CLICK Here are some possible molecular formulas When x=1, we have NO2. QUESTION: A compound with an empirical formula of NO2 has a molar mass between 43 and 47 g/mol. What is the molecular formula of the compound? A. NO2, B. N2O, C. N2O3, D. N2O4 Subscripts of the molecular formula must be multiples of the subscripts of the empirical formula. Possible molecular formulas if empirical formula is NO2 are of the form NxO2x where x is 1, 2, 3... NO2 N2O4 N3O6 NxO2x Molar Mass, g/mol 46.01 92.02 138.03 (46.01)(x) A compound with an empirical formula of NO2 has a molar mass between 43 and 47 g/mol. What is the molecular formula of the compound? A. NO2, B. N2O, C. N2O3, D. N2O4 PAUSE CLICK Subscripts of the molecular formula must be multiples of the subscripts of the empirical formula. For a compound whose empirical formula is NO2, the possible molecular formulas are of the form NxO2x, where x is a counting number. CLICK Here are some possible molecular formulas When x=1, we have NO2. HIGHLIGHT When x=2, we have N2O4 HIGHLIGHT WHen x=3, we have N3O6 and so on... Obvoiusly, choices B and C are incorrect. CROSS OUT The nitrogen-to-oxygen ratio in these formulas are incorrect. Since the Nitrogen-to-Oxygen ratio is NO2 is 1-to-2, if the subscript of nitrogen is 2, then the subscript of oxygen must be 4. So, how do we choose between choices A and D. We look at the molar mass. By now, you should know how to calculate molar mass. If you calculated the molar mass of NO2, you will find that it is 46.01 g/mol For N2O4, it is 92.02 Therefore, the correct answer is A. The molar mass according to the question is between 43 and 47 grams per mole. HIGHLIGHT “between 43 and 47 g/mol” in problem CLICK PAUSE END RECORDING

Video ID: 4-7-2 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08