- Subtract exponents when dividing exponential terms(5.4 x 104)/(1.23 x 102)

= (5.4/1.23) x 10 4-2

= 4.4 x 102

MEASUREMENT SYSTEMS

Two measurement systems:

English System of Units (commercial measurements): pound, quart, inch, foot, gallon

Metric System of Units (scientific measurements)SI units (Systeme International d’Unites)

liter, meter, gramMore convenient to use

FUNDAMENTAL (BASE) UNITS

Physical Quantity

MassLengthTimeTemperatureAmount of substanceElectric currentLuminous intensity

Name of Unit

KilogramMeterSecondKelvinMoleAmpereCandela

Abbreviation

kgms (sec)KmolAcd

Area = length x length = m x m = m2

Volume = m x m x m = m3

Volume may also be expressed in LITERS (L)1L = 1000 mL = 1000 cm3 or cubic centimeters

(c.c.)Implies 1mL = 1c.c.

mL is usually used for volumes of liquids and gasesc.c. is usually used for volumes of solids

Density = kg/ m3

DERIVED UNITS

DERIVED UNITS

Physical Quantity

Force PressureEnergyPowerFrequency

Name of Unit

NewtonPascalJouleWattHertz

Abbreviation

N (m-kg/s2)Pa (N/m2; kg/(m-s2)J (N-m; m2-kg/s2)W (J/s; m2-kg/s3)Hz (1/s)

Prefix

GigaMegaKiloDeciCentiMilli

MicroNanoPico

Femto

Abbreviation

GMkdcmµnpf

Notation

109

106

103

10-1

10-2

10-3

10-6

10-9

10-12

10-15

UNIT CONVERSIONS

UNIT CONVERSIONS

1 gigameter (Gm)

1 megameter (Mm)

1 kilometer (km)

1 decimeter (dm)

1 centimeter (cm)

1 millimeter (mm)

1 micrometer (µm)

1 nanometer (nm)

1 picometer (pm)

1 femtometer (fm)

= 109 meters

= 106 meters

= 103 meters

= 10-1 meter

= 10-2 meter

= 10-3 meter

= 10-6 meter

= 10-9 meter

= 10-12 meter

= 10-15 meter

UNIT CONVERSIONS

Length/Distance

2.54 cm = 1.00 in.12 in. = 1 ft1 yd = 3 ft1 m = 39.4 in.1 m = 1.09 yd1 km = 0.621 mile1 km = 1000 m

Time

1 min = 60 sec1 hour = 60 min24 hours = 1 day7 days = 1 week

Volume

1 gal = 4 qt1 qt = 0.946 L1 L = 1.06 qt1 L = 0.265 gal1 mL = 0.034 fl. oz.

Mass

1 Ib = 454 g1 Ib = 16 oz1 kg = 2.20 lb1 oz = 28.3 g

UNIT CONVERSIONS

1 km = 1000 m orm1000

km 1

km 1

m 1000»

Conversion Factors

1 L = 1000 mL

24 hours = 1 day

1 kg = 2.20 lb

»

»

»

mL 1000

L 1

day1

hours24

lb 2.20

kg 1

or

or

or

L 1

mL 1000

hours24

day1

kg 1

lb 2.20

UNIT CONVERSIONS

given number · unit new unit

unit to be converted= new number · new unit

quantity to beexpressed in

new unitsconversion factor

quantity nowexpressed in

new units

given data desired unit

unit of given data= answer in desired unit

Convert 34.5 mg to g

How many gallons of juice are there in 20.0 liters of the juice?

gallon5.30liter1

gallon0.265xliters20.0

g10x3.45org0.0345mg1000

g1xmg34.5 2

UNIT CONVERSIONS

Convert 4.0 gallons to quarts

quarts16quarts15.9559liter0.946

quart1x

gallons0.265

liter1xgallons4.0

Convert 2.64 μg to kg

Convert 3.912 m2 to km2

2623

22 km10x3.912

m)(10

km) (1xm3.912

kg10x2.64g10

kg1x

μg1

g10xμg2.64 9

3

-6

UNIT CONVERSIONS

Convert 4.0 cm3 to μm3

μm10x4.0cm)(10

μm)(1xcm4.0 12

34-

33

DENSITY

- The amount of mass in a unit volume of a substance

Ratio of mass to volume =Density =

UnitsSolids: grams per cubic centimeter (g/cm3)

Liquids: grams per milliliter (g/mL)Gases: grams per liter (g/L)

- Density of 2.3 g/mL implies 2.3 grams per 1 mL

- Density usually changes with change in temperature

volume

mass

For a given liquid:

- Objects with density less than that of the liquid will float

- Objects with density greater than that of the liquid will sink

- Objects with density equal to that of the liquid will remainstationary (neither float nor sink)

DENSITY

The liquid level in a graduated cylinder reads 12.20 mL.The level rises to 18.90 mL when 129.31 g of piece of

gold is added to the cylinder. What is the density of gold?

Volume of the piece of gold = 18.90 mL – 12.20 mL = 6.70 mLMass of the piece of gold = 129.31 g

Density = mass/volume = 129.31 g/6.70 mL = 19.3 g/mL or 19.3 g/cm3

DENSITY

TEMPERATURE

- The degree of hotness or coldness of a body or environment

3 common temperature scales Metric system: Celsius and Kelvin

English system: Fahrenheit

Celsius Scale (oC): Reference points are the boiling and freezing points of water (0oC and 100oC) - 100 degree interval

Kelvin Scale (K): Is the SI unit of temperature (no degree sign)

The lowest attainable temperature on the Kelvin scale is 0 (-273 oC) referred to as the absolute zero

TEMPERATURE

Fahrenheit Scale: Water freezes at 32oF and boils at 212oF- 180 degree interval

or

10o, 40o, 60o may be considered as 2 significant figures

100o may be considered as 3 significant figures

32F9

5C oo 32C

5

9F oo

273KCo 273CK o or

TEMPERATURE

C21.73)(9

53229

9

5C oo

F8484.23252.232295

9F oo

C 244- 27329C oo

K 302 27392K Convert 29 oC to K

Convert 29 K to oC

Convert 29 oF to oC

Convert 29 oC to oF