Chapter 1

1

ChemistrySecond Edition

Julia Burdge

Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or

1 ChemistryThe Central

General Information:

Urs Jans, MR-1218212 650 [email protected]

General Chemistry 10301

- solve problems - ask questions- come to class - take advantage of work shop- read text book

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A+understand chemistry application for real life

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Chemistry: The Central Science1

1.1The Study of ChemistryChemistry You May Already KnowThe Scientific Method

1.2Classification of MatterStates of MatterElementsCompoundsMixtures

1.3Scientific MeasurementsSI Base UnitsMassTemperatureDerived Units: Volume and Density

1.4The Properties of MatterPhysical PropertiesChemical PropertiesExtensive and Intensive Properties

1.5Uncertainty in MeasurementSignificant FiguresCalculations with Measured NumbersAccuracy and Precision

1.6Using Units and Solving ProblemsConversion FactorsDimensional Analysis Tracking Units

The Study of Chemistry

Chemistry is the study of matter and the changes that matter undergoes.

Matter is anything that has mass and occupies space.

1.1

The Study of ChemistryScientists follow a set of guidelines known as the scientific method:

· gather data via observations and experiments· identify patterns or trends in the collected data· summarize their findings with a law· formulate a hypothesis· with time a hypothesis may evolve into a theory

Classification of MatterChemists classify matter as either a substance or a mixture of substances.

A substance is a form of matter that has definite composition and distinct properties.

Substances can be either elements or compounds.

Substances differ from one another in composition and may be identified by appearance, smell, taste, and other properties.

1.2

Classification of Matter

All substances can, in principle, exist as a solid, liquid or gas.

Solids and liquids are referred to collectively as the condensed phases.

The three states of matter can be interconverted without changing the chemical composition of the substance.


Solids have particles that are held closely together in an ordered fashion.

Particles in a liquid are close together but are not held rigidly in position.

Particles in a gas have significant separation from each other and move freely.


An element is a substance that cannot be separated into simpler substances by chemical means.

An element may consist of atoms or molecules. Atoms of an element

Molecular form of an element


A compound is a substance composed of two or more elements chemically united in fixed proportions.

A compound cannot be separated into simpler substances by any physical process.

Separation of a compound into its constituent elements requires a chemical reaction.

A compound may consist of molecules or ions, which will be discussed later.

Molecules of a compound


A mixture is a physical combination of two or more substances.

A homogeneous mixture is uniform throughout.

A heterogeneous mixture is not uniform throughout.


A mixture can be separated by physical means into pure components without changing the identities of the components.

Scientific Measurement1.3

Properties that can be measured are called quantitative properties.

A measured quantity must always include a unit.

The English system has units such as the foot, gallon, pound, etc.

The metric system includes units such as the meter, liter, kilogram, etc.

Scientific Measurement

The revised metric system is called the International System of Units and was designed for universal use by scientists.

There are seven SI base units

Scientific MeasurementThe magnitude of a unit may be tailored to a particular application using prefixes.

Scientific MeasurementThere are two temperature scales used in Chemistry:

The Celsius scale (⁰C)

Freezing point (pure water): 0⁰CBoiling point (pure water): 100⁰C

The Kelvin scale (K)

The absolute scaleLowest possible temperature:

0 K (absolute zero)

K = oC + 273.15


Ethylene glycol is a liquid organic compound that is used as an antifreeze in car radiators. It freezes at –12⁰C and boils at 197⁰C. Express the two temperatures using the Kelvin scale.

Solution:

Step 1: Use the equation

Freezing point: –12⁰C + 273 = 261 K

Boiling point: 197⁰C + 273 = 470 K


The Fahrenheit scale is common in the United States.

The size of a degree on the Fahrenheit scale is only 5/9 of a degree on the Celsius scale.

Temp in oF = (9/5 x temp in oC) + 32 oF


The temperature of the surface of the sun is about 6300⁰C. What is this temperature in degrees Fahrenheit?

Solution:

Step 1: Use the equation

(9/5 x 6300⁰C) + 32⁰F = 1.1x104 ⁰F

Scientific MeasurementThere are many units (such as volume) that require units not included in the base SI units.

The derived SI unit for volume is the meter cubed (m3).

A more practical unit for volume is the liter (L).

1 dm3 = 1 L

1 cm3 = 1 mL

Scientific MeasurementThe density of a substance is the ratio of mass to volume.

d = densitym = massV = volume

SI-derived unit: kilogram per cubic meter (kg/m3)

Other common units: g/cm3 (solids) g/mL (liquids) g/L (gases)


Given that 25.0 mL of mercury has a mass of 340.0 g, calculate (a) the density of mercury and (b) the mass of 120.0 mL of mercury.

Solution:

Step 1: Use the equation d = m/V to calculate density or mass as needed.

Part (a)

d = m/V = 340.0 g / 25.0 mL = 13.6 g/mL

Part (b)

m = d x V = 13.6 g/mL x 120.0 mL = 1.63 x 103 g

The Properties of Matter

There are two general types of properties of matter:

1) Quantitative properties are measured and expressed with a number

2) Qualitative properties do not require measurement and are usually based on observation.

1.4


A physical property is one that can be observed and measured without changing the identity of the substance.

Examples: color, melting point, boiling point

A physical change is one in which the state of matter changes, but the identity of the matter does not change.

Examples: changes of state (evaporation, melting, condensation, freezing, ...)


A chemical property is one a substance exhibits as it interacts with another substance.

Examples: flammability, corrosiveness

A chemical change is one that results in a change of composition; the original substances no longer exist.

Examples: digestion, combustion, oxidation


An extensive property depends on the amount of matter.

Examples: mass, volume

An intensive property does not depend on the amount of matter.

Examples: temperature, density

Uncertainty in Measurement

There are two types of numbers used in chemistry:

1) Exact numbers which have defined values

1 kg = 1000 g1 dozen = 12 objectany number obtained by counting

2) Inexact numbers

numbers obtained by any method other than counting

1.5


An inexact number must be reported so as to indicate its uncertainty.

Significant figures are the meaningful digits in a reported number.

The last digit in a measured number is referred to as the uncertain digit.


The number of significant figures can be determined using the following guidelines:

1) Any nonzero digit is significant

2) Zeros between nonzero digits are significant

3) Zeros to the left of the first nonzero digit are not significant

1129 m 4 significant figures

109 cm 3 significant figures

0.0003 kg 1 significant figure


The number of significant figures can be determined using the following guidelines:

4) Zeros to the right of the last nonzero digit are significant if a decimal is present.

5) Zeros to the right of the last nonzero digit in a number that does not contain a decimal point may or may not be significant.

9.550 m 4 significant figures

1200 m ambiguous


In addition and subtraction, the answer cannot have more digits to the right of the decimal point than any of the original numbers.

102.50 ← two digits after the decimal point + 0.231← three digits after the decimal point

102.731← round to 102.73

143.29 ← two digits after the decimal –20.1 ← one digit after the decimal

123.19 ← round to 123.2


In multiplication and division, the number of significant figures in the final product or quotient is determined by the original number that has the smallest number of significant figures.

1.4 x 8.011 = 11.2154 ← round to 11 (limited by 1.4 to two significant figures)

11.57/305.88 = 0.0378252 ← round to 0.03783 (limited by 11.57 to four significant figures)

1.46: Express the answer to the following calculation in scientific notation:a) 147.75 + (2.3 x 10-1)

b) 79,000 : (2.5 x 102)


Exact numbers can be considered to have an infinite number of significant figures and do not limit the number of significant figures in a result.

In calculations with multiple steps, round at the end of the calculation to reduce any rounding errors.

Uncertainty in MeasurementAn empty container with a volume of 150.0 cm3 is weighed and found to have a mass of 72.5 g. The container is filled with a liquid and reweighed. The mass of the container and the liquid is 194.37 g. Determine the density of the liquid to the appropriate number of significant figures.

Solution:

Step 1: Determine the mass of the liquid

194.37 g – 72.5 g

121.87 g ← do not round this number yet, but remember it is good to only one decimal place or a total of 4 sig. figs.

Step 2: Calculate the density

d = 121.87 g / 150.0 mL = 0.812466 g/mL ← this number rounds to 0.8125 g/mL


Accuracy tells us how close a measurement is to the true value.

Precision tells us how closely multiple measurements of the same thing are to one another.

Good accuracy and good precisionPoor accuracy but good precisionPoor accuracy and poor precision

Uncertainty in MeasurementThree students were asked to find the mass of an aspirin tablet. The true mass of the tablet is 0.370 g.

Student A: Results are precise, but not accurate

Student B: Results are neither precise nor accurate

Student C: Results are both precise and accurate

Uncertainty in MeasurementA conversion factor is a fraction in which the same quantity is expressed one way in the numerator and another way in the denominator.

1 in = 2.54 cm

Uncertainty in MeasurementThe use of conversion factors in problem solving is called dimensional analysis or the factor-label method.

Example: Convert 12.00 inches to meters.

1 in = 2.54 cm (exact)

1 m = 100 cm

Uncertainty in MeasurementThe American Heart Association recommends that healthy adults limit dietary cholesterol to no more than 300.0 mg per day. Convert this mass of cholesterol to ounces.

1 oz = 28.3459 g

Solution:

Step 1: The problem requires a two step dimensional analysis conversion:mg to grams; grams to oz.

1.56: The average speed of helium at 25 oC is 1255 m/s. Convert this speed to miles per hour (mph). 1 mi = 1609 m

Online Homework Problems for Chapter 1:16, 24, 38, 46, 48, 50, 56, 63, 106

Chapter 1

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