Mystery Powder Lab

Mystery Powder Lab Purpose To identify the components of an unknown mixture, based on the results of individual tests of each unknown, and to identify chemical changes. Materials Unknowns Water Spot plates Aluminum foil Hot plate Scoopula Universal indicator Vinegar Iodine solution Tongs Stirring rod Procedure: Perform all tests on all of the unknowns including the mystery powders. Record your observations in both Chart 1: Qualitative Observations and Chart 2: Chemical/Physical Change on the back of this page. 1. 2. 3. 4. 5. 6. Observe the physical properties of the unknown powders and record in the chart. Mix a very small amount of each unknown in water. Observe whether the unknowns dissolved in water (if the solution becomes clear). Record in the chart. Place a small scoop of each unknown in a pre-made aluminum foil cup and heat on high on a hot plate for 3 minutes. Record your observations in the chart. Add two drops of Universal Indicator to a small sample or each unknown. Record. Add two drop of iodine solution to a small sample of each unknown. Record. Add a few drops of vinegar to a small sample of each unknown. Record. Questions Record your answers in FULL SENTENCES on a separate piece of paper. Hand in this sheet and your questions next day. 1. Explain the difference between a chemical and physical change. The difference between a chemical and a physical change is whether or not a new substance is formed. In a physical change, the change is most of the time only a change in appearance or a change of state. A chemical change is when two substances form to make something new. 2. For unknown D, explain the results of each test, including what you saw and whether what you saw was a chemical or physical change. The results of the first test showed the appearance of the powders. This specific one is very powdery and thick however; it was finer than some of the other powders. It is smooth, a bit heavier and the colour is not a pure white, but more of an off white. The next test was, dissolving the powder in water. This powder easily dissolved and caused the water to become thick and milky. The test only changed the state/ appearance of the powder, so this test was a physical change. The third test we preformed was to heat the powder in an aluminum foil cup, on a hot plate. The mystery powder D turned slightly brown, mainly at the bottom of the cup, which is a sign it was most likely burning. This test represents a chemical change because the state does not change, but the colour does. It is burning and creating smoke. Next, we added the universal indicator to the powder, and it caused the powder to go a light, pale yellow, and it became thicker. This is also a chemical change, which is easily identified because the colour changed. The next test we preformed was with the iodine solution. After only putting one drop into the powder, it turned very hard, thick and sticky, similar to playdough. Since only the texture/ appearance changed, this is a physical change. Finally, we added vinegar to the powder. This made the powder foam however, it went away after a minute. This test was a chemical change. 3. Based on your results identify which two powders make up Mystery Powder X and which two powders make up Mystery Powder Z? Looking just at the physical appearance of the powders, my partner and I could make a prediction of what two powders make up the mystery x and z. By taking a close look at the texture and size of the different powders we thought that X was made up of powder E and C and mystery powder Z, was made of B and D. After preforming the different tests, we could confirm those predictions. We looked at how the mystery powders X and Z reacted to the substances we added and how those results related to the reactions of the other single powders. One of the biggest hints was what mixture of colours are in X and Z. 4. Explain any experimental sources of error from this lab (where could you have possibly made a mistake?) During this experiment, my partner and I noticed some mistakes we may have done. Sometimes, when we were scooping the powders into the spot plates, we dropped some of one powder into another spot, causing the powders to mix. This may have affected the results even after we tried to separate the powders into their correct spot. Chart 1: Qualitative Observations Test A B C Appearance Small Grainy, Chunky, pieces, tiny darker thick, crystals, white, smooth, grains, shiny, light, pure rough, bigger white, circle in crystals sticks to center the sides D Powdery, thick, finer, off white, weight, smooth E Tiny, tiny crystals, fine, pure white, smooth, grainy, a bit shiny, choppy Mystery X Fine powder, pure white, choppy E&C Mystery Z Powdery, shiny, off white, chunky, sticks to sides, grain B&D Dissolves in Water No No Yes Yes Yes Half Yes Heated in Aluminum foil Does not change colour Turns brown/ orange Bottom turns brown Burnt light brown Does not change colour Turns light orange/ yellow Universal Indicator Bright yellow yellow Pale yellow Light yellow Dark green Outside turns slightly yellow green Iodine Solution No change Stuck to sides Harder, thicker hardness Sticks to sides, crunchy Smooth, pasty Vinegar Sticks to sides No reaction Powder sunk to bottom A bit of foam Bubbly Sunk to bottom, bubbles Liquid/ smooth at first, turns crumbly Lots of foam/ bubbles E physical Mystery X physical Mystery Z physical Chart 2: Identifying Chemical and Physical Changes Test A B C D Dissolves in Physical physical physical physical Water Yellow Heated in Aluminum foil Universal Indicator Physical chemical chemical chemical physical chemical chemical chemical chemical chemical chemical chemical chemical chemical Iodine Solution physical physical physical physical physical physical physical Vinegar physical physical physical chemical chemical chemical chemical