Background information : Step 9 : Carefully decant the supernatant solution from

Question

Background information: Step 9: Carefully decant the supernatant solution from both test tubes into a clean 150mL beaker. Use a pipet to add 25 drops of 2.0 M HCl solution to the solid in each test tube. Centrifuge the mixtures again, and carefully decant the supernatant liquid from both test tubes into the beaker containing the other supernates.

Briefly explain whether each of the following procedural errors would result in a high, low, or an unchanged calculated mass of Ca2+ ion in the analyzed tablet. ANSWER THE FOLLOWING:

(1). A student had difficulty decanting the supernatant solution from the test tubes in Step 9, causing him to transfer some of the solid along with the solution.

(2) Briefly explain why you can use this experiment's procedure to determine the number of milligrams of Ca2+ ion in a food sample in which the Ca2+ ion is present in a form other than CaCO3.

Explanation / Answer

Q1.

Transfering the solid will cause the next:

a) will decrease the mass of solid Calcium salt, meaning that if we measure this nad calcualted sotichioemtry, the values will be LOWER

b) If we measuer the solubilty of Ca+2 ions in saturation solution, then we will have a higher amount that the equilibrium

Q2.

in order to determine mg of Ca+2 ions from a sampe, other than CaCO3:

Saturate all CO3-2 left... such as

2Ag+ + CO3-2 <--> Ag2CO3(s)

separate Ag2CO3

then, saturate Ca+2 with any other species, so only Calcium will be precipitated ( selective precipitation)

Then, measure the mass of the Calcium Salt, relate to calcium via stoichioemtry

measure mass, via mol = MV and mass = mol*MW

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