What are molecular and empirical formulas?, Exams of Chemistry

Download What are molecular and empirical formulas? and more Exams Chemistry in PDF only on Docsity! What are molecular and empirical formulas? An empirical formula is the lowest whole number ratio of the elements combined to form the substance. A molecular formula is the ratio of elements which form the molecule. Example: NO2 and N2O4 NO2 is the empirical formula and N2O4 is the molecular formula A compound was analyzed and found to contain 13.5 g Ca, 10.8 g O, and 0.675 g H. What is the empirical formula of the compound? Step 1: convert to moles Step 2: identify the least number of moles Ca at 0.337 mol Step 3: Divide by the smallest number of moles Step 4: CaO2H2 or Ca(OH)2 What is the empirical formula of a compound if a 50.0 g sample of it contains 9.1 g Na, 20.6 g Cr, and 22.2 g O? Step 2: convert to moles Given J PT.t 57.14 gC x Doge =4.76mol C 6.16 gH x Cot pif =6.10mel H 9.52 gM x og = 0.68 mol N 1lmol 0 2718 80 xT eT omslo Step 3: ID lowest moles It is Nitrogen Step 4: perform molar ratios Step 5: write the empirical formula C7H9NO2.5 Step 6: multiply by 2 C14H18N2O5 After you have found the empirical formula, the problem would need to give you a molecular mass. You would find the gram formula mass for your empirical formula first. Then you divide the two numbers. The result is the ratio by which you need to multiply the empirical formula subscripts. Problem: The empirical formula is C3H7, and the molecular weight 86 g/mole. What is the molecular formula? C = 12.01* 3 = 36.03g/mol H = 1.01 * 7 = 7.07 g/mol 43.10 g/mol 86g mol-1/ 43.10g mol-1 = 2 C6H14 Practice The empirical formula is CH, and the molecular weight 26 g/mole. What is the molecular formula?