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Chapter 3: Problem 84

A sample of urea contains \(1.121 \mathrm{~g} \mathrm{~N}, 0.161 \mathrm{~g} \mathrm{H}, 0.480 \mathrm{~g} \mathrm{C}\), and \(0.640 \mathrm{~g} \mathrm{O}\). What is the empirical formula of urea?

Short Answer

Expert verified
The empirical formula of urea is \(NH_2CO\), which consists of 2 nitrogen atoms, 4 hydrogen atoms, 1 carbon atom, and 1 oxygen atom in the simplest whole-number ratio.

Step by step solution

01

Convert masses to moles

To convert the mass of each element to moles, we'll need the atomic weights of nitrogen (N), hydrogen (H), carbon (C), and oxygen (O). Using the periodic table, we can find their atomic weights: - N: 14.01 g/mol - H: 1.01 g/mol - C: 12.01 g/mol - O: 16.00 g/mol Now, divide the given masses by their respective atomic weights to get the number of moles: moles of N = 1.121 g N / 14.01 g/mol = 0.0800 moles moles of H = 0.161 g H / 1.01 g/mol = 0.159 moles moles of C = 0.480 g C / 12.01 g/mol = 0.0400 moles moles of O = 0.640 g O / 16.00 g/mol = 0.0400 moles
02

Determine the mole ratio

Now, divide each number of moles by the smallest number (which is 0.0400 moles in this case) to get the simplest whole-number ratio: N: 0.0800 / 0.0400 = 2 H: 0.159 / 0.0400 = 3.98, which can be rounded to 4 C: 0.0400 / 0.0400 = 1 O: 0.0400 / 0.0400 = 1
03

Write the empirical formula

Based on the obtained mole ratio, the empirical formula is: \( NH_2 CO \) To clarify, there are 2 nitrogen atoms, 4 hydrogen atoms, 1 carbon atom, and 1 oxygen atom in the simplest whole-number ratio.

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Most popular questions from this chapter

Ascorbic acid, or vitamin \(\mathrm{C}\left(\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6}\right)\), is an essential vitamin. It cannot be stored by the body and must be present in the diet. What is the molar mass of ascorbic acid? Vitamin C tablets are taken as a dietary supplement. If a typical tablet contains \(500.0 \mathrm{mg}\) vitamin \(\mathrm{C}\), what amount (moles) and what number of molecules of vitamin C does it contain?

ABS plastic is a tough, hard plastic used in applications requiring shock resistance. The polymer consists of three monomer units: acrylonitrile \(\left(\mathrm{C}_{3} \mathrm{H}_{3} \mathrm{~N}\right)\), butadiene \(\left(\mathrm{C}_{4} \mathrm{H}_{6}\right)\), and styrene \(\left(\mathrm{C}_{8} \mathrm{H}_{8}\right)\). a. A sample of ABS plastic contains \(8.80 \% \mathrm{~N}\) by mass. It took \(0.605 \mathrm{~g}\) of \(\mathrm{Br}_{2}\) to react completely with a \(1.20-\mathrm{g}\) sample of ABS plastic. Bromine reacts \(1: 1\) (by moles) with the butadiene molecules in the polymer and nothing else. What is the percent by mass of acrylonitrile and butadiene in this polymer? b. What are the relative numbers of each of the monomer units in this polymer?

Cumene is a compound containing only carbon and hydrogen that is used in the production of acetone and phenol in the chemical industry. Combustion of \(47.6 \mathrm{mg}\) cumene produces some \(\mathrm{CO}_{2}\) and \(42.8 \mathrm{mg}\) water. The molar mass of cumene is between 115 and \(125 \mathrm{~g} / \mathrm{mol}\). Determine the empirical and molecular formulas.

Some bismuth tablets, a medication used to treat upset stomachs, contain \(262 \mathrm{mg}\) of bismuth subsalicylate, \(\mathrm{C}_{7} \mathrm{H}_{3} \mathrm{BiO}_{4}\), per tablet. Assuming two tablets are digested, calculate the mass of bismuth consumed.

Considering your answer to Exercise 79, which type of formula, empirical or molecular, can be obtained from elemental analysis that gives percent composition?
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