Assignment 4 Chemical Detectives at the Molecular Level LO: To explain the differences between chemical and physical changes through observable evidence. EQ: What evidence can be used to tell the difference between chemical and physical changes. AGENDA 1. Discuss lab 2. Lab 3. Reading LEVEL ZERO VOICE CATALYST (10 minutes, individual work): 1. Counting atoms HOMEWORK 1. Finish processing tasks 2. Define: endothermic exothermic physical change chemical change
Class discussion: How do you know when a chemical reaction has taken place?
Guiding Question: How can I explain the differences between a chemical change and a physical change through observable evidence? You will be observing several ways in which matter interacts. Your task is to collect evidence to prove whether the interaction demonstrates a physical change or a chemical change.
Now you will be testing the following compounds Sugar C 12 H 22 O 11 Wax C 31 H 64
Sugar Cubes Rows (1-3) Write observations
Row 1: Crush sugar https://www.youtube.com/watch?v=qcfevnaigum
Row 2: sugar in water https://www.youtube.com/watch?v=qc1z84mdkxe
Row 3: burning sugar https://www.youtube.com/watch?v=8gvyaaxkjd4
Row 4: melt wax https://www.youtube.com/watch?v=lk-vmxg0gjs
Row 5: burn candle wick https://www.youtube.com/watch?v=b-ajhrtiwg0&disable_polymer=true
Now you will be testing the following compounds Vinegar (acetic acid) C 2 H 4 O 2 Citric acid C 6 H 8 O 7 Baking soda (sodium bicarbonate) NaHCO 3 Cornstarch C 6 H 12 O 5 Iodine solution I 2 Washing soda (sodium carbonate) Na 2 CO 3
Lab safety: These are all household chemicals that you don t need gloves to handle but you do need goggles because they can t get in your eyes. Do not get on your skin. Do not ingest. Proper smelling technique
¼ spoonful of solids 2 droppers for liquids Swirl Observe: bubbles, form solid, smell, color change Vinegar (acetic acid) C 2 H 4 O 2 Citric acid C 6 H 8 O 7 Baking soda (sodium bicarbonate) NaHCO 3 Cornstarch C 6 H 12 O 5 Iodine solution I 2 Washing soda (sodium carbonate) Na 2 CO 3
Lab safety: These are all household chemicals that you don t need gloves to handle but you do need goggles because they can t get in your eyes. Do not get on your skin. Do not ingest. Proper smelling technique
Reaction observations for iodine: Iodine/citric acid: clump together, no reaction Iodine/baking soda: no reaction Iodine/cornstarch: changes color, turns black
We will use the following mixture to highlight what happens at the molecular level: citric acid and washing soda.
The mixture between citric acid (C 6 H 8 O 7 ) and washing soda (Na 2 CO 3 ) showed evidence of a chemical reaction. Scientists write chemical reactions as equations to show what happened before and after. It makes carbon dioxide, water, and trisodium citrate. Write the chemical equation and label each item with its name (found above): C 6 H 8 O 7 + Na 2 CO 3 CO 2 + H 2 O + Na 3 C 6 H 5 O 7
C 6 H 8 O 7 + Na 2 CO 3 CO 2 + H 2 O + Na 3 C 6 H 5 O 7 Reactants Products
Before chemical reaction
After chemical reaction
Processing Task Cl.Ev.Re.: Prove how you know the citric acid and washing soda mixture produced a chemical change with evidence and reasoning. Make sure you include the what happens at the molecular level. You may include labeled diagrams, but you need to explain your ideas in words as well. Claim: Write your claim. (chem rxn?) Evidence: What is your evidence to support your claim? State evidence without reasoning. List lines of evidence. Reasoning: Explain why your evidence supports your claim.