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SCIENCE EXPERIMENTS ON FILE ™ Revised Edition

The Test-Tube Mystery Valeria Alston

Topic Observing chemical reactions; using logical deduction Time 2 hours

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Safety Please click on the safety icon to view the safety precautions. The solutions must be prepared by a teacher. All solutions should be treated as if they were poisonous and corrosive. If you spill any solution on yourself, wash it off immediately with large amounts of water. Avoid inhaling fumes. Wear safety goggles, lab apron, and gloves. Clean up all residue, and containerize it for proper disposal. Dispose of all chemicals in accordance with all local, state and federal laws.

Materials spotting plate red and blue litmus paper box containing 10 dropping bottles of solutions numbered in sequence from 1 to 10. In each bottle will be a .1 M solution of one of the following compounds: Name

ammonium chloride, NH4Cl barium chloride, BaCl2 copper sulfate, CuSO4 hydrochloric acid, HCl potassium iodide, KI sodium bromide, NaBr sodium hydroxide, NaOH sodium sulfide, Na2S sulfuric acid, H2SO4 silver nitrate, AgNO3

Compound Type

salt salt salt acid salt salt base salt acid salt

Procedure 1. Your goal is to identify which solution is in each bottle. You will figure this out by testing each solution with litmus paper and by combining all possible pairs of the solutions (1 with 2, 1 with 3, etc.). After describing each reaction on the data table and thinking carefully about the facts listed later, in “What’s Going On,” you should be able to identify each solution. 2. First, put 2 drops of solution 1 in the depression of the spotting plate. Do not

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SCIENCE EXPERIMENTS ON FILE™ REVISED EDITION

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poke the end of the dropping bottle into the pool on the spotting plate. Screw the top back on the bottle tightly after you have used it. 3. Test solution 1 with red litmus paper and then with blue. Write the result in the top box on the data table. If the solution turned red litmus paper blue, write R to B. If it turned blue litmus paper red, write B to R. If there was no reaction, write NLR.

D ATA T A B L E (Litmus paper test results recorded in boxes on far right.)

Sol. #

Names of solutions

1

Keys:

Red litmus to blue – R to B Blue litmus to red – B to R No litmus reaction – NLR Color of precipitate – color PPT No reaction – NR

2

1

3

2

4

3

5

4

6

5

7

6

8

7

9

8

10

9 10 1

2

3

4

5

6

7

8

9

10

4. Wash and rinse the spotting plate. Then put 2 drops of solution 2 on the plate, test it with red and blue litmus paper, and note the results on the data table in the far right box of horizontal row 2. 5. Now combine 2 drops of solution 1 with 2 drops of solution 2 on the plate. Observe the reaction, and describe it in the box on the data table where vertical column 1 meets horizontal row 2. For example, if a white precipitate formed when you mixed the two solutions, write “white PPT.” If nothing happened, write “NR.” 6. Continue in this way until you have filled in every box on the data table. This means you will have tested each individual solution with litmus paper and will have combined all possible pairs of the solutions. Remember not to touch the top of any bottle to the plate, to wash and rinse the plate after each combination, and to screw the bottle caps on carefully after each use. 7. Compare the observations recorded on your data table with the following: a. Acids will turn blue litmus paper red. b. CuSO4 solutions are blue. c. Bases will turn red litmus paper blue. d. Acids will react with Na2S to release a gas, hydrogen sulfide, which smells like rotten eggs. It is very poisonous—be very careful. e. If a base is mixed with NH4Cl, the odor of ammonia (NH3) is given off. © Facts On File, Inc.

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SCIENCE EXPERIMENTS ON FILE™ Revised Edition

Ammonia vapor will turn damp red litmus paper blue. f. AgNO3 will react with compounds containing halogen (Br, Cl, or I) to form white or yellowish precipitates. g. BaCl2 will react with H2SO4 and CuSO4 to form a white precipitate, BaSO4. h. CuSO4 gives an orange-yellow precipitate when mixed with KI, but doesn’t give a precipitate with NaBr. i. A white cloudy precipitate, Ba(OH)2, forms when an excess of NaOH is added to BaCl2. j. HCl will react with AgNO3 to produce a white precipitate, AgCl. By using logical reasoning and the process of elimination, you should be able to identify each solution. Write its name next to its number on the data table. 8. After you have identified all the solutions, write balanced equations for each of the reactions you performed. What’s Going On

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SCIENCE EXPERIMENTS ON FILE™ REVISED EDITION

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

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silver nitrate AgNO3 sulfuric acid H2SO4 sodium sulfide Na2S sodium hydroxide NaOH sodium bromide NaBr potassium iodide KI hydrochloric acid HCl copper sulfate CuSO4 barium chloride BaCl2 ammonium chloride NH4Cl

FORMULAS

(3,1) Na2S + 2AgNO3 ➝ Ag2S + 2Na+ + 2NO3(4,1) 2NaOH + 2AgNO3 ➝ Ag20 ➝ 2NaNO3 + H2O (5,1) NaBr + AgNO3 ➝ AgBr + Na+ + NO3(6,1) KI + AgNO3 ➝ AgI + K+ + NO3(7,1) HCI + AgNO3 ➝ AgCl + H+ + NO3(8,1) CuSO4 + 2AgNO3 ➝ Ag2SO4 + Cu++ + 2NO3(9,1) BaCl2 + 2AgNO3 ➝ 2AgCl + Ba++ + 2NO3(10,1) NH4CI + AgNO3 ➝ AgCI + NH4+ + NO3(3,2) Na2S + H2SO4 ➝ H2S + 2Na+ + SO4+ 2H2SO4 ➝ S + H2SO3 + H2O + 2Na+ + SO4(9,2) BaCl2 + H2SO4 ➝ BaSO4 + 2Cl- + 2H+ (7,3) 2HCl + Na2S ➝ H2S + 2Na+ + 2Cl(8,3) CuSO4 + Na2S ➝ CuS + SO4- + 2Na+ (9,3) BaCl2 + Na2S ➝ BaS + 2Cl- + 2Na+ (8,4) CuSO4 + 2NaOH ➝ Cu(OH)2 + SO4- + 2Na+ (9,4) BaCl2 +2NaOH ➝ Ba(OH)2 + 2Cl- + 2Na+ (10,4) NH4CI + NaOH ➝ NH3 + H2O + Na+ + Cl(8,6) 2CuSO4 + 4KI ➝ 2CuI + 4K+ + 2SO4- +I2 (9,8) BaCl2 + CuSO4 ➝ BaSO4 + Cu++ 2Cl-

Note: (3,2) and (8,6) give two results on table; (3,2) requires two equations to explain the results. (8,6) gives both results in one equation. Connections Chemists, like detectives, attempt to identify unknowns through a process of careful and creative analysis. This often involves observing reactions of unknown substances and comparing them with reactions of known substances. In this experiment, you have tried to identify 10 different chemical compounds by reacting them with each other, observing the results, and comparing the results with the known characteristics of some common chemicals.

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Safety Precautions READ AND COPY BEFORE STARTING ANY EXPERIMENT

Experimental science can be dangerous. Events can happen very quickly while you are performing an experiment. Things can spill, break, even catch fire. Basic safety procedures help prevent serious accidents. Be sure to follow additional safety precautions and adult supervision requirements for each experiment. If you are working in a lab or in the field, do not work alone. This book assumes that you will read the safety precautions that follow, as well as those at the start of each experiment you perform, and that you will remember them. These precautions will not always be repeated in the instructions for the procedures. It is up to you to use good judgment and pay attention when performing potentially dangerous procedures. Just because the book does not always say “be careful with hot liquids” or “don’t cut yourself with the knife” does not mean that you should be careless when simmering water or stripping an electrical wire. It does mean that when you see a special note to be careful, it is extremely important that you pay attention to it. If you ever have a question about whether a procedure or material is dangerous, stop to find out for sure that it is safe before continuing the experiment. To avoid accidents, always pay close attention to your work, take your time, and practice the general safety procedures listed below. PREPARE

• Clear all surfaces before beginning work. • Read through the whole experiment before you start. • Identify hazardous procedures and anticipate dangers. PROTECT YOURSELF

• Follow all directions step by step; do only one procedure at a time. • Locate exits, fire blanket and extinguisher, master gas and electricity shut-offs, eyewash, and first-aid kit. • Make sure that there is adequate ventilation. • Do not horseplay. • Wear an apron and goggles. • Do not wear contact lenses, open shoes, and loose clothing; do not wear your hair loose. • Keep floor and work space neat, clean, and dry. • Clean up spills immediately. • Never eat, drink, or smoke in the laboratory or near the work space. • Do not taste any substances tested unless expressly permitted to do so by a science teacher in charge. USE EQUIPMENT WITH CARE

• Set up apparatus far from the edge of the desk. • Use knives and other sharp or pointed instruments with caution; always cut away from yourself and others. • Pull plugs, not cords, when inserting and removing electrical plugs. • Don’t use your mouth to pipette; use a suction bulb. • Clean glassware before and after use. • Check glassware for scratches, cracks, and sharp edges. • Clean up broken glassware immediately. v © Facts On File, Inc.

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Safety

SCIENCE EXPERIMENTS ON FILE™ REVISED EDITION

• Do not use reflected sunlight to illuminate your microscope. • Do not touch metal conductors. • Use only low-voltage and low-current materials. • Be careful when using stepstools, chairs, and ladders. USING CHEMICALS

• Never taste or inhale chemicals. • Label all bottles and apparatus containing chemicals. • Read all labels carefully. • Avoid chemical contact with skin and eyes (wear goggles, apron, and gloves). • Do not touch chemical solutions. • Wash hands before and after using solutions. • Wipe up spills thoroughly. HEATING INSTRUCTIONS

• Use goggles, apron, and gloves when boiling liquids. • Keep your face away from test tubes and beakers. • Never leave heating apparatus unattended. • Use safety tongs and heat-resistant mittens. • Turn off hot plates, bunsen burners, and gas when you are done. • Keep flammable substances away from heat. • Have a fire extinguisher on hand. WORKING WITH MICROORGANISMS

• Assume that all microorganisms are infectious; handle them with care. • Sterilize all equipment being used to handle microorganisms. GOING ON FIELD TRIPS

• Do not go on a field trip by yourself. • Tell a responsible adult where you are going, and maintain that route. • Know the area and its potential hazards, such as poisonous plants, deep water, and rapids. • Dress for terrain and weather conditions (prepare for exposure to sun as well as to cold). • Bring along a first-aid kit. • Do not drink water or eat plants found in the wild. • Use the buddy system; do not experiment outdoors alone. FINISHING UP

• Thoroughly clean your work area and glassware. • Be careful not to return chemicals or contaminated reagents to the wrong containers. • Don’t dispose of materials in the sink unless instructed to do so. • Wash your hands thoroughly. • Clean up all residue, and containerize it for proper disposal. • Dispose of all chemicals according to local, state, and federal laws. BE SAFETY-CONSCIOUS AT ALL TIMES

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