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# Determining concentration of limewater [ Ca(OH)2] Solution

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Introduction

Determining concentration of limewater [ Ca(OH)2] Solution Calcium hydroxide, Ca(OH)2, is an ionic solid that is slightly soluble in water. A saturated solution (dissolved in water) is an equilibrium, that can be represented by the following equation: Ca(OH)2(aq) + 2HCl (aq)? 2 H2O(l) + CaCl2(aq) In this plan, I will design and collect the data that will allow me to calculate accurately the concentration of Ca(OH)2 from a volume of the solution. The hydroxide ions formed when Ca(OH)2(s) dissolves can be measured by titration with an acid. From the balanced equilibrium equation, we can see that we do not need to measure the Ca2+ ions, since they are equal to one half of the concentration of OH- ions. An acid-base titration is a process in which a measured volume of an acid or base is added to a reaction mixture until some acid-base indicator changes color. In the procedure used in this lab, a dilute solution of HCl is titrated with a saturated solution of Ca(OH)2 to the endpoint of phenolphthalein. ...read more.

Middle

Moles of solution = I require a O.1M HCl dilute and I am using 2M to begin with. So I can substitute these values into the equation, however, I must also swap the 1000 constant for 250ml because this is the amount of HCl I require. 0.1M = rearrange to find volume: [0.1M X 250 ] / 2 = volume V= 12.5ml. This tells me that if I distill 12.5ml of 2molar HCl with 250ml of distilled water, I will get 0.1M of HCl. Alternatively, I could also use the formula, M1V1=M2V2 Which would show 2 x V1 = 0.1 x 250, therefore V1 = 12.5ml. To actually make this solution up, I will be using the 250ml volumetric flask. I will measure 12.5ml of 2M HCl using a pipette into the flask. Then fill the flask upto the marker line which indicates 250ml, making sure the meniscus is resting on this line. ...read more.

Conclusion

6. Clear up: * rinse all beakers that contained the Ca(OH)2 solution with distilled water. rinse the burette with distilled water. * pour any excess solution back. Recording results: Record results in this table: Titration NO. 1 (rough) 2 3 4 average Volume of HCl at beginning 0 0 0 0 0 Volume of Hcl used in titration Calculations to find molarity of Ca(OH)2: HCl Ca(OH)2 Ratio 2 1 Volume 25.0 cm3 20ml Number of Moles 0.005 mols 0.0025 Concentration 0.2M To find moles of HCl used: n=mV/1000 n=0.2 x 25/1000 n=5/1000 n=0.005 mols the ratio of HCl to Ca(OH)2 is 2:1 so that means there is 0.005 / 2 mols of limewater used. So I can fill this is also. So, by using the solution formula and rearranging for the m I will be able to find the concentration of Ca(OH)2 used in the titration. n=mV/1000 1000n=mV (1000n)/V=m so m=(1000n)/V And we have all the data we need to make this calculation, so: m=(1000n)/V m=(1000 x 0.0025)/20 m=2.5/25 m=0.125mol-1 ?? ?? ?? ?? 1 Arun Subbiah Page 2 of 4 Arun Subbiah Page 1 of 4 ...read more.

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