Chemistry Problem Set: Empirical and Molecular Formulas, Atomic Weights, and Moles, Assignments of Chemistry

Download Chemistry Problem Set: Empirical and Molecular Formulas, Atomic Weights, and Moles and more Assignments Chemistry in PDF only on Docsity! Chemistry 1151 Problem Set 3 1. a. A compound is analyzed in the laboratory and found to consist of 27% carbon and 73% oxygen. Determine the empirical formula. b. The molecular weight of this compound is 44 g/mole. What is the molecular formula? 2. a. A sample is determined to consist of only carbon, hydrogen and chlorine. Analysis shows it is 24.3% carbon and 4.1% hydrogen. What is the empirical formula? b. The molecular weight is about 99 g/mole. What is the correct molecular formula of this compound? 3. Calculate the percentage of (a) magnesium; (b) sulfur; (c) oxygen; in the compound magnesium sulfate, MgSO4. 4. Using the Table of Natural Occurrence of Isotopes found in your textbook, calculate the atomic weight for natural occurring magnesium, Mg. 5.* Boron has two isotopes, 10B and 11B. Its atomic weight is 10.811 grams/mole. Determine the percentage abundance of each of the boron isotopes. 6. We know that atoms emit or absorb light under certain conditions. We also know that atoms are made of three types of particles: electrons, protons, and neutrons. Which particle(s) is (are) responsible for this interaction with light? Explain. 7. Consider the chemical commonly known as baking soda, sodium bicarbonate, NaHCO3. If you have 84 grams of NaHCO3… a. How many moles of sodium bicarbonate do you have? b. How many molecules of sodium bicarbonate do you have? c. How many moles of hydrogen atoms are there in the sample? d. How many moles of oxygen atoms are there in the sample? e. How many atoms of sodium are there in the sample? 8. Calculate moles for : 15.5 g Sn (tin); 3.6 g H2O (water); 160.0 g CCl4 (carbon tetrachloride). Watch significant figures. 9. What is the mass, in kilograms, of a 5 lb bag of sugar? 10.Calculate the weight in grams for: 0.20 moles of methanol, CH3OH; 0.05 mole of phosphoric acid, H3PO4; 6.02 x 1023 molecules of ammonia, NH3. 11.* If exactly 3.0 grams of a metal, M, combine with 6.0 grams of oxygen, O, to give a compound having the formula MO2, what is the molecular weight of the metal, M? 12. An oxide of nitrogen contains 30.4% nitrogen (the rest is oxygen). What is the simplest formula of the compound, NxOy? 13. Complete this chart for neutral atoms. Name Symbol Atomic # Protons Electrons Neutrons Mass # Aluminu m 27 At 125 78 195 25 30 238U 2 3 2 2 2 14. A compound consists of Ca, Cr, and O. It was analyzed and found to contain 7.80 grams of Ca, 20.3 grams of Cr, and 21.84 grams of O. Calculate the empirical formula. 15. A compound is 92.3% carbon and 7.7% hydrogen and has a molecular weight of 78 g/mole. What is the molecular formula of this compound? 16. Tetraethyl lead, a gasoline additive, is Pb(C2H5)4. What percent lead (by weight) is present in this compound? 17. Find the number of moles of helium, He, that weigh the same as 2.0 moles of neon, Ne. 18. Find the number of moles of helium, He, that has the same number of atoms as 2.0 moles of neon, Ne. 19. How many moles of chlorine atoms are in 0.20 grams of DDT, C14H9Cl6? 20. The density of 38.0% sulfuric acid (the rest is water) is 1.30 g/ml. How many ml volume will be occupied by 50.0 grams of the acid? How many grams of water will be present in this volume of H2SO4? 21. Test yourself by knowing the following elements: P, Mg, Ag, Na, Hg, C, Cu, Fe, Cl and Pb. 22. What is the molecular weight of Al(NO3)3? 23. How many significant figures in each of these: 4001, 0.0089, 369000, 400.002, 770.0110?