AP Chemistry Summer HW Test Review Chapters 1, 2, 3

Significant Figures and Uncertainty Read each measurement: a.28  1 mL b.28.3  0.1 mL c  0.01 mL

Precision v. Accuracy Precision –how closely individual measurements agree (repeatability) Accuracy – how closely individual measurements agree with the correct or “true” value (bullseye)

Density Calculations  Density = Mass  Volume  The units for mass are grams (g)  The units for volume are usually mL or cm 3

Physical v. Chemical Changes

Metric Conversions 10 3 kilo, k hecto, h deca, da base unit deci, d centi, c milli, m10 -3 king henry died by drinking chocolate milk MEGA, M 10 6 micro, µ10 -6

Ionic Compounds Compounds formed by electrons transferred from a Metal (or positively charged polyatomic ion) to a and Nonmetal (or negatively charged polyatomic ion)

Writing Ionic Compound Formulas Example: Iron (III) chloride 1. Write the symbols for the cation and anion, including CHARGES! Fe 3+ Cl - 2. Check to see if charges are balanced. 3. Balance charges, if necessary, using subscripts. Use the criss-cross method to balance subscripts. 4. Fe 3+ + Cl -  FeCl 3 Not balanced! 3 Now balanced. = FeCl 3 1

Predicting Ionic Charges Group 1A: Lose 1 electron to form 1+ ions H+H+H+H+ Li + Na + K+K+K+K+ Rb +

Predicting Ionic Charges Group 2A: Loses 2 electrons to form 2+ ions Be 2+ Mg 2+ Ca 2+ Sr 2+ Ba 2+

Predicting Ionic Charges Group 3A: Loses 3 Loses 3 electrons to form 3+ ions B 3+ Al 3+ Ga 3+

Predicting Ionic Charges and Pb and Sn (Group 4A) Many transition metals and Pb and Sn (Group 4A) more than one have more than one possible charge. Use Roman Numerals to indicate the positive CHARGE of the metal ion. Iron (II) = Fe 2+ Iron (III) = Fe 3+ Transition Metals

Predicting Ionic Charges Some transition elements have only one possible charge. Memorize – they will not use Roman Numerals. Some transition elements have only one possible charge. Memorize – they will not use Roman Numerals. Zinc = Zn 2+ Silver = Ag + Cadmium = Cd 2+

Predicting Ionic Charges Group 4A: Do they lose 4 electrons or gain 4 electrons? Do they lose 4 electrons or gain 4 electrons? Neither! Group 4A elements rarely form ions EXCEPTION: Sn and Pb!! Treat like transition metals

Predicting Ionic Charges Group 5A: Gains 3 Gains 3 electrons to form 3- ions N 3- P 3- As 3- Nitride Phosphide Arsenide

Predicting Ionic Charges Group 6A: Gains 2 Gains 2 electrons to form 2- ions O 2- S 2- Se 2- Oxide Sulfide Selenide

Predicting Ionic Charges Group 7A: Gains 1 electron to form Gains 1 electron to form 1- ions F 1- Cl 1- Br 1- Fluoride Chloride Bromide I 1- Iodide

Predicting Ionic Charges Group 8A: Stable noble gases do not form ions! Stable noble gases do not form ions!

Naming Ions NAMING CATIONS (positive metal ions): Representative Elements: Just write the name of the metal. Ca 2+ = calcium ion Li+ = lithium ion

Naming Ions NAMING ANIONS (non-metal, negative ions): Anions are always the same charge (Cl always -1) Change the monatomic element ending to – ide F - a Fluorine atom will become a Fluoride ion. N 3- a Nitrogen atom will become a Nitride ion.

Polyatomic ions are… Groups of atoms that stay together, have an overall charge, and one name. Usually end in –ate or -ite Acetate: CH 3 COO - Carbonate: CO 3 2- Sulfate: SO 4 2- Sulfite: SO 3 2- Nitrate: NO 3 - Nitrite: NO 2 - Phosphate: PO 4 3- Phosphite: PO 3 3-

Ammonium: NH 4 + (One of the few positive polyatomic ions) More Common Polyatomic Ions The two polyatomic ions ending in –ide: Hydroxide: OH - Cyanide: CN -

Covalent Compounds (Molecules) Compounds formed by sharing electrons between two NON-METALS.

Naming Covalent Compounds (Molecules) Guidelines: Name the elements in the order listed in the formula. Use prefixes to indicate the number of each kind of atom. Do not use the prefix mono- when the first element in the formula contains only one atom. The suffix of the name of the second element is -ide.

Molar Mass of a Compound –To calculate, sum up the atomic mass of each element in the compound. MgCl 2# atomsatomic masstotal mass Mg Cl Molar Mass: 95.3 g per 1 mole

Convert between mass and moles How many moles is 350 g CO? Molar Mass = (12.0x1) + (16.0x1) = 28.0 g = 12.5 moles CO What is the mass of 6.8 mols MgCl 2 ? Molar Mass = (24.3x1) + (35.5x2) = 95.3 g = 648 g MgCl g CO1 mol CO 28.0 g CO 6.8 mol MgCl g MgCl 2 1 mol MgCl 2

Groups (Families) on the Periodic Table Columns known Groups of Families Elements in the same column have similar properties Group 1 Alkali MetalsGroup 7 Halogens Group 2 Alkaline Earth MetalGroup 8 Noble Gases

Balancing Equations Same numbers of each type of atom on each side of the equation Al + S  Al 2 S 3 Not Balanced 2Al + 3S  Al 2 S 3 Balanced

Percent Composition You have 4 oranges and 5 apples. What percent of the total is oranges? You have 4 oranges and 5 apples. What percent of the total is oranges? 30 (Look at p. 88 in your text, Sample Exercise 3.6)

Percent Composition Each compound has a different percent composition Each compound has a different percent composition 31

Percent Composition Percent by mass of each element in a compound 1. Find the molar mass of the compound 2. Calculate the mass of each element in the compound (ex. Mass of oxygen in CO 2 is 2 x 16 g = 32 g)

Calculating Percent Composition Example What is the percent composition of each element in NH 3 ? What is the percent composition of each element in NH 3 ? Determine the contribution of each element Molar mass 33

Calculating Percent Composition Example What is the percent composition of each element in H 2 O? What is the percent composition of each element in H 2 O? Determine the contribution of each element Molar mass 34

MOLE CONVERSIONS Molar Mass (g) Volume in Liters Particles: atoms, ions, molecules, formula units Mass in grams particles 1 = = =

Converting Mass to Particles Convert 14 g N 2 to number of molecules: Identify the conversion factors: 1 mole = _______________ g 1 mole = 6.02 x molecules = 3.01 x molecules N 2 14 g N 2 1 mole6.02 x molecules 28.0 g N 2 1 mole (14.0x2) = 28.0

Converting Particles to Mass Convert 9.4x10 25 molecules of H 2 to grams: 1.First identify the conversion factors: 1 mole = ______________________ g 1 mole = 6.02 x molecules 2. Draw a 2-step “T” chart: = 312 g H 2 9.4x10 25 molecules1 mole2.0 g H x molecules1 mole (1.0g x 2) = 2.0

Converting Moles to Liters (gases at STP only!) 1 mole = 22.4 L is the conversion factor at STP* for gases only STP: Standard Temperature and Pressure 0 ˚ C and 1 atm What is the volume of 0.05 mol Ne at STP? = 1.12 L Ne 0.05 mol Ne22.4 L 1 mol

Stoichiometry - Mole-Mole Conversions 2 H 2 + O 2  2 H 2 O Given (moles of the known) # moles unknown = calculated moles of unknown # moles known MOLE RATIO USING COEFFICIENTS FROM CHEM. RXN. 8 moles O 2 2 moles H 2 O = 16 moles H 2 O 1 mole O 2

Stoichiometry: Mass↔Mass Calculations Problem: If I have 2.0 grams of N 2 and excess H 2, how many grams of NH 3 can I make? N H 2  2 NH 3 Given (grams known) 1 mole known# moles unknown grams unknown = calculated mass (g) of unknown grams known# moles known 1 mole unknown MOLAR MASS OF KNOWN MOLE RATIO USING COEFFICIENTS FROM CHEM. RXN. MOLAR MASS OF UNKNOWN 2.0 g N 2 1 mole N 2 2 moles NH grams NH 3 = 2.4 g NH grams N 2 1 moles N 2 1 mole NH 3

Empirical Formulas The simplest whole number mole ratio of elements in a compound The simplest whole number mole ratio of elements in a compound 41 Ethyne (C 2 H 2 ) is a gas used in welder’s torches. Styrene (C 8 H 8 ) is used in making polystyrene. Both have the same empirical formula (CH) but different molecular formulas.

Empirical Formulas What is the empirical formula? What is the empirical formula? 42 Ethyne (C 2 H 2 ) is a gas used in welder’s torches. Styrene (C 8 H 8 ) is used in making polystyrene. Both have the same empirical formula (CH) but different molecular formulas.

Molecular Formulas The molecular formula of a compound is: The actual number of atoms of each element in a substance. Three compounds that have the same empirical formula (CH 2 O): Formaldehyde (CH 2 O) acetic acid (C 2 H 4 O 2 ) glucose (C 6 H 12 O 6 )

Molecular Formula of a Compound How to determine Molecular Formula from Empirical Formula: Step 1: Calculate the molar mass of the empirical formula. Step 2: Divide the molar mass of the molecular formula by the molar mass of the empirical formula: Step 3: Multiply the subscripts in the empirical formula by the number calculated in Step 2.

Molecular Formula of a Compound Calculate the molecular formula of a compound whose molar mass is 60.0 g/mol and empirical formula is CH 4 N. Step 1: Calculate the molar mass of CH 4 N = 30.0 g/mol Step 2: Divide the molar mass of the molecular formula by the molar mass of the empirical formula: Step 3: Multiply the subscripts in the empirical formula by the number calculated in Step 2:CH 4 N x 2 = C 2 H 8 N 2

Molecular Formula of a Compound Calculate the molecular formula of a compound whose molar mass is 93.0 g/mol and empirical formula is CH 3 O. Step 1: Calculate the molar mass of CH 3 O: = 31.0 g/mol Step 2: Divide the molar mass of the compound by the molar mass of the empirical formula: Step 3: Multiply the subscripts in the empirical formula by the number calculated in Step 2:CH 3 O x 3 = C 3 H 9 O 3