Chemistry Prep booklet 2011 - University of Texas at … · Simplify the following with no parentheses or negative exponents. (x-5)4 (f-2)7 (-3z2x4)3 (b2 ... Sum the following three

Chemistry Workbook

Summer 2011

The University of Texas at Austin College of Natural Sciences

Welcome! Welcome to the college prep materials for Chemistry. This workbook is provided to help you level out and level up on select high school chemistry topics ranging from exponent math to limiting reactants and molarity. Afterall, the more you know about these topics before college classes begin, the more you can focus on new college-level items of interest. We have created this workbook to be used in tandem with our online videos located at http://www.chemprep.cm.utexas.edu or on Quest. Additional tutorials are available through ALEKS. This booklet is not intended to teach material from scratch. Its purpose is to review the main points of select topics in order to refresh your memory. For more information on a given topic than is shown here, refer to a chemistry textbook such as (shown alphabetically by first author):

Atkins, Chemical Principles: The Quest for Insight Whitten, Davis, Peck, General Chemistry Zumdahl, Chemical Principles Or other chemistry textbook of your choosing

The information herein is arranged by Units:

Please note that these categories differ slightly from those in ALEKS. Refer to the website (above) to view the videos arranged according to ALEKS’ categories.

Unit01: Math Unit02: Math - Measurement Unit03: Matter Unit04: Atoms, Ions, and Molecules Unit05: Stoichiometry – Moles and Molar Mass Unit06: Stoichiometry - Reactions Unit07: Stoichiometry - Molarity A few additional comments:

In many cases, we have prepared a video to provide explanation to a problem or to give brief review of a topic. In such a case, we provide an icon (shown at left) to let you know that a video is available at our ChemPrep website. (http://www.chemprep.cm.utexas.edu)

For those who would like to know which topics our instructors consider prior knowledge for their college-level classes, please refer to the ALEKS list of learning objectives in the Appendix. Let’s get started!

UT Austin College of Natural Sciences: Prep Materials for College Level Chemistry

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Table of Contents

Welcome! ........................................................................................................... 3

Periodic Table ......................................................................................................... 6

Commit to Memory ................................................................................................. 8

Unit 00: Refresher .................................................................................................. 9

Unit01: Math ........................................................................................................ 10

The Power Rule and Negative Exponents ............................................................. 10

The Distributive Property.................................................................................... 10

Multiplying Monomials ........................................................................................ 11

Working with Percentages .................................................................................. 11

Mini-Lecture: Slope of a Line .............................................................................. 12

Mini-Lecture: Graphing a Line in Slope-Intercept Form ......................................... 13

Graphing a Line – Standard Form Equation .......................................................... 14

More Practice Graphing Lines ............................................................................. 15

Unit02: Math - Measurement ................................................................................. 17

Significant Figures (Significant Digits) .................................................................. 17

Scientific Notation.............................................................................................. 19

English-Metric Conversions and Other Values Considered “Common Knowledge” .... 19

Temperature Conversions .................................................................................. 19

Table of Metric Prefixes ...................................................................................... 20

Metric Prefixes .................................................................................................. 21

Practice Problems: Interconversion of Prefixed and Based SI Units ........................ 22

Unit03: Matter ...................................................................................................... 23

Periodic Table ................................................................................................... 23

More on Periodic Table ...................................................................................... 24

Unit04: Atoms, Ions, and Molecules ....................................................................... 25

The Atom and Subatomic Particles ...................................................................... 25

Mini-lecture: Atoms and Isotopes – Counting Protons, Neutrons and Electrons ...... 25

Practice Problems: Counting Protons, Neutrons and Electrons ............................... 26

Periodic Table showing Ionic Charge ................................................................... 27

Predicting Ions .................................................................................................. 28

Naming Ions ..................................................................................................... 28

Table of Polyatomic Ions .................................................................................... 29


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Special Metal Ions ............................................................................................. 29

Table of Prefixes for Naming Binary Molecules ..................................................... 30

Naming Binary Molecules ................................................................................... 30

Naming Ionic Compounds .................................................................................. 31

Nomenclature: Compounds Involving Polyatomic Ions .......................................... 31

Nomenclature: Acids I ........................................................................................ 32

Nomenclature: Acids II (with oxoanions) ............................................................. 32

The 7 Strong Acids ............................................................................................ 33

Creating (or Breaking) Ionic Compounds ............................................................. 34

Naming Organic Hydrocarbons ........................................................................... 35

Unit05: Stoichiometry – Moles and Molar Mass ........................................................ 37

Molecular Mass, Avogadro’s Number, and the Mole .............................................. 37

Avogadro’s Number and “The Mole” (Part II) ....................................................... 38

Working with Moles ........................................................................................... 38

Mastering Molecular Weights .............................................................................. 39

Interpreting Chemical Formulas (Chemical Stoichiometry) ..................................... 40

Mole Ratios and Chemical Formulas .................................................................... 40

Mass Per Cent ................................................................................................... 41

Unit06: Stoichiometry – Reactions ......................................................................... 43

Solubility Rules .................................................................................................. 43

Table of Reaction Types ..................................................................................... 44

Reaction Types .................................................................................................. 45

Mini-Lecture: Limiting Reactant and Percent Yield ................................................ 46

Acids ................................................................................................................ 47

Unit07: Stoichiometry - Molarity ............................................................................. 49

Molarity ............................................................................................................ 49

Practice Problems - Molarity ............................................................................... 50

Molarity: Dilution ............................................................................................... 51

Molarity: Dilution (Type 2) ................................................................................. 52

Now Your Turn: Molarity and Limiting Reactant.................................................... 52


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PERIODIC TABLE We provide two versions. One to keep “clean” or free of notes and the next one for notes.


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(this one for writing your notes on)


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COMMIT TO MEMORY It will be of benefit to memorize some items. The following are contained in this booklet and should be committed to memory.

Select elemental names and symbols from the periodic table Select English-Metric conversions and Other Values Considered Common

Knowledge Temperature Conversions Metric Prefixes Solubility Rules Prefixes for Naming Binary Molecules Special Metal Ions The Seven Strong Acids Polyatomic Ions Reaction Types

UT Austin College of Natural Sciences: UNIT01: Math Prep Materials for College Level Chemistry

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UNIT 00: REFRESHER Ok, I’m jumping ahead here and starting you off with a review problem from high school chemistry that covers limiting reactant with molarity, nomenclature, etc. The truth is, if you can do this problem by yourself without peeking at anything other than a periodic table, then perhaps you don’t need the rest of this booklet. You rock. Then again if you can’t, then you’re an absolutely normal genius and could use a review of a few items—by the end of this problem you should have some idea of what warrants review. Here it is: What is the molarity of the salt that results from the addition of 0.48 g lithium hydroxide with 50.0 mL of 0.50 M hydrobromic acid? If 1.3 g of the salt is precipitated, what is the percent yield of the product? For a video that quickly works out the problem, go to http://www.chemprep.cm.utexas.edu/Refresher.html or Quest. If you’d like the problem worked out stepwise in more detail, see the Refresher learning module in Quest. The remaining pages are for the other videos offered on ChemPrep or on Quest.


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UNIT01: MATH Exponents Exponents are indicated by a superscript (102) or a carat (10^2). Positive exponents indicate values larger than one whereas negative exponents indicate values smaller than one.

The Power Rule and Negative Exponents Simplify the following with no parentheses or negative exponents.

(x-5)4 (f-2)7 (-3z2x4)3 (b2/2a3)4 (z-3)-2 (v-6)-8

The Distributive Property Definition: Simplify the following so that there are no parentheses:

12(v + 3t) 4x(2y – 8x) (-2x + 3z – 3y)-6 -2(-4t3 - 2z2 + 3)


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Multiplying Monomials Simplify the following with no parentheses.

4y6(3t2y2)(2t3) 3u2w7(4w2)(uw4) 2a3 x 4a2b4 x 6ab3c

Working with Percentages What is 36% of 54? 60 is 15% of what? What is 70% of 93? 14 is 88% of what?


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Mini-Lecture: Slope of a Line Practice:

1. Find slope between the two points (2 , 4) and (3 , 7)

2. Slope = -1. y-intercept = 3. Write the slope-intercept form of the equation of the line and graph the line.

3. Slope = 1/3. y-intercept = 0. Write the slope-intercept form of the equation of the line and graph the line.

4. (see video) Use the graph of the line to determine x- and y- intercepts. Find the slope.


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5. (see video) Use the graph of the line to determine x- and y- intercepts. Find the

slope.

Mini-Lecture: Graphing a Line in Slope-Intercept Form Finding y- intercepts and slope. Practice:

(a) y = 2x + 1 Find y- intercepts and slope. Graph the line.

(b) y = 3/2x - 3 Find y- intercepts and slope. Graph the line.


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Graphing a Line – Standard Form Equation Finding x- and y- intercepts and slope. Practice: 3x – 4y = 12. Find x-, y- intercepts and slope. Graph the line.


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More Practice Graphing Lines Graph the line y = -4/3 x. What is the y-intercept and slope?

Graph the line: y = 1/2x – 5 What is the slope and y-intercept?

2x – 3y = 18. Graph the line and state what it’s x-, y- intercepts and slope are.


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5x + 3y = 15. Graph the line and state what its x-, y- intercepts and slope are.

y = 2x + 1 Find y- intercepts and slope. Graph the line.

y = 3/2x - 3 Find y- intercepts and slope. Graph the line.

UT Austin College of Natural Sciences: UNIT02: Measurement Prep Materials for College Level Chemistry

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UNIT02: MATH - MEASUREMENT

Significant Figures (Significant Digits) If we give 40 people ten Vernier calipers and one line to measure, there is very little chance that all 40 people will come up with the exact same number for their measurement. They’ll get things like 4.45, 4.46, 4.43, 4.44, 4.45, etc. So what is the true measurement? Significant figures help us handle such cases. Significant figures rules exist for measurements and for computations with measurements. This section introduces these rules.

The Point: Report only ONE questionable digit for measurements.

In the example with the Vernier caliper above, everyone agrees on the “4.4” part of the measurement. The hundredths-place is the questionable digit.

The Exceptions:

Counting Numbers and Defined Quantities

The Exceptions: Counting numbers are said to have infinite significant digits. That is to say, if there are three people in the room, no one will say there are 2.999 people in the room. (That would be awkward!) We will all agree there are 3.00000000000… people exactly. Definitions also follow this exception. When something is defined, there is no question. For example, 1 inch is defined as 2.54 cm. Because it’s defined, the 2.54 has infinite significant figures (and yes, so too the 1 inch).

The Sig Fig Rules for a Measurement: A measurement consists of multiple digits. Each digit is tested to determine whether it is significant. Nonzero numbers are significant. (that is, 1,2,3,4,5,6,7,8, and 9) Zeros between significant figures are significant. Zeros to the right of the decimal AND to the right of a significant figure are

significant. Small counting numbers (under, say, 10,000) are usually considered exact and

have infinite significant figures. (ex. 2 chickens)

Examples: How many significant figures are there in each of the following numbers?

2.0 2.00 0.0002

0.0200 0.2000 2.0e-3


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Answers to exercise on previous page: 2.0 (2 sf) 2.00 (3sf) 0.0002 (1sf) 0.0200 (3sf) 0.2000 (4sf) 2.0e-3 (2 sf)

The Sig Fig Rules for Computation—Addition and/or Subtraction The answer cannot be more precise than the least precise measurement. TIP: Solve by using decimal place. Example: Sum the following three measurements and report to the correct sig figs. 2.58 2.6 2.575 -------- The simple sum is 7.755. One number goes to the tenths place. That’s the least precise number. (final digit is farthest to left) So the answer can only be reported to the tenths place. The answer is 7.8.

The Sig Fig Rules for Computation—Multiplication and/or Division Solving long-hand identifies the sig figs, or TIP: the answer will always have the same number of sig figs as the measurement with the fewest total sig figs. For the computation (6.341 x 9.24) = ? The calculator gives me: 58.59084 The actual answer is 3 sig figs (due to the 9.24, as it has the least number of sig figs). Answer is 58.6


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Scientific Notation Generic: The Rules for Scientific Notation: Only one digit to the left of the decimal in the mantissa Number on exponent represents the multiplier needed to get the number back to its

original state Examples: Number Scientific Notation

0.0000000003410900 0.0001030 6745 4350 (3 sf) 4350 (4sf)

1.020 x 106 5.25 x 10-3 7.0 x 10-9

English-Metric Conversions and Other Values Considered “Common Knowledge” Commit these to memory. 1 lb = 453.59 g 1 in = 2.54 cm (defined) 1.059 qt = 1 L 12in = 1 ft 3 ft = 1 yd

5280 ft = 1 mile 1 cm3 = 1 mL 1 atm = 760 torr 1 calorie = 4.184 J (defined) Density of water at 250C = 1 g/mL

Temperature Conversions K = oC + 273.15 oF = 32 + (1.8)(oC) oC = 9/5 (oF – 32)


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Table of Metric Prefixes Commit the prefix name and mathematical equivalent to memory.

Incr

easi

ng

Prefix Abbrev. Multiplier

Exa E 1,000,000,000,000,000,000 1018

Peta P 1,000,000,000,000,000 1015

Tera T 1,000,000,000,000 1012

Giga G 1,000,000,000 109

Mega M 1,000,000 106

kilo k 1,000 103

hecto h 100 102

deka da 10 101

Base Unit (meter, liter, seconds, etc.)

deci d 1/10 10‐1

centi c 1/100 10‐2

milli m 1/1000 10‐3

micro μ 1/1000000 10‐6

nano n 1/1000000000 10‐9

pico p 1/1000000000000 10‐12

femto f 1/1000000000000000 10‐15

atto a 1/100000000000000000 10‐18

*Angstrom is a special unit for length to memorize: 10-10 m.


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Metric Prefixes Reliable method: Down with the old,

up with the new

Procedure: 1. Remove the given prefix to get to root unit. 2. Add desired prefix to get to answer.

Assumption: Example: A keychain drive has a capacity of 2 GB. How many MB is that? Example: The diameter of a typical human hair is on the order of 1.0 x 10-4 meters. How long is that in microns? Example: The smallest insect is the fairy fly which is about 0.5 mm in length. How long is that in centimeters?


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Practice Problems: Interconversion of Prefixed and Based SI Units A baby carrot is measured to have a diameter of 0.0051m. What is the diameter in mm? Write as a decimal. The pressure in a borehole is measured to be 6.23 x 107 Pa. What is the pressure in MPa? Write as a decimal. The thickness of a wood plank is 14.3 dm. What is it in meters? A biochemist needs to use 42 mL to run a cloning experiment. How many liters is this? Write as a decimal. A satellite transmission is found to have a frequency of 6.89 x 1011 Hz. What is it in GHz? Write as a decimal. Hydrogen bonds are typically have a length of 1.97 Ǻ. How many meters is this?

UT Austin College of Natural Sciences: UNIT03: Matter Prep Materials for College Level Chemistry

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UNIT03: MATTER

Periodic Table

Legend: Rows are named “periods”. Columns are named “groups” or “families”. “A” columns = representative elements “B” columns = transition elements (includes the two rows at bottom) “Grey” boxes denote metalloids Left of metalloids are metals Right of metalloids are nonmetals

Valence Electrons: For the representative elements, the number of valence electrons = the “A” column number. Example: Li has 1 valence electron, N has 5, O has 6, Kr has 8.

Number of Shells: Row number = number of shells for that element Example: H has 1 shell, K has 4 shells, Ar 3 shells, Cu has 4 shells

Atomic Size: Elements lower on the periodic table are larger.

UT Austin College of Natural Sciences: UNIT03: Matter Prep Materials for College Level Chemistry

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More on Periodic Table Memorize the names and symbols for these elements:

Row 1 : all (H, He) Row 2: all Row 3: all Row 4 : all Row 5 : Rb, Sr, Zr, Ru, Pd, Ag, Cd, Sn, Sb, Te, I, Xe Row 6 : Cs, Ba, Pt, Au, Hg, Pb, Rn Row 7 : Nd, U, Pu, Cm, Es

There may be others you must memorize in class for your particular instructor, but these will give you a solid head start. Memorize the following family (group) names:

Group 1A alkaline metals Group 2A alkaline earth metals Group 7A halogens Group 8A noble gases

UT Austin College of Natural Sciences: UNIT04: Atoms, Ions, and Molecules Prep Materials for College Level Chemistry

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UNIT04: ATOMS, IONS, AND MOLECULES

The Atom and Subatomic Particles The atom is made of protons and neutrons in the nucleus, and protons outside the nucleus. Name Symbol Charge Mass(amu) Location

Mini-lecture: Atoms and Isotopes – Counting Protons, Neutrons and Electrons


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Practice Problems: Counting Protons, Neutrons and Electrons How many protons, electrons and neutrons in the following? 93Nb Ba2+ Fill in the table.

Symbol 52Cr Protons 33 77 Neutrons 42 20 Electrons 20 86 Mass No. 222 193

How many electrons, protons and neutrons are there in a) Al3+ and b) Te2-


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Periodic Table showing Ionic Charge Ionic charge per column, for representative elements:

Metals lose electrons to form cations (kat-eye-ons). Nonmetals gain electrons to form anions. Examples: The ionic charge applies to the entire column. Li forms the cation: Li+ Mg forms the cation: Mg2+; Ca becomes Ca2+, Sr forms Sr2+ N forms the anion N3-; P forms P3-

All of the halogens form anions with 1- charge, such as F-. Exceptions: The “Noble gases” do not form stable ions. The group 4A elements do not form long-term stable ions.


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Predicting Ions Key: Position on periodic table

Example: Predict the ionic charge for each of the following elements. P S Cl Ar K Ca Identify the Isoelectronic ions.

Naming Ions Ion Name: element name + ion

(including polyatomic ions)

Examples: K+ potassium ion O2- oxide NO3

- nitrate


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Table of Polyatomic Ions Commit these to memory. Name Formula

ammonium NH4+

acetate CH3COO- or C2H3O2

-

bromate BrO3-

carbonate CO32-

perchlorate ClO4-

chlorate ClO3-

chlorite ClO2-

hypochlorite ClO-

chromate CrO42-

cyanide CN-

dichromate Cr2O72-

hydrogen carbonate (bicarbonate)

HCO3-

hydrogen sulfate (bisulfate)

HSO4-

hydrogen phosphate

HPO42-

(biphosphate)

hydroxide OH-

iodate IO3-

nitrate NO3-

nitrite NO2-

oxalate C2O42-

periodate IO4-

permanganate MnO4-

peroxide O22-

phosphate PO43-

phosphite PO33-

silicate SiO44-

sulfate SO42-

sulfite SO32-

thiocyanate SCN-

thiosulfate S2O32-

Special Metal Ions Memorize the symbol and charge for each of these metals. These do not require the use of roman numerals in naming their compounds.

zinc ion Zn2+

silver ion Ag+


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Acids Most acids are easily recognized because the chemical formula starts with an “H”. Examples include: HF, HCN, HCl, HNO3, and H2SO4. Nomenclature means system of naming.

Table of Prefixes for Naming Binary Molecules Molecules use prefixes mono, di, tri, …

1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa

7 hepta 8 octa 9 nona 10 deca 11 undeca 12 dodeca

Examples: IF5 iodine pentafluoride N2O5 dinitrogen pentoxide

Naming Binary Molecules Guidelines: Nonmetal + nonmetal; covalent bonds The name of has two words, one for each element.

o First word = prefix+stem o Second word = prefix+stem+ide

To note: o Reduce double vowels to single o Omit “mono” when it is for first word

Molecules use prefixes mono, di, tri, …

Examples: CO N2O sulfur hexafluoride


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Naming Ionic Compounds Guidelines: For simple ionic compounds, the name consists of two words. First word is the name of the cation, minus the “ion”. Second word is the name of the anion. Roman numerals are used for metals that may have multiple oxidation states

(typically, the transition metals).

Ionic Compounds: cation name + anion name

Examples: KCl MgO Al2O3

Roman Numerals Examples:

CuF2 SnCl4

Nomenclature: Compounds Involving Polyatomic Ions

Compound Name = cation name + anion name

Chemical Formula

Ions Combined Name

NH4NO3

Na2SO4

ammonium sulfide

calcium carbonate

potassium chlorate


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Nomenclature: Acids I

The Key: Are there O’s?

Key Question to ask yourself: Is there an oxoanion on the acid? If no, name is hydro + stem + ic If yes, identify oxoanion name first

Examples (without oxoanions): Name the following acids

HF

HCl

HBr

Nomenclature: Acids II (with oxoanions)

The Key: Know the Polyatomic ions!

Anion Anion Name Acid Name Acid

ClO- hypo-chlor-ite hypo-chlor-ous

acid

HClO

ClO2- chlor-ite chlor-ous

acid

HClO2

ClO3- chlor-ate chlor-ic

acid

HClO3

ClO4- per-chlor-ate per-chlor-ic

acid

HClO4

Summary of Rules:


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Examples: Name the following acids

HBrO3

HIO4

HNO3 Write the formulas:

Nitrous acid

Sulfuric acid

The 7 Strong Acids Memorize these 7 strong acids:

HCl hydrochloric acid HBr hydrobromic acid HI hydroiodic acid H2SO4 sulfuric acid HNO3 nitric acid HClO3 chloric acid HClO4 perchloric acid


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Creating (or Breaking) Ionic Compounds Ionic Compound = cation + anion (opposites

attract)

Key: Know the ion and its charge

Examples: Cation Anion Chemical Formula

Na+ F-

Mg2+ F-

Na+ S2-

potassium chloride

silver nitrate

aluminum chloride

Examples: What compound is created from the combination of aluminum and chloride? Predict the products for the dissociation of copper(II) nitrite in water.


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Naming Organic Hydrocarbons This topic will be studied further in your college-level course, but you should start learning these stems.

# C in main chain

Stem is:

1 meth

2 eth

3 prop

4 but

5 pent

6 hex

7 hept

8 oct

9 non

10 dec

11 undec

12 dodec

Examples: CH4 methane C3H8 propane C8H18 octane

UT Austin College of Natural Sciences: UNIT05: Stoichiometry – Moles and Molar Mass Prep Materials for College Level Chemistry

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UNIT05: STOICHIOMETRY – MOLES AND MOLAR MASS

Molecular Mass, Avogadro’s Number, and the Mole Atoms are very small. So small, in fact, that the tiniest bit of sugar that I could see in my hand (or on my fingertip) would have a great many molecules. Indeed, when we do experiments, even if we use a very small amount, we work with many molecules—so many that keeping track of all of them would result in our writing very large numbers all of the time. (For history buffs or those seeking more information on how the mole and Avogadro’s number came about, see http://dept.physics.upenn.edu/courses/gladney/mathphys/java/sect1/subsubsection1_1_3_2.html ) One very large number in particular keeps popping up: the mole, which is Avogadro’s number of molecules in one molecular weight of a substance = 6.022x1023. In practice, this means that we can use mass as a way to keep track of atoms or molecules because:

1 mole of items = 6.022 x 1023 items

Molecular weight identifies the weight in grams of 1 mole of a substance.

(or atomic weight)

Avogadro’s Number and “The Mole” A can of Coca-Cola has roughly 10 teaspoons, or 0.004 kg of sugar. How many molecules of sugar are there in a can of coke? MWsugar = 180.16 g/mol


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Avogadro’s Number and “The Mole” (Part II) A raindrop weighs 50.0mg. The Pacific Ocean weighs 7.08 x 1020 kg. What is the mass of one mole of rain drops? Write your answer in scientific notation and round the mantissa to one decimal place. How many moles of raindrops equal the mass of the Pacific Ocean?

Working with Moles Several gemstones, including the emerald, contain the alkali earth metal beryllium. How many grams of beryllium are there in 1.94 moles of beryllium? Diamond is one of the strongest and most precious materials on earth, and an allotrope of elemental carbon. A carat weighs 200mg. How many moles of carbon are there in a 1 carat diamond? Round to the third decimal place. Acetic acid (H3CCOOH) is the key component of vinegar, a common cooking ingredient. What is the mass of one molecule of acetic acid?


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Composition Stoichiometry We use information in the chemical formula to answer questions. No reaction required--also known as chemical stoichiometry.

Mastering Molecular Weights The molecular formula for strontium oxide is SrO. A chemist decomposes strontium carbonate to make 24.7 grams of strontium oxide. How many moles of SrO are made? Chlorine is a toxic gas that irritates the respiratory system. How many moles of chlorine is there in 11.5 grams? Formic acid is a natural carboxylic acid that is present in the venom of bee stings and ant bites. Its formula is HCOOH. How many grams are there in 12.6 mmol of formic acid?


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Interpreting Chemical Formulas (Chemical Stoichiometry) Chemical formulas identify relative numbers of atoms. Substance

Al2O3 Examples: How many moles of carbon are in 6 moles of sugar (C6H12O6)? You analyze a sample of Fe2O3 (hematite) and discover the presence of 0.051 mol Fe. How much atomic oxygen (O) was in the sample? Give your answer in moles.

Mole Ratios and Chemical Formulas A chemist analyzed a sample of an unknown chlorocarbon, C2Clx, which contains 7.1 moles chlorine and 2.38 moles of carbon. What is the molecular formula? Calcium carbonate (CaCO3) is the main of component of eggshells, pearls and chalk. An analytical chemist determined that a sample of CaCO3 contains 14.7 moles of oxygen. How many moles of calcium are there?


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Percent Percent is always (part)/(whole) x 100% as long as the units cancel.

Mass Per Cent Calculate the mass per cent of each element in magnesium fluoride. Round the percentages to 1 decimal place. Calculate the mass per cent of each element in water. Round the percentages to 1 decimal place.

UT Austin College of Natural Sciences: UNIT06: Stoichiometry - Reactions Prep Materials for College Level Chemistry

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UNIT06: STOICHIOMETRY – REACTIONS Chemical reactions involve chemical changes—those changes in which bonds are broken and new bonds are formed such that one or more new substances are made. To memorize all possible chemical reactions would be daunting at best—there are so many. Instead, we prefer to classify reactions by type. In order to identify precipitation reactions, one must know the solubility of the products formed. It helps to memorize the two solubility rules listed below. Beyond that, look up a solubility table.

Solubility Rules Memorize these two most commonly applicable solubility rules:

o Group 1A compounds (alkali metals) are soluble o Nitrate (NO3

-) containing compounds are soluble. Note: Your instructor may ask you to memorize additional solubility rules. And note that there are exceptions to the above rules. Solubility tables are available (online and in textbooks, for example) to use as reference when needed.


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Table of Reaction Types Reaction Types with Examples Recognizing chemical changes by reaction type is valuable for being able to predict products and to predict reactivity/stability. It is also an important concept for stoichiometry, acid/base, equilibrium, and many more. Combustion Complete combustion:

Fuel + O2 CO2 + H2O

Incomplete combustion: Fuel + O2 CO + H2O

C + O2 CO2

Combination Two or more substances combine into a single product.

H2O + SO3 H2SO4

Dissociation Ionic compound separates into component ions (often, in water).

KCl K+(aq) + Cl‐(aq)

Displacement Single element replaces another element, forming a new compound. Required: single element must be more reactive than that it replaces.

Fe(s) + 2HCl(aq) FeCl2(aq) + H2(g)

Decomposition Single compound breaks into component elements.

2HgO(s) 2Hg(l) + O2(g)

Metathesis aka Double-displacement “Trade partners”

AgNO3(aq) + NaCl(aq)

AgCl(s) + NaNO3(aq)

Neutralization Acid + Base Salt + Water HCl + NaOH HOH + NaCl

(all aqueous)

Precipitation Any reaction that produces a solid product.

AlCl3(aq) + 3NaOH(aq)

Al(OH)3(s) + 3NaCl(aq)

Reduction –

Oxidation

(REDOX)

Any reaction that involves a change in oxidation state for its atoms.

Fe2O3 + 3CO 2Fe + 3CO2

Notes: To identify precipitation reactions, you must know about solubility (previous page). Precipitation and Redox will be co-classifications. Example next page.


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Reaction Types Key: Learn the reaction types

There are only a few types of reactions: (see website for full table with examples)

Reaction Type Identify by:

Combustion Complete combustion: Fuel + O2 CO2 + H2O Incomplete combustion: Fuel + O2 CO + H2O

Combination A + B C

Dissociation AB A+ + B- , note ions!

Displacement C + AB CB + A

Decomposition AB A + B

Metathesis aka Double-displacement “Trade partners”

Neutralization Acid + Base Salt + Water

Precipitation Any reaction that produces a solid product.

Reduction – Oxidation (REDOX)

Any reaction that involves a change in oxidation state for its atoms.

NOTE: Reactions can be of more than one type for the last three types listed above. For example, a redox reaction can also be metathesis or displacement.

Examples: Identify the type of reaction for each of the following. Reaction Reaction Type

C6H12O6 + 6 O2 6 CO2 + 6 H2O

2 HgO 2 Hg(l) + O2(g)

AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO2(aq)

Note: Every reaction above may be co-classified as redox or precipitation as follows. The first: is redox, as well. The second is redox, as well. The third is precipitation, as well. For ChemPrep, you do not have to be able to recognize redox reaction types.


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Mini-Lecture: Limiting Reactant and Percent Yield

1. The following reaction is the Haber process, a reaction which fixes nitrogen for ammonia production.

If 55.3 grams of ammonia are isolated when the reaction is completed, what is the %yield?

2. Consider the following reaction:

Suppose a solution contains 5.3 g of Na3PO4, which is mixed with 6.4 g of Ba(NO3)2. How many grams of barium phosphate can be formed? What is the % yield if 4.10 g is isolated? (MWNa3PO4: 164 g, MWBa(NO3)2: 261 g, MWBa(PO4)2: 602 g)


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Acids There are several theories for acids and bases. Study Tip: When encountered with several theories for one concept, concentrate on learning how the theories are defined, how they differ, and what uses each serves.

Theory Name Acid is Base is Notes

“Ancient” theory Sour taste Bitter taste One of first definitions

Arrhenius

Gives H+ in water

Gives OH- in water

Acids have H+; bases have OH-

Bronsted-Lowry

Proton donor Proton acceptor

No water required; no OH- required

Lewis

Electron-pair acceptor

Electron-pair donor

No H+ or OH- or water required.

NOTE: H+ is just a proton and may be referred to as such. Also, H3O+ is the hydronium ion, which is a hydrated H+ in solution. You will see H+ and H3O+ used interchangeably. Practice: The following is a list of acids and bases. For each, identify the theory or theories that matches the substance. The first one is done for you as an example.

Substance Acid or Base?

Arrhenius Bronsted-Lowry Lewis

Water Both √ √ √

HCl

HClO4

Ba(OH)2

BCl3

NH4+

A strong acid reacts with water to produce hydronium (H3O+) ions:

HCl + H2O H3O+ + Cl-

UT Austin College of Natural Sciences: Appendix Prep Materials for College Level Chemistry

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UNIT07: STOICHIOMETRY - MOLARITY

Molarity

Molarity = moles solute / Liters solution

M = mol/L

Example: Identify the molarity of hydrochloric acid when 0.00625 moles of HCl are stirred into 32.0 mL of water.

Example: If 2.1 g of NaOH are dissolved in enough water to make a total solution volume of 200.0 mL, what is the molarity of NaOH?


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Practice Problems - Molarity 1. What is the molarity of a solution made by adding 24.3g of Na2SO4 in 125 mL of water? (MW: 142 g/mol)

2. A 500 mL solution of glucose is found to be 0.278 M. How many grams of glucose is in solution? (MW:180.16 g/mol)

3. What amount of water must be added to 15.4g of NaOH to make a 0.5 M solution? Answer in mL.

4. How many grams of KHSO4 are needed to make 0.35 L of a 0.4 M solution?

5. How many mL of 0.5 M NaCl are needed to provide 0.038 moles of NaCl?

6. What is the molar concentration of Cs+ in a 0.015M solution of Cs2CO3?

7. How many mL of methanol are there in 67.5 mL of a 0.3 M solution? d = 0.792 g/mL


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Molarity: Dilution Let X = solute

The Key: moles Xbegin = moles Xend

Two main types of dilutions: 1. Use all of the original solution, or 2. Use some of the original solution

Each type uses the same formula, but has subtle differences. Example Type 1: Thuy needs to dilute the existing 10.0 mL of 1.3 M sulfuric acid solution to 0.20 M H2SO4. How much water does she add to the existing solution?


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Molarity: Dilution (Type 2) Let X = solute

The Key: moles Xbegin = moles Xend

Two main types of dilutions: 1. Use all of the original solution, or 2. Use some of the original solution

Each type uses the same formula, but has subtle differences. Example Type 2: Sandra needs half-liter of a 0.25M HCl solution. She has a liter of 10. M HCl in stock. How shall she make her desired solution?

Now Your Turn: Molarity and Limiting Reactant Identify the molarity of the salt that results from the addition of 0.40 g sodium hydroxide to 50.0 mL of 0.10 M nitric acid.

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Chemistry Prep booklet 2011 - University of Texas at … · Simplify the following with no parentheses or negative exponents. (x-5)4 (f-2)7 (-3z2x4)3 (b2 ... Sum the following three