Separation of a Mixture of Solids

PURPOSE The purpose of this experiment is to become familiar with the separation of mixtures of solid and learn separation techniques based on the chemical properties of a substance. PROCEDURES 1. Separating out the Iron a. Use your digital scale to determine the mass of your weighing dish. b. Empty the entire mixture of solids from the plastic bag into the weighing dish and determine the gross mass of the total mixture and weighing dish. Compute the net mass of the mixture: this is equal to the gross mass of the weighing dish with the mixture less the mass of just the weighing dish determined in 1-A. c.

Spread the mixture into a very thin layer over a full sized piece of paper. d. Cut a second piece of paper into a 10-cm square. Weigh and record its mass and set it aside. e. Wrap a small square of clear plastic over the magnet. Remove the iron powder/filings by passing the magnet closely over the surface of the entire mixture. Repeat several times to make sure you’ve collected all the iron. f. Holding the magnet over the 10-cm square of paper, carefully remove the plastic and allow all the iron to fall onto the paper. Weigh and determine the net mass of the iron powder/filings. 2. Separating out the Sand a.

Put the remaining mixture, containing sand, benzoic acid, and table salt into your beaker and add 50 mL of distilled water. b. Set up the beaker stand and burner fuel and heat the beaker of solids and water to near boiling. Stir the mixture to make sure all soluble material dissolves. At this point, the benzoic acid and the sodium chloride should have dissolved and been extracted from the insoluble sand. c. Decant (pour) the liquid while it is hot into a small paper or Styrofoam® cup. d. Pour another 10 to 15 mL of distilled water into the beaker containing the sand, bring the mixture to a boil, and decant again into the same cup used in 2-C.

This assures that any remaining salt and benzoic acid is removed from the sand. e. Make an ice bath by placing a small amount of crushed ice and tap water into a coffee cup or similar container that is large enough to hold your paper cup of benzoic acid and salt solution. Make sure the ice bath level is higher than the solution level but low enough so that no additional water can pour into the solution cup. f. Place the cup containing the water solution of benzoic acid and salt into the ice bath. Observe the benzoic acid crystallizing out of the solution as it cools. Set this water bath assembly aside until the next section. g.

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Heat the sand in the beaker over low heat until the sand is completely dry. Sand has a tendency to splatter if heated too rapidly. The possibility of sample loss can be reduced by covering the beaker with a small saucer and heating it very slowly. You might accomplish this also by placing the beaker in a warm oven. Alternatively, you may dump the wet sand onto a double layer of paper towels and let it air-dry. h. When the sand is completely dry allow the beaker to cool to room temperature. i. After the sand and any paper towels used are completely dry transfer the sand to a weighing dish of known mass and determine the net mass of the sand. . Separating out the Benzoic Acid: a. The benzoic acid crystals from Step 2-f above can be separated out by filtration. Use the following instructions to set up a filtration assembly: i. Weigh a paper cup and record the weight (mass). ii. Set the paper cup inside a slightly larger coffee cup or similar container to give the paper cup support and prevent it from tipping over when you add a funnel. iii. Fold a sheet of filter paper in half and then in half again as illustrated. Weigh it. iv. Open one section of the folded filter paper as shown in the bottom illustration. . Place the opened filter paper into the funnel and the funnel into the paper cup supported by the coffee cup. b. Remove the paper cup of salt and benzoic acid crystals from Step 2f from its ice bath. Fill a graduated cylinder with about 5 mL of distilled water and place the cylinder in the ice bath to chill the distilled water. c. Swirl the cup containing the salt and benzoic acid crystals to dislodge any crystals from the sides. Then, while holding the filter paper in place and open, pour the contents of this cup into the filter paper-lined funnel. d.

After the sodium chloride solution has fully drained through the filter paper, slowly pour 2 to 5 mL of chilled distilled water around the inside surfaces of the filter paper-lined funnel to make sure all the sodium chloride has been removed from the benzoic acid crystals. e. After all the liquid has drained from the funnel lay the filter paper containing the benzoic acid crystals on folded layers of paper towels and put this someplace where it will not be disturbed while the filter paper and its contents air dry. Depending upon the humidity in your area this can take several hours or days. . When the filter paper containing the benzoic acid crystals is completely dry, weigh it and subtract the weight of the filter paper to obtain the net weight of the benzoic acid crystals. 4. Separating out the Salt a. Remove the funnel from the above filtration assembly and set the paper cup of sodium chloride solution someplace where it will not be disturbed while the water evaporates. Depending upon the humidity in your area this might take several days. When all the water has completely evaporated only sodium chloride will be left in the paper cup. b.

Weigh the paper cup with the dried salt crystals inside and then subtract the weight of the cup to get the net weight of the table salt. c. Prepare a data table listing the various components of the mixture and record both their masses in grams to at least 1 decimal place, (i. e. , 0. 1 or 1/10th of a gram) and their percentage of the total mixture. 5. Cleanup: Thoroughly clean, rinse, and dry all equipment and return it to the LabPaq. Throw all used paper cups and paper towels in the trash. OBSERVATIONS, DATA, AND CALCULATIONS Part 1 Mass of weighing dish = 0. 5g Total mixture = 7. 5g Net mass of mixture =6. g Piece of paper =0. 8g Iron fillings + paper =2. 7g Net mass of Iron fillings = 1. 9g Part 2 Net mass of sand =2. 0g Part 3 Paper cup mass =6. 2g Filter paper =1. 0g Filter paper + benzoic acid =2. 7g Net mass of benzoic acid =1. 7g Part 4 Paper cup + salt =7. 1g Net mass of salt =0. 9g Data Table 1: Experiment Data GramsPercent of mixture Iron filings1. 927. 94 % Sand2. 029. 41 % Table salt0. 911. 76 % Benzoic acid1. 725. 00 % Total6. 595. 59 % QUESTIONS A. How did your proposed procedures or flow charts at the beginning of this experiment compare to the actual procedures of this lab exercise?

It was similar to the procedure described. The only difference was the last step when separating out the Table Salt. I had proposed that we would have to heat the mixture instead of letting it evaporate. B. Discuss potential advantages or disadvantages of your proposed procedure compared to the one actually used. If heated, the salt and water mixture would not have formed any crystals and there would be a chance of losing salt with the excessive heat. C. How would you explain a sand recovery percentage that is higher than the original sand percentage?

It would be explained by the possibility of some iron fillings, benzoic acid, or salt remaining in the sand and not separated properly. D. What were potential sources of error in this experiment? First, there were always remains that did not properly detach from the beaker or the stirrer. This occurred especially when separating out pure sand. Second, there is a possibility that some salt remained with the benzoic acid crystals and did not filter through the filter paper causing the mass of benzoic acid to be higher than expected and causing the mass of salt to be lower than expected.

CONCLUSIONS This experiment was designed to teach separation of mixtures of solid and learn separation techniques based on the chemical properties of a substance. It utilized several techniques such as filtration, evaporation, crystallization, and separation. Overall, the experiment was very interesting; however, it was challenging at times. The salt water solution at the end took a very long time to fully evaporate and the masses did not add up to the total original mass indicating a loss of substance at some point in the experiment.

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