Activity 38 Follow-up: Based on your observation in Activities 37 & 38, what do you think determines how much of a substance dissolves? The identity of the solvent and solute determine whether some dissolving is going to occur. How much dissolves or whether the solution becomes saturated depends on the relative amounts of solvent & solute.

Activity 45: Precipitating Specific Contaminants

Signs of a chemical reaction: Color change (of a solution) Energy change (temperature change, light, or generation of electricity) Odor change Disappearance of an original substance (reactant consumption) Formation of bubbles (gaseous product) Formation of a precipitate (solid product) Change in the results of a chemical test (such as a pH change detected with an indicator)

Reactants and Products Reactants  Products Reactants go into the reaction Products come out of the reaction

Read C-78 Challenge Question: How can you use a chemical reaction to remove a contaminant from a solution?

Procedure: Step 1: Create Liquid following chart into SEPUP Cup A Step 2: Record Observations Step 3: Filter solution through filter paper Step 4: Wait until all liquid goes through filter paper. Step 5: Record observations Filter paper (What do you see on paper?) Filtrate (liquid that went through)

Step 6: Test Filtrate (Add 10 drops of Sodium Carbonate  If something happened, does filtration method work?) Step 7: Record Observations of Filtrate 1 Drop – (what happened?) 2 Drops – (What happened?) 3 Drops – (What happened?) … Repeat for the other three liquids…

Student Sheet 45.1, “A Precipitation Reaction” Filter paper - fold and moisten with water Test 1 = Cup A, Test 2 = Cup B, etc. Test of Filtrate: Added 10 drops of sodium carbonate one at a time Filtrate: liquid that leaks down

Results Test 1: Not all contaminant has precipitated because there is blue solution remaining around the edges of the precipitate. Test 2: Not all contaminant has precipitated, but more than Test 1. Test 3: Not all contaminant has precipitated, but more than Test 2. Test 4: All of the contaminant has precipitated because there is no blue solution remaining; there is only solid blue precipitate present.

Analysis Question #1 What was the contaminant in this activity? Copper Chloride

Analysis Question #2 What evidence indicates that a chemical reaction occurred when you mixed solutions of sodium carbonate and copper chloride? There is a color change and the appearance of a new solid material or precipitate.

Analysis Question #3 a.Where did the solid that appeared come from? It is a precipitate formed in a chemical reaction. b. Why does the precipitate get stuck in the paper? It is an undissolved solid. It is insoluble. c. What properties do all solid precipitates that settled to the bottom when two solutions are mixed have? Slightly soluble in the surrounding liquid (they appear as solids and do not remain dissolved). The solids settle to the bottom which indicates that they must be more dense than the liquid.

Analysis Question #4 Describe two ways the control in Test 1 helped you analyze the data. –It was used for comparison to help determine if all of the contaminant had precipitated out.