a warm hotplate, and heat gently. After 3-4 minutes, transfer the beaker to a ce
ID: 483705 • Letter: A
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a warm hotplate, and heat gently. After 3-4 minutes, transfer the beaker to a ceramic pad using beaker tongs, and allow any un-dissolved solid to settle and the beaker and its contents cool to room temperature. The solution may continue to appear cloudy depending on the nature of the binders and fillers used in the calcium pill Label two 25 mL centrifuge tubes with your initials and stand them up in a test tube rack or appropriate sized beaker Carefully decant the contents of the beaker in equal amounts to the two centrifuge tubes with as little transfer of the un-dissolved solid as possible. Rinse the beaker with about 10 drops of 2.0 MHCI solution two times and carefully decant both rinses into the test tubes. The addition of the acidic solution should no longer produce Co_2 gas If necessary, add distilled water drop-wise to one of the centrifuge tubes so that both test tubes contain the same volume, place the test tubes in opposite positions in a centrifuge, and spin the samples in the centrifuge for about 5 min Remove the centrifuge tubes from the centrifuge and carefully decant the contents into a beaker. Add about 20 drops of 2.0 MHCI to the solid remaining in each test tube. If the mixture continues to evolve CO_2 (signified by bubbling) when the last drop is added, you may add an additional 10 drops. If the mixture continues to evolve Co_2 it is likely that the experiment will need to be restarted Centrifuge the two centrifuge tubes again for about 5 min, taking care that they contain about the same volume and that they are occupy opposite positions in the centrifuge. Remove the centrifuge tubes from the centrifuge and carefully decant the contents into the beaker used in step (10). Obtain 25 mL of 1.0 M sodium carbonate (Na_2CO_3) in a clean, dry 50 mL graduated cylinder and slowly transfer this solution to the beaker used i step (12) gently stir the mixture with a clean glass stirring rod and wait at least 5 min for the um carbonate (CaCO_3) to fully form obtain some red litmus paper and place a piece on a watch glass. Touch the litmus paper with the end of the glass stirring rod to transfer a drop of the solution. If the litmus paper turns blue, signifying a basic pH for the solution, you may go on to step otherwise continue to add 3-5 mL increments of 1.0 M Na_2CO_3 solution, stir and repeat the litmus paper test until the solution has a basic pH obtain a piece of circular filter paper, mark it with your initials, determine the mass to the nearest mg (0.001 g), and record the value on your data sheet Fold the filter paper in half and in half again as shown in left side of Fig.2 Left: folding filter paper; Right: filtering apparatus setup again as shown in left side of Fig. 2, open the cone, place in a glass funnel, and set up a filtering apparatus as shown in the right side of Fig. 2. To improve the seal between the filter paper and funnel, the outside comer can be torn off and the piece placed in the filter paper cone. Moisten the filter paper with distilled water and be sure the filter is lying flat against the funnel wall before using the apparatus. Carefully and slowly pour the liquid from the beaker in step (12) into the filtering apparatus taking care that the liquid never fills more than about 2/3 of the filter paper cone. When only about 5 mL of solution remains, swirl the beaker to suspend the solid and transfer this slurry into the filtering apparatus. Rinse the beaker with 3-5 mL of distilled water and transfer the rinse to the filtering apparatus. Continue to rinse and transfer until no solid remains in the beaker. When no liquid can be seen in the funnel, remove the filter paper from the funnel, very carefully open the filter paper, and lay it on a clean watch glass being sure that all of the wet calcium carbonate remains on the filter paper. Sometimes a spatula can be helpful in separating the filter paper from the funnel. Place the watch glass and its contents in a drying oven set at 110-120 degree C for 12-15 min. Using crucible tongs remove the watch glass from the oven and place it on a ceramic pad. Never place hot glassware directly on the bench top. Use a spatula to break up the CaCC_3 into small pieces being very careful that all of CaCC_3 remains on the filter paper and return the watch glass and its contents to the drying oven for 10 additional minutes. The larger surface area created by smaller pieces will allow the CaCO_3 to dry more efficiently Using crucible longs remove the watch glass from the oven, place it on a ceramic pad, and allow it to cool for 3-5 min or until it reaches room temperature. Carefully transfer the filter paper and its contents from the watch glass to a balance, determine its mass, and record the value on your data sheet as "first heating" Carefully transfer the filter paper and its contents back on the watch glass and return the watch glass and its contents to the drying oven for 5 min. Repeat steps (22-23) except record the mass value as "second heating". If the first and second heating mass values differ by more than 10 mg (0.010 g). repeat steps (24-25) up to two more times recording the measured masses as "third heating" and fourth heating", respectively. Dispose of the solid waste produced in step (8), the liquid waste produced in step (18). and the filter paper and CaCO_3 as directed.Explanation / Answer
We can use this experiment to determine the number of milligrams of Ca+2 ions in a food sample in which the Ca+2 ion is present in a form other than CaCO3 because CaCO3 dissociate when dissolved in water. hence it is present in the form of Ca+2 ions. Even if we take a sample which has Ca+2 and not CaCO3 we will still be having Ca+2 ions which will still turn the litmus paper blue because it will form Ca(OH)2.. Hence this experiment would still be usefull in determining the number of milligrams of Ca+2
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