Formula of Solid Formal Lab Report.

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Chemistry

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Jan 9, 2024

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Formula of Solid Tiffany Nguyen Salazar Purpose :

The purpose of this lab was to determine the empirical formula of a compound formed from Cu+S. Theory : When determining the empirical formula of the compound, we will need to measure the masses of the different elements in the compound. In this experiment the different elements include the mass of the crucible on its own, mass of crucible + copper, and mass of the crucible + copper sulfide after the heating. These values will be used to eventually solve for a ratio of the products (Copper & Sulfur). With this information and with the atomic weight of Copper we will be able to determine the number of moles of Copper (Cu) with the formula: 1. Moles of Cu = ???? ?? 𝐶? ????𝑖? 𝑤?𝑖?ℎ? ?? 𝐶? The following formula is similar and used to find moles of Sulfur (S). 2. Moles of S = ???? ?? 𝑆 ????𝑖? 𝑤?𝑖?ℎ? ?? 𝑆 After calculating the moles for each element, we can use those values to solve for the ratio of Copper to Sulfur with the formulas: 3. Value for Cu (X) = ????? ?? 𝐶? ???????? ???? ???𝑤??? 𝐶? & 𝑆 4. Value for S (Y) = ????? ?? 𝑆 ???????? ???? ???𝑤??? 𝐶? & 𝑆 Using equations 3 and 4 led us to equation 5, our empirical formula, which represents the simplest whole-number ratio of different atoms present in a compound: 5. XCu + YS → Cu X S Y Our % composition of Cu tells us what percent of each element is present in a compound and can be found using the following formula: 6. % Composition of Cu = x 100 ???? ?? 𝐶? ???? ??????? We will also be able to solve for the % composition of Sulfur by subtracting our % Composition of Cu from 100:

7. % Composition of S = 100 - % Composition of Cu Procedure : 1. Clean a porcelain crucible and then heat on clay triangles over bunsen burner flame until bottom glows red hot. 2. Use tongs to transfer crucible to porcelain evaporating dish, allow to cool completely. Take crucible on dish to balance room, use tongs to transfer crucible to balance pan and weigh to nearest 0.0001 g. 3. Add about 0.4 copper wire to the crucible and reweigh crucible + copper to the nearest 0.0001 g. Coiled copper wire should be pressed to the bottom of the crucible. 4. Crucible should be filled halfway with the sulfur, always using tongs to handle the crucible. Take copper + sulfur mixture to a ring stand and clay triangle set up in the hood. 5. Gently heat mixture with small blue single-cone bunsen flame. Observe then slowly increase the size of flame, to boil off excess sulfur. After the sulfur disappears, heat the crucible until it glows red for at least 3 min.. 6. Allow crucible and contents to cool on a fireproof board. Then take into the balance room and weigh to the nearest 0.0001 g. Reheat crucible and contents in hot flames in the hood for 2-3 min., then re-cool. 7. Reweigh assembly; mass should be slightly less. If copper subscript is greater than 2.2, add more sulfur and heat for 5 min., remove excess sulfur, keep crucible at red heat for 3 min.. Allow to cool, weigh again to nearest 0.0001 g. Reheat for 3 min., cool and reweigh. Reweigh after a longer time of cooling. 8. Use microspatula to test the malleability of the product or check to see if it’s brittle. After this, place the contents of the crucible in one of the marked solid waste containers. Data : Mass of Crucible (g) Mass of Copper (g) Mass of Crucible + Copper (g) Mass of Sulfur (g) Mass of Crucible + Copper Sulfur (g) Mass of Product (g) 9.7341g 0.4227g 10.1568g 0.1083g 10.2651g 0.796g Table 1: Recorded Masses of Crucible, Copper, & Sulfur Moles of Copper 26.86 mol Cu

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Moles of Sulfur 3.47 mol S Ratio for Copper 1 Ratio for Sulfur 8 Empirical Formula Cu 1 S 8 Table 2: Calculations Relating to Empirical Formula Copper (before heating) - Shiny - Malleable/flimsy - Very easy to coil Copper (after heating) - Dirty gray - Washer-like Sulfur (before heating) - Neon yellow powder Sulfur (after heating) - Blood-like odor - Red smoke Brittle Test - Brittle, but still needs effort to break Table 3: Observations of Copper & Sulfur (before/after heating & brittle test) % Composition of Cu 79.6% % Composition of S 20.4% Table 4: Percent Composition of Copper and Sulfur Results & Discussion: Table 1 Calculations: Mass of Copper = 10.7568 - 9.7341 = 0.4227g Mass of Sulfur = 10.2651 - 10.1568 = 0.1083g Mass of Product = 10. 2651 − 9. 7341 = 0.796g

Table 2 Calculations: Moles of Cu = 0.4227g of Cu x = 26.86 mole of Cu 1 ???? 63.55? ?? 𝐶? Moles of S = 0.1083g of S x = 3.47 mole of S 1 ???? 32.06? ?? 𝑆 Ratio for Cu = = 1 3.47 3.47 Ratio for S = = 7.74 → 8 26.86 3.47 Empirical Formula = 1Cu + 8S → Cu 1 S 8 Table 4 Calculations: % Composition of Cu = x 100 0.4227 10.2651−9.7341 = x 100 0.4227 0.796 = 79.6% % Composition of S = 100-79.6 = 20.4% After completing this experiment we can see that there was 1 mole of Copper for every 8 moles of Sulfur. As seen in table 2, our empirical formula was Cu 1 S 8. , meaning that the ratio of copper to sulfur was 1:8. With this information we know a reaction took place, we also know because of the physical observations we recorded in table 3. Once our powdery yellow sulfur was in the crucible and placed on the flame, after some time it began to transform into red smoke, followed by a strong sour-like odor. It was obvious that copper also had a reaction because it started off as shiny and malleable, but after the experiment it became a dusty gray color and looked like a flattened washer. Although the experiment was completed and the outcome was successful, there may have been errors relating to how we collected our weights for the crucible and products. The scale was precise, but if we accidentally left the doors open that would’ve affected our overall results. Another mistake that may have happened would be how the flame was controlled. From the start we set our bunsen burner to have the tip of the blue flame touching the bottom of our crucible. Looking back at our lab manual it stated that the flame should gradually increase instead of being at his fullest from the start. This mix up could have affected the results relating to the masses of our Copper and Sulfur. Mistakes can occur without our knowledge until the end, that is why it is best to conduct an experiment more than once, to confirm results.

Conclusion: In this experiment we were able to successfully determine the empirical formula of a compound formed from Cu+S. Weighing out our materials was the first major step into calculating our empirical formula. Having a scale that precisely weighed our crucible to the nearest 0.0001g was very important because it was more accurate compared to if we were to round. After the first weigh in of our crucible the following steps of weighing it with the copper wire was fairly simple. Turning the bunsen burner on and adjusting its flame was also much more simple after our first attempt. Each weight collected played a huge role in helping us find our empirical formula, which was Cu 1 S 8. While conducting this experiment, it was also very important to record observations in order to figure out if a reaction happened or not. Although you can also determine if a reaction happened mathematically, recording your observations can confirm whether or not a reaction within a specific step did occur. Observations can also help you familiarize certain characteristics or factors that can cause a reaction. References: Goldwhite, H., Tikkanen, W., Kubo-Anderson, V., Mathias, E., and Jalali Heravi, M.. Experiment 02: Density and Composition of Solutions. Experiments in General Chemistry . 6th Edition. (69-74)

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