Observations: (could be called “results” – don’t explain anything) Change # Summary Description Before Change Description Of Change Magnesium ribbon (MGM) added to hydrochloric acid (HCI) MGM – solid, metal, grey medium luster, malleable, ductile, opaque HCI – liquid, transparent, colorless, low viscosity, odorless Test tube felt warm bubbles 2 Burning splint placed near mouth of test tube MGM ribbon disappearing Liquid is still colorless and clear Bubbles still rising through liquid. “pop” sound when burning splint placed near mouth of test tube 3 Copper (II) sulfate (Cuscus) added to water
Cuscus – solid, blue, powder, odorless, opaque Water – liquid, colorless, transparent, low viscosity, odorless Cuscus dissolved in the water and created a blue solution (transparent, blue, low viscosity) 4 Steel wool added to Cuscus Steel Wool – solid, grey, metal, ductile, medium luster Cuscus – liquid, blue, transparent, low viscosity Dark red solid appears as steel wool disappears Solution in test tube turns greenish blue (still transparent, low viscosity) 5 Add sodium hydroxide (Noah) to test tube from change 4 NEXT, add hydrochloric acid (HCI) Test tube has greenish blue, transparent, liquid
Noah – liquid, transparent, colorless, low viscosity, odorless HCI – liquid, transparent, colorless, low viscosity, odorless AFTER Noah – when Noah drops hit the greenish blue solution, brown precipitate formed AFTER HCI – brown precipitate disappeared and solution became colorless and transparent 6 L uric acid (C12H2402) is heated and then cooled L uric acid – solid, white, powdery, opaque, brittle, flowery dour When HEATED – turned into a colorless, transparent, low viscosity, liquid, which smelled like soap When COOLED – turned into a white, opaque, brittle, solid that smells like soap
Analysis: (could also be called “discussion” – explain results) Part 1 : Textbook Questions and Answers (See “Nelson Science Perspectives 10” page 181) a) The following table classifies each change as either physical or chemical and justifies why based on the observations: Type of Change Justification Chemical Increased temperature and bubbles/new gas “Pop” showed evidence of hydrogen gas present 3 Physical Solid dissolving in a liquid 4 New color of the solution (greenish-blue) and new color solid (reddish-brown) appeared 5 Brown precipitate formed when Noah added, then disappeared when HCI added
Melting and freezing (change of state) b) Change 6 was the most difficult to classify because when I saw the solution go back to a solid, it looked a little different than it started, it wasn’t powdery anymore, so I thought at first maybe a new substance was created. But then I heated it up again and realized that it was definitely just a change of state that was happening in change 6. C) One example from my everyday life when a physical change is reversible is when I boil water on the stove in a pot.
The liquid water turns into a gas as it boils, but when the gaseous water hits the lid of the pot, it condenses and turns jack into liquid water. One example from my everyday life when a physical change is NOT reversible is when I chop up carrots for dinner. After chopping them I can’t put them back together, so the physical change is irreversible. D) The chemical change in this activity that was reversible occurs in change 5. A brown precipitate was formed when Noah was added in change 5.
Then when HCI was added in the second part of of change 5, the precipitate disappeared. Therefore a new substance was created (chemical change) and when HCI was added that chemical change was reversed (the precipitate disappeared)! In order to reverse this change again (and create the precipitate once more) you could add more of the Noah, which created the precipitate in the first place. E) When I heard the “pop” sound in change 2, it showed that hydrogen gas was present.
This is obvious because the starting reactants were MGM and HCI, so if a gas was created, and elements can’t just magically appear, then it must have been H that turned into a gas. We know it wouldn’t have been CLC because that gas is deadly and wouldn’t be created in a science classroom! Part 2: SOUrces of Error There are sources of error in this lab, meaning there are parts of the procedure where errors could occur, and thus create errors in the observations and results.
Sources of error in this lab include the following: Source of Error Amount of hydrochloric acid added to test tube Amount of magnesium ribbon added to the test tube Trouble lighting the Bunsen burner could create a problem because all of the gas from the test tube could escape before you get the burning split to the mouth of the test tube 3 Amount of water added to the test tube Amount of copper(al) sulfate added to the water
Some solution could spill if the test tube stopper wasn’t in properly 4 Size of steel wool ball added Some solution could spill if the test tube stopper wasn’t in properly Not waiting long enough for the new reddish-brown solid to form and to settle in the test tube 5 Amount of sodium hydroxide added to test tube Adding enough hydrochloric acid to make the brown precipitate disappear 6 If water wasn’t warn enough the Laurie acid wouldn’t melt If the cool water was too warm the Laurie acid wouldn’t solidify again Conclusion: In conclusion, this lab allows you to collect evidence and use that evidence to lassies each of six changes.
There are pieces of evidence that can suggest either a chemical or a physical change. For example in this lab, the following clues suggested a chemical change: bubbles/gas produced, heat produced, color change, and precipitate formed. The following clues suggested a physical change: dissolving and change of state. My hypotheses were all correct. Change 1 was a chemical change, change 2 was a chemical change, change 3 was a physical change, change 4 was a chemical change, change 5 was a chemical change, and change 6 was a physical change.