Percent yield Combustion analysis. General Chemistry I Dr. Stone Chapter 3 clicker 5

Transcription

1 Percent yield Combustion analysis General Chemistry I Dr. Stone Chapter 3 clicker 5

2 % Yield = Actual x 100% Theoretical Actual= what is made Theoretical = the amount that could be made from the limiting reagent. How many brownies can be made from 2 boxes of Ghirardelli Brownie mix and 1 egg? Balanced reaction: 1 box + 1 egg + oil + H2O > 16 brownies Since there is only one egg, only 16 brownies could be made= theoretical If you actually end up with 12 brownies on the plate, what is the % yield? 12 x 100 = 75% yield 16

3 Sodium chloride reacts with ammonia gas, carbon dioxide and water to make sodium hydrogen carbonate and ammonium chloride. If 5.8 grams of sodium chloride are reacted with excess of all other reactants and 4.4 grams of sodium hydrogen carbonate is made, what is the percent yield? NaCl + NH3 + CO2 + H2 O NaHCO3 + NH4Cl 5.8 g NaCl x 1 mole NaCl x 1 moles NaHCO3 x 84 g = 8.3 g NaHCO mole NaCl mole NaHCO3 A. 1.9% B. 75% C. 53% D. 47% E. None of these 4.4 x 100% = 53% 8.3

4 Sodium chloride reacts with ammonia gas, carbon dioxide and water to make sodium hydrogen carbonate and ammonium chloride. If 5.8 grams of sodium chloride are reacted with excess of all other reactants and 4.2 grams of sodium hydrogen carbonate is made, what is the percent yield? NaCl + NH3 + CO2 + H2 O NaHCO3 + NH4Cl 5.8 g NaCl x 1 mole NaCl x 1 moles NaHCO3 x 84 g = 8.3 g NaHCO mole NaCl mole NaHCO3 A. 1.9% B. 92% C. 53% D. 47% E. None of these 4.4 x 100% = 53% 8.3

5 Combustion Analysis When any hydrocarbon is combusted, the products are carbon dioxide and water. All of the carbon becomes carbon dioxide. All of the hydrogen becomes water. Moles of carbon dioxide = moles of Carbon 1 mole C 1 mole CO2 Moles of water = 2 x moles of Hydrogen 2 moles H 1 mole H2O 1. Covert grams of CO2 to moles of CO2 = moles C 2. Convert grams of H2O to moles of H2O then multiply by 2 = moles H 3. Divide all terms by smallest number of moles to get empirical formula.

6 Combustion of grams of limonene yielded grams of carbon dioxide and 0.71 grams of water. What is the empirical formula of limonene? 1. Covert grams of CO2 to moles of CO2 = moles C 2. Convert grams of H2O to moles of H2O then multiply by 2 = moles H 3. Divide all terms by smallest number of moles to get empirical formula. A. C5H8 B. CH2 C. CH D. C3H E. None of these

7 Combustion of grams of limonene yielded grams of carbon dioxide and 0.71 grams of water. What is the empirical formula of limonene? 1. Covert grams of CO2 to moles of CO2 = moles C 2. Convert grams of H2O to moles of H2O then multiply by 2 = moles H 3. Divide all terms by smallest number of moles to get empirical formula. A. C5H8 B. CH2 C. CH D. C3H E. None of these g CO2 x 1 mole CO2 x 1 moles C = moles C 44 g 1 mole CO2 0.71g H2O x 1 mole H2O x 2 moles H = moles H 18 g 1 mole H2O moles H = moles C CH1.6 Multiply both C and H by 5

8 If the molar mass of limonene is , what is the molecular formula? The empirical formula is C5H8. A. C8H12 B. C20H32 C. C10H16 D. C15H24. E. None of these The molar mass of the empirical formula is 68g/mole. 135 = 2 68 Multiply all atoms in the empirical formula by 2.

9 Combustion of grams of a compound from coral yielded grams of carbon dioxide and grams of water. What is the empirical formula of this compound? 1. Covert grams of CO2 to moles of CO2 = moles C 2. Convert grams of H2O to moles of H2O then multiply by 2 = moles H 3. Divide all terms by smallest number of moles to get empirical formula. A. C4H5 B. C5H8 C. CH D. C2H E. None of these g CO2 x 1 mole CO2 x 1 moles C = moles C 44 g 1 mole CO g H2O x 1 mole H2O x 2 moles H = moles H 18 g 1 mole H2O moles H = moles C CH1.6 Multiply both C and H by 5

10 Vanillin contains carbon, hydrogen and oxygen. Combustion of 30.4 mg of vanillin yielded 70.4 mg of carbon dioxide and 14.4 mg of water. What is 1. Covert grams of CO2 to moles of CO2 = moles C 2. Convert grams of H2O to moles of H2O then multiply by 2 = moles H 3. Mass of oxygen= total mass - (mass of Carbon + mass of Hydrogen 4. Convert grams of oxygen to moles of oxygen 5. Divide all terms by smallest number of moles to get empirical formula. A. C5H8 B. C8H8O3 C. CHO D. C3H E. None of these 70.4 x 10-3 g CO2 x 1 mole CO2 x 1 moles C = 1.6 x 10-3 moles C 44 g 1 mole CO x 10-3 g H2O x 1 mole H2O x 2 moles H = 1.6 x 10-3 moles H 18 g 1 mole H2O 1.6 x 10-3 moles C x 12 g/mole = 1.92 x 10-2 g C 1.6 x 10-3 moles H x 1 g/mole = 1.6 x 10-3 g H 30.4 x 10-3 g of sample - (1.92 x 10-2 g C x 10-3 g H ) = 9.6 x 10-3 g O 9.6 x 10-3 g O x 1 mole = 6 x 10-4 moles O 16 grams 1.6 x 10-3 moles C = x 10-4 moles O 2.66 = 2 and 2/3, multiply all by 3 3 x 2.66 = 8

11 How many moles of oxygen are required to react with 4 moles of ammonia? 2NH3 + 2O2 N2O + 3H2O A. 2 B. 1 C. 4 D. 8 E. None of these 4 moles NH3 x 2 moles O2 = 4 moles oxygen 2 moles NH3

12 Balance the following reaction. How many moles of oxygen are needed to react with one mole of B2H6? B2H6(g) + 3 O2(g) --> B2O3(s) + 3H2O(g) A. 1 B. 2 C. 3 D. 4 E. None of these

13 What is the molar mass of cobalt(ii) phosphate? A g/mole B g/mole C g/mole D g/mole E. None of these Co3(PO4)2