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Chapter 7: Problem 17

Summarize briefly the process of using empirical formula and the value for experimental molar mass to determine the molecular formula.

Short Answer

Expert verified
The molecular formula is found using the empirical formula and the molar mass of a compound. First, determine the empirical formula by finding the ratio of atoms. Calculate the molar mass of the empirical formula, then divide the given experimental molar mass by the molar mass calculated in the previous step. The result is the number of empirical formula units per molecule. Multiply the subscripts in the empirical formula by this number to find the molecular formula.

Step by step solution

01

Understand and Calculate Empirical Formula

First, the empirical formula (simplest formula) for a compound needs to be known or calculated. It provides the lowest whole-number ratio of the atoms in a compound. If only percentages are given, assume a 100 g sample of the compound and convert these percentages to g. Convert the mass of each element to moles by dividing by the atomic weight. Then, divide each mole quantity by the smallest number of moles calculated, to get the atom ratio. Round these to the nearest whole number to get the empirical formula.
02

Calculate Molecular mass of Empirical Formula

The molecular mass of the empirical formula you derived in step one must then be calculated. Add up all the atomic masses of the atoms included in the empirical formula to get the total molecular mass for the empirical formula.
03

Calculate Molecular Formula

The final step is to determine the molecular formula. Divide the experimental molar mass by the molar mass of the empirical formula (calculated in Step 2). Round this to the nearest whole number. This is the number of empirical formula units per molecule. Multiply the subscripts in the empirical formula by this number to get the molecular formula.

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Most popular questions from this chapter

Calculate the average atomic mass of iron. Its composition is 5.90\(\%\) with a mass of 53.94 amu, 91.72\(\%\) with a mass of 55.93 amu, 2.10\(\%\) with a mass of 56.94 amu, and 0.280\(\%\) with a mass of 57.93 amu.

What is the molar mass of the amino acid glycine, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NO}_{2} ?\)

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Determine the percentage composition of the following compounds: a. ammonium nitrate, NH \(_{4} \mathrm{NO}_{3},\) a common fertilizer b. tin(IV) oxide, SnO \(_{2},\) an ingredient in fingernail polish

Find the molar mass of isopropyl alcohol, \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH},\) used as rubbing alcohol.
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