chemistry 2

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timer Asked: Dec 10th, 2018
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hey i have a lab due in couple of hours the 2 files down below should be filled properly and submitted back to me the only chalenge here is the time because i need it asap

Determining the Ksp of Calcium Hydroxide Carolina Distance Learning Investigation Manual World-Class Support for Science & Math 2 Table of Contents Overview ............................................................................................................................ 3 Objectives .......................................................................................................................... 3 Time Requirements............................................................................................................ 3 Background ....................................................................................................................... 4 Materials ............................................................................................................................. 6 Safety .................................................................................................................................. 7 Preparation ........................................................................................................................ 7 Activity 1: ............................................................................................................................ 7 Activity 2: ............................................................................................................................ 9 Disposal and Cleanup.................................................................................................... 10 Data Tables ...................................................................................................................... 11 ©2015 Carolina Biological Supply Company 3 Overview In this experiment, students will determine the solubility product (Ksp) of calcium hydroxide, a solid that is slightly soluble in water, by titrating a sample of calcium hydroxide with an acid. In Activity 2, a common ion will be added and the solubility of the new solution will be determined. Objectives    Calculate the molar solubility of a solution. Determine the Ksp of a molecule. Interpret the effect of a common ion on the molar solubility of a solution. Time Requirements Preparation.....................10 minutes Activity 1 .........................45 minutes Activity 2 .........................60 minutes ©2015 Carolina Biological Supply Company 4 Background An important property of molecules is their solubility, or the degree to which they dissociate in different solvents (water, alcohols, other organic solutions, etc.) Many chemicals have some measureable solubility in a solvent. The general classifications of solubility are insoluble, slightly soluble, or soluble. Insoluble compounds have a concentration (or molarity) of less than 0.01 mol/L. Slightly soluble compounds have a molarity between 0.01 and 0.1 mol/L, whereas soluble compounds have a molarity greater than 0.1 mol/L. Solubility is determined using an equilibrium equation between the solid molecule and its dissolved ions. An example using silver sulfide (Ag2S) is given below, where the “s” subscript indicates a solid and the “aq” subscript indicates aqueous ions. + 2− 𝐴𝑔2 𝑆 𝑆 ⇔ 2𝐴𝑔𝑎𝑞 + 𝑆𝑎𝑞 Solubility is determined by the application of an equilibrium equation. Typically, an equilibrium equation is used to determine the equilibrium constant (Keq): 𝐾𝑒𝑞 = [𝐴]𝑤 [𝐵] 𝑥 [𝐶]𝑦 [𝐷] 𝑧 The bracketed letters indicate the concentration of each ion in a reaction, and the exponent is the stoichiometric coefficient of that ion. The products are on the top, and the reactants are on the bottom: [𝐴𝑔+ ]2 [𝑆 2− ]1 𝐾𝑒𝑞 = [𝐴𝑞2 𝑆]1 However, only aqueous (dissolved) components are included in the equilibrium equation. Because solubility is the equilibrium between a solid and its aqueous ions, the overall equilibrium equation can be simplified: 𝐾𝑠𝑝 = [𝐴]𝑤 [𝐵]𝑥 𝐾𝑠𝑝 = [𝐴𝑔+ ]2 [𝑆 2− ]1 Ksp is known as the solubility product, which is the product of the concentrations of the ions from a parent molecule. At standard pressure and temperature (1 atm and 20°C, respectively), Ag2S has a Ksp of 6.0 x 10-51. However, the solubility of many solids increases as the temperature of the system increases; thus, Ksp is a fixed value at a given temperature. The Ksp of Ag2S increases with temperature, which leads to increased solubility of the salt. The solubility product can be used to determine the maximum concentration of ions in a solution. Using this information, we can determine the equilibrium concentration of Ag2S in a saturated solution: 6.0 × 10−51 = [𝐴𝑔+ ]2 [𝑆 2− ]1 In this example, the silver and sulfide ions have different stoichiometric ratios. The sulfide ion has the lower coefficient (1 for sulfide versus 2 for silver), so it is assigned the variable “𝑥.” Because there are twice as many silver ions, the silver concentration is represented by “2x.” 6.0 × 10−51 = [2𝑥]2 [𝑥] Note that when solving for concentration (𝑥), in addition to the concentration of silver being double that of sulfide, it is also raised to the second power. ©2015 Carolina Biological Supply Company 5 Therefore, solving for 𝑥: 6.0 × 10−51 = 4𝑥 3 1.5 × 10−51 = 𝑥 3 1.4 × 10−17 = 𝑥 The calculations indicate that in a saturated solution of silver sulfide, there are1.4 x 10-17 mol/L of sulfide ions. Thus, because there are twice as many silver ions (2x), the concentration of silver ions at equilibrium in this solution is 2.8 x 10-17 mol/L. The molar solubility refers to the number of moles of a molecule that will dissolve in 1 L of solution. In the above example, the molar solubility of silver sulfide is 1.4 x 10-17 mol/L. Molar solubility is determined by dividing the concentration of an ion by its stoichiometric coefficient in the parent molecule. In this investigation, you will determine Ksp of calcium hydroxide by titrating a sample of saturated calcium hydroxide [Ca(OH)2] with hydrochloric acid. You will also determine the concentration of each ion in calcium hydroxide and the overall molar solubility. A titration is the precise addition of a titrant, which is a solution of known concentration and composition, to an analyte, which is a solution of unknown concentration or composition. In this acid-base titration, the titrant calcium hydroxide (a base) is delivered using a syringe in order to measure the volume of base added within an error range of (±0.1 mL). The equivalence point of a titration is the point at which the moles of acid are exactly equivalent to the moles of base in solution. The equivalence point is achieved when sufficient titrant has been added to react with all of the analyte in a given solution. The endpoint is the experimental estimate of the equivalence point. In this investigation, the endpoint is identified by a color change in the indicator solution methyl orange. The molarity and volume of the titrant are known, as well as the volume of the analyte. To determine the concentration of the analyte, you must first determine the number of moles of titrant that are needed to reach the endpoint. Next, you will use the balanced chemical equation to calculate the moles of analyte present. Finally, you will use the volume of the analyte to determine the concentration of the analyte. In Activity 2, the equilibrium will be artificially shifted back towards the solid calcium hydroxide by the addition of calcium chloride. Calcium chloride is exceptionally soluble and will easily dissolve in water. This portion of the investigation demonstrates the common ion effect and its impact on the equilibrium of solutions. 2+ − 𝐶𝑎(𝑂𝐻)2 𝑠 ⇔ 𝐶𝑎𝑎𝑞 + 2𝑂𝐻𝑎𝑞 By adding additional calcium ions in Activity 2, the equilibrium shifts back towards calcium hydroxide, meaning that there should be less hydroxide ion available to react. Molar solubility will then be calculated for the sample under these non-standard conditions. ©2015 Carolina Biological Supply Company 6 Materials Included in the materials kit: Syringe, 1-mL Lime water (calcium hydroxide) Calcium chloride Hydrochloric Acid, 0.10 M Methyl orange indicator Needed from the equipment kit: 10-mL graduated cylinder 25-mL Erlenmeyer flask Electronic balance Disposable pipet Needed, but not supplied: Plain sheet of white paper Bottled water Reorder Information: A replacement kit for Determining the Ksp of Calcium Hydroxide, item number 580368, can be ordered from Carolina Biological Supply Company. Call 1-800-334-5551 to order. ©2015 Carolina Biological Supply Company 7 Safety Wear your safety goggles, chemical apron, and gloves at all times while conducting this investigation. Read all of the instructions for this laboratory activity before beginning. Follow the instructions closely, and observe all established laboratory safety practices, including the use of appropriate personal protective equipment (PPE) described in the Safety and Procedure sections. Hydrochloric acid and calcium hydroxide are corrosive. In the event of contact with skin or eyes, the affected area should be immediately flushed with water for 15 minutes. Calcium chloride can be harmful is swallowed and is a serious eye irritant. Do not eat, drink, or chew gum while performing this activity. Wash your hands with soap and water before and after completing the investigation, and clean up the work area with soap and water. Keep pets and children away from lab materials and equipment. Preparation 1. Read through the Procedure. 2. Obtain all materials. 3. Answer any pre-lab questions. Activity 1: Titration of Saturated Calcium Hydroxide with Hydrochloric Acid 1. Place the 25-mL flask on the balance. Record the mass in Data Table 1. 2. Measure 3-mL of lime water with the 10-mL graduated cylinder. 3. Pour the lime water into the flask. 4. Record the exact mass of the flask + lime water in Data Table 1. 5. Add 5 drops of methyl orange to 3 mL Ca(OH)2. ©2015 Carolina Biological Supply Company 8 6. Fill the syringe with hydrochloric acid, drawing the plunger back with the tip of the syringe positioned in the HCl to fill the syringe. Try to minimize the amount of air in the syringe. The amount of air in the syringe must be minimized. If there are any air bubbles in the syringe, empty the syringe and refill until no air bubbles are visible. 7. Record the initial volume of HCl solution in the syringe to the nearest 0.01 mL in your Data Table 1 for Sample 1. 8. Place the flask containing 5 mL Ca(OH)2 on the white sheet of paper. The white background will make the color change more noticeable. Read the volume of the syringe at the edge of the plunger. 9. Add HCl drop wise from the syringe with constant swirling of the flask, until a single drop of HCl causes a color change that persists for a few seconds after addition. This indicates that the endpoint has been reached. To gain more control of single drops from the syringe, move the plunger by holding it where it enters the syringe instead of pressing the end of the plunger. 10. Once the endpoint has been reached, record the final volume of HCl left in the syringe in Data Table 1 for Sample 1. 11. Calculate the total volume of HCl that was required to reach the endpoint by subtracting the end volume from the start volume and record the volume in Data Table 1. 12. Dispose of the titrated Ca(OH)2 sample in the sink. 13. Rinse the 25-mL flask with bottled water. 14. Repeat steps 1–13 for samples 2 and 3 and record the values in Data Table1. 15. Calculate the concentration of OH- in your sample based on your experimental data. 16. Calculate the concentration of Ca2+, molar solubility, and Ksp CAUTION: Complete all trials and calculations for Activity 1 before continuing to Activity 2. ©2015 Carolina Biological Supply Company 9 Activity 2: Titration of Saturated Calcium Hydroxide + Calcium Chloride with Hydrochloric Acid. 1. Carefully remove the tip of the lime water bottle. 2. Place the bottle on the electronic balance and tare the balance. 3. Add ~0.02 – 0.04g of calcium chloride to the bottle. 4. Reinsert the dropper tip and recap the bottle. 5. Shake thoroughly. 6. Allow the bottle to sit from approximately 10 minutes. 7. Place the 25-mL flask on the balance. Record the mass in Data Table 2. 8. Measure 3 mL of calcium hydroxide + calcium chloride with the 10-mL graduated cylinder. 9. Pour the calcium hydroxide + calcium chloride into the flask. 10. Record the exact mass of the flask + calcium hydroxide + calcium chloride in Data Table 2. 11. Add 5 drops of methyl orange to 3 mL Ca(OH)2. 12. Fill the syringe with hydrochloric acid. Try to minimize the amount of air in the syringe. 13. Record the initial volume of HCl solution in the syringe to the nearest 0.01 mL in your Data Table 2 for Sample 1. 14. Place the flask containing the 3 mL Ca(OH)2 + CaCl2 on the white sheet of paper. The white background will make the color change more noticeable. 15. Add HCl drop wise from the syringe with constant swirling of the flask, until a single drop of HCl causes a color change that persists for a few seconds after addition. This indicates that the endpoint has been reached. 16. Once the endpoint has been reached, record the final volume of HCl in the syringe in Data Table 2 for Sample 1. 17. Calculate the total volume of HCl that was required to reach the endpoint and record the data in Data Table 2. 18. Dispose of the titrated Ca(OH)2 + CaCl2 sample in the sink. 19. Rinse the 25-mL flask. 20. Repeat steps 7–19 for samples 2 and 3 on Data Table 2. ©2015 Carolina Biological Supply Company 10 21. Calculate the concentration of hydroxide in your sample based on your experimental data. 22. Calculate the concentration of Ca2+ and molar solubility. Disposal and Cleanup 1. Dispose of titrated samples in the sink. 2. Clean and dry the flask and return it to the equipment kit. 3. The specimen jars can be washed and disposed in the trash or recycled. ©2015 Carolina Biological Supply Company 11 Data Tables Data Table 1: Titration of Calcium Hydroxide with Hydrochloric Acid Sample 1 Mass of Erlenmeyer Flask Mass of Erlenmeyer Flask + Calcium Hydroxide Solution (lime water) Mass of Calcium Hydroxide solution Volume of Ca(OH)2 Density = 1.000 g/mL Concentration of HCl (M) Initial HCl volume in syringe Final HCl volume in syringe Volume of HCl Delivered Moles of HCl Delivered Moles of OH- in Sample Moles of Ca2+ in Sample Molar Solubility (M) Calculated Ksp Average Calculated Ksp ©2015 Carolina Biological Supply Company Sample 2 Sample 3 12 Data Table 2: Titration of Saturated Calcium Hydroxide + Calcium Chloride Name of Vinegar Sample Sample 1 Mass of Erlenmeyer Flask Mass of Erlenmeyer Flask + Calcium Hydroxide +CaCl2 solution Mass of Calcium Hydroxide +CaCl2 solution Volume of Ca(OH)2 Density = 1.000 g/mL Initial HCl volume in syringe Final HCl volume in syringe Volume of HCl Delivered Moles of HCl Delivered Moles of OH- in Sample Moles of Ca2+ in Sample Molar Solubility ©2015 Carolina Biological Supply Company Sample 2 Sample 3
Determining the Ksp of Calcium Hydroxide Pre Lab Questions 1. Determine the Ksp of calcium fluoride (CaF2), given a molar solubility of 4.58 x 10-5 mol/L. 2. Determine the molar solubility of potassium chromate (K2CrO4) given a Ksp of 142. 3. When a common ion is introduced, should the molar solubility of a molecule increase, or decrease? Why? Discussion Questions 1. Based on your results, could you predict the solubility of a calcium hydroxide solution following the addition of a known amount of calcium chloride? Why or why not? 2. What other factors besides a common ion, can affect solubility? Design an experiment to determine molar solubility that involves changing a different variable. World-Class Support for Science & Math

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Robertmariasi
School: Rice University

Hello there,I just finished the task you requested. I am attaching to this message 2 Words file. One is the pre and post lab q...

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Anonymous
Good stuff. Would use again.

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