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Chapter 5: Problem 65

What amount (moles) is represented by each of these samples? a. \(150.0 \mathrm{g} \mathrm{Fe}_{2} \mathrm{O}_{3}\) b. \(10.0 \mathrm{mg} \mathrm{NO}_{2}\) c. \(1.5 \times 10^{16}\) molecules of \(\mathrm{BF}_{3}\)

Short Answer

Expert verified
The amounts in moles for the given samples are: a. \(0.939 \: \mathrm{mol} \: \mathrm{Fe}_{2}\mathrm{O}_{3}\) b. \(2.17 \times 10^{-4} \: \mathrm{mol} \: \mathrm{NO}_{2}\) c. \(2.49 \times 10^{-8} \: \mathrm{mol} \: \mathrm{BF}_{3}\)

Step by step solution

01

Determine the molar masses of the substances

First, we need to find the molar masses of Fe₂O₃, NO₂, and BF₃ using the atomic masses of each element. Molar mass of Fe₂O₃: Fe = 55.845 g/mol (2 atoms) O = 16.00 g/mol (3 atoms) Molar mass of Fe₂O₃ = (2 × 55.845) + (3 × 16.00) = 159.69 g/mol Molar mass of NO₂: N = 14.01 g/mol O = 16.00 g/mol (2 atoms) Molar mass of NO₂ = 14.01 + (2 × 16.00) = 46.01 g/mol Molar mass of BF₃: B = 10.81 g/mol F = 19.00 g/mol (3 atoms) Molar mass of BF₃ = 10.81 + (3 × 19.00) = 67.81 g/mol
02

Convert masses to moles and molecules to moles

Now that we have the molar masses, we can use the amounts given for each sample to find the number of moles. We will also need to convert the given mass for NO₂ from milligrams to grams. a. Moles of Fe₂O₃: Moles = (mass) / (molar mass) Moles = (150.0 g) / (159.69 g/mol) = 0.939 mol b. Convert 10.0 mg of NO₂ to grams: 1 g = 1000 mg 10.0 mg = 0.0100 g Moles of NO₂ = (mass) / (molar mass) Moles = (0.0100 g) / (46.01 g/mol) = 2.17 × 10⁻⁴ mol c. Convert the number of molecules of BF₃ to moles: Moles = (number of molecules) / (Avogadro's number) Moles = (1.5 × 10¹⁶ molecules) / (6.022 × 10²³ molecules/mol) = 2.49 × 10⁻⁸ mol
03

Write the final answers

Now we can write the final answers for the amount of moles for each sample: a. 150.0 g of Fe₂O₃ = 0.939 mol b. 10.0 mg of NO₂ = 2.17 × 10⁻⁴ mol c. 1.5 × 10¹⁶ molecules of BF₃ = 2.49 × 10⁻⁸ mol

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Most popular questions from this chapter

Which of the following statements about chemical equations is(are) true? a. When balancing a chemical equation, you can never change the coefficient in front of any chemical formula. b. The coefficients in a balanced chemical equation refer to the number of grams of reactants and products. c. In a chemical equation, the reactants are on the right and the products are on the left. d. When balancing a chemical equation, you can never change the subscripts of any chemical formula. e. In chemical reactions, matter is neither created nor destroyed so a chemical equation must have the same number of atoms on both sides of the equation.

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