Ch.13 - Solutions & Their Properties

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.13 - Solutions & Their Properties

Problem 4

Chapter 13, Problem 4

Rubbing alcohol is a 90% (by mass) solution of isopropyl alcohol, C3H8O, in water. How many moles of isopropyl alcohol are in 50.0 g of rubbing alcohol? (LO 13.4) (a) 45 mol

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Determine the mass of isopropyl alcohol in the solution by multiplying the total mass of the rubbing alcohol by the percentage of isopropyl alcohol. Use the formula: \( \text{mass of isopropyl alcohol} = \text{total mass of solution} \times \text{percentage of isopropyl alcohol} \).

Convert the mass of isopropyl alcohol to moles by using the molar mass of isopropyl alcohol, C3H8O. The molar mass is calculated by summing the atomic masses of all the atoms in the molecular formula (C=12.01 g/mol, H=1.008 g/mol, O=16.00 g/mol).

Use the formula for moles: \( \text{moles} = \frac{\text{mass}}{\text{molar mass}} \) to find the number of moles of isopropyl alcohol.

Ensure the units are consistent when performing the calculations (grams and moles).

Verify your calculations by checking the units and ensuring that all steps logically follow from one to the next.

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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). For isopropyl alcohol (C3H8O), the molar mass can be calculated by summing the atomic masses of its constituent elements: carbon (C), hydrogen (H), and oxygen (O). This value is essential for converting between grams and moles in stoichiometric calculations.

Mass Percent Concentration

Mass percent concentration is a way to express the concentration of a solute in a solution, calculated as the mass of the solute divided by the total mass of the solution, multiplied by 100. In the case of rubbing alcohol, a 90% (by mass) solution means that 90 grams of isopropyl alcohol are present in every 100 grams of the solution, which is crucial for determining the amount of solute in a given mass of solution.

Stoichiometry

Stoichiometry is the area of chemistry that deals with the relationships between the quantities of reactants and products in chemical reactions. It allows chemists to calculate the amount of substances involved in a reaction based on balanced chemical equations. In this problem, stoichiometry is used to convert the mass of rubbing alcohol into moles of isopropyl alcohol, facilitating the understanding of the composition of the solution.

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