Introduction: Equation Writing and Predicting Products Chemistry I Acc If you examine your bicycle after it has been left out in the rain a number of times you will find that it has begun to rust. Rust is a slow chemical reaction of the iron in the bicycle with oxygen. If a piece of sodium is put in water, a much more rapid chemical reaction occurs. Sodium reacts with water to produce sodium hydroxide and hydrogen gas. During this reaction, enough heat is liberated to ignite the hydrogen gas, causing it to explode. Chemists observe what is happening in a chemical reaction and try to describe it in language that is clear and simple. A chemical equation uses formulas and symbols to describe the substances involved in a reaction, the physical state of the substance, the use of a catalyst, and relative proportions. The general form of an equation is: Reactants --------> Products In this investigation, you will perform a series of reactions and make careful observations of the changes that occur. Using simple tests and your knowledge of chemistry, you will determine the identity of the products. With this information, you will write and balance chemical equations to describe the reactions. Materials goggles lab burner crucible tongs magnesium ribbon watch glass 6 test tubes triangular file glycerin wooden splints copper strip bent glass tube rubber tubing cobalt chloride paper test tube tongs graduated cylinder manganese(iv) oxide (MnO 2 ) potassium iodide (KI) 0.1M lead(ii) nitrate (Pb(NO 3 ) 2 ) 0.1M limewater (Ca(OH) 2 solution) copper(ii) carbonate (CuCO 3 ) one-hole rubber stopper ammonium carbonate ((NH 4 ) 2 CO 3 ) hydrogen peroxide (H 2 O 2 ) 10% solution Safety Warnings Wear your goggles at all times during this investigation. Avoid looking directly at the burning Magnesium. The bright light could seriously damage your eyes. Tie back loose hair. Hydrochloric acid is corrosive. Avoid direct contact with it. If you get some on your skin, immediately wash it off with copious amounts of water. Ammonia is a skin and respiratory irritant so avoid inhaling it deeply. Lead compounds are poisonous so be sure to avoid contact with skin. If contact occurs immediately wash it off with copious amounts of water and inform your teacher. Glass tubing breaks easily. Exercise caution when working with it and use glycerin. Procedure: 1. Put on your goggles and wear them throughout the lab. For each of the reactions, record your observations in the data table. Observations should include any evidence that a chemical reaction has taken place; the results of any test performed on any gases produced; the appearance of the products; and any other relevant data. 2. Obtain a 2 cm long piece of Mg ribbon. This length is approximate. The exact size is not important. Holding the Mg ribbon with the crucible tongs, carefully light the ribbon with the lab burner. Once lit hold the Mg ribbon over a watch glass to collect any ash and debris. When the Mg is done burning turn off the burner. CAUTION: Make sure hair is tied back. The tongs will be hot even after the Mg has finished burning. Do not touch them for at least five minutes. Place them on the watch glass to cool. Do not look directly at the Mg while it burns.
3. Read steps 3 and 4 completely before starting step 3. Place a medium test tube in a test-tube rack. Have a second test tube of the same size ready in a pair of test-tube tongs. Add 2 fingers worth of 3.0M hydrochloric acid (HCl) to the first test tube. Drop a 2-cm piece of Mg into the acid. Again, the length is approximate. The exact size is not important. CAUTION: Hydrochloric acid is corrosive. Avoid spills and splashes. If you do spill acid immediately rinse the area with plenty of water and notify your teacher. 4. Invert the second test tube over the mouth of the first test tube. When the reaction appears to have ended, light a wooden splint and quickly test the collected gas for flammability by holding the test tube and inserting the burning splint into the mouth of test tube #2. CAUTION: The gas in the test tube will make a LOUD popping sound, do not be startled. 5. Obtain a copper strip. Scratch it with the triangular file. Light the lab burner. Grasp the piece of copper with the crucible tongs and heat it in the burner until it blackens. Remove from the flame and allow it to cool. Try now to scratch the blackened part with the file. 6. Carefully place about one heaping spatula in of ammonium carbonate ((NH 4 ) 2 CO 3 ) in a medium test tube. CAUTION: The odor produced in this reaction is quite noxious. Make sure to only waft and not inhale directly. The gas coming from the tube is a respiratory and skin irritant, so avoid inhaling it deeply. Hold the test tube with test tube tongs and slowly heat the test tube by placing it in the flame for a few seconds and then removing it for a few seconds. Continue heating in this manner for a total of about 1 minute. As you heat the solid carefully waft the air towards your nose to detect any odor. CAUTION: When heating the test tube, make sure the open end points away from any person. After you have detected the odor continue to heat the test tube in the fume hood. Place a burning wooden splint in the mouth of the test. Finally, as the heating continues, place a piece of Cobalt chloride paper just inside the mouth of the test tube. Put the test tube in the rack to cool. Turn the burner off. 7. Place approximately two fingers of 10% hydrogen peroxide (H 2 O 2 ) into a medium test tube. Add a small amount of (about the tip of a spatula or wooden splint) of Manganese(IV) oxide (MnO 2 ) to the hydrogen peroxide. Then wait ten minutes. Light a wooden split and allow it to burn for a few seconds. Then blow out the flame and quickly place the glowing embers halfway into the test tube to see if they relight. Do not stick the splint in the liquid. 8. Place two drops of potassium iodide solution, KI, into a small test tube. Add two drops of lead nitrate solution, Pb(NO 3 ) 2. CAUTION: Lead compounds are poisonous so be sure to avoid contact with the skin. If contact occurs, immediately wash the area with plenty of water and inform the teacher. Clean up all spills immediately. 9. Assemble the one-hole stopper, with the glass elbow in the stopper and attach the rubber tubing to the glass tube. CAUTION: Glass tubing breaks easily. Exercise caution when working with it. Use glycerin as a lubricant. Place one heaping spatula of copper carbonate CuCO 3 in an extra large test tube. Prepare a second medium sized test tube with three to four fingers of limewater. Light the lab burner. Holding the test tube containing the Copper carbonate with the test tube tongs, heat the copper carbonate. As the copper carbonate is heated place the rubber tubing into the test tube with the limewater. The open end of the rubber tubing must be submerged in the limewater so the gas produced by heating the copper carbonate can bubble through the limewater. Record any change you observe with the copper carbonate or the limewater. 10. Clean up your work area and wash your hands before leaving the laboratory.
Chemistry I Acc Pre-Lab Name Equation Writing and Predicting Products Read the entire laboratory assignment and the relevant pages in your textbook. Answer all pre-lab question before beginning the lab. 1. What constitutes a positive test for each of the following gases? a. oxygen b. hydrogen c. carbon dioxide d. water vapor e. ammonia 2. What is the proper way to small a substance in the lab? Why should care be taken when smelling a gas such as ammonia? 3. What is the role of a catalyst in a reaction? How can you tell when a substance serves as a catalyst? 4. One way to identify limestone (Calcium carbonate - CaCO 3 ) is to drop a small amount of hydrochloric acid on it. A positive test results in a fizz of carbon dioxide being produced. Predict the other two products and balance the equation. Data and Observations Data Table 1 Reaction Write observations of reaction here burning of Mg Mg and HCl
Reaction Write observations of reaction here Burning Cu Heating Ammonium Carbonate Hydrogen peroxide plus the catalyst manganese dioxide KI and Pb(NO 3 ) 2 Heating Copper Carbonate Analysis and Synthesis 1. Write a balanced equation for each reaction performed. Include the physical state of each substance. a. b. c. d. e. f. g.
2. Classify each of the reactions as direct combination, decomposition, single replacement or double replacement. a. b. c. d. e. f. g. 3. Limewater is an aqueous solution of Ca(OH) 2. What is the cloudy white precipitate that forms with carbon dioxide gas. Write a balanced chemical equation for this reaction. 4. A positive test for hydrogen was the pop test. What category of chemical reaction was occurring? Write a balanced chemical equation to represent this reaction. 5. For each of the following situations, determine the identity of the gas produced from the information given and write a balanced chemical equation that represents the reaction. a. When potassium bromate (KBrO 3 ) is heated it decomposes into potassium bromide and a gas that reignites a glowing splint. b. Sodium metal reacts violently with water to produce sodium hydroxide and a gas that pops in the presence of a burning splint.
c. The recipe for the volcanic eruption used in many science projects is the reaction of baking soda (NaHCO 3 ) and vinegar (CH 3 COOH). When these compounds are mixed together, the salt sodium acetate (NaCH 3 COO) is formed as well as a gas that extinguishes a burning flame and also a liquid substance that turns cobalt chloride paper from blue to pink. 6. Cobalt chloride paper is a hydrated salt used for making humidity gauges. The formula of the hydrated form is CoCl 2 2H 2 O. What color is associated with the hydrated form of cobalt chloride? How might is be to predict weather changes? 7. Manganese dioxide is considered to be a catalyst in the decomposition of hydrogen peroxide. Design an experiment in general terms to show that manganese dioxide is a catalyst.