Need help with prelab and postlab questions SOLUTION To hine gravimetric and dat

Question

Need help with prelab and postlab questions SOLUTION To hine gravimetric and data to calculate concentrations of solutions. To apply limiting reactant calculations to chemical problems. pelab uestions Describe how you know what the limit reagent in today's lab will be. ing 2. computation. If 5.00 mL of 0.100 M Bac 2 is combined with 10.0 mL of 0.0500 M Na,PO (mol) solid Bas(PO4 can be formed? When two solutions are added together and a precipitate is formed, the quantity of the ate will be controlled by the solution not in excess. When CaCl2 is added to an excess rred to Since a fixed volume of the CaCI be used, knowledge of the moles of CaCI calculated. produce the precipitate will allow the molarity of the CaCi2 solution to be CaCl2 CaCO (s) 2NaCl In Part I, a Calcium Chloride solution of known molarity will be and the percent be calculated. In Part II, a concentration CMD used will be for an determined. PROCEDURE PART MOLARITY OF A KNowN SOLUTION (DAY ONE) l. obtain a 25 mL pipet, suction bulb, Buchner Funnel, and filter flask from the stockroom. 2. Place approximately 40 mL of a 1 M solution of Nazco3 in a 250 mL beaker. ipet known (approximately 0.5 M) of Caci2 into the 250 mL beaker. Stir thoroughly with a glass stiming rod and rinse any precipitate on the stirring rod back into the beaker with deionized water Set up the Buchner funnel, filter flask, and the hose line to the vacuum as demonstrated. Weigh piece offilter paper and a Petri dish together (t0.0001 g) and record the weight on your data sheet. Place the filter paper in the Buchner funnel Turm the vacuum on low and wet the filter paper with deionized water from a wash bottle Using a glass stirring rod with a on the end, contents of the 250 mL beaker onto the filter paper 8, Tum the up if the liquid through the filter paper and into the flask. Be careful not to turn the vacuum up too high for the precipitate will seep through the filter paper Continue pouring the contents of the beaker onto the filter paper. As the precipitate collects on the filter paper, it may be necessary to spread it out with your stirring rod to 10, help drain any solution trapped by the precipitate you have finished pouring the solution, remove as much as possible any ofthe remaining precipitate in the beaker with your rubber policeman. Any residual precipitate in the beaker and on the stirring rod must be washed off and on to the filter paper with water (use the deionized water sparingly. Immediately after, rinse the beaker the ll. thoroughly in sink. otherwise, the beaker will be stained. wil filter paper remain in the Buchner funnel for a couple of minutes er paper and precipitate making it easier to remove from the Buchner help dry

Explanation / Answer

Question 1.

Describe how to find the limiting reagent

We will do this via stoichiometric calculations, that is, the amount of "expected" product vs. the amount of "actual" product.

We will define the excess of the reagnet and, therefore, the limiting reactant

Question 2.

The reaction

BaCl2 + Na3PO4 --> NaCl + Ba3(PO4)2

balance

3BaCl2 + 2Na3PO4 --> 6NaCl + Ba3(PO4)2(s)

then

mmol of BaCl2 = MV = 5*0.1 = 0.5 mmol

mmol of Na3PO4 = MV = 10'*0.05 = 0.5 mmol

then

mmol of BaCl2 --> 0.5 mmol; will need --> 2/3*0.5 = 0.333 mmol of Na3PO4, which we DO have, actually in excess, with 0.50 mmol, therefore

BaCl2 is limiting reactions

3 mmol of BaCl2 = 1 mmol of Na3(PO4)

0.5 mmol of BAcl2 = --> 1/3/*0.5 = 0.1667 mmol of  Na3(PO4)

mass = mmol*MW =  0.1667*163.94 = 27.328 mg of Na3PO4 expected

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