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# Download A Student want to prepare 250mL of .10 M NaCl solution

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ACS Review • Quick refresher of materials • Some sample questions and short cuts Sections in ACS prep book to review • • • • • • • Atomic Structure Molecular Structure and bonding Stoichiometry States of Matter/ Solutions Energetics Descriptive Chemistry/ Periodicity Laboratory Chemistry Basics • Dimensional analysis is very very important – Know how to make conversions • • • • cent, kilo, ect. Grams moles (MM) Vol grams (density) Vol moles (concentration) The periodic table Notation and Calculation 56 26 Fe Remember this? 26 protons 30 neutrons 26 electrons Calculations: you may need to do weighted averages. 20% of a sample is 32grams/mol and 80% 28grams/mol what is the average? 20x32 + 80x28 /100 = 28.8g/mol The table • • • • • Which has the highest electronegativity? Which is isoelectric to X? Which is likely to form the same structure as __ ? What has 25 protons? If it has 24 neutrons and a mass of 52 what is the element? formulas Know how to use charges to determine formula Example: the correct formula for the compound formed between Al and S? Al+3 and S-2 Al2S3 Even more useful, use formula to determine charge. Example: you can’t remember if Ag has a +1 or +2 charge. if AgCl is a formula given in the question or in some other question, knowing Cl is -1 tells you Ag is +1 Formulas from % • Given mass % or total mass of each element determine empirical formula. A sample contains 11.1% H and 88.9% O 11.2grams H (1 mol/1.001g)=moles H =11.18 88.9grams O(1 mol/16.0g)=moles O =5.55 2 1 H2O Reactions • • • • • • Single Double Composition Decomposition Combustion Acid / Base • Balance equations know difference in – General – Ionic – Net ionic • stoichiometry Acid base theories • Bronsted/ lowry • Lewis • Arrhenius • Protons • electron pairs • What’s produced in water You should have your six strong acids and bases memorized. HCl, HBr, HI, HNO3, H2SO4, HClO4 LiOH, NaOH, KOH, CaOH2, SrOH2, BaOH2 Why? a) It helps identify weak acids and weak bases b) It will help with determining solubility •Balance equations Yields •Use stoichiometry •Limiting reagents • Grams------mole------mole------gram • Amt------mole------mole-----amt • Amt -------- Mole – Grams (molar mass) – Liters of solution (concentration) – Gas (Ideal gas law) Solution •Molarity(M) Vs Molality(m) mole L of solution mole Kg of solvent Total solution solvent and solute Solvent only Dilution: C1V1=C2V2 Titration: naMaVa=nbMbVb Gas laws • PV=nRT – Mostly the relationships (when P goes from 1020, V does what?) • Remember T is in K – When gases are non ideal (correct for molecular volume and intermolecular forces) – Diffusion small things faster Structure • Quantum numbers – – – – n l ml s is the major shell(1,2,3… is the subshell (0=s, 1=p) is the axis (x, y, z) spin (+ ½ ) • Filling the orbital (use the table) Bonding and geometry • Ionic vs. Covalent • Electronic vs. Molecular geometry (VSEPR) – – – – – – Drawing Lewis structures Dipoles Hybrids Pi bonds MO Delocalized bonds (resonance) Lewis structures • Multiple Choice Test Just be able to pick the correct drawing!! • Some things to look for – Octets on non-central atoms (all atoms if central is 1st row) – Happy elements – Charges • Negative usually carried by single bonded O (one for each charge) • Positive usually carried by a four bond N or P O -1 O N Cl O O Cl O O -3 O O P O O H +1 H N H H States of matter Know the basic properties Remember this: Freezing / melting Liquid Solid Condensing / boiling Gas Sublimation / Deposition Triple point energy – Heat of formation ( to form from the elements) DHf of MgCl2 is Mg(s) + ½ Cl2(g) MgCl2 DH=___kJ – Heat of combustion(react with O2) DH of CH4 is CH4 + 2O2(g) CO2 + 2H2O DH=___kJ Solid at STP Diatomic gas at STP State function have D which means final - initial Energy Bond Enthalpy = Sum of bond energy of reactants - sum of bond energy of products (Breaking bonds- forming bonds) Enthalpy of reaction using DHf= sum of products – sum of reactants Hess’s Law===Get to the goal by manipulating reaction information given and adding up the reactions used When Solving Problems • Look for the easiest way to solve! There are 70 questions and only 110 minutes so THERE MUST BE SHORT CUTS! 1. Which of these compounds contains the greatest percentage of nitrogen? A) C6H3N307 B) CH4N20 C6H3N307 229 g/mol C) LiNH2 CH4N20 60.1 g/mol D) Pb(N3)2 LiNH 23.0 g/mol 2 Pb(N3)2 229.1 g/mol The long way: calculate the %N for each one mass N x100 total mass The quicker way: all N have the same mass so, Which has the highest N to mass ratio or Even better which has the lowest total mass per N A cursory glance tells us it is not B or A D has 6 N it may need a second look 229/6=38 The answer is C The Number of atoms in 9.0g of Aluminum is equal to the Number of atoms in A) 8.1g Mg B) 12.1g Mg The Long way: C) 9.0g Mg Calculate # of atoms in 9.0 g Al D) 18.0g Mg Then calculate mass of that # of Mg atoms Look for ratios: Al has a molar mass of 27 This is 1/3 of a mole Al Which one is 1/3 mole of Mg 24.3 x 1/3 = 8.1g So “A” When NF3 and BF3 are reacted together they form BF3NF3 what is the geometry of the B and N atoms. A) Both tetrahedral B) B is triganal planer and N is tetrahedral C) Both triganal planer D) N is triganal planer and B is tetrahedral How many things are around each? B and N each will have 4 bonds Both tetrahedral A student wants to prepare a 250mL sample of 0.10 M NaCl. Which procedure is the most appropriate? Molar mass of NaCl 58.4 g ·mol-1 A) Add 5.84g NaCl to 250mL of water B) Add 1.46g of NaCl to 250mL of water C) Dissolve 5.84g of NaCl in 50mL and Dilute to 250mL D) Dissolve 1.46g of NaCl in 50mL and Dilute to 250mL Mol/L of solution ¼ L of 0.1M So A and B are out 5.84 is 0.1 mole NaCl 1.46 is ¼ of that So “D” The oxidation number of chlorine in KClO3 is a) +6 b) +5 c) -1 d) -2 e) +2 O only oxidation is –2 (unless peroxide) 3 x -2 = -6 K only oxidation +1 1 x +1 =+1 -5 +5 to Balance it out B Which one of the following sets of quantum numbers is not allowed? a) n = 3, l = 2, ml = +1 b) n = 3, l = 3, ml = 0 c) n = 3, l = 0, ml = 0 d) n = 4, l = 3, ml = -2 l must be less than n ml absolute value must be less than or equal to l B Which ion has 26 electrons? a) b) c) d) Cr+2 Fe+2 Ni+2 Cu+2 Its really asking “Which is iso-electronic to Fe?” On the table “What minus 2 electrons looks like iron?” C Ni+2 Element X has two isotopes 13X with 80% abundance and 12X with 20% abundance, what is the average mass of the element? a) 12. amu b) 12.8 amu c) 12.5 amu d) 13.0 amu Long way: (13 X 80) + (12 X 20)/100 But why bother: the weighted average will be closer to the larger abundance B GOOD LUCK!!! • 10 AM class your final is Friday April 27 at 8 am in LCTR 346 • 11 AM class your final is Monday April 30 at 8 am in LCTR 346 • You must get permission to switch from one time to another. SI sessions and Office Hours • SI sessions in RHSC 317 Tuesday at 5 pm and Wednesday 8 pm • Offices Hours— – Wednesday (April 25th)11-4 – Thursday (April 26th) 11-4 – Sunday (April 29th)12-3