1405_MOL lab2022 (1)

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Fayetteville State University *

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1405

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Chemistry

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Jan 9, 2024

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8

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CHEM 1405: Mols and Molarity Lab Objectives: In this activity, you will Use laboratory equipment and dimensional analysis to calculate the number of molecules in an ice cube Use laboratory equipment and dimensional analysis to measure an exact amount of water molecules Perform molarity calculations to prepare a saturated solution of baking soda Background: This lab will give you hands-on experience with measuring and calculating amounts using the “Mole”. You will practice a variety of conversions, using the chemist’s favorite unit (the Mole). This will be using Dimensional Analysis, in which we multiply a given quantity by a conversion factor (equal to one), which will change the units. The three basic conversions we will use are Avogadro’s number (6.022 x10 23 ) and Molar Mass (g/mol), and Molarity (mol/L). A mole (or mol) is defined as 6.022 x10 23 entities -this is Avogadro’s number. While we can have a mole of anything (just like we can have a dozen, or 12, of anything), we will most commonly use this quantity for atoms or molecules. 1 mol = 6.022 x 10 23 atoms (or molecules) The mass of a mole is quantified by the molar mass (or formula mass), in grams/mol. To determine this, we add up the atomic masses for all elements in a compound. For example: H 2 O: 2 H + 1 O = 2 (1.00794) + 1 (15.9994) = 18.0153 g/mol Examples of these conversions are shown below: In Part 3, you will be preparing a solution. Solutions are homogeneous mixtures , meaning that the
composition of the mixture is uniform across its entire volume. If the solution has two components: the one in the least amount is called solute and the second component in the higher proportion is called solvent . If water is the solvent the solution is called aqueous solution . We can describe the concentrations of solutions (which are homogeneous mixtures of solute and solvent) either qualitatively or quantitatively. Qualitatively , we can use the following terms: Quantitatively, we can describe the relative amount of a given solution component as its concentration. Molarity (M) is the one of the most used concentrations units and is defined as the number of moles of solute in exactly 1 liter (1L) of the solution: Molarity = number of moles of solute Litersof solution Safety/Disposal: Always wear proper protective equipment (like your safety glasses). Used filter paper should go in the garbage. Aqueous solutions should be poured down the drain with running water. Required Materials: Digital balance Graduated cylinders Beaker Ice cube Water Baking Soda “Weighing paper” (can be coffee filter, sheet of paper) “Stirring rod” (can be coffee stir stick, straw, spoon….) Procedure: Show all work, and insert pictures as indicated. Part I: Ice Cube 1. Determine the mass of one ice cube: a. I recommend putting some “weighing paper” on the balance before putting the ice cube on.
b. Quickly take a picture of your sample on the balance and record the mass in Table 1 below. c. Remove the ice cube before it melts/gets your balance wet! 2. Calculate the number of molecules in your sample. Show all work and record your value in Table 1 below. This can be done in 1 dimensional analysis sequence, or as two separate steps: a. Grams of water to mols of water (using molar mass, shown in Background information) b. Mols of water to molecules of water (using Avogadro’s number) Part II: Water 1. Calculate the mass (in grams) of 3.34 x10 23 H 2 O molecules. Show all work and record your value in Table 1 below. This is essentially Part I in reverse! 2. Measure out that exact amount of water molecules, either by mass or volume (keeping in mind the density of water is exactly 1.0 g/mL). 3. Take a picture of your measured quantity of water in a graduated cylinder and insert a picture below: Table 1: Mole Calculations
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