Please complete my lab report by doing the calulcations to find the unknown salt
Chem 1B. Lab 3: Ammonium Salts Alyssa Ramirez 07.05.21 Chem 1B. Lab 3 Objective: The goal of the experiment is to analyze unknown salts and identify them. There are five salts that are identified already. In order to determine the remaining unknown salt, calculation must be performed to identify it. Data: Table 1: Equivalent Weight of the Five Possible Ammonium Salts Salt Formula Molar Mass (g/mol) Number of equivalents (eq/mol) Equivalent Weight (g/eq) Ammonium Bromide NH4Br 97.9 01 97.9/1 = 97.9 Ammonium Chloride NH4Cl 53.5 01 53.5/1 = 53.5 Ammonium Iodide NH4I 145 01 145/1 = 145 Ammonium Nitrate NH4NO3 80.0 01 80.0/1 = 80.0 Ammonium Sulfate (NH4)2SO4 132 02 132/2 = 66.0 Table 2: Identification of Unknown Salt: 634 Trial 1: Molarity of NaOH Molarity of HCl Mass salt (g) Vol HCl (mL) Total Moles OH- 0.2213M 0.1834M 0.4439g 16.01mL Moles of Leftover OH- Moles of OH- w/NH4+ Equivalents of NH4+ Equivalents mass (g/eq) %Error Trial 2: Molarity of NaOH Molarity of HCl Mass salt (g) Vol HCl (mL) Total Moles OH- 0.2213M 0.1834M 0.4331g 15.53 mL Moles of Leftover OH- Moles of OH- w/NH4+ Equivalents of NH4+ Equivalents mass (g/eq) %Error Trial 3: Molarity of NaOH Molarity of HCl Mass salt (g) Vol HCl (mL) Total Moles OH- 0.2213M 0.1834M 0.4210g 16.62mL Moles of Leftover OH- Moles of OH- w/NH4+ Equivalents of NH4+ Equivalents mass (g/eq) %Error Calculations: Do calculations in a separate sheet of paper. Make sure these are neat, and each calculation is clearly labeled. All calculations must be done using dimensional analysis. Take pictures and insert them here (into your report). Results: In a table, include equivalent mass for each trial and the average equivalent mass for the three trials. Include identification, percent error, and relative range. Conclusion Questions: Answer following questions using full sentences (It will require more than 2 sentences for each)!! Refer to your data or results when necessary. 1. Why was it important to heat the reaction until the red litmus paper remains red (no longer turns blue?) Be specific, don’t just say “because I know the reaction is over” For example, what specifically is the blue litmus paper telling you? Why does it turn blue? Etc. 2. What would happen to the equivalent weight value that you calculated if the reaction is stopped too early (while the litmus paper is still turning blue)? Be specific, will it increase the value of your calculated equivalent weight, decrease its value, or have no effect? Explain. 3. Students have a very difficult time with this titration since it is hard to determine the exact end point (green → yellow). What would happen to the equivalent weight value that you calculated if you added too much HCl? Be specific, will it increase the value of your calculated equivalent weight, decrease its value, or have no effect? Please explain using full sentences 4. Ailsa was clearly worried that this experiment may need to be repeated a second time since she had a hard time determining if the red litmus paper turns blue and she had a hard time identifying the end point. Based on your data, do you believe this experiment needs to be repeated? Why or why not? Be specific! For example, were you able to clearly identify your unknown salt based on your average equivalent mass, or did you have difficulty distinguishing between the different salts? CamScanner 03-05-2021 09.50 kekan Typewritten Text Since we don't know the molecular formula of the unknown, we cannot calculate the moles of unknown to find molar mass. So we use equivalents and equivalent mass. 1 Experiment 3 : Identification of an Unknown Ammonium Salt Goals: • To gain experience in the use of the concept of equivalent mass in acid-base calculations • To determine the equivalent mass and thus the identity of an unknown crystalline solid which has the general formula (NH4)aX. Theory: What is an Equivalent and an Equivalent Mass? Equivalents (Eq) is a unit that is regularly used when dealing with acid-base neutralization reactions and the concentration of ions in blood. When dealing with acid-base reactions, an equivalent (Eq) is the quantity that donate or accept one mole of protons. Equivalent mass (g/Eq) is defined as the mass in grams that provides one mole of protons or hydroxide ions in a neutralization reaction. For example, 1 mole of NaOH contains 1 equivalent of hydroxide ions and 1 mole of Mg(OH)2 contains 2 equivalents of hydroxide ions. The same concept applies for acids; 1 mole of HCl contains 1 Eq of H+ ions. Equivalent mass is then used to relate the equivalents of acid or base contained within a substance, to its mass. It is not too different from the molar mass, but instead of relating total mass to number of moles, you are instead relating the total mass to the number of equivalents: Molar mass = g/mol Equivalent mass = g/Eq The reaction: When analyzing ammonium salts, the one mole of protons (or 1 Eq) will come from NH4+. 1 mole of NH4+ = 1 Eq Equation 1 illustrates the reaction between ammonium ions and a strong base (OH−). As you can see, one mole of ammonium ions neutralizes 1 mole of OH− ions (or you could instead think of it as one mole of ammonium ions provide 1 equivalent of H+ ions). 2 In this experiment, a large excess of NaOH will be added to the ammonium salt. The ammonia product (NH3, the conjugate base formed in the reaction) will then be driven out of the solution by heating, see equation 2. As the NH3 is removed from equation 1, the reaction will keep shifting to the right until all of the NH4+ is consumed; the reaction is driven to completion by the loss of NH3 (Le Chatelier’s principle). The remaining excess NaOH will then be “back titrated” with a standardized acid solution. If you know how much NaOH you initially added to the ammonium salt AND you know how much NaOH remains after the reaction, you can calculate the quantity of NaOH that reacted with your ammonium salt. Once you have calculated the moles (or equivalents) of NaOH that reacted with the ammonium salt, you have all the information you need to calculate the equivalent mass of your unknown salt, and thus determine the identity of the salt (see Table 1) Pre Lab: Before you begin the lab, you must calculate the equivalent weight of the 5 ammonium salts listed in table 1. The equivalent weight that you obtain from the experiment will match the equivalent weight of one of these salts. Like with molar mass, each salt will have its own unique equivalent weight. Use table 1 as a guide when performing your calculations and work from the left side of the table to the right side. For example, for each salt, first write the formula, then calculate the molar mass. Next look at your formula and determine the number of equivalents. Finally, with the number of equivalents and the molar mass in hand, you can calculate the equivalent weight. See below for some hints on how to complete the table: Table 1: Equivalent Weight of the Five Possible Ammonium Salts Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Text Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Text Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez Alyssa Ramirez 3 Hints for Completing Table 1: Determining the Formula: You should be an expert at this! Calculating the molar mass: You should be an expert at this! Determining the number of equivalents: Equivalents, for acids and bases, represent the moles of H+ accepted or donated per mole of substance. For example, with NaOH, the number of equivalents is 1eq/mol because there is one mole of OH− per 1 mole of NaOH. For Mg(OH)2, the number of equivalents is 2 (2 Eq/mol). There are 2 moles of OH− per 1 mole of Mg(OH)2. As a final hint 1 mole of NH4+ is equal to 1 equivalent. You should be able to determine the number of equivalents by simply looking at the molecular formula. No math is needed. Determining the equivalent weight: This is simply dimensional analysis. If you know the molar mass in g/mol and the number of equivalents in Eq/mol, you can multiply them in such a way that moles cancel out and you are left with the units g/Eq (equivalent weight). Significant figures: Don’t forget this! I will take off serious points for not reporting your answer with the proper number of significant figures or for rounding errors! The Experiment: Before you Begin, Organize Your Thoughts! As you read through the procedure below, visualize what is done in each step. A flow chart/pictures will help you to visualize what is happening in the experiment and it will help you organize your thoughts. You will find that the calculations are quite trivial. It is just multiplication, division, addition, and subtraction. The organization and the understanding of all the steps (the chemistry theory) is the hard part! Find your name on the data table (Table 2) and record your unknown number! You will only be performing the calculations for the data listed to the right of your unknown number. Finally, make sure you read and answer the conclusion questions once you have finished identifying your unknown salt. Your Goal Ailsa was analyzing unknown salts and identifying them. So far, she was able to narrow down the identity of the salt to the five possibilities listed in table 1. Ailsa then performed one final experiment to finally ascertain the identity of the salt. The procedure for this final experiment was taken directly from her notebook and contains her observations and commentary in case the experiment needs to be repeated. Read it thoroughly and perform all necessary 4 calculations to determine the identity of the unknown salt. Note: This procedure was taken from Ailsa’s lab notebook. It is written in first person form as she was doing the experiment. We avoid first person form when writing lab reports. Procedure: Ailsa’s Final Experiment: First, I put on my safety goggles and laboratory coat! Then I grabbed an unknown salt, which was observed to be a white/off white crystalline solid and recorded the sample number (this is your unknown number listed