chemistry Lab 3 stoichiometric reactions report PDF

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lab report for chemistry lab 3 stoichiometric reactions and net ionic equations sacred heart university academic year 2020/2021...

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STOICHIOMET RIC REACTIONS WITH PHOSPHORIC ACID Lab 3

Purpose The goal of the experiment is to analyze the stoichiometric relationship between phosphoric acid with multiple molar equivalents of sodium hydroxide through performing three acid-base neutralization reactions. Through this, formula weight of the products as well as identity of the salt produced can be determined.

Introduction Stoichiometry is defined as the study of the quantitative relationships or ratios between two or more substances undergoing a physical or chemical change. Stoichiometric calculations deal with the mass and/or volumes of reactants and products1, and are used to determine the number of moles present in a substance. The relationship between the mass and moles of each compound depends on its specific molecular or empirical formula. The molecular formula of a substance shows the quantity and type of atoms that are present in a molecule.2 The empirical formula of a substance represents the lowest whole number ratio of the specific elements present in the compound.3 For example, the molecular formula of glucose is C6 H 12 O 6 , and the empirical formula is CH 2 O . In order to find the number of moles present in a substance, the atomic weights of each atom in the compound must first be added together to determine the molecular weight in atomic mass units. The molar mass is then found by converting atomic mass units to grams per mole. For example, nitric acid or HNO3 has a molecular weight of 63.02 amu which can be found by adding the atomic weights of hydrogen, nitrogen, and three oxygen atoms or [1.008 + 14.01 + 16.00(3)]. In this case, nitric acid has the same atomic and formula weights, with the formula weight being 63.02 g/mol. A polyprotic acid is an acid that can provide more than one proton per molecule of acid. It has the ability to react with at least one molar equivalent of sodium hydroxide in a neutralization reaction. The process consists of one acid proton reacting with one equivalent of the base hydroxide anion, thus producing water and the salt. This can also be classified as a metathesis reaction as the anion and cation charges stay the same. The experiment performed consisted of three neutralization reactions between 1

Anne Marie Helmenstine, P. D. (2019, January 6). What is stoichiometry? ThoughtCo. Retrieved October 9, 2021, from https://www.thoughtco.com/definition-of-stoichiometry605926.

2

Anne Marie Helmenstine, P. D. (2019, July 3). What is a molecular formula? ThoughtCo. Retrieved October 9, 2021, from https://www.thoughtco.com/molecular-formuladefinition-606378.

3

Mott, V. (n.d.). Introduction to chemistry. Lumen. Retrieved October 9, 2021, from https://courses.lumenlearning.com/introchem/chapter/empirical-formulas/.

phosphoric acid ( H 3 PO 4 ) and different molar equivalents of sodium hydroxide (NaOH). Through the reactions, the names and mass of the salts produced were determined.

Procedure For the first reaction, 1.00 mL of a 6.00 M phosphoric acid solution was transferred to a 125 mL Erlenmeyer flask using a volumetric pipette. 6.00 mL of a 3.00 M sodium hydroxide solution was transferred to a 50 mL beaker using a volumetric pipette. While swirling, the sodium hydroxide was added to the flask of 1.00 mL of phosphoric acid a few drops at a time using a disposable pipette. The 50 mL beaker was rinsed with 2 mL of deionized water, which was then added to the reaction mixture. An evaporating dish covered with a watch glass and weighed to 0.001 g. The solution was swirled again for another minute, and then transferred to the evaporating dish. The 50 mL beaker was rinsed with another 2 mL of deionized water, which was added to the evaporating dish. The dish was covered with the watch glass and the water was heated to a boil using a Bunsen burner, while ensuring it did not spill over. The sample was heated until all the water had evaporated from the dish and had turned into a salt. The dish, salt, and watch glass were left to cool, and then weighed to 0.001 g. All values were recorded on the data sheet. The second reaction was a repeat of the first, but instead used 1.00 mL of a 6.00 M phosphoric acid solution and 4.00 mL of a 3.00 M sodium hydroxide solution. For the third reaction, the first procedure was repeated again except using 1.00 mL of a 6.00 M phosphoric acid solution and 2.00 mL of a 3.00 M sodium hydroxide solution.

Data and Results Reaction 1 Volume of acid used Molarity of acid used Moles of acid used

1.00 mL = 0.001 L 6.00 M 0.006 mol

Volume of base used Molarity of base used Moles of base used

6.00 mL = 0.006 L 3.00 M 0.018 mol

Mass of the empty evaporating dish + watch glass Mass of the evaporating dish + watch glass + salt Mass of the salt

74.708 g 75.884 g 1.176 g

(Experimental) Formula weight of the salt Empirical formula of the salt Name of the salt

163.9 g/mol Na3 PO 4 Trisodium phosphate

Reaction 2 Volume of acid used Molarity of acid used Moles of acid used

1.00 mL = 0.001 L 6.00 M 0.006 mol

Volume of base used Molarity of base used Moles of base used

4.00 mL = 0.004 L 3.00 M 0.012 mol

Mass of the empty evaporating dish + watch glass Mass of the evaporating dish + watch glass + salt Mass of the salt

59.492 g 60.437 g 0.945 g

(Experimental) Formula weight of the salt Empirical formula of the salt Name of the salt

141.9 g/mol Na2 HPO4 Disodium phosphate

Reaction 3 Volume of acid used Molarity of acid used Moles of acid used

1.00 mL = 0.001 L 6.00 M 0.006 mol

Volume of base used Molarity of base used Moles of base used

2.00 mL = 0.002 L 3.00 M 0.006 mol

Mass of the empty evaporating dish + watch glass Mass of the evaporating dish + watch glass + salt Mass of the salt

65.308 g 66.065 g 0.757 g

(Experimental) Formula weight of the salt Empirical formula of the salt Name of the salt

118.9 g/mol Na HPO 4 Sodium phosphate

Calculations Reaction 1:

H 3 PO 4 (aq) + NaOH(aq)

Na3 PO 4 (aq) + H 2 O (l)

Discussion For reaction 1, the salt formed was trisodium phosphate ( Na3 PO 4 ) and was opaque and white. The salt produced in reaction 2 was disodium phosphate ( Na2 HPO4 ) and had more of a crystalline appearance. However, it began to decompose during the heating process as it was most likely heated for too long. Out of all three reactions, the second was considered the second-most difficult to successfully produce the perfect salt. Reaction 3 formed sodium Na HPO 4 phosphate ), which began to look muddy, meaning the salt decomposed and a ¿ hydrate was formed. Due to the fact that varying volumes and molarities of sodium hydroxide were used, the number of sodium molecules in each reaction were different.

Conclusion The reaction between 1.00 mL of a 6.00 M phosphoric acid solution and 6.00 mL of a 3.00 M sodium hydroxide solution produced trisodium phosphate ( Na3 PO 4 ). The reaction between 1.00 mL of a 6.00 M phosphoric acid solution and 4.00 mL of a 3.00 M sodium hydroxide solution produced disodium phosphate ( Na2 HPO4 ). The reaction between 1.00 mL of a 6.00 M phosphoric acid solution and 2.00 mL of a 3.00 M sodium hydroxide solution produced sodium phosphate ( NaHP O4 ).

References Anne Marie Helmenstine, P. D. (2019, January 6). What is stoichiometry? ThoughtCo. Retrieved October 9, 2021, from https://www.thoughtco.com/definition-of-stoichiometry-605926. Anne Marie Helmenstine, P. D. (2019, July 3). What is a molecular formula? ThoughtCo. Retrieved October 9, 2021, from https://www.thoughtco.com/molecular-formuladefinition-606378. Mott, V. (n.d.). Introduction to chemistry. Lumen. Retrieved October 9, 2021, from https://courses.lumenlearning.com/introchem/chapter/empirical-formulas/....