Solutions Molarity

# Solutions Molarity - Solutions Molarity A Introduction 1 B...

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Solutions: Molarity. A. Introduction. ................................................................................................... 1 B. Molarity. ......................................................................................................... 1 C. Making “molar” solutions. ............................................................................. 2 D. Using “molar” solutions . ............................................................................... 4 E. Other mole-based concentration units [optional]. .......................................... 6 F. Answers. ......................................................................................................... 7 A. Introduction This handout introduces solutions, and one of the common mole-based units used to describe them. It requires mass-mole interconversion (and its prerequisites). A solution is a homogeneous (uniform) mixture of two (or more) chemicals. The solutions of most common interest involve dissolving a solid solute in a liquid solvent . Solutions of sodium chloride in water or sugar in water are good examples of common solutions. We will focus our discussion on such solutions. Unless stated otherwise, we will consider aqueous solutions, with one solute. To describe a solution we need to specify the amounts of two chemicals, the solute and the solvent -- directly or indirectly. The resulting description is called the concentration of the solution. There are several ways to express concentration. It is not important that you master all of them. What is important is that you realize the basis of the complexity, so that you are sensitive to the differences between different concentration units (especially when they have similar names). We will focus on two common concentration units: molarity and (in the next handout) weight percentage. We will mention some others, to illustrate the variety of ways to describe concentration. (I will be happy to work with you privately on other concentration units that interest you.) B. Molarity Molarity is moles solute  liters solution We noted previously that there are many ways one might describe a solution. In the definition of molarity, all four words are important. The numerator is “moles solute”, not grams solute and not moles solvent; etc. You must know the meaning of molarity.

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Solutions: Molarity. Page 2 Expressing the amount of solute in moles, rather than in grams, aids the chemist. Remember that the mole is a certain number of molecules (or formula units); the chemist who wants equal “amounts” of two chemicals probably wants equal moles. Expressing the denominator in volume of solution makes it easy to measure out portions of the solution.
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Solutions Molarity - Solutions Molarity A Introduction 1 B...

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