Physical and Chemical Changes Lab Takeup Intro to the lab • Purpose: To observe changes and determine whether they are physical or chemical changes. • Hypothesis: If a chemical change is observed, one or more of the five clues for a chemical change will be observed, because these are clues that a new substance has been produced. Expected Results Step Before During and After Physical or Chemical? 1 -Copper penny, shiny -Nitric acid, clear colourless liquid. Vigorous bubbling, reddish brown gas produced. Nitric acid begins to turn deep blue/green colour. Chemical. (gas produced, colour change) 2 -Water, clear colourless liquid Water boiled, some condensed on the watchglass, steam produced. Physical (change of state). 3 -Magnesium, metal, malleable, somewhat dull. Sparks, then a bright flame. Chemical (colour White powder left over change, heat and after reaction. light produced). 4 -Potassium iodide, transparent solution, slight yellow colour. -Lead nitrate, clear colourless solution. Yellow precipitate produced instantly. Chemical (precipitate, new colour). Expected Results Substance Colour and Form Solubility Fusibility Sucrose Fine powder, crystalline, white solid Dissolves in water, some powder remained at bottom of test tube. Melts, then caramelizes in tray. Calcium Shiny metal, small lump Vigorous reaction with water. Bubbles produced, along with a white precipitate. Does not melt easily. Conclusion • Several changes were observed. The reactions in steps 1, 3 and 4 were chemical changes. They all displayed one or more of the 5 clues for a chemical change as predicted in my hypothesis. The change observed in step 2 was a physical change, as it did not display these clues. It was easily reversed during the experiment. Conclusion continued • In the second part of the lab, a couple of unexpected chemical changes occurred. • Solubility is a physical property, however calcium underwent a chemical reaction with water. • Melting, which is also supposed to be a physical change, was accompanied by a smell and colour change, indicating that the sugar had a chemical reaction with the air. Sources of Error • Observations made are subjective. One person may classify a physical change as chemical because of the gas bubbles produced. An improvement to this would be to direct the experimenter to observe reversibility in the procedure. • (I’ll be honest, since there is not a lot of measurement in this lab errors are difficult to find). Questions • This is where I would answer analysis questions from the lab (if there were any) Class questions? • You might want to look in to questions that the class might have. Be creative, and try to think of anything you might get asked. • Ex: What was the yellow precipitate in Step 4? – Lead (II) iodide was formed in a double displacement reaction. • Ex: Why did calcium produce a precipitate in water? – Calcium displaces hydrogen from water, producing calcium hydroxide, which does not dissolve. • Ex: Would the hydrogen “pop” if set alight? – Yes, hydrogen is explosive.