Empirical Formula of a Hydrate, Cheat Sheet of Chemistry

Download Empirical Formula of a Hydrate and more Cheat Sheet Chemistry in PDF only on Docsity! Name IB Chemistry SL Unit 2 Determination of the Formula of a Hydrate (Adapted from Pearson Baccalaureate Chemistry 2016 Edition) Research Question: How does the mole ratio of copper (II) sulfate to water in the hydrate CuSO, * xH,O determine its empirical formula? Introduction: Many crystals occur commonly in hydrated form, which means that they contain water molecules within the crystal structure in definite proportions. This water is called water of crystallization. The formula for these crystals shows the number of water molecules present per formula unit of crystal using a dot before the water. For example, hydrated magnesium sulfate is MgSO, * 7H,O and is named magnesium sulfate heptahydrate (Latin prefixes indicate the number of moles of water). When these crystals are heated, they lose their water of crystallization and are then said to be anhydrous. Write the formulas for the following hydrates: a. Barium chloride dihydrate BaCl, ¢ 2H,O b. Cobalt (II) chloride hexahydrate CoCl, * 6H,0 c. Sodium carbonate decahydrate Na,CO, * 10H,O d. Magnesium carbonate pentahydrate MgCO, * 5H,0 In this experiment, we will heat hydrated copper (II) sulfate crystals to drive off all the water of crystallization. We will assume that the loss in mass is equal to the mass of water in the crystals, and that the final mass will be the mass of the anhydrous crystals. Materials: copper (II) sulfate hydrate, evaporating dish, Bunsen burner, crucible tongs, electronic balance, scooper, mesh plate, ring stand, iron ring. Procedure (regular): 1. Be sure to record all qualitative observations before, during, and after heating the sample. 2. Make sure to title your data table and record the absolute uncertainty of your digital balance before starting the experiment. 3. Record the mass of a clean, dry evaporating dish. 4. Put approximately 2 scoops of the crystal hydrate in the dish and weigh the dish and its contents. 5. Heat the dish gently for about 7 minutes. Using a spatula, gently break apart the crystals periodically to ensure all water has been evaporated. 6. After cooling for about 5 minutes, weigh the evaporating dish and contents. ***7_ “Heat to constant mass” by repeating steps 3-4 until you get consistent readings. Procedure (digital): 1. Record your qualitative observations based on the given pictures before, during, and after. 2. Title your data table and put the appropriate absolute uncertainty based on the given data. 3. Complete the calculations and propagate the uncertainties. MG 9/20 Name IB Chemistry SL Unit 2 Pre-Lab: (Read the procedures above first and use the “regular” procedure for ideas for a controlled variable) 1. The independent variable is the one that you (the scientist) is changing throughout the experiment. What is the independent variable in this experiment? heated Mol ratio of CuSO, _to water__or number of times 2. The dependent variable is the one that you are measuring in response to the independent variable. What is the dependent variable in this experiment? Empirical formula 3. Controlled variables are all other variables (aside from the independent and dependent variables) that must remain the same throughout the experiment. Changing these variables could negatively affect your data. Identify one variable that must be controlled in this experiment, explain how you will control it, and why it must be controlled. Controlled Variable How Will it Be Controlled Why Must it Be Controlled 1. 2: Size of evaporating dish Same amount of heating or cooling time 1. Use the same dish throughout the experiment without changing it. Carefully set a time limit with a stopwatch. 1. So that the crystals have the same amount of room for water to evaporate each trial or same mass of dish. 2. So that the amount of time allowed for the water to escape is equal for each trial. MG 9/20 Name IB Chemistry SL Unit 2 Water coefficient 5/26=0.19 Multiply this mol ratio by your total percent uncertainty and divide by 100 to get your absolute uncertainty for the experiment. 0.19) (3.57) = 0.00686..... rounded to 1 sig fig = 0.007 (absolute uncertainty) 100 5. Write your mol ratio with your absolute uncertainty (correct number of decimal places in each). 0.190 + 0.007 Conclusion: a. Discussion and justification: - describe your findings and answer the research question. - be sure to justify your conclusion based on your data AND relate it to your knowledge about the topic. - talk about any systematic errors here and how they have impacted your data. The mole ratio of the water:anhydrate in my experimental data was 26:5 which shows that the empirical formula from my data is 5CuSO, * 26H,O. By determining the mass of the water and anhydrate, converting them to mole values, and then dividing each by the smallest mole value, | was able to determine the empirical formula of the hydrate in question. When looking at the accepted value, my measured individual values of 26:5 appear to be five times larger than the actual empirical formula of 5:1. However, using the decimal values, the percent error is relatively low at 5.0%. My mole ratio of 0.190 was slightly lower than the accepted at 0.20. This means that my mole value of the copper (II) sulfate was too small or my mole value of water was too large. This could be from some of the hydrated crystal becoming attached to the spatula during heating. | have to consider using a different tool in the future. In addition,! could have heated the sample for more trials until reaching a constant mass if more time was permitted to limit some of my random error. b. Comparison to literature values: - calculate the percent error given the accepted mol ratio is 1:5 or 0.20 [Copper (II) sulfate:water]. - show your work below. - compare your percent error to your total percent uncertainty. Which was higher? Were there more systematic or random errors based on these values? - which measurement had the highest percentage uncertainty? What does this suggest about that measurement? 0.0190-0.20 X 100 = 5.0% 0.20 MG 9/20 Name IB Chemistry SL Unit 2 Both my percent error and my total percent uncertainty were fairly low at 5.0% and 3.57%, respectively. This indicates that there were few systematic errors, but even fewer random errors regarding my data. Having already discussed my biggest systematic error, | imagine that a more precise digital balance that went to the thousandths place would help lower my percentage uncertainty. In addition, repeating the experiment more times would also alleviate any additional random errors | have not accounted for. c. Error analysis: - Complete the following for each error given. Description of Error Systematic or Impact on Empirical Possible Modification Random? Formula Water vapor still remained in crystals | | . _ Systematic Water vapor left in the Heat the crystals for an additional 5 due to insufficient : " time for heating. crystal will cause a greater | minutes. mass of anhydrate and a smaller mass of water calculated. This will make a larger mole value for the anhydrate and a smaller mole value for the water. Crystals were left out too long to cool and . . . Systematic The re-entering of water | Reduce the time for which the water vapor i h Is will tal is allowed t | by 1-2 reentered the vapor into the crystals will | crystal is allowed to cool by 1- cause the mass of the minutes. crystals. ; anhydrate to increase. This will increase the mole value of the anhydrate and decrease the mole value for the water. Some crystals attached to the oo | Systematic This will cause a decrease | Clear the spatula or use a material spatula during heating. in the mass of the anhydrate which will decrease the moles of the anhydrate and an that is less likely to capture the crystals during heating. MG 9/20 Name IB Chemistry SL Unit 2 increase in coefficient of water. MG 9/20