Runner Posted January 12, 2004 Posted January 12, 2004 Greetings, I was wondering if someone could help me with some of my chemistry difficulty. I have to do an experiment to find the solubility of calcium hydroxide. I have gone as far as to prepare the saturated solution of calcium hydroxide and to plan a titration with HCl. My problem is that I do not know what concentration of HCl I should use, how would I calculate a reasonable amount? Also, correct me if this is wrong. If I measure out 0.5g of calcium hydroxide dissolve it in water, filter it through a funnel and then titrate the saturated solution, I will be able to compare it with the original mass I measure out. To compare the solubility would I just say the mass of calcium hydroxide that was not saturated is evidence to suggest that it is sparingly soluble? Or is there a standard method of doing this? Please, any help would be much appreciated. Thank you in advance.
wolfson Posted January 12, 2004 Posted January 12, 2004 In this experiment you will need to measure the concentration of Ca2+(aq) in equilibrium with (delib) soluble Ca(OH)2(s) and then calculate the Ksp (Constant soluble product) for Ca(OH)2. Ca(OH)2 Ca2+ + 2OHKsp = [Ca2+][OH-]2 You will need to Titrate Ca2+ with ethylenediamine tetraacetate. So collect the Ca(OH)2 and then titrate the Ca2+ ions with a solution of ethylenediamine tetraacetate. One mole of ethylenediamine tetraacetate will react with one mole of Ca2+ to form Ca(EDTA)2-, a "complex ion", 1:1 ratio. Ca2+ + EDTA4- Ca(EDTA)2- Is this helping???
wolfson Posted January 12, 2004 Posted January 12, 2004 You can also use HCL (hydrochloric acid) for the titration.
Runner Posted January 12, 2004 Author Posted January 12, 2004 Thanks for the reply. What I can duduct is that there is a method of calculating the solubility by determining the Ksp, although I have no idea how to do that . Also, will the solubility be in g dm^-3 . Unfortunatelly my teacher told me that the titration will have to be done with HCl, he also told me that I have to calculate a reasonable concentration of HCl that needs to be used in the titration. The only way I can think of calculating is by trial and improvement. So it doesn't matter what mass of Ca(OH)2(s) I use in the experiment? Thanks again
wolfson Posted January 12, 2004 Posted January 12, 2004 Chemical equation time for ya: Determine the concentration of the HCl solution by dividing the number of moles of HCl for each sample by the volume of HCl solution required to reach the endpoint in liters. HCL standard = moles of HCl added / volume in Litres added. Standardization of ~0.1 M HCl solution 1- Obtain a sample of previously dried sodium carbonate (Na2CO3). 2- In three separate 125 mL erlenmeyer flasks, weigh 0.20-0.25 g samples of the dried Na2CO3 to the nearest 0.1 mg on the analytical balances. Record the masses of Na2CO3 on your data sheet. 3- Dissolve each sample of Na2CO3 in about 25 mL of distilled water. Add 3 drops of bromocresol green to each sample. 4- Titrate each sample with the HCl solution until the color changes from blue to green. Once the color change occurs, boil the sample for 2 to 3 minutes, then cool to room temperature. The color of the solution should have gone back to blue. Add a small amount of HCl to the flask until the color changes to green again (Warning!! This second addition will probably be a small amount, use care!!). Record the total amount of HCl added to the nearest 0.01 mL. Discard the solutions in the erlenmeyers and rinse them for later use. Determination of Ksp for Ca(OH)2 5- Dilute the standardized HCl solution by a factor of 10 by diluting 25.00 mL of the standardized HCl solution to 250 mL in a 250 mL volumetric flask. Measure 25 mL of the standardized HCl solution in a 25 mL volumetric pipette. This diluted solution is to be used in future titrations. 6- Empty the buret used in step 4 and rinse it with distilled water. Take a small portion of the diluted HCl solution and rinse the insides of the buret with it. Fill the buret with the diluted HCl solution. 7- Obtain about 75 mL of a saturated Ca(OH)2 solution provided to you in the lab. Take the temperature of the solution with your thermometer and record it. 8- Filter the saturated Ca(OH)2 solution through a piece of filter paper in a long stemmed funnel. Collect about 50 mL of filtered solution (or filtrate) in a 100 mL beaker. 9- Using a 10 mL graduated cylinder, measure out 10.00 mL of the filtered solution. Pour the 10.00 mL of solution into a clean 125 mL erlenmeyer. Add 25 mL of distilled water to the solution and about 3 drops of bromothymol blue. 10- Titrate with the diluted HCl until the color of the solution changes from blue to green. Record the volume of HCl solution added to the nearest 0.01 mL. 11- Repeat steps 9 and 10 two more times for a total of 3 titrations. Rinse out the erlenmeyer flasks after use. 12- Using a 250 mL beaker, heat approximately 100 mL of distilled water to boiling. Add about 2 g of Ca(OH)2 gently to the boiling water and stir for 2 minutes. Record the temperature of the solution to the nearest degree. 13- Quickly filter about 45 mL of this solution. After it is filtered, quickly measure out three 10.00 mL portions of the filtered solution into three 125 mL erlenmeyer flasks. Add 25 mL of distilled water to each flask and let the solutions cool to room temperature. Add 3 drops of bromothymol blue to each flask. 14- Titrate with the diluted HCl until the color of the solution changes from blue to green. Record the volume of HCl solution added to the nearest 0.01 mL.
chemistry Posted January 13, 2004 Posted January 13, 2004 Runner, I have replied to your question which you posted on GeneralChemistryHomework http://groups.msn.com/GeneralChemistryHomework/challengequest.msnw?action=get_message&mview=1&ID_Message=36
wolfson Posted January 13, 2004 Posted January 13, 2004 "chemistry" you have failed to mention the basic idea of solubility constant (Ksp) in your link/chemistry club.
wolfson Posted January 13, 2004 Posted January 13, 2004 For example, suppose you find that there are 15.0 grams of the acid in 120 cm3 of water. The solubility would be 15 x 100 /120 grams in 100 g of water. Solubility is usually expressed as grams of solute in 100 g of solvent or in 1 dm3 of solution.
chemistry Posted January 13, 2004 Posted January 13, 2004 I mentioned solubility constant, molar solubility, and everything else. Read the last paragraph, I mentioned every concept in detail including everything you mentioned in your last two posts; three alternatives to express solubility. Your last post deals with more with percent dissociation, acid base equilibria. Solubility deals more with heterogeneous substances with respect to water in that the mass of the solid is impertinent.
Runner Posted January 13, 2004 Author Posted January 13, 2004 wolfson said in post # :For example, suppose you find that there are 15.0 grams of the acid in 120 cm3 of water. The solubility would be 15 x 100 /120 grams in 100 g of water. Solubility is usually expressed as grams of solute in 100 g of solvent or in 1 dm3 of solution. Ahh ... So if I find the mass of the saturated Ca(OH)2 to be 0.3g and I originally added 0.5g to 0.1 dm^3. The solubility would be 0.3g x 1 dm^3/0.1 dm^3 ?
chemistry Posted January 13, 2004 Posted January 13, 2004 The solubility is in g/L or whichever you prefer; but make sure that the volume is the original volume of the saturated solution...that is the volume of the solution before you added HCL. I will answer the question you posted back at Genchemhwk by the end of today; as of now I am kind of busy.
wolfson Posted January 14, 2004 Posted January 14, 2004 chemistry said in post # :I mentioned solubility constant, molar solubility, and everything else. Read the last paragraph, I mentioned every concept in detail including everything you mentioned in your last two posts; three alternatives to express solubility. Your last post deals with more with percent dissociation, acid base equilibria. Solubility deals more with heterogeneous substances with respect to water in that the mass of the solid is impertinent. My paragraph (the first one) describes the Ksp constant for solubility product, the nest paragraph(s) are giving Runner the ability to show the experimental skills needed to carry out this test. And yes Runner you have the right idea, anymore questions just fire away!!!!!!!!!!!!1
YT2095 Posted January 14, 2004 Posted January 14, 2004 the soluability of calcium hydroxide at 20c is 0.156. taken as 100 times the mass of anhydrous solute per unit mass of water. as a direct response to post #9 if that helps anyone at all?
Guest Huh? Posted January 23, 2005 Posted January 23, 2005 as i think this is a related Q/ i just wanted to know how to figure out solubilty of calcium hydroxide i have found the mass is 0.37g of Ca(OH)2 in 250cm³ of H²O and Concentration of HCl = mole = 0.01 × 1000 = 0.4 dm³ Volume 25cm³ but i am not sure what to do from here plz can som1 help me asap!!
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