17_Lab_113

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University of Kentucky *

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Chemistry

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Apr 3, 2024

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sDetermining K sp of Calcium Hydroxide with Hydrogen Concentrations Introduction: The purpose of the experiment is to calculate the K sp value of calcium hydroxide through experimentation with primary standards and saturated solutions while understanding the solubility of slightly soluble salts (French et al. 97). The hypothesis is that this will be determined through finding the hydrogen concentration in a saturated calcium hydroxide solution. According to French et al. “a saturated solution is one in which the maximum amount of solute has been dissolved.” A saturated solution can be made over a long period of time hence why the lab is split up into two weeks. Once the maximum amount has been dissolved, one must filter the solution to rid it of excess solute. Filtering is crucial in this as excess calcium hydroxide will result in a skewed equilibrium as increased HCl will need to be added to establish equilibrium. This is indicative of Le Châtelier’s principle as removing OH - from an unfiltered solution dissolved more Ca(OH) 2 to restore equilibrium (French et al. 98). Filtering will also aid in assuring the titration results are accurate. The titration relationship of calcium hydrogen with hydrochloric avid is denoted by equation 1: Ca(OH) 2 + 2 HCL CaCl 2 + 2 H 2 O (French et al. 98). To obtain K sp , equal to K sp = [Ca 2+ ][OH - ] 2 , it is imperative to standardize the concentration of HCl through primary standard experimentation. In this experiment, the primary standard will be composed of sodium carbonate denoted in relationship 2: Na 2 CO 3 + 2 HCl CO 2 +H 2 O + 2 NaCl (French et al. 98).
According to French et al. “Once the exact concentration of HCl has been found, the concentration of hydroxide in the solution can be found,” which will allow for the K sp to be solved for of the reaction denoted in relationship 1. Methods: List of Materials (French et al. 99): Na 2 CO 3 HCl solution Ca(OH) 2 Storage bottles (2) pH sensor Drop counter MeasureNet Glassware as needed Funnel Filter paper Buffers (pH: 4 & 10) Burette and clamp Ring stand Procedure (French et al. 98-99):
Day 1 Experimentation: 1. MeasureNet Calibration: a. Power On b. MAIN MENU c. pH/mV d. pH vs. Volume e. CALIBRATE f. Enter 22 for room temperature g. Place pH in beaker and flush with DI water h. Set 4 for the buffer, place probe in the pH 4 buffer solution and then press enter. i. Flush the probe with DI water and place in the pH 10 buffer solution then press enter j. Flush probe with DI water and place in storage solution k. Press DISPLAY on MeasureNet, flush the probe with DI water and insert into the buffer solution. 2. Preparing Calcium Hydroxide Solution a. Obtain large beaker and fill with water, at least 100 mL b. Stir in the solute to the water adding more than one would think could be dissolved while ensuring not to add more than 4g/L of water. c. Obtain storage container and label with section #, TA, name(s) and “NOT FOR HUMAN CONSUMPTION” d. Add solution to the storage container and let sit 3. Standardization of HCl
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