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Chapter 3: Problem 155

Para-cresol, a substance used as a disinfectant and in the manufacture of several herbicides, is a molecule that contains the elements carbon, hydrogen, and oxygen. Complete combustion of a \(0.345-\mathrm{g}\) sample of \(p\) -cresol produced \(0.983 \mathrm{~g}\) carbon dioxide and \(0.230 \mathrm{~g}\) water. Determine the empirical formula for \(p\) -cresol.

Short Answer

Expert verified
The empirical formula for para-cresol is C7H8O.

Step by step solution

01

Find the moles of carbon and hydrogen in para-cresol

To find the moles of C and H in para-cresol, first, find the moles of CO2 and H2O that were formed during combustion. For CO2: Given mass = 0.983 g Molar mass of CO2 = 12.01 g/mol (for C) + 2 * 16.00 g/mol (for O) = 44.01 g/mol Moles of CO2 = \(0.983 \frac{\text{g}}{44.01\text{g/mol}}\) = 0.0223 mol CO2 For H2O: Given mass = 0.230 g Molar mass of H2O = 2 * 1.01 g/mol (for H) + 16.00 g/mol (for O) = 18.02 g/mol Moles of H2O = \(0.230 \frac{\text{g}}{18.02\text{g/mol}}\) = 0.0128 mol H2O Each mole of CO2 contains 1 mole of carbon, and each mole of H2O contains 2 moles of hydrogen. So, Moles of C = Moles of CO2 = 0.0223 mol Moles of H = 2 * Moles of H2O = 2 * 0.0128 mol = 0.0256 mol
02

Find the moles of oxygen in para-cresol

First, find the total mass of C and H in para-cresol: Mass of C = Moles of C * Molar mass of C = 0.0223 * 12.01 = 0.2679 g Mass of H = Moles of H * Molar mass of H = 0.0256 * 1.01 = 0.0258 g Now we can find the mass of oxygen in para-cresol by subtracting the total mass of C and H: Mass of O = 0.345 g (para-cresol) - (0.2679 g (C) + 0.0258 g (H)) = 0.0513 g Now, find the moles of O: Molar mass of O = 16.00 g/mol Moles of O = \(0.0513 \frac{\text{g}}{16.00\text{g/mol}}\) = 0.0032 mol
03

Calculate the molar ratio of C, H, and O

Divide each mole amount by the smallest mole amount to find the molar ratio: Molar ratio of C = 0.0223 mol / 0.0032 mol = 7 Molar ratio of H = 0.0256 mol / 0.0032 mol = 8 Molar ratio of O = 0.0032 mol / 0.0032 mol = 1
04

Determine the empirical formula

The empirical formula is the simplest whole-number ratio of moles. Thus, the empirical formula for para-cresol is C7H8O.

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Most popular questions from this chapter

Consider samples of phosphine \(\left(\mathrm{PH}_{3}\right.\) ), water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\), hydrogen sulfide \(\left(\mathrm{H}_{2} \mathrm{~S}\right)\), and hydrogen fluoride (HF), each with a mass of \(119 \mathrm{~g}\). Rank the compounds from the least to the greatest number of hydrogen atoms contained in the samples.

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