BIO 135 Lab Report: Cations and anion reactions

BIO 135 Lab Report: Cations and anion reactions Cations and anion reactions II. Introduction • Reaction between cations and anions will be examined in this lab. The resulting precipitate is indicative of the reaction that occured. • In our lab a lead nitrate solution, Pb(NO3)2 will be mixed with a solution of potassium chromate, K2CrO4 , a yellow precipitate will forms. This precipitate must be a combination of K+ or Pb2+ cation and CrO4 2- or NO3 2- anion. Since most potassium salts and nitrates are soluble in water, PbCrO4 must be the precipitate. The equation for this reaction is: • Pb2+ + CrO4 2- - PbCrO4 Purpose—a concise statement about the lab’s objective Background— For this week's lab, I will conduct the following Model ChemLab experiment: Cations and Anion Reaction. This experiment will demonstrate a double replacement reaction of ionic compounds. This experiment demonstrates ionic compounds. In this experiment, I will mix two ionic compounds. Both compounds are soluble in water. If a reaction occurs between these two compounds, then a precipitate will form because one of the two resultant compounds is not soluble in water. This is evidence that a reaction occurred. Findings— The following reaction will occur: Lead nitrate + Potassium chromate = Potassium nitrate + Lead chromate. The following is the balanced chemical reaction: Pb(NO3)2 + K2CrO4 à 2 KNO3 + PbCrO4. III. Procedure Step 1 Add 50 ml(s) of potassium chromate 1M solution in a 100 ml beaker. Use the Chemicals selection from the Toolbar. Select All Chemicals from the dropdown menu. Using the dropdown menu, select 1 M potassium chromate. Change the volume to 50 mL. Make sure that on the lower part of the window that you have indicated that the potassium chromate is to be added to a new 100 mL beaker. Click OK. A beaker will appear on the workspace. Half of the beaker will appear white—this is the 50 mL of potassium chromate. Step 2 Add 50 ml of lead (II) nitrate 1M into the same 100 beaker. Left click, using your mouse, the beaker on the workspace. A dotted line will appear around the beaker. You have selected the beaker. Use the Chemicals selection from the toolbar. Select All Chemicals from the dropdown menu. Using the dropdown menu, select 1 M lead nitrate. Change the volume to 50 mL. Make sure that the lower part of the window indicates that the lead nitrate is to be placed in picked 100 mL beaker. Click OK. You will see the volume increase to 100 mL. You will also see the solution become dotted with a line on the bottom of the beaker. This is your indication that a reaction occurred and a precipitate has formed and settled on the bottom of the beaker. Step 3 Filter the resulting precipitate into a 250 ml Erlenmeyer flask with a Buchner funnel. Now, you want to set up an Erlenmeyer flask with a Buchner funnel. From the Toolbar, select Equipment. From the dropdown menu, select Erlenmeyer Flask - 250 mL. Using your mouse, right click on the Erlenmeyer flask and choose Buchner Funnel from the available selections. This adds a Buchner funnel to your Erlenmeyer flask. On the 100 mL beaker, right click on pour/decant. The flask will turn on its side. Move the beaker above the Buchner funnel. When you have it positioned correctly, the solution will pour into the funnel. You will now see a white area in the bottom of the flask. This indicates that you have filtered your solution. Step 4 Record weight of resulting precipitate by removing Buchner funnel and placing resulting precipitate into a test tube. Right click on the flask. Select Buchner Funnel. A window will appear. The message indicates that an amount of solid was found present in the filter on this piece of equipment. Select Place Solid into 50 mL test tube. Click OK. IV. Observations and Results During this lab I observed a chemical reaction take place between the potassium chromate and lead (II) nitrate in a 100mL beaker. After the reaction was complete I set up an Erlenmeyer flask with a Buchner funnel. Once I ran the solution through the funnel and got the solution separated from the filtered precipitate I was able to weigh them. The solution came out to be 130.109 grams while the filtered precipitate came out to only 36.160 grams. V. Discussion During this lab I observed a chemical reaction take place between the potassium chromate and lead (II) nitrate in a 100mL beaker. After the reaction was complete I set up an Erlenmeyer flask with a Buchner funnel. Once I ran the solution through the funnel and got the solution separated from the filtered precipitate I was able to weigh them. The solution came out to be 130.109 grams while the filtered precipitate came out to only 36.160. I also demonstrated a double replacement reaction of ionic compounds. I mixed two ionic compounds both which are soluble in water. And since a reaction occurred after mixing them, a precipitate formed because one of the two resultant compounds is not soluble in water. This is also evidence that a reaction occurred. VI. Conclusion The following reaction occurred: Lead nitrate + Potassium chromate = Potassium nitrate + Lead chromate. The balanced chemical reaction is : Pb(N03)2+ K2CrO4 à 2 KNO3 + PbCrO4. Almost all alkali metal compounds and nitrates are soluble, but most lead compounds are insoluble (except for acetates and nitrates and a few others). Therefore, when soluble salts lead nitrate and potassium chromate are mixed, insoluble lead chromate forms and precipitates out. Cations (positively-charged ions) and anions (negatively-charged ions) are formed when a metal loses electrons, and a nonmetal gains those electrons. The electrostatic attraction between the positives and negatives brings the particles together and creates an ionic compound.