CHEM 111 expt. 2 id. of a compound PDF

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Destiny Cambero CHEM 111 – Farnum MTWR 9:40 AM 08/09/18

Experiment 2: Identification of a Compound: Chemical Properties For this experiment, the objectives were to identify a compound based on its chemical properties. A chemical property can be defined as a characteristic of a substance that changes based on its environment and the chemicals present. Examples of chemical reactions are color change, precipitate, odor, etc. The chemicals we used to produce our chemical reactions were AgNO3, NaOH, and HCl, these are our primary solutions. We partnered these aqueous solutions with our secondary solutions which were NaCl, Na2CO3, MgSO4, NH4Cl, water, and our unknown, and observed the chemical reactions that took place. To test the solutions we used a 24-well plate, where we added 1ml into a separate well of our secondary solutions. Then we added 5-10 drops of our primary solutions (one row AgNO3, one row NaOH, etc.) into each well with the secondary solution to observe whether or not a chemical reaction occurred. By performing these chemical reactions we can make a template on what chemical combinations produce a chemical reaction and compare this to the result of our unknown. For my unknown, no precipitate formed when mixed with AgNO3 or HCl but it did when it was paired up with NaOH. Therefore, my primary solution would be NaOH. In the row containing NaOH no reactions occurred with any of the secondary solutions besides MgSO4. When NaOH and MgSO4 are paired together, the chemical reaction produced a white precipitate similar to my unknown. Based on the characteristics of the chemical reaction of my unknown I can conclude that my unknown solution was an aqueous solution of MgSO4.

Experiment 2: Identification of a Compound: Chemical Properties – Post lab questions 1. Identify a chemical reagent used in this experiment that can be used to distinguish solid CaCl2 (soluble) from solid CaCO3 (insoluble). What is the distinguishing observation? A chemical reagent that we could have used for this experiment to distinguish the two soluble and insoluble solids is HCl. If we mix CaCl2 and HCl the solid will be soluble, no reaction will occur. If we mix HCl and CaCO3 then a reaction will occur, bubbles will form. 2. What test reagent used in this experiment will distinguish a soluble Cl- salt from a soluble SO42- salt? What is the distinguishing observation? A test reagent that we can use for this experiment to distinguish the soluble Cl- and the soluble SO42-, is AgNO3. If we mix AgNO3 and Cl- a reaction will occur forming a precipitate. If we mix it with SO42- no reaction will occur.

3. Predict what would be observed (and why) from an aqueous mixture for each of the following (all substances are water soluble). a. Potassium carbonate and hydrochloric acid By mixing the two we get potassium chloride. CO2 and water will also be present but no precipitate will form. b. Zinc chloride and silver nitrate By mixing zinc chloride and silver nitrate we will get zinc nitrate and silver chloride. The silver chloride will form a precipitate because it is not soluble in water. c. Magnesium chloride and sodium hydroxide By mixing magnesium chloride and sodium hydroxide, we would get magnesium hydroxide and sodium chloride. Since magnesium hydroxide is insoluble it will produce a precipitate. d. Ammonium nitrate and sodium hydroxide By mixing ammonium nitrate and sodium hydroxide we get sodium nitrate, ammonia, and water. No precipitate would form in this situation because they are all soluble. 4. Three colorless solutions in the test tubes, with no labels, are in a test tube rack on the lab bench. Lying beside the test tubes are three labels: 0.10 M Na2CO3, 0.10 M HCl, and 0.10 M KOH. You are to place the labels on the test tubes using only the three solutions present. Here are your tests: • A few drops of the solution from the test tube 1 added to a similar volume of the solution in the test tube 2 produces no visible reaction but the solution becomes warm. • A few drops of the solution from the test tube 1 added to a similar volume of the solution in test tube 3 produces carbon dioxide gas. • Identify the labels for test tubes 1,2, and 3. Test tube 1: 0.10 M HCl Test tube 2: 0.10 M KOH Test tube 3: 0.10 M Na2CO3 5. Three colorless solutions in test tubes, with no labels, are in the test tube rack on the lab bench. Lying beside the test tubes are three labels: silver nitrate, AgNO3; hydrochloric acid, HCl; and sodium carbonate, Na2CO3. You are to place the labels on the test tubes using only the three solutions present. Here is your analysis prodedure: • A portion of test tube 1 added to a portion of test tube 2 produces CO2. • A portion of test tube 2 added to a portion of test tube 3 produces a white silver carbonate precipitate. a. On the basis of your observations, how would you label the three test tubes? Test tube 1: HCl Test tube 2: Na2CO3 Test tube 3: AgNO3 b. What would you expect to happen if a portion of test tube 1 is added to a portion of test tube 3? If we mixed a portion of test tube 1 and test tube 3 then we would get AgCl, this will form a precipitate because it is insoluble.

6. For individual solutions of the cations Ag+, Ba2+, Mg2+, and Cu2+, the following experimental observations were collected: NH3(aq) HCl(aq) H2SO4(aq) Ag+ No change White ppt. No change No change No change White ppt. Ba2+ 2+ White ppt. No change No change Mg Blue ppt/ dark blue No change No change Cu2+ solm. with excess From these experimental observations, a. Identify a reagent that distinguishes the chemical properties of Ag+ and Mg2+. What is the distinguishing observation? The reagent that distinguishes the chemical properties would be HCl because this forms a precipitate with Ag+ forming AgCl. If we mix it with Mg+ then we get MgCl2. b. Identify a reagent that distinguish the chemical properties of the HCl and the H2SO4. What is the distinguishing observation? The reagent that distinguishes the chemical properties would be Ag+, when it reacts with HCl we get AgCl which forms a precipitate. If mixed with H2SO4 no precipitate forms because it is soluble. c. Identify a reagent that distinguishes the chemical properties of Ba2+ and Cu2+. What is the distinguishing observation? The reagent that distinguishes the chemical properties would be NH3, when it reacts with Cu2+ we see a blue solution form due to its reaction with ammonia. When Ba+ is mixed with NH3 a reaction will not occur because it is soluble. d. Identify a reagent that distinguishes the chemical properties of Cu2+ and Mg2+. What is the distinguishing observation? The reagent that distinguishes the chemical properties would be NH3, when we react it with Cu2+ we get a blue colored solution indicating there was a reaction. If we mix it with Mg2+ no reaction would form.

Experiment 6: Acids, Bases, and Salts -Discussion The goal of this experiment was to learn about acids, bases, and salts, along with their chemical properties. We tested different things such as pH, solubility, and how to interpret and observe chemical reactions so that we could then write out their equations. Almost all chemical compounds can be identified as an acid, base, or salt. By understanding the nomenclature of these compounds, we can express chemical reactions and balance these equations to better understand their stoichiometry. Stoichiometry is a study in which is used to interpret a reaction by balancing the equation. Acids have a sour taste and can cause burning or irritation to the skin depending on the concentration. When using litmus paper to test for acidity, acids turn blue litmus paper red. All acids share a similar quality in which they all produce hydronium ions, H3O+. Acids can be either diprotic, inorganic, or organic. Cations containing hydrated ferric ions can also produce acidic solutions. Bases on the other hand are bitter tasting and slippery to the touch. When testing for basicity of solutions, bases turn red litmus paper blue. A common quality among all bases is that they all produce hydroxide ions, OH-. There are many different types of hydroxides but the most common is sodium hydroxide, NaOH. Many anions also have the ability to produce basic solutions. Lastly, salts are produced from a combination of both acids and bases. This mixture can also be defined as a neutralization reaction, which is just a chemical reaction between the two. This reaction plays a role on whether or not a salt is soluble or insoluble. If a salt is soluble then it exists in the form of ions, if the salt is insoluble then it exists as a precipitate. Therefore, salts are ionic compounds made up as a result of an acid-base reaction. These reactions can be expressed through ionic equations and net ionic equations. An ionic equation expresses two separate and combined solutions. A net ionic equation represents only the ions in a chemical reaction, ions not involved are known as spectator ions. For this lab we had many different short experiments that was divided evenly amongst the three lab benches, therefore I did not perform each and every individual experiment. However, the experiments we were assigned tested the pH and the reactions of salt mixtures. We were assigned to find the pH of 0.10 M concentration of NaCl, Na2CO3, Na3PO4, NH4Cl, and AlCl3. We collected five test tubes, one for each salt solution, and added 10 drops of each solution into their individual tube. After that we added two drops of the universal indicator and observed the color change. We want to make sure that we don’t use too much of the indicator, this could alter the pH reading. We utilized a pH booklet in order to observe and approximate what the pH of every salt solution was. When testing the reaction, we collected six test tubes, one for each solution, and followed the protocol order for mixing the solutions. We the observed and recorded our data. It is important to make sure that the solutions are being mixed correctly so that the results and observations made are accurate.

I had a hard time hypothesizing just because there were so many experiments and I was unsure whether or not we would be splitting the work and what section I would be required to work on. However, the experiment I worked on was simple, it consisted mainly of observing chemical reactions for salt mixtures. There wasn’t much room for error just due to the fact that the experiments were so short and straight to the point. My group split up parts D and E. I worked on part D and all I had to do was place the correct number of drops in each solution being tested. For the following salt solutions, I approximated their pH: 0.10M NaCl ~ 9.5, 0.10M Na2CO3 ~ 9.5, 0.10M Na3PO4 ~10, 0.10M NH4Cl ~ 8.5, 0.10M AlCl3 ~ 5. Most of my solutions were over 7 pH which means that the solutions are basic, solutions under pH 7 were acidic. When testing for the reactions of salt mixtures the crystals and solutions were already mixed together so the solutions just had to be poured into their individual tubes and then mixed accordingly to observe a reaction and change in the solution. Errors There weren’t any errors that I encountered in my experiment. I guess if I wanted to be very picky I could say that I many have not added the same amount of indicator in each tube. This could have possibly given me a false color change and an incorrect pH reading. I also did not wash my tubes or pipettes, maybe there is a possibility that there is some residue in the tubes and this could have altered the results. Two errors that could have occurred during the experiment was that I mixed up the tubes and their solutions resulting in a mix up of the pH readings. A second error that could have occurred could have been that I didn’t use the correct volumes of the solutions in the tubes. Perhaps this could alter the pH reading due to the difference in volume.

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Experiment 6: Acids, Bases, and Salts –Post lab questions Part A.1. The observation for the reaction of 6M HCl was obviously different from that of 6M CH3COOH. What were the contrasting observations? How do the two acids differ? Explain. The contrasting observations made between the two is that HCl appeared to be the stronger acid because it had a faster reaction rate compared to the CH3COOH. When testing the different metals it seemed that Mg and Zn reacted quicker than CH3COOH. For the Cu metal both acids had no reaction. So, despite the fact that they have the same molar concentration HCl was stronger than CH3COOH. A.2. As the molar concentration of an acid deceases the reaction rate with an active metal, such as magnesium, is expected to _________. Explain. As the molar concentration of an acid decreases, it is expected for the reaction rate to also decrease because they both correlate. The higher the concentration of an acid the stronger the acid will be and the faster the reaction. Therefore, if there is a decrease in the concentration then there will be a decrease in the reaction rate when reacting with an active metal. Part B.1. 6M H2SO4, is carefully substituted for 6M HCl. Will more or fewer drops of 6M H2SO4 be required for the litmus to change color? Explain. If there is a substitution then fewer drops of H2SO4 will be required to change the color of the litmus paper. This is because H2SO4 is more acidic than HCl, so to turn the solution acidic you will need less drops of H2SO4. Part B.1. Write a net ionic equation for the reaction of hydrochloric acid with sodium hydroxide.

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HCl(aq) + NaOH(aq) à NaCl(aq) + H2O(l) H+(aq) + OH-(aq) à H2O(l) Part B.3. Sodium carbonate dissolved in water produces a basic solution. Water soluble potassium phosphate, K3PO4, also produces a basic solution. Write an equation that accounts for the basicity of K3PO4. K3PO4(aq) + 3H2O(l) à 3KOH(aq) + H3PO4(aq) Part B.3. The setting of mortar is a time-consuming process that involves a chemical equation of quicklime, CaO, with the carbon dioxide and water of the atmosphere, forming CaCO3 and Ca(OH)2 respectively. Write the two balanced equations that represent the setting of mortar. CaO(aq) + H2O(l) à Ca(OH)2(aq) Cao(aq) + CO2(g) à CaCO3(s) Part C.1. the unboiled, deionized water has a measured pH less than 7. Explain. The unboiled water is slightly acidic, this is because there is carbonic acid that is found in water, which is where the CO2 found in water comes from. Carbonic acid is obviously acidic, which is why it has a pH of less than 7, which would have been neutral. Part E.1. Of the six solids placed into the respective test tubes according to Table 6.1, identify the metal ion that has a characteristic: a. green color, b. blue color, c. pink color. a. Green color: Ni b. Blue color: Cu c. Pink color: Co Part E.2. According to the data collected, identify which of the following ion pairs form a precipitate: a. Fe3+ + Cl-, b. Cu2+ + CO32-, c. Ni2+ + PO43a. Fe3+ + Cl-: soluble b. Cu2+ + CO32: precipitate c. Ni2+ + PO43: precipitate...