Chemistry Problem Solving: Percent Composition, Empirical Formulas, and Molar Masses, Lecture notes of Chemistry

Download Chemistry Problem Solving: Percent Composition, Empirical Formulas, and Molar Masses and more Lecture notes Chemistry in PDF only on Docsity! Sample Questions – Chapter 7 CP Chemistry 1. Calculate the percent composition of iron (II) nitrate. Fe(NO3)2 Fe: 1 x 55.85 = 55.85 g % Fe = 55.85/179.87 *100 = 31.05% N: 2 x 14.01 = 28.02 g % N = 28.02/179.87*100 = 15.58% O: 6 x 16.00 = 96.00 g % O = 96/179.87*100 = 53.37% Molar mass = 179.87 g/mol 2. A compound’s empirical formula is NO2. If the formula mass is 138 g/mol, what is the molecular formula? NO2 – molar mass = (14.01) + (2*16.00) = 46.01 g/mol 138 g/mol ÷ 46.01 g/mol = 3, so molecular formula is N3O6 3. You have 9.45 g of the compound dinitrogen pentoxide. How many molecules are contained in this mass? 9.45 g ÷ 108.02 g/mol = 0.0874837 mol * 6.02E23 = 5.27 * 1022 molecules N2O5 4. If you have 3.5 x 1024 formula units of CaI2, how many moles of the compound do you have? 3.5 * 1024 formula units ÷ 6.02E23 = 5.8 moles 5. Find the empirical formula of a compound that is 41.67% magnesium, 54.87% oxygen, and 3.46% hydrogen? 41.67/24.31 = 1.714 mol Mg 1.714/1.714 = 1 MgO2H2 54.87/16.00 = 3.429 mol O 3.429/1.714 = 2 3.46/1.01 = 3.425 mol H 3.425/1.714 = 2 6. What is the molar mass (in grams) of Li3PO4? Li: 3 * 6.94 = 20.82 Molar mass = 115.79 g/mol P: 1 * 30.97 = 30.97 O: 4 * 16.00 = 64.00