Moles and Molecules Moles and Chemical Reactions Moles, Chemical Reactions, and Molarity All done as UNIT CONVERSIONS!!! and practice, practice, practice CHM 1010 Sinex 1 Mass moles particles conversions Mass of substance in grams Molar mass of substance g/mole Moles of substance Conversion factors Avogrado s number 6.02 x 10 23 particles/mole Number of particles of substance (atoms, molecules, or ions) Molar mass sum of atomic masses from periodic table Practice, practice, practice... 1
How many molecules of aspirin (C 9 H 8 O 4 ) in a dose of 1000 mg? Find MM of aspirin: MM = 9*12+8*1+4*16 = 180 g/mole First find moles: moles = 1000 mg *1g/1000mg * 1mole/180g = 0.0055 moles Now find molecules: Conversion factors in boxes molecules = 0.0055 moles * 6.02x10 23 molecules/mole = 3.3 x 10 21 molecules How many atoms of carbon? atoms C = 9 atoms/molecule * 3.3 x 10 21 molecules = 3.0 x 10 22 atoms from the formula 3 For 12.6g NaHCO 3, how many moles do you have? MM How many CO 2 molecules in 0.17 moles CO 2? 6.02 x 10 23 Molecules of substance A 4 Practice, practice, practice... 2
Another way to find moles For a solution (homogeneous mixture), there are two components: solute (substance being dissolved) and solvent (dissolving medium, usually water) A unit of concentration amount solute per amount solution or solvent Molarity = moles of solute/volume of solution in liters (moles/l) Rearranging the definition of molarity: moles = M x V L Another way to find moles! How many moles NaCl in 50 ml of 0.28 M NaCl? 50 ml x 1L/1000 ml x 0.28 mole/l = 0.014 mole NaCl 5 What is the molarity if 35g KCl are dissolved to make 350 ml of solution? Molarity How many moles are in 300 ml of a 0.23 M NaOH solution? 6 Practice, practice, practice... 3
The ratio of moles in a reaction 2C 4 H 10 + 13O 2 8CO 2 + 10H 2 O s 2 13 8 10 4 26 16 20 20 130 80 100 1 6.5 4 5 6 1.3 32 50 1.37 X 13/2 X 8/2 X 10/2 1.37 8.91 5.48 6.85 Click for answers 7 Mole to mole conversions This comes from the balanced chemical reaction! and it relates substances in the reaction! 2HCl + CaCO 3 CaCl 2 + H 2 O How many moles of HCl react with a mole of CaCO 3? 1 mole CaCO 3 x 2 mole HCl/1 mole CaCO 3 = 2 mole HCl mole ratio 8 Practice, practice, practice... 4
Stoichiometry Conversion factors Molarity (M) = moles of solute/volume in liters of solution moles/l 9 How many grams of O 2 are required to reaction with 10g C 3 H 8? C 3 H 8 + 5O 2 3CO 2 + 4H 2 O 10g C 3 H 8 x 1 mole/44g = 0.23 moles C 3 H 8 Conversion factors in boxes 0.23 moles C 3 H 8 x 5 moles O 2 /1mole C 3 H 8 = 1.15 moles O 2 1.15 moles O 2 x 32.0g/mole = 37 g O 2 This is a classic stoichiometry problem! 10 Practice, practice, practice... 5
How many grams of O 2 are required to reaction with 10g C 3 H 8? 1 2 3 Another view of solving C 3 H 8 + 5O 2 3CO 2 + 4H 2 O Step 1 10g C 3 H 8 x 1 mole/44g = 0.23 moles C 3 H 8 Step 2 0.23 moles C 3 H 8 x 5 moles O 2 /1mole C 3 H 8 = 1.15 moles O 2 Step 3 1.15 moles O 2 x 32.0g/mole = 37 g O 2 11 If 74g O 2 react, how many grams of CO 2 will be produced? C 3 H 8 + 5O 2 3CO 2 + 4H 2 O 12 Practice, practice, practice... 6
What volume of stomach acid, 0.16 M HCl, reacts with 1.0 g CaCO 3? 2HCl + CaCO 3 CaCl 2 + H 2 O 1.0 g CaCO 3 x 1 mole/100g = 0.010 mole CaCO 3 0.010 mole CaCO 3 x 2 mole HCl/1 mole CaCO 3 = 0.020 mole HCl 0.020 mole HCl x 1L/0.16 moles = 0.13 L = 130 ml stomach acid 13 What volume of 0.25 M CH 3 COOH will reaction with 25.0 ml of 0.37M NaOH? CH 3 COOH + NaOH CH 3 COONa + H 2 O 25.0 ml x 1L/1000 ml x 0.37 mole/l = 0.0093 moles NaOH 0.0093 moles NaOH x 1 mole CH 3 COOH/1 mole NaOH = 0.0093 mole CH3COOH 0.0093 mole x 1L/0.25 moles = 0.037 L = 37 ml CH 3 COOH This is a classic titration problem! 14 Practice, practice, practice... 7
Could you find one of the conversion factors? Suppose 2.0g CaCO 3 reacted with 25.0 ml of HCl. What is the molarity of the HCl? 2HCl + CaCO 3 CaCl 2 + H 2 O 2.0 g CaCO 3 x 1 mole/100g = 0.020mole CaCO 3 0.020 mole CaCO 3 x 2 mole HCl/1 mole CaCO 3 = 0.040 mole HCl Molarity = moles/ V L = 0.040 mole HCl / (25.0 ml x 1L/1000mL) = 1.6 M HCl 15 How many grams of Al(OH) 3 will react with 100 ml of 0.15 M HCl? Al(OH) 3 + 3HCl AlCl 3 + 3H2O 16 Practice, practice, practice... 8
For a 1.0 kg of Al 2 O 3, how much aluminum metal, in grams, can be produced? 2Al 2 O 3 (l) + 3C (s) 4Al (l) + 3CO 2 (g) How many atoms of carbon are consumed for the problem above? 17 How many grams of CH 3 COOH are needed to react with 27.3 ml of 0.21 M NaOH? CH 3 COOH + NaOH CH 3 COONa + H 2 O If 0.121g HX react with 26.2 ml of 0.229 M NaOH, what is the molar mass of HX? HX + NaOH NaX + H 2 O What is element X? 18 Practice, practice, practice... 9
What if two reagents are added, how much product do you get? Suppose 10 g Na and 10 g Cl 2 are mixed together. How much NaCl can be produced? 2Na + Cl 2 2NaCl First find the moles of each reactant: 10 g Na x 1 mole/23.0 g = 0.43 mole Na 10 g Cl 2 x 1 mole/71.0 g = 0.14 mole Cl 2 Find the moles of NaCl produced for each reactant: 2Na + 1Cl 2 2 1 Have 0.43 Need 0.28 Need 0.22 Have 0.14 0.43 mole Na x 2 mole NaCl/2 mole Na = 0.43 mole BrCl 0.14 mole Cl 2 x 2 mole NaCl/1 mole Cl 2 = 0.28 mole NaCl This is what can be produced! Cl 2 is limiting reagent. 19 A chemical analysis problem A chemist decides to check the molarity of H 2 SO 4 in her car battery. A 10.0 ml sample is reacted with 31.03 ml of 2.73M NaOH. What is the molarity of H 2 SO 4? H 2 SO 4 + 2NaOH Na 2 SO 4 + 2H 2 O 20 Practice, practice, practice... 10
Answers to problems by slide number: 4 0.15 mole NaHCO3; 1.0 x 10 23 molecules CO2 6 1.3 M KCl; 0.069 mole NaOH 12 61g CO2 16 0.39g Al(OH)3 17 5.3 x 10 2 g Al; 8.9 x 10 24 atoms C 18 0.34g CH3COOH; MM = 20.2 g/mole; X = F 20 4.2M H2SO4 21 Practice, practice, practice... 11