Double Displacement Reactions Lauren Busch & Bailey Culp February 25, 2017 p. 7

Background: Double displacement reactions is a type of chemical reaction that two cations and two anions of the reactant switch places to form to new compounds in the product. Insoluble Salts, also known as precipitates, are the many ionic metal compounds that do not dissolve in water. Copper solutions form a blue precipitate when combined with sodium hydroxide. Copper hydroxide is used to make rayon, battery electrodes, and insecticides. Silver iodide will produce a yellow precipitate. Silver iodide is primarily used in weather modification but can be used as antiseptic material and a photosensitive material in photography.

Purpose: The purpose of carrying out a double replacement reactions lab is to create tangibly observable examples of what occurs when two compounds undergo double displacement. By testing various compound combinations, it is evident that the purpose of combining some compounds that create precipitates and some compounds that create soluble products is to differentiate between compounds that are able to complete this reaction. By being able to physically see the reaction that occurs by looking for colorful and texturous substances, it is applicable to understand that it underwent a double displacement reaction. Because these observations may also be faint or minute, the follow up balancing of chemical equations including net ionic equations can visually show the “switching of compounds” that occur when a double displacement reaction happens.

Materials: In order, procedurally speaking, our materials included a six by four well plate that only used sixteen of its twenty four wells during the experiment. Eight different pipettes were used that each had contained drops of the following eight chemicals: silver nitrate (labeled AgNO3), magnesium sulfate (labeled MgSO4), sodium hydroxide (labeled NaOH), lead(II) nitrate (labeled Pb(NO3)2), copper sulfate (labeled CuSO4), iron(III) chloride (labeled FeCl3), potassium iodide (labeled KI), and trisodium phosphate (labeled Na3PO4). Six wooden toothpicks were used, along with two q-tips. Water and paper towels were used in the cleaning process after the lab was concluded, as well as goggles and aprons which were used throughout the lab as a safety precaution.

Prediction of Reaction 1
Prediction of Reaction 2

Procedure: Before the Lab was started, safety goggles and aprons were put on and worn throughout the whole lab. The procedure was started by holding the pipette vertically and placing 2 drops of each solution in the boxes in the well. Then each mixture was stirred carefully using a clean toothpick. After each solution was mixed, the data was collected and R was written if there was a Reaction and NR was written for no reaction. Then the results were photographed. After the lab was completed, the contents were dumped down the sink with plenty of water and the wells were cleaned using a q-tip. Last the lab area was cleaned up and dried. Hands were washed and then a clean-up stamp was received from the teacher.

The following picture shows the four by six well plate that was used in the experiment, along with the sixteen wells that contain a combination of two compounds in each. Along the top of the well plate, it is labeled numerically one through six, and along the side of the well plate it is labeled alphabetically A through D. The two reactions that were chosen for this lab occurred in wells C1 and A3, these being: sodium hydroxide and copper sulfate in C1, and potassium iodide and silver nitrate in A3.

Data & Observations: The two reactions that were chosen for this lab occurred in wells C1 and A3 which contained sodium hydroxide and copper sulfate in C1, and potassium iodide and silver nitrate in A3 respectively. For the compounds in C1, their reaction created an insoluble product that was amassed after stirring them together using a toothpick. The substance was thicker than if it was soluble and created a murky precipitate that floated inside the cloudy liquid. There was a blue color in the well, as well as a lowly tinted white hue to the precipitate inside the well. The reactant formula for the reaction in C1 was 2Na + CuSO4, and the product formula for the same reaction was Cu(OH)2 + Na2SO4. The compounds in A3, once reacted with each other, also created a yellow tinted precipitate. The precipitate was thick and murky and had formulated together in a cloudy liquid surrounding. Making it evident that an insoluble product was produced and that double displacement had occurred. The reactant formula for the reaction in A3 was KI + AgNO3, and the product formula for the same well was AgI + KNO3.

Data Analysis Reaction 1: Cu2+ (aq) + 2OH- (aq) to produce Cu(OH)2 (s). Our product matches the product description from the background. It formed a blue precipitate. The results are validated because it matches the background information and the color it should be.

Data Analysis Reaction 2: Ag+ (aq) + I- (aq) to produce AgI(s). Our product is similar to the product description from the background. It formed a cream, yellow color and it was supposed to be a straight yellow color. The results are validated because it for the most part matches the color listed in the background information.

Conclusion: The purpose of the experiment was met, as verified by the creation of two precipitates through double displacement. This purpose was also supported by the use of balancing equations and using net ionic equations in correlation to double displacement with two compounds. The background research stated that copper solutions form a blue precipitate when combined with sodium hydroxide, and this was confirmed through the lab, as seen by the blue color in well C1. By showing the blue precipitate solution being formed, the hypothesis of a copper compound reacting with sodium hydroxide to undergo double displacement is supported. The background research also states that silver iodide will produce a yellow precipitate, and this was confirmed through the lab, as seen by the yellow color in well A3. With this yellow/white tinted precipitate being created, the aforementioned hypothesis of potassium iodide and silver nitrate reacting to undergo double displacement is supported. Through the balancing of equations and using net ionic equations, as well as observing the physical properties of these compounds, it was determined that compounds that would go through double displacement would produce a precipitate and vice versa.

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