Name. Final empirical ratio. Multiply until whole. Element Mass Molar mass moles Mole ratio 12.01g/mol

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1 EMPIRIAL FRMULA WRKSEET Problems that involve percentages, mass or moles of elements: Follow the poem. Show your work. Fill in the chart. Sometimes, the multiplier is 1. After awhile, you will not need the chart to help you with the problems. ne last reminder: the formula and the molecular formula are related by a number 1. A compound is 24.7% alcium, 1.2% ydrogen, 14.8% arbon, and 59.3% xygen. Write the formula and name the compound. % mass mass moles Divide by small Multiply until Element Mass Molar mass moles Mole g/mol a Empirical formula and combustion analysis worksheet Page 1 of 8 9/24/17

2 2. Excessive physical activity, lactic acid molecular mass g per mole, forms in muscle tissues and is responsible for muscle soreness. Elemental analysis shows that this compound has 40.0% carbon 6.71% hydrogen and 53.3% oxygen. Determine the formula of lactic acid. Determine the molecular formula. % mass mass moles Divide by small Element Mass Molar mass moles Mole 12.01g/mol Multiply until Show your work for the calculation of the molecular formula here Empirical formula and combustion analysis worksheet Page 2 of 8 9/24/17

3 3. A compound is 21.20% Nitrogen, 6.06% ydrogen, 24.30% Sulfur, and 48.45% xygen. Write the formula for the compound. % mass mass moles Divide by small Multiply until Element Mass Molar mass moles Mole N S Empirical formula and combustion analysis worksheet Page 3 of 8 9/24/17

4 4. Nicotine is an addictive compound found in tobacco leaves. Elemental analysis of nicotine gives the following data: 74.0 %, 8.65 %, % N. What is the formula of nicotine? The molar mass of nicotine is less than 170 g/mol. What is the molecular formula? % mass mass moles Divide by small Element Mass Molar mass moles Mole N Multiply until Show your work for the calculation of the molecular formula here Empirical formula and combustion analysis worksheet Page 4 of 8 9/24/17

5 5. A sample of an unknown compound contains 0.21 moles of zinc, 0.14 moles of phosphorus, and 0.56 moles of oxygen. What is the formula? % mass mass moles Divide by Multiply until small Element Mass Molar mass moles Mole Empirical formula and combustion analysis worksheet Page 5 of 8 9/24/17

6 ombustion problems: combustion analysis problems are more challenging, but with a little practice and organization of data, you will find they are similar to the percentage problems. Some helpful rules: a. You are working backwards from 2 and 2. b. onvert grams of 2 to grams and moles of c. onvert grams of 2 to grams and moles of (not 2) d. Mass of the and mass of the should add to the mass of the sample. If it does not, the mass that is missing is oxygen (again, not 2) e. onvert grams of oxygen to moles of oxygen. f. Now divide by small and multiple until. g. Sometimes the element left over is not oxygen, so read the question carefully! h. Use the chart! i. And no, you can t use stoichiometry. You don t have a balanced equation. I have started most of the problem below using the rules. Let s finish it. You need to fill in the chart with the calculated data. Then find the s. nce you find the s, you can find the and the molecular formula. 1. Vitamin, M= g/mol, is a compound of composed of carbon, hydrogen, and oxygen. Vitamin is found in many natural sources especially citrus fruits. When a g sample of vitamin is burned in a combustion apparatus 1.50 g of 2 and g of 2 are produced. What is the formula of Vitamin? What is the molecular formula of Vitamin? Mass Molar mass moles Mole Multiply until g 44.01g/mol g g/mol g 12.01g/mol g/mol g/mol The answers are in bold 1.50 g 1 mol 2 1 mol mol 12.01g g 2 mol g 2 1 mol 2 1 mol 0.410g 2 1 mol 2 2 mol mol 1.008g g mol 18.02g 2 1 mol 2 1 mol 1.000g ( g g ) = g g 1 mol mol Re-write set-ups, show your work, finish the vitamin problem here 16.00g Empirical formula and combustion analysis worksheet Page 6 of 8 9/24/17

7 2 2. Sometimes, athletes illegally use anabolic steroids to increase muscle strength. A forensic chemist analyzes some tablets suspected of being a popular steroid. e determined that the substance in the tablets contains only carbon, hydrogen, and oxygen in and has a molar mass of g/mole. When a g sample of this study by combustion analysis, g of 2 and g of 2 are collected. What is the molecular formula for the substance? Mass Molar mass moles Mole Multiply until 44.01g/mol g/mol 12.01g/mol g/mol g/mol 2 g 1 mol 2 1 mol mol mol 12.01g g g 2 1 mol 2 1 mol 2 g 1 mol 2 2 mol Mol mol 1.008g g 18.02g 2 1 mol 2 1 mol ) g ( g + g g g 0 1 mol mol 16.00g Empirical formula and combustion analysis worksheet Page 7 of 8 9/24/17

8 g sample of quinine 324g/mol is combusted and found to produce g carbon dioxide g water and g nitrogen. Determine in and molecular formula (hint there is one element missing!) 4. After combustion with excess oxygen, a g of a petroleum compound produced g of carbon dioxide and of water. A previous analysis determined that the compound does not contain oxygen. Establish the formula of the compound 5. A hydrocarbon fuel is fully combusted with g of oxygen to yield g of carbon dioxide and g of water. Find the formula for the hydrocarbon g of a biochemical substance was burned in an atmosphere of g of oxygen. Subsequent analysis of the gaseous result yielded g carbon dioxide, g of water and g of oxygen. Determine the formula of the substance. 7. A gram sample of a smelly compound was tested by combustion analysis. The products were grams of 2, grams of 2, and grams of N 2 5. Further analysis showed that oxygen was NT present in the molecule. What is the formula of the compound? 8. When a 10.0 g sample of an unknown organic acid is subjected to combustion analysis 21.2 grams of 2 and 3.25 g of 2 are produced. What is the formula of the acid? Answers: N 0, 20 24N when I re-did the answer, I noticed that the was off. The answer is not , there is no oxygen in the compound and the amount of oxygen reacted is excess. 6. 2, oxygen is in excess. You can t use it to find the amount of oxygen in the compound N Empirical formula and combustion analysis worksheet Page 8 of 8 9/24/17