CHEM121 General Chemistry Lab – I Fall 2024 PDF

KADİR HAS UNIVERSITY FACULTY OF ENGINEERING AND NATURAL SCIENCES CHEM121 General Chemistry Lab – I FALL 2024 PREPARED BY Dr. M. Mustafa Cetin Technical Specialist Mine Cengiz Cetin 1 EXPERIMENT 1...

KADİR HAS UNIVERSITY FACULTY OF ENGINEERING AND NATURAL SCIENCES CHEM121 General Chemistry Lab – I FALL 2024 PREPARED BY Dr. M. Mustafa Cetin Technical Specialist Mine Cengiz Cetin 1 EXPERIMENT 1 PHYSICAL PROPERTIES PURPOSE Identifying unknown solid and liquid substances using their physical properties. Before You Come to Lab Read the entire lab manual, including the introduction and discussion, and the entire procedure. Be prepared for a pop-up quiz for the experiment. Complete the Pre-Lab below and turn the pre-lab into your instructor/TA with your report. PRE-LAB QUESTIONS 1. What are the physical properties? Give five examples. 2. Use the density to determine the mass different between a sample of silver and a sample of gold if both samples have a volume of 20 mL. (dAg = 10.49 g/mL, dAu = 19.32 g/mL) INTRODUCTION Characteristics of a substance that can be specified without changing the composition of the substance are called physical properties. Some easily recognized physical properties include mass, volume, color, melting point, boiling point, density, solubility, electrical conductivity, thermal conductivity, malleability (deformation of a solid under pressure), ductility (drawing a solid into a wire), and viscosity (resistance of a fluid to flow). Physical properties can be extensive or intensive. An extensive property depends on how much of the substance is present, and an intensive property is the same for any size sample of the same substance. Mass and volume are examples of extensive properties because they clearly increase as the amount of substance increases. Alternatively, color, melting point, boiling point, and solubility would all be examples of intensive properties. An intensive physical property can also arise from a combination of extensive physical properties, such as the intensive property of density, which is the ratio of mass to volume. The mass will be measured using an electronic balance, in grams (g). Pan balances, which are accurate to ±0.01 g, are used for quick measurements where greater precision is not required. Analytical balances (accurate to ±0.0001 g) are used for more precise measurements. Density is a physical property that relates the mass of material to the amount of space it takes up, or volume. Any units of mass and volume can be used to define density, but the most frequently used units in general chemistry are g/mL for liquids, g/cm3 for solids and g/L for gases. Density is also an intensive property of matter. This means that the value of density is independent of the quantity of matter present. For example, the density of a silver coin and a silver statue are the same, even though the silver statue consists of the greater quantity of silver. mass m density = or D= volume V 2  1000g 1g 1g density of water = = = 1L mL cm3 10490 g 10.49 g 10.49 g density of silver = = = 1L mL cm3 The density of solid will be determined using solid pellets. However, since the pellets have irregular shapes, their volume must be measured indirectly using the technique of water displacement (also known as Archimedes Principle presented in Figure 1). This is because the volume of water that the solid displaces when it is immersed in the water is the same as the volume of the solid itself. The accuracy of this experimentally determined density will also be evaluated by comparison to the true, accepted density of solid. Figure 1. Measuring the Volume of an Irregularly Shaped Solid. Volume is an amount of space, in three dimensions, that a sample of matter occupies. The number and the phase of the molecules in the sample primarily determine the volume of a substance. Volume will be measured in many ways in this course, but the units are usually milliliters (mL) or cubic centimeters (cm3). Methods for determining or delivering precise volumes include volumetric pipets and pycnometers; less precise methods include burets, graduated cylinders, and graduated pipets. Making quality measurements in the laboratory requires knowing how to use the equipment properly, which is not always obvious even for a very simple equipment. For example, most liquids in a container will have a curved upper surface called meniscus, which needs to be considered properly in a volume determination shown in Figure 2. The meniscus will be curved up (concave) if the liquid has a greater attraction to the container’s surface than it does to itself. This is the case for water in a glass container. Alternatively, the meniscus will be curved down (convex)if the liquid has a greater attraction for itself than it does for the container’s surface. The meniscus formed by a non-wetting liquid, such as mercury (Hg), is convex with the highest point in the center. In the case of a convex meniscus, the highest point is used to make the reading. The reading of a mercury barometer or thermometer is a classic example of this kind. 3 When reading any meniscus, it is important to ascertain that it is in an equilibrium position. Tapping of sight glasses and/or small motions of containers may be used to induce slight displacements of the meniscus. Return to the same reading is evidence of a stable meniscus. Figure 2. A) The bottom of concave meniscus. B) The top of convex meniscus. The meniscus of most liquids is concave-up, with the lowest point in the center that is used to determine the meniscus reading. Your eye must be on the same level as the bottom of the meniscus to read the volume correctly. Keep in mind that when reading the measurement, you need to keep the graduated cylinder on a level desk, lower your eyes to the level of the meniscus, and you read the volume accordingly. Be sure to include one point of estimation in your reading. The graduated cylinder markings are every 1-milliliter. When read from the lowest point of the meniscus, the correct reading is 10.0 mL. The first 2 digits 10.0 are known exactly. The last digit 10.0 is uncertain. Even though it is a zero, it is significant and must be recorded. Common experience has given rise to the phrase ‶Oil and water don’t mixʺ as a way of saying that certain characteristics do not go together. This phrase owes its validity to a molecular level consideration of solubility. Water is polar molecule, while which means that electrons in the molecule shift a bit to one side of the molecule (the oxygen side in this case). This electron charge shift is not so great as to from positive and negative ions, it does cause the water molecule to have a somewhat positive side and somewhat negative side. Alternatively, typical oil molecules are nonpolar, meaning that the electrons in the molecule are largely uniform in their distribution. So, the first solubility lesson from the polarity consideration is that liquids of polar and nonpolar molecules do not dissolve in each other. The second lesson is that ‶like dissolve like,ʺ meaning that polar molecules will dissolve in polar solvents and nonpolar molecules will dissolve in nonpolar solvents. Considering the three solvents used in this experiment, water is very polar, ethanol is somewhat polar, and cyclohexane is nonpolar. The boiling point of a compound is the temperature at which it changes from a liquid to a gas when the vapor of the liquid is equal to the atmospheric pressure. This is a physical property often used to identify substances or to check the purity of the compound. It is difficult, though, to find a boiling point. 4 The melting point 0 °C of a compound is the temperature at which it changes from a solid to a liquid. Since this requires that the intermolecular forces that hold the solid together must be overcome. The melting point is a physical property often used to identify compounds. MATERIALS Unknown Metal Test Tubes Unknown Liquid Test-Tube Rack Distilled Water Boiling Chip Ethanol (C2H5OH) Hotplate Methanol (CH3OH) Ring Stand 2-Propanol (C3H7OH) Beakers (100 mL, 250 mL) Cyclohexane (C6H12) Thermometers Clamp Analytic Balance Weighting Boats Graduated Cylinders (100 mL, 10mL) Pipettes SAFETY CONSIDERATIONS Safety in the Laboratory Ethanol (C2H5OH) is flammable, keep away from the heat. Methanol (CH3OH) is flammable liquid and vapor. Harmful if inhaled or absorbed through skin. Causes irritation to skin, eyes, and respiratory tract. 2-propanol (C3H7OH) is highly flammable liquid and vapor. Causes serious eye irritation. May cause drowsiness or dizziness. Cyclohexane (C6H12) is highly flammable liquid and vapor. May be fatal if swallowed and enters airways. Causes skin irritation. May cause drowsiness or dizziness. Very toxic to aquatic life with long lasting effects. Broken thermometers may contaminate the laboratory with spilled mercury, a poison. Consult your instructor for clean-up procedures. The toxic vapor from spilled mercury also poses a health hazard. Special care must be taken to avoid the burn hazard presented by the hotplate. Waste Disposal and Cleanup All solutions should properly be poured into the waste collection bucket provided. It is not permissible to pour cyclohexane (C6H12) down the drain. Carefully follow the direction for disposing waste in the designated waste bottle located in the fume hood. Wash all glassware that touches cyclohexane with acetone in the hood and then clean with soap and water. Before You Leave the Lab Have your instructor/TA check your lab bench for cleanup. Get your data sheet to be signed by your instructor/TA. Wash your hands before leaving the lab. 5 PROCEDURE PART A. Determination of an Unknown Solid The identity of a metal will be determined by comparing the measured value for its density to the known density of a series of metals that are candidates to be the unknown metal. 1. Obtain three different-sized samples of the same unknown metal and record the number of the unknown on the data sheet. 2. Place a sheet of weighting boat on the balance and use the function to "zero" the measurement. 3. Place the one of the unknown metal samples on the weighting boat, determine the mass of the sample, and record the value on your data sheet. 4. Fill a 100 mL-graduated cylinder about half full of water and record the volume of water on the data sheet. 5. Place the sample of the material into the 100 mL-graduated cylinder containing the water and measure the value of the combined volumes. Record this value on your data sheet. 6. Repeat steps (2) through (5) for the intermediate and the other samples of the material and record all the measurements on the data sheet. Table 1. Density of Metals. Metal Symbol Density (g/cm3) Aluminum Al 2.712 Copper Cu 8.940 Gold Au 19.320 Iron Fe 7.850 Zinc Zn 7.133 Lead Pb 11.320 Silver Ag 10.490 Tin Sn 7.280 PART B. Determination of an Unknown Liquid The solubility properties, density, and boiling point of an unknown liquid will be determined, and the values of these properties will be compared to the known values of a series of liquids that are candidates to be the unknown liquid. 1. Obtain a sample of the unknown liquid and record the unknown number on the data sheet. 2. Determine the solubility properties of the unknown liquid by the following procedure. a. Arrange three clean, dry test tubes in a test-tube rock, labeling each with one of the three solvents: Tube-1 DI-water (H2O) Tube-2 ethanol (C2H5OH) Tube-3 cyclohexane (C6H12) b. Add approximately 5 mL of each solvent to the correspondingly labeled test tube. c. Add about 5 drops of the unknown liquid to each test tube and mix the contests by gently tapping or flicking the bottom of the tube with your finger. 6  d. Observe the solubility properties of the unknown liquid in each of the solvents. If only one layer is visible after mixing, then the unknown liquid is soluble in that solvent. However, if the mixture separates into two layers, then the unknown liquid is insoluble in that solvent. Record the solubility test results on the data sheet. 3. Determine the density of the unknown liquid by the following procedure. a. Place a clean, dry 10 mL-graduated cylinder on the balance, and record its mass on the data sheet. b. With the graduated cylinder removed from the balance, transfer about 3.0 mL of the unknown liquid (sample) to the graduated cylinder, and record the exact volume transferred on the data sheet. NOTE: Never add the unknown liquid (sample) while the graduate cylinder is on the balance. c. Place the graduated cylinder removed from on the balance, determine the value of the mass of the graduated cylinder plus the unknown liquid, and record this value on the data sheet. d. Pour the unknown liquid in a beaker for use in step 5. e. Repeat steps (3a) through (3d) for two additional times and record the results on the data sheet. Be sure to begin each density determination with a clean and dry graduated cylinder. 4. Determine the boiling point of the unknown liquid (presented in Figure 3). Figure 3. Boiling Point Determination Apparatus of Unknown Liquid. a. Transfer about 2 mL unknown liquid saved in the beaker from part 4 to a clean, dry test tube. Add a boiling chip to facilitate boiling when the boiling-point temperature is reached. b. Assemble the heating bath apparatus depicted in Figure 3. The beaker on the heat source should be a 250 mL size and contain about 180 mL of water, i.e., it should be about 3/4 full. The test tube containing the unknown liquid should be clamped to the ring stand and positioned so that the level of the unknown liquid is below the level of water in the beaker. c. Position on thermometer in the test tube with the bulb about 1-2 mm above the surface of the unknown liquid. Position the second thermometer in the water bath. Heat the water bath and record the temperature in the test tube when unknown liquid first begins to boil. 7  d. Raise the test tube and its included thermometer so that the test tube is out of the water batch. Allow the test tube and unknown liquid to cool for 30-60 s. e. Return the test tube to water bath, reposition the included thermometer as in step (4c), and record the temperature at which the unknown liquid again begins to boil. f. Repeat steps (4d) and (4e) to obtain a third determination of the boiling point. If necessary, additional unknown liquid can be added to the test tube. Table 2. Density, Boiling Point, and Solubility Data for Organic Liquids. Substance Density Boiling Point Solubilitya (g/cm3) (°C) water ethanol cyclohexane Acetone 0.791 56 S S S 2,3-butanedione 0.990 88 S S S Chloroform 1.483 61 i S S Cyclohexane 0.779 81 i S S Ethyl propyl ether 0.74 64 S S S Hexane 0.655 68 i S S 2-Propanol 0.786 83 S S S Methanol 0.792 65 S S SS Methylene chloride 1.33 40 i S S Propionaldehyde 0.81 46 S S i a solubility symbols: S=soluble, SS=slightly soluble, i=insoluble DATA & ANALYSIS Determine the density of the unknown liquid using equation (2) and the three sets of mass and volume measurements. Identify the unknown liquid by comparing the measured density, boiling point, and solubility properties to the values listed in Table 2. Part A. Identifying an Unknown Metal Sample 1 Sample 2 Sample 3 Mass of Sample g g g Volume of Water mL mL mL Volume of Water +Sample mL mL mL Volume of sample (by subtraction) mL mL mL Density of sample (by equation (2)) g/mL g/mL g/mL Determine the volume of a sample using the equation (1) and record the result. Vsample = Vwater+sample − Vwater (1) Determine the density of the sample using the equation (2) and record the result. masssample d= (2) Vsample Repeat the calculations in steps (1) and (2) using the measurements obtained for the other two samples of the unknown metal and record the results. 8  Identify the unknown metal by comparing the mean density to the values listed in Table 1. Identify of unknown metal…………………………. Part B. Identifying an Unknown Liquid 1.Solubility (Part B-3) Water Ethanol Cyclohexane Solubility (soluble(s)/insoluble(i) Identify the unknown liquid by comparing solubility properties to the values listed in Table 2. 2.Density (Part B-4) Trial 1 Trial 2 Trial 3 Mass graduated cylinder g g g Mass graduated cylinder + sample g g g Volume of Sample mL mL mL Mass sample (by subtraction) g g g Density of sample(by equation (2)) g/mL g/mL g/mL Determine the density of the sample using the equation (2) and the three sets of mass and volume measurements. mass d = V sample (2) sample Identify the unknown liquid by comparing the mean density to the values listed in Table 2. Identify of unknown liquid………………………………. 3. Boiling Point Trial 1 Trial 2 Trial 3 Temperature of °C °C °C Boiling Point Identify the unknown liquid by comparing the average boiling point with the values listed in Table 2. Identify of unknown liquid…………………………. POST-LAB QUESTION(S) The post-lab questions will be posted to the LEARN platform in the Lab Report Template. 9