You need to determine the mass percent of sulfate in an unknown soluble sulfate

Question

You need to determine the mass percent of sulfate in an unknown soluble sulfate salt. You have the following equipment available: electronic scale, funnel, graduated cylinder, distilled water, a ring stand, a beaker; stirring, filter paper, a drying oven. You also have a solution of 0.20 M BaCl2. A) Describe a procedure appropriate to determine the mass percent of the sulfate. B) List the experimental data that needs to be collected to determine the mass percent of the sulfate. C) List the calculations necessary to determine the mass % in the unknown. D) Could a 0.20 M solution of MgCl2 be used in place of BaCl2? Explain

Explanation / Answer

Steps/ procedure would be as follows:

1. weigh the beaker in the analytical balance and note down the readings in your notebook.

2. now accurately weigh 0.30-0.35 gm of sample in your beaker. To this add 50 ml of distilled water and few drops of 6M HCl. now mix the contents thoroughly.

3. Take the ring stand and heat the solution but not boil.

4. now, prepare 0.1 M BaCl2. take 25 ml of this using the graduated cylinder.

Now,add this solution really slowly to the contents in the beaker. this will cause the formation of precipitate. for the formation of the complete precipitate add slowly 0.1M BaCl2. now. Allow the beaker to settle down for about 20 min. if there is ny precipitate on the stirring rod, that can also be washed with the distilled water and allowed to settle.

5. now, take a filter paper, make its cone and add it to the funnel. wet it a little so that it sticks to it. leave it for sometime. now, filter the contents of the beaker. now, if there are contents left in the beaker sticking to the walls or to the stirring rod, they can be taken along on to the filter paper by using small amounts of the distilled water.

6. After the transfer is complete, gently pick up the paper, press it a little by folding its two ends and now pack it into a small package on a preheated crucible, the weight of which is already , measured when empty.

7. now heat the crucible without the lid to evaporate all the water. Once the paper is dry, heat it vigorously to char the paper. once the paper is charred further vigous heating would cause the paper to get evaporated in the form of CO2. further heating would leave only crystals in the crucible.

8. now weigh the crystals.

B) and since the precipitation reaction goes to completion, we can assume that all of the sulfate is transferred from unknown sulfate to the ppt.

Mass of sulfate in Ppt = Mass of sulfate in unknown sample

C) (mass of sulfate/initial mass of unknown ) X 100 = mass %

D) as magnesium sulfate is very soluble in water so, it cannot be used.

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