Laboratory report Heat Effects and Calorimetry PDF

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Experiment No. 5. Interacting with each other in definite proportions, different chemical elements form compounds....

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27.02.2022

Experiment No. 5 Title of Experiment: Heat Effects and Calorimetry I. INTRODUCTION Interacting with each other in definite proportions, different chemical elements form compounds. Usually arranged in certain patterns due to chemical bonds, the elements in the compounds are present in a fixed ratio [1]. This fixed ratio is called molar ratio. Molar ratio illustrates the ratio between the quantities of moles of different chemical elements involved in a chemical reaction [2]. Any compound can be represented by a molecular or empirical formula. Molecular and empirical formulas of compounds give general information about how many moles/atoms of a certain element are present in a solution. In order to determine the formula of a chemical component, the mole ratio should be calculated first. The molar ratio can be found using chemical analysis, or in other words experimental analysis. Experimental analysis consists of several steps: first, the relative masses of elements in compound should be estimated; second, the number of moles of each element needs to be calculated; and last, chemical formula of compound can be found. In this experiment, the formula of copper chloride hydrate needs to be found. To do so, a number of chemical reactions and calculations must be performed. A copper chloride hydrate is a compound with a general formula Cu(x)Cl(y)×(z)H2O, where x, y, and z are numbers that illustrate the formula of the compound. The copper chloride hydrate is green-blue in color, which easily decomposes into elements, and in the absence of water changes its color to brown, turning into anhydrous copper chloride. Using the chemical properties of this compound in its interaction with water and aluminum, and also performing some reactions and mass weighing, the chemical formula of the copper chloride hydrate can be found. Techniques used In given experiment, the chemical and experimental analyses are used. Aim of the experiment Determine the formula of the copper chloride hydrate using the Cu: Cl: H2O mole ratio. Importance of the experiment This experiment has an important laboratory value, because it includes the most necessary and prior knowledge about the components and elements, develops experience in the correct execution of the practical part of the work, and teaches to identify the chemical formulas of the components knowing only their mass.

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II. RESULTS, DISCUSSIONS AND CONCLUSIONS Results/Observations As a result of a performed experiment, it was found that the chemical formula of copper chloride hydrate is CuCl2*H2O. The formula of the compound given was revealed by calculating the molar ratio of the elements (Cu, Cl, and H2O) present in the sample. To find the moles of the constituents, the masses of the elements have to be known. The mass of the water present in the compound was found by calculating the difference in mass of the samples before and after heating. During the heating process, the color of copper chloride hydrate changed from green-blue to brown as the water evaporated, and the hydrated sample turned dehydrated. Later, water moles were calculated by the formula: Next, water and aluminum wire were added to the dehydrated solution. The copper chloride in the solution reacted with the aluminum, resulting in the formation of copper metal on the surface of the Al wire. As the reaction proceeded, hydrogen was released, and the solution slowly turned colorless. After that, a few drops of hydrochloric acid were added to the solution, and the resulting copper was carefully separated from the aluminum. To get rid of the aluminum salts in the solution, and obtain copper in its pure form, the collected copper was placed on a Buchner funnel. The Buchner funnel filtered the copper, after which its mass was weighed, and its moles are found. The moles of chloride were calculated by subtracting the mass of copper from that of the anhydrous copper chloride. Knowing the moles of the elements, the molar ratio was found, and the chemical formula was determined. The source of error The source of error in this experiment may be that some copper will be lost while repositioning it from the beaker to the filter paper. It will lead to inaccuracies in the calculations and will cause difficulties in the determination of the compound's formula. To prevent this source of error, it should be checked that ALL of the copper has moved to the filter paper. Also, the experiment could be done several times, and average measurements can be taken into account so that the calculations are more accurate. Conclusion Generally, the experimental results were successful. In order to avoid any inaccuracies in the laboratory procedure, the work should be done cautiously, the equipment used correctly and carefully, especially while heating the hydrated sample. During this laboratory procedure it has been learned that the determination of a chemical formula of any compound can be found using experimental and chemical analyses.

III. APPENDIX

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Data and Calculations: Heat Effects and Calorimetry A. Specific Heat Trial 1 Trial 2 Mass of stoppered test tube plus metal ____________ g → ____________ g Mass of test tube and stopper ____________ g → ____________ g Mass of calorimeter ____________ g → ____________ g Mass of calorimeter and water ____________ g ____________ g Mass of water ____________ g ____________ g Mass of metal ____________ g → ____________ g Initial temperature of water in calorimeter ____________ °C ____________ °C Initial temperature of metal (assume 100°C unless directed to do otherwise) ____________ °C → ____________ °C Equilibrium temperature of metal and water in calorimeter ____________ °C ____________ °C Δt water (t final − t initial) ____________ °C ____________ °C Δt metal ____________ °C ____________ °C q(H20) ____________ J ____________ J Specific heat of the metal (Eq. 3) ____________ J/g°C ____________ J/g°C Approximate molar mass of metal ____________ ____________ Unknown no. ____________ B. Heat of Solution Mass of calorimeter plus water ____________ g Mass of beaker ____________ g Mass of beaker plus solid ____________ g Mass of water, ____________ g Mass of solid, ms ____________ g Original temperature ____________ °C Final temperature ____________ °C q(H2O) for the reaction (Eq. 1) (S.H. = 4.18 J/g°C) ____________ joules ΔH for the reaction (Eq. 5) ____________ joules The quantity you have just calculated is approximately* equal to the heat of solution of your sample. Calculate the heat of solution per gram of solid sample. ΔHsolution = ____________ joules/g The solution reaction is endothermic exothermic. (Underline correct answer.) Give your reasoning. Solid unknown no. ____________ Formula of compound used (if furnished) ____________ Molar mass ____________ g Heat of solution per mole of compound ____________ kJ

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C. Heat of Neutralization Original temperature of HCl solution ____________ °C Original temperature of NaOH solution ____________ °C Final temperature of neutralized mixture ____________ °C Change in temperature. Δt (take average of the original temperatures of HCl and NaOH) ____________ °C q(H2O) (assume 50.0 mL of solution and use average density of 1.02 g/mL) ____________ J ΔH for the neutralization reaction ____________ J ΔH per mole of H+ and OH− ions reacting ____________ kJ Advance Study Assignment 1. Molar masses of: Cu ___63.546___ g Cl _35.453__ g H __1.0079__ g O _15.9994_ g H2 O __18.0152_________ g 2. a) There are 0.00887 moles of Cu in the sample. b) The mass of the O is 0.071 grams. c) 0.0044 moles of oxygen. d) The mole ratio is 2:1. e) The formula of the oxide: Cu2O f) The molar mass of the copper oxide is 143.091 g/mol References 1. Compound vs. Element. https://www.diffen.com/difference/Compound_vs_Element 2. What is molar ratio? How is it calculated? https://www.quora.com/What-is-molarratio-How-is-it-calculated

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