CHM202 H1 and H2 Virtual Lab Activity: Solids and Solutions 2\/8\/21 and 2\/9\/21*<\/p>\n
*Please write a full laboratory report from the background information and data provided below and in the video posted on our Moodle Course Website. Guidelines for laboratory reports are posted in Topic 1 on the course website.<\/p>\n
INTRODUCTION AND BACKGROUND INFORMATION:<\/p>\n
Purpose:<\/p>\n
This laboratory is concerned with the physical properties of solids and solutions. Crystalline solids exist in a lattice of repeating structural units. The student will gain greater appreciation of how atoms are spatially arranged in a solid. The solubility of an ionic compound will be evaluated as a function of temperature. Phase changes associated with super-cooled liquids, supersaturated solutions and sublimation will also be presented.<\/p>\n
Introduction:<\/p>\n
Everywhere we look we see matter as pure elements, compounds and mixtures. Most of the things that we observe as physical materials are either solids or liquids. Many of the solids we see have a complex structure that is polymeric based from either natural (wood is an example) or synthetic (plastics are an example) sources. Simpler crystalline materials are also observed such as the sugar that we put in our coffee or the salt in the food we eat. We also observe liquid matter normally as water or as solutions of things in water (coffee, tea and soda are examples). It is known that these materials are all comprised of atoms, but how are these atoms arranged? This laboratory session should provide some insight into how atoms and molecules are arranged into the materials that we come into contact with daily.<\/p>\n
Crystalline solids exist in an extended network of repeating structural units called a crystalline lattice. This extended network provides additional stability to the solid (related to the lattice energy) and the repeating unit is called a unit cell. We will examine the arrangement of some simple unit cells by making models on a scale we can easily observe. In addition we will calculate the free volume in these structures and calculate the density of some pure metals using these geometric measurements.<\/p>\n
Solutions are homogeneous mixtures of one or more compounds in a liquid called the solvent. In our examinations the solvent used will be water and we will determine the solubility of potassium nitrate in water at various temperatures and generate a solubility curve. When determining the solubility of a compound in a solvent, we will be looking for the point at which the solution exists at its maximum concentration that is called the saturation point. We will also examine systems where a compound exists as a liquid below its normal melting point and a solution contains more solute than present in a saturated solution. These systems (supersaturated solutions and super-cooled liquids) are said to be thermodynamically unstable and if given enough time will form a solid but require a seed crystal or shock to initiate crystal formation. Finally a demonstration of sublimation will be observed whereby iodine will be converted from a solid to a gas (sublimation) and then back to a solid (deposition).<\/p>\n
Reading Assignments:<\/p>\n
You are required to complete the following assignment as part of this laboratory session: Please watch the video from the live session for this virtual laboratory activity. Please review Chapter 10 and 11 from our textbook: Chemistry: The Science in Context 5th Edition Thomas Gilbert.<\/p>\n
Grading:
\nGrading will be as described in the general laboratory handout.<\/p>\n
Procedure:<\/p>\n
1. Models of Crystalline Unit Cells<\/p>\n
1.1\tFrom the Styrofoam balls available in the laboratory take a package of the full and partial balls to prepare models. Record the radius of the balls used. It may be helpful to refer to Figure 11.22<\/p>\n
1.2 \tUsing the Styrofoam balls and toothpicks provided prepare a unit cell for the simple cubic, body-centered cubic and face-centered cubic (also called cubic closest-packed; ccp) crystal lattice unit cells.<\/p>\n
1.3 \t Measure the dimensions (unit cell length, l) of each unit cell with a ruler and include this data in the table provided. Also calculate the ratio of the cell length (all are cubes) to the atomic radius (l\/r ratio). Draw what you have made to the best of your ability including a representation of the unit cell dimensions. Determine the number of atoms present in each unit cell and enter this data into the table provided.<\/p>\n
1.3\tPlace your finished face centered cubic unit cell at the instructor\u2019s desk along with other student\u2019s unit cells to create a portion of a face- centered cubic lattice structure.<\/p>\n
1.4\tCalculate the following and enter into the table provided:
\n1.4.1\tThe dimensions (geometric unit cell length, l) of the unit cell as a function of radius by using geometry (as opposed to direct measurement of the model). Note: For the body and face-centered cubic you will need to apply the Pythagorean theorem (c2 = a2 + b2 for a right triangle).
\n1.4.2\tThe volume of the \u2018atoms\u2019 used to prepare the models (4\/3\uf070r3)
\n1.4.3\tThe total volume of the unit cell occupied by the atoms (number of atoms x volume of each atom) and the total volume of the cell (volume of the cube, l3).
\n1.4.4\tThe percentage of space occupied by atoms (volume of space occupied\/volume of unit cell x 100%) and the percentage of free space for each unit cell (100% – Pct. filled).<\/p>\n
1.6\tUsing the information on crystal structures from Figure 1 below and the following atomic radii, calculate the density that you would expect for the metals Cu (r = 128 pm), Fe (r = 124 pm), and Pb (r = 175 pm). Compare the values you obtained with the reported values for density listed in the table. Note: You will need to calculate the mass (using Avogadro\u2019s number) and volume (using the atomic radius and the volume of a sphere) of each metal atom.<\/p>\n
2. Determination of the Solubility Curve for Potassium Nitrate.<\/p>\n
2.1 \tUsing a heating block set near 90oC (or a water bath) heat the samples described below to up to 90 degrees C. (Note that higher concentrations will require higher temperatures to dissolve.) The instructor may request that you substitute a thermocouple temperature probe for the thermometer.<\/p>\n
2.2\tAdd the following amounts of potassium nitrate to four separate test tubes: 2, 4, 6, and 8 grams. Record the weight to within at least 0.01 grams.<\/p>\n
2.3\tPipette 5.00 mL of water into each test tube.<\/p>\n
2.4\tHeat the test tubes until the samples completely dissolve using a glass stir rod to gently mix the contents. Do not remove the glass stir rod from the mixture until it is completely dissolved.<\/p>\n
2.5\tMove the test tube containing the KNO3 solution to a test tube rack and quickly place the thermometer into the KNO3 solution. If the sample crystallizes upon the addition of the thermometer then heat the sample and the thermometer together in the heat block until re-dissolved.<\/p>\n
2.6 \tSlowly raise and lower the thermometer in the test tube and record the temperature at which a crystal is first observed. Record this temperature as accurately (within 0.1 degree) as possible. This is the temperature of a saturated KNO3 solution.<\/p>\n
2.7\tRepeat with the other concentrations of KNO3 recording the temperature for each tube (Note: The temperature required to completely dissolve the sample will be lower at lower concentrations).<\/p>\n
2.8\tGraph the solubility of KNO3 in g\/100 mL as a function of temperature on the graph paper provided.
\n2.9\tDispose of the KNO3 solutions in the container provided in the laboratory.<\/p>\n
3. Super-cooled Liquids and Supersaturated Solutions (Acetic Acid and Sodium Acetate)<\/p>\n
3.1\tRemove a bottle of pure acetic acid which has been cooled from the instructor\u2019s desk. Record the temperature of the ice\/water bath that the acetic acid was held in and compare to the melting point of acetic acid. Handle the bottle carefully and observe if there is any solid present in the solution. Dry off the thermometer and use the thermometer to gently stir the solution and record any observations.<\/p>\n
3.2\tTake one of the flasks of concentrated sodium acetate solution which is at or below room temperature. Make sure that there are no crystals evident in the solution used (if there are then use another flask of sodium acetate which does not have crystals).<\/p>\n
3.3\tObserve carefully the beaker containing the sodium acetate solution which has been cooled and confirm that there is no solid present.<\/p>\n
1.4\tAdd a spatula of sodium acetate crystals to the sodium acetate solution and record the results<\/p>\n
4. Sublimation (Iodine)<\/p>\n
4.1\tObserve the demonstration at the instructor\u2019s desk where iodine is being sublimed. What do you observe about the solid in the bottom of the beaker and the solid on the watch glass? What about the \u201cair\u201d in the beaker. Record your observations.<\/p>\n
DATA AND RESULTS<\/p>\n
Please watch any video provided for each section for analyzing Results and Data below. Also consult with online virtual laboratory session Tuesday 10\/13\/20 posted on Moodle Course Website with Chapter 10 content.<\/p>\n
PART 1 Models for Crystalline Unit Cells
\nTable 1 Building Cubic Unit Cells (Student Data from Previous Semester)<\/p>\n
Atomic Radius: r = 3.78 cm<\/p>\n
Volume of one atom: V = _<\/p>\n
Simple Cubic (SC)
\nR: 1.25
\nA: 2.5
\nBody Centered Cubic (BCC)
\nR: 1.38
\nA: 2.75
\nFace Centered Cubic (CCP)
\nR: 1.88
\nA: 3.75
\nMeasured unit cell length (l) \t6.6cm
\nNo. Atoms per cell<\/p>\n
Ratio of L\/r
\nGeometric unit cell length (l)<\/p>\n
Volume of atoms in cell
\nTotal Volume of Unit Cell<\/p>\n
Percent volume filled<\/p>\n
Percent free space<\/p>\n
Table 2 Theoretical Unit Cell Calculations
\nCopper
\nIron
\nLead
\nCrystal Form \tCCP
\nBCC
\nCCP
\nRadius (pm)<\/p>\n
No. atoms per cell<\/p>\n
Dimensions of unit cell<\/p>\n
Volume of unit cell<\/p>\n
Mass of one atom<\/p>\n
Total mass of atoms in one unit cell<\/p>\n
Mass of atoms per unit cell volume (calculated density)<\/p>\n
Reported Density (g\/cm3)<\/p>\n
Notes on Calculations for Tables 1 and 2:
\n\u2022\tRatio of l\/r: Length divided by radius
\n\u2022\tGeometric unit cell length:
\n\u2022\tVolume of atoms in cell: (4\/3\u03c0r3) x Number of atoms\u2028Total volume of unit cell: length3
\n\u2022\tPercentage of space occupied by atoms: (Volume of atoms \/ volume of unit cell x 100%)
\n\u2022\tMass of one atom: Atomic mass \/ Avogadro\u2019s Number
\n\u2022\tDimensions of unit cell: atomic radius x ratio of l\/r of that particular unit cell model
\n\u2022\tTotal mass of the unit cell: Mass of one atom x number of atoms per cell
\n\u2022\tCalculated density: Mass of atoms per unit cell \/ Total volume of unit cell Percentage of free space for each unit cell: (100% – Pct. Filled)
\nPART 2 Determination of the Solubility Curve for Potassium Nitrate<\/p>\n
Potassium nitrate solubility curve<\/p>\n