Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
AP Chemistry Notes: Ch. 3 – Empirical Formulas Empirical Formula: simplest, “reduced subscript” formula of a compound. The subscripts in an empirical formula represent atoms, number of ions, or number of moles in a compound. Ex. C6H6 empirical formula = CH Ex. C6H12O6 empirical formula = CH2O When the formula of a compound is unknown, the compound can be broken down in a mass spectrometer to determine the elements that make it up. A separate analysis determines the mass of each element in the compound. All of this information can then be used to determine the empirical formula of the compound (not necessarily the true formula). Through these exercises, you will learn the basic procedure for determining empirical formulas. Example 1: After several steps, assume it is determined a compound contains 0.063 mol of Cl and 0.22 mol O. Step 1: Write the formula Step 2: In formulas, the subscripts MUST be Step 3: If a subscript is still not whole after Step of the compound using the whole numbers. Turn the decimal subscripts 2, find the closest fraction to the decimal part into whole numbers by dividing every moles of each element as (ex. “.33” 1/3; 0.27 1/4; etc.). Multiply every its subscript. subscript by the smallest subscript. subscript by the denominator of that fraction to get all whole numbers. Cl0.063O0.22 ( by 0.063) ClO3.49 (“.49” ½) (ClO3.49)2 => Cl2O7 NOTE: DO NOT round off decimals to whole numbers UNLESS it is VERY close to a whole number (ex. 1.96 can be rounded, but 1.80 cannot). If you round off, you will arrive at the wrong answer. 1. A compound is determine to have 0.039 mol Fe and 0.052 mol O. Determine its empirical formula. 2. A sample of nicotine contains 6.16 mol C, 8.56 mol H, and 1.23 mol N. Determine the empirical formula for nicotine. 3. It is determined that a compound consists of 2.45 g Si and 12.4 g Cl. A) Determine the moles of each element in the B) Using the moles you calculated in part (A), determine the compound. empirical formula of the compound. 4. A sample of cortisol, used to treat arthritis, contains 69.6 g C, 8.34 g H, and 22.1 g O. A) Determine the moles of each element in B) Using the moles you calculated in part (A), determine the cortisol. empirical formula of cortisol.