01 lecture - University of Minnesota Duluthberna228/chem1153/01_lecture.pdf · Derived Units: Volume and Density ... A mixture is a physical combination of ... included in the base

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Welcome to Chem 1153, section 61 – General Chemistry I

The best seats are up front & you don’t have to pay extra! Be in your place and ready to go at 1PM. Laptops are a distraction to your neighbors if... Your friends can wait an hour for you to text them.

Courtesies:

• Syllabus excerpts: – Romesh Lakhan

•  Office hours Tu 2-3 PM, W 10-11am, 2-3pm & by appointment

•  Chem 233 •  e-mails returned within 48 hours

– Class is at 1PM (not 1:05PM). – Grades:

•  300 pts. Hour exams (3X100 pts each) •  100 pts. Quizzes in discussion (~13 x 9 pts each) •  75 pts. Connectplus homework (~14 x 6 pts each) Due

Thursdays. •  150 pts. Final exam (cumulative multiple guess exam from

the ACS) •  25 pts. Connectplus Flashcards. (~14 x 2.15 pts each) Due

Sundays


• What you should expect: – Expect to read 30–40 pages per week – Expect to spend ~15 hours – Each semester exam (3) will cover ~150

pages of material – Lab meets every week

•  This week is check-in and safety training •  Next week we start actual experiments •  A lab report for the previous experiment is due at the

beginning of the following lab session •  Bring safety goggles (not safety glasses). •  No open toed shoes or shorts.


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• What you should expect: – Discussion sections meet every week

•  Quizzes are given at the beginning of discussion •  Bring your calculator, book, notes, and questions


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Chemistry Second Edition

Julia Burdge

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

1 Chemistry

The Central Science

Chemistry: The Central Science 1

1.1 The Study of Chemistry Chemistry You May Already Know The Scientific Method

1.2 Classification of Matter States of Matter Elements Compounds Mixtures

1.3 Scientific Measurements SI Base Units Mass Temperature Derived Units: Volume and Density

1.4 The Properties of Matter Physical Properties Chemical Properties Extensive and Intensive Properties

1.5 Uncertainty in Measurement Significant Figures Calculations with Measured Numbers Accuracy and Precision

1.6 Using Units and Solving Problems

Conversion Factors Dimensional Analysis Tracking Units

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The Study of Chemistry

is the study of matter and the changes that matter undergoes. is anything that has mass and occupies space.

1.1

Chemistry Matter

The Study of Chemistry

Scientists 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 Matter

Chemists 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

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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. Take the shape of their container.

Particles in a gas have significant separation from each other and move freely. Take the shape of their container.


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. Take the shape of their container.

Particles in a gas have significant separation from each other and move freely. Take the shape of their container.

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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

Most elements can combine with other elements to form compounds.


A mixture is a physical combination of two or more substances. A homogeneous mixture is uniform throughout. A heterogeneous mixture is not uniform throughout.

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


Scientific Measurement 1.3

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.

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Scientific Measurement

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

Only three nations have not officially adopted SI Units. They are Myanmar (Burma), Liberia, and the United States.


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


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

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There are two temperature scales used in Chemistry:

The Celsius scale (⁰C) Freezing point (pure water): 0⁰C Boiling point (pure water): 100⁰C

The Kelvin scale (K)

The absolute scale Lowest possible temperature: 0 K (absolute zero)

K = ⁰C + 273.15

Anders Celsius 1701-1744 CE


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 below to convert to Kelvin.

Freezing point: –12⁰C + 273 = 261 K

Boiling point: 197⁰C + 273 = 470 K

K = ⁰C + 273.15

Lord Kelvin 1824-1907 CE


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 ⁰F = (9/5 × temp in ⁰C ) + 32⁰F

Daniel Fahrenheit 1686-1736 CE

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The temperature of the surface of the sun is about 6300⁰C. What is this temperature in degrees Fahrenheit? Solution: Step 1: Use the equation below to convert to Fahrenheit.

(9/5 x 6300⁰C) + 32⁰F = 1.1x104 ⁰F

Temp in ⁰F = (9/5 × temp in ⁰C ) + 32⁰F


There 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


The density of a substance is the ratio of mass to volume.

d = density m = mass V = volume SI-derived unit: kilogram per cubic meter (kg/m3) Other common units: g/cm3 (solids)

g/mL (liquids) g/L (gases)

md =V

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Solution: Step 1: First, note that 1 cm3 = 1 ml

Use the equation d = m/V to calculate mass.

Part (a)

d = m/V or m = dV = (19.2 g/cm3)(941ml) = 18,067.2 g

Problem: Gold (Au) has a density of 19.2 g/cm3. What is the mass of 941 mL of Au?


Solution:

Part (b)

Convert mass (g) to mass (lb)

Problem: Gold (Au) has a density of 19.2 g/cm3. What is the mass of 941 mL of Au?

mass(lb) =18,066.2gx 1lb454g

= 39.8lb

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

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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 sate of matter changes, but the identity of the matter does not change. Examples: changes of state


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

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Uncertainty in Measurement

There are two types of numbers used in chemistry:

1) Exact numbers which have defined values

1 kg = 1000 g

1 dozen = 12 object

any 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

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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)

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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.


An 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 194.3 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 precision

Poor accuracy but good precision

Poor accuracy and poor precision

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Three 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


A 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

1in2.54 cm

2.54 cm1in


The use of conversion factors in problem solving is called dimensional analysis or the factor-label method. Example: Convert 12 inches to meters.

12.00 in 1m× = 0.3048 m100cm

2.54cm×1in

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The 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 g 1 oz300.0 mg = 0.01058 oz1000 mg 28.3459 g

× ×

Chapter Summary: Key Points 1

The Scientific Method States of Matter Elements Compounds Mixtures SI Base Units Mass Temperature Volume and Density Physical Properties Chemical Properties Extensive and Intensive Properties Significant Figures

Documents

01 lecture - University of Minnesota Duluthberna228/chem1153/01_lecture.pdf · Derived Units: Volume and Density ... A mixture is a physical combination of ... included in the base