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 EXPERIMENT 3 IN...

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 EXPERIMENT 3 INTRODUCTORY LABORATORY TECHNIQUES (SIMPLE DISTILLATION, SUBLIMATION & CRYSTALLIZATION ) PURPOSE To construct a simple laboratory apparatus and gain experience about some methods by which chemical substances may be separated. Before You Come to Lab Read the entire lab manual, including the introduction and discussion, and the entire procedure. Complete the Pre-Lab below and turn the pre-lab into your instructor/TA with your report. PRE-LAB QUESTIONS 1. What are the similar and different aspects of sublimation and deposition? How are they distinguished? 2. Is simple distillation used to separate homogeneous or heterogeneous mixtures? INTRODUCTION Distillation is a widely used technique in organic chemistry for separating compounds based on differences in their boiling points (b.p.). It is the process of vaporizing (liquid → gas) a liquid form out of one container then condensing (gas → liquid) the vapors back to the liquid form in a second container. Distillation can be used to separate both a liquid from a solid and a liquid from another liquid. It requires that one or more components of a mixture be volatile, that is, can evaporate. If a mixture is composed of two liquids, the one with the lower b.p. (higher vapor pressure, VP) can be removed from the other with higher b.p. (lower VP) by distillation. To perform the distillation, the mixture in a flask connected with a condenser is heated. As the mixture is heated, its temperature rises, and at some point, of time, the lower b.p. component begins to vaporize (while the temperature is constant in a certain range). When the vapors are passed into the cool condenser, they are condensed back to the liquid state, called distillate, which is then collected in a second container. As the distillation continues, and most of the lower b.p. component is distilled off, the temperature of the mixture in the flask will rise again and the higher b.p. component will begin to distill. Distillation can also be used to remove nonvolatile substances (dissolved minerals, for example) from liquids. Sea water contains dissolved minerals that must be removed to make it suitable for human consumption. As sea water is boiled in a distillation apparatus, only the water vaporizes, and the salt remains behind. When the vapors are condensed and collected, the water is free of salt and safe for drinking. Several different techniques exist for specific applications. The most used method is the simple distillation apparatus (Figure 1). This results in the vapors being collected and affords a solution in moderate purity. It is difficult to separate compounds by this method unless they have a larger difference in their b.p.  Figure 1. Simple Distillation Apparatus. Sublimation is the physical property of some substances to pass directly from the solid state to the gaseous state (solid → gas) without the appearance of liquid state. Not all substances possess this characteristic. If one component of a mixture sublimates, this property may be used to separate it from the other components of the mixture. Iodine (I2), naphthalene (C10H8), ammonium chloride (NH4Cl) and dry ice (solid CO2) are some examples of substances that are sublime. In this process, a large amount of substance can be recovered in condensing crystals. The heated substance evaporates and condenses on the cooled surface above. Impurities are left behind with pure crystals forming on the cold surface. A) B) C) D) Figure 2. Different Sublimation Apparatuses. Sublimation has additional advantages: It can be the technique of choice for purifying heat-sensitive materials. Solvents are not involved and, indeed, final traces of solvents are effectively removed. Impurities most likely to be separated are those with lower solubilities, exactly those materials very likely to be contaminants in a recrystallization. Solvated materials tend to desolvate during the process. In the specific case of water solution, it is very effective even with substances that are deliquescent. A typical single-component phase diagram is shown Figure 3, which relates the solid, liquid, and vapor phases of a substance to temperature and pressure. Where two areas (solid, liquid, and vapor) touch, there is a line, and along each line the two phases exist in equilibrium. Line BO is the sublimation-vapor pressure curve of the substance in question; only along line BO can solid and vapor exist together in equilibrium. At temperatures and pressures along the BO curve, the liquid state is thermodynamically unstable. Where the three lines representing pairs of phases intersect, all three phases exist together in equilibrium. This point is called the triple point. Figure 3. Single-Component Phase Diagram. Crystallization is one of the methods used in the separation and purification of solid organic matter. It is preferred not only in organic chemistry but also in other areas of chemistry due to its simplicity and effectiveness of application. The first step of crystallization involves dissolving the organic matter in a minimum volume of hot solvent and removing insoluble impurities by filtration. In the next step, the hot solution containing the product and undissolved impurities is allowed to cool and crystallization of the organic solid is achieved. The crystallization process is completed by separating the crystals from the solution by filtration and drying. Whether the crystals obtained are pure or not is determined by appropriate methods such as comparison of melting point or chromatography. If the purity is not sufficient, recrystallization is performed. Factors Affecting Crystallization: Several factors affecting the crystallization process are, Presence of Another Substance: Sodium chloride crystallized from aqueous solutions produces cubic crystals. If sodium chloride is crystallized from a solution containing a small amount of urea, the crystals obtained will have octahedral faces. Solvent Used: The solvent with moderate solubility is preferred for crystallization. The presence of benzene can help crystal growth. Avoid highly volatile solvents. Nucleation: Nucleation refers to the formation of the very first atom of a crystal. The first atom that grows is called Nucleus. It acts like a seed that allows the growth of more atoms around it. Crystals initially form via “nucleating events.” After crystallite has nucleated it must grow. Nucleation sites are necessary for the formation of crystals. Excess nucleation sites cause smaller average crystal sizes. Crystal Growth: Crystals grow by the ordered deposition of the solute molecules onto the surface of a pre-existing crystal. Crystal growth is facilitated by the environment changing slowly over time. Keep crystal growth vessels away from sources of mechanical agitation (e.g., vibrations). Set up away from vacuum pumps, hoods, doors, drawers, and so on.  Rate of Cooling: Quality crystals grow best over time in near-equilibrium conditions. The longer the time, the better the crystals. Faster crystallization is not as good as slow crystallization. Faster crystallization has a higher chance of lower quality crystals. Properties of the solution to be used in crystallization: 1. While the solubility of the substance to be crystallized increases in heat, it should dissolve the impurities in it only in hot or cold conditions. 2. Does not react with the substance to be crystallized, 3. Possible volatility that can easily move away from the crystal, 4. The boiling point is lower than the melting point of the crystallized substance, 5. Non-toxic and non-flammable, 6. It must be capable of dissolving the substance to be crystallized when it is hot and not when it is cold. Table 1. Recommended Solutions for Crystallization. Compound Recommended Solvent Hydrocarbons Hydrocarbons, Toluene, Ether Ethers Ethers, Dichloromethane Halides Dichloromethane, Chloroform Nitriles Esters Aldehydes and Ketones Alcohol, Ethly Acetate, Acetone, Dioxane, Acetic Acid Phenols Alcohol, Dioxane, Acetic Acid Amines, Alcohols, Acids Alcohol, Water Salts Water MATERIALS Sodium Chloride (NaCl) Solution A Simple Distillation Apparatus Iodine (I2) Beakers Potassium Nitrate (KNO3) – Copper Nitrate Crystallization Dish (Cu(NO3)2) Mixture Hot Plate DI Water Ring Stand Cold DI Water Large Clamp Watch Glasses Ice Spatula Funnels Analytical Balance Weighing Boats Filter Paper Test Tube Test Tube Holder Glass Stirring Rod Graduated Cylinder SAFETY CONSIDERATIONS Safety in the Laboratory Safety glasses or safety goggles (PPE) must be always worn while in the laboratory. Special care must be taken to avoid the burning hazards presented by the hot plate and boiling water. Iodine (I2) is toxic and corrosive! It can damage the eyes and skin on contact. It is readily absorbed through skin and harmful if inhaled in high concentrations. Potassium nitrate (KNO3) can affect you when breathed in. Contact can cause eye and skin irritation. Copper(II) nitrate (Cu(NO3)2) is harmful if swallowed. Irritating to eyes and skin. Contact with combustible material may cause fire. Very toxic to aquatic organisms may cause long-term adverse effects in the aquatic environment. Waste Disposal and Cleanup All solutions should be poured into the waste collection bucket provided. After returning to room temperature, Iodine (I2) was washed from the flask with methanol into a labeled waste container and placed in the waste laboratory for shipment. Before You Leave the Lab Have your instructor/TA check your lab bench for cleanup. Get your data sheet signed by your instructor/TA. Wash your hands before leaving the lab. PROCEDURE PART A. Separation by Distillation 1. A simple distillation apparatus must be constructed as shown in Figure 1. 2. Pour 20 mL sodium chloride (NaCl) solution into flask. 3. Insert the short end of the glass tubing and set up the apparatus as shown in Figure 1. 4. Heat sodium chloride solution until about 15 mL of liquid have been distilled into the receiving flask. PART B. Sublimation of Iodine (I2) 1. Weigh 2 g iodine (I2) in a 250-mL beaker. 2. Take a crystallization dish and fill about half-full of water. 3. Place crystallization dish on a hot plate; the hot plate should be on a ring stand with a large clamp. 4. Heat the water slowly. REACTION: I2(s) → I2(g) → I2(s) 5. Place the beaker in the utility clamp on the ring stand. Adjust the position of the clamp. 6. Place a clean, dry watch glass on top of beaker containing iodine (Figure 4). 7. Place crushed ice in the watch glass, being careful not to get any water underneath the watch glass or inside beaker. 8. Your final setup should look like Figure 2d.  Figure 4. Sublimation Experimental Setup. 9. Carefully heat the beaker. Vapors will appear in the beaker and solid crystals should be collected under the watch glass. NOTE: Very carefully drain the ice and any liquid on the top of the watch glass down the drain. 10. Collect the crystallized solids by scraping it off the watch glass into another clean watch glass (reweighed) with a spatula. 11. Weigh and record the collected mass of iodine on your data sheet. PART C. Crystallization 1. Put about 10 g of potassium nitrate (KNO3) – copper nitrate (Cu(NO3)2) mixture in a beaker and add 10 mL of distillated water. 2. Heat the beaker gently, from the sides by changing the position of the tube frequently, until all the solid has dissolved. 3. Cool the test tube to room temperature. 4. Cool the solution in test tube by passing cold tap water from outside of the beaker until no more crystals appear to form. 5. Filter the solution. 6. Save the filtrate (solution that passes through a filter). Wash the solid once or twice with a small amount of cold water. 7. Observe the color of the solid and filtrate. Figure 5. Experimental Setup of Crystallization. DATA & ANALYSIS PART A. Separation by Distillation The temperature at which the first distillate was collected is………………………°C. Observe the differences between the distillate and the original solution, write your observations on the data sheet. …………………………………………………………………………………………............... PART B. Sublimation of Iodine Mass of iodine (theoretical) : ………………. g Mass of crystallized solid iodine (actual) : ……………...... g %error = 100 – %yield PART C. Crystallization Compound Color Which compound(s) is/are Which compound(s) is/are present present in the solid? in the filtrate? KNO3 Cu(NO3)2 POST-LAB QUESTIONS The post-lab questions will be posted to the LEARN platform in the Lab Report Template.