the question is regarding step 9 and 12, i put the most of the prodcedure up jus
ID: 504233 • Letter: T
Question
the question is regarding step 9 and 12, i put the most of the prodcedure up just in case . please help me understand it becasue it doesn't make sense to me. question at the bottom
the steps as to what we did
PROCEDURE
2. Label three beakers (the ones that can be wet) A-1, B-1, and C-1. Put about 50 mL of distilled water into each beaker. Bring a clean, dry shell vial to your instructor to obtain about 4.5 g of calcium iodate. Using the balances in the lab, weigh out approximately 1.0 g of calcium iodate and place it in beaker A-1. Again using the balances in the lab, weigh out approximately 1.5 g of calcium iodate and place it in beaker B-1. Weigh out approximately 2.0 g of calcium iodate and put it in beaker C-1.
3. Stir the contents of each beaker with a separate clean stir rod. Allow the solutions to sit for at least 20 minutes, stirring every few minutes. Calcium iodate is only slightly soluble and the saturated solution forms slowly. Use this time to prepare for titration (Steps 4-7). If you have put cylinders, beakers, and/or funnels into the oven, remove them now and allow them to cool. 53
4. Using one of the cooled, clean, and dry beakers, obtain about 100 mL of standardized sodium thiosulfate. Record the exact molarity of the sodium thiosulfate solution.
5. Using the clean, dry graduated cylinder that you prepared, measure out three separate samples of about 1 cm3 (1 mL) each of solid KI. (A paper funnel might help you pour the KI into the cylinder without spills. Clean up any spilled KI!) Set these aside for use in step 14.
6. In each of three clean test tubes (they can be wet) put about 2.0 mL (40 drops) of 1% starch solution. You will need this indicator solution later in the titrations.
7. Clean the buret, rinse and fill it with the sodium thiosulfate solution.
8. Set up the three clean, dry funnels you have prepared using buret clamps. Place the three clean, dry beakers labeled A-2, B-2, and C-2 under these funnels. Put dry filter paper cones into each funnel.
9. After allowing the calcium iodate mixtures to come equilibrium (it takes at least 20 minutes) pour each solution through its own filter cone, catching each filtrate in its own dry beaker. Do not add water. Any precipitate remaining in the beakers can be discarded. It is the solution filtering into the beakers that you will be titrating and you do not want to change its concentration by adding rinse water. After the solution has filtered through, discard the filter papers and precipitates.
10. Set up three clean 125 mL titration flasks (they can be wet) labeled A-3, B-3, and C-3.
11. Clean the 10.0 mL volumetric pipet. Shake as much water as possible from the pipet and then rinse the pipet twice (each time with 1 to 2 mL) with the filtered solution from beaker A-2. Pipetting carefully (do not pipet by mouth; use a pipet pump or a bulb!), transfer exactly a 10.0 mL sample (aliquot) of the solution from beaker A-2 to flask A-3. Rinse the pipet twice with the filtered solution from beaker B-2 and transfer 10.0 mL of solution from beaker B-2 to flask B-3. Repeat the procedure for beaker C-2/flask C-3. 12. Add about 20 mL of water to each flask. (Think about why is it okay to add water now.)
13. Add about 8 drops of 6 M HCl to each flask.
Question
1)How would adding water in step 9 to wash the solid calcium iodate precipitate onto the filter paper change the Ksp value which was determined experimentally? Would the calculated value for the constant be higher, lower, or unchanged if extra water had been used in this step? Explain.
2)In step 12, extra water is added to the titration flask. This added water does not alter the value obtained for the Ksp. Explain why.
Explanation / Answer
1. Calcium iodate is a sparingly soluble compound. You are actually making a saturated aqeous solution of calcium iodate (~20 mins strring in water) in step-9. if you add any extra water to the precipiate on the filter paper (i.e. calcium iodate), you would not know the extra water would take how much more calcium iodate along with it to the filtrate (neither you add meausrable quantity of water nor you can keep it for another 20 mins stirring). therefore, it would change the concentration of this saturated solution.
2. In step-12, you know the exact volume of satuarted solution you have taken. Further diluting this solution will not change the concentration i.e. moles of ions present in it.
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