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## 4/4/11

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**4/4/11**• Quarter test Thursday 4/7 • What will be on this test? • Redox,net ionic, emp formula, molecular form, % comp, moles and molarity. • Some stuff from throughout the first 3 quarters. Still only have 48 minutes**Emp. Formula**4/4/11 A compound contains 25.9% nitrogen and 74.1% oxygen. What is the empirical formula of the compound? Oh, and welcome back, hopefully refreshed and excited. 75% of this school year is over!!! assume 100gram sample and convert % to grams convert to moles divide by smallest moles make sure the ratios are whole numbers**Emp. Formula**4/4/11 25.9g N x 1 mole N/14 g N = 1.85 mol N 74.1g O x 1mol O/16g O = 4.63 mol O N1.85 O4.63 which is weird 1.85mol/1.85 =1 4.63/1.85 = 2.50 N1O2.5 still can’t have fraction of atoms must be N2 O5**Molecular Formula**Calculate the molecular formula of a compound whose molar mass is 60.0 g/mol and empirical formula is CH4N.**Molecular Formula**Either same as Emp Formula or a simple whole number multiple of the EF Molar mass must be given to you, calculate efm. C2H8N2**take this slow**Warm-up 4/4/11 What is the percent composition of Iron in Iron (II) carbonate? What is the empirical formula of a compound that is 54.1% Calcium, 43.2 % Oxygen, and 2.7% Hydrogen? YeeHaw!! Test Thursday! WHOOHOO!**Molecular Formula**4/4/11 A compound is 75.46% carbon, 4.43% hydrogen, and 20.10% oxygen by mass. It has a molecular weight of 318 g/mol. What is the molecular formula?**Molecular formula**= 4.98 or 5 / 1.26 75.46g/12=6.28 4.43g/1 = 4.43 20.10g/16 = 1.26 Divide by smallest moles = 3.5 / 1.26 / 1.26 = 1 So Ratio is C5H3.5O1 Which is not whole numbers So multiply by 2 Empirical Formula is C10H7O2**Molecular formula**So multiply by 2 Empirical Formula is C10H7O2 C20H14O4**Homework**4/4/11 Answer question 26-31 p 303 on notebook paper by tomorrow Read Section 16.2 p480 and take notes Answer questions 8,9 on p481 Due tomorrow 10,11 on p 482**So quarter test, Huh!?**Warm-up 4/5/11 Predict product and write the net ionic equation for the following. MgS + CuNO3 ? Mg(NO3)2 + Cu2S (S) precipitate Net Ionic Equation 1st Find the precipitate using solubility rules all Nitrates are soluble all Sulfides insoluble except Group 1&2 and ammonium**Net ionic Review**MgS(aq) + 2CuNO3 (aq) Mg(NO3)2 (aq) + Cu2S (s) Break up all aqueous solutions, DO NOT break apart the solid Mg+2 + S-2 + 2Cu+1 + 2NO3–1 Mg+2 + 2NO3–1 + Cu2S (s) / / / / Net Ionic Equation S-2 + 2Cu+1 Cu2S (s) Must have charges. Short cut : What 2 ions make up the solid and write**Daily EQ:What is molarity?**What is formula and Mass? 4/6/11 warm-up What is the mass of lithium dichromate needed to make 473 ml of a 2.5M solution? Li2Cr2O7 229.8 g/mol Must convert to liters .473 L Substitute in equation 2.5M = X .473L Solve for X X 229.8 g/mol X = 1.18 moles 271.2 grams**Molarity Lab**3/22/10 Let’s make a solution or 2. 1) With a partner, make 20 milliliters of a 2.0 Molar solution of NaCl. 2)Next, make exactly 175 mL of a 0.147M solution of NaCl. 3) How much solution is created, if a 0.45M solution if we use 25.6 grams of sucrose (in yellow packet) to make the solution. Be sure to record the mass of salt used in each. Make this neat and easy for me to read/grade.**Molarity cont.**4) Now actually do this. Dilute the 0.147M solution to a 0.08 M solution? How do you do this? What is new volume? How much water?