Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 92b

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Chapter 3, Problem 92b

(b) Hemoglobin, the oxygen-carrying protein in red blood cells, has four iron atoms per molecule and contains 0.340% iron by mass. Calculate the molar mass of hemoglobin.

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Determine the mass of iron per mole of hemoglobin. Since hemoglobin contains 0.340% iron by mass, this means that for every 100 g of hemoglobin, there are 0.340 g of iron.

Calculate the molar mass of iron. The atomic mass of iron (Fe) is approximately 55.85 g/mol.

Use the mass percentage to find the total molar mass of hemoglobin. If 0.340 g of iron corresponds to 100 g of hemoglobin, you can set up a proportion to find the molar mass of hemoglobin based on the molar mass of iron. Let M be the molar mass of hemoglobin, then \(0.340 \, \text{g Fe} = \frac{4 \times 55.85 \, \text{g/mol}}{M} \times 100 \, \text{g hemoglobin}\).

Solve the equation for M to find the molar mass of hemoglobin. Rearrange the equation to isolate M on one side.

Check the units and make sure they are consistent throughout the calculation to ensure the accuracy of your result.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all the atoms in a molecule. Understanding molar mass is essential for converting between grams and moles, which is crucial in stoichiometric calculations in chemistry.

Mass Percent Composition

Mass percent composition refers to the percentage by mass of each element in a compound. It is calculated by dividing the mass of the element in one mole of the compound by the molar mass of the compound, then multiplying by 100. This concept is important for determining the contribution of specific elements, such as iron in hemoglobin, to the overall mass of the compound.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the relationships between the quantities of reactants and products in chemical reactions. It involves using balanced chemical equations to calculate the amounts of substances involved. In the context of hemoglobin, stoichiometry helps in understanding how the mass of iron relates to the total mass of the protein and aids in calculating its molar mass.

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