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An Experiment to Determine the Empirical Formula of Lead Iodide

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Introduction

An Experiment to Determine the Empirical Formula of Lead Iodide Aim: The empirical formula shows the simplest whole number of ratio of atoms of each element in a molecule of a compound. In this experiment, we will determine the empirical formula of lead iodide. An insoluble lead iodide compound is formed by dissolving the lead in nitric acid and reacting with potassium iodide. Then, the lead iodide is filtered and dried for a week. In the end of the experiment, the mass of lead, filter papers and filter paper with lead iodide are recorded. The ratio of moles of lead to moles of iodine in the compound can be obtained either by weighing/calculating the mass of each element from the experiment raw data. In order to get the mass of iodide in the lead iodide compound, we can calculate by deducting the initial mass of lead from the mass of the precipitate. By knowing the mass of each element, we can determine the amount of each element (moles) than the ratio of the compound. . Variables: Controlled 30 cm3 3M HNO3 ; distilled water ; 1.2g potassium iodide (KI) Independent Amount of Lead (Pb) Dependent Amount of lead iodide formed Method for controlling variables: Glassware, electronic balance Materials: Equipment: - 3 x 250 cm3 beaker - 1 x 150 cm3 beaker - 3 x watch glass - 1 x Electronic balance (300 g, readability �0.001 g) ...read more.

Middle

21) The precipitate was washed twice with cold distilled water and transferred completely from the beaker to the filter paper. 22) After the water was completely drained through the filter, the filter paper I, II and III were removed from the funnel and were dried by wrapping it in paper towel to absorb the water. 23) Each filter paper was air dried for one week at room temperature. 24) Each filter paper with lead iodide was weighed for each trial on the electronic balance to the nearest 0.001 g and the mass was recorded. Data Collection and Processing Raw Data: Table 1: Mass of lead, filter paper and filter paper with lead iodide Run 1 Run 2 Run 3 Mass of granulated lead /g � 0.001 g 0.151 0.152 0.129 Mass of filter paper /g � 0.001 g 0.837 0.858 0.865 Mass of filter paper with lead iodide /g � 0.001 g 1.129 1.168 1.127 Observations: Color of solution: Potassium iodide and nitric acid containing lead were all colorless. When the potassium iodide was added in the beaker containing lead and nitric acid, the solution turned into bright yellow component. State of solution: Potassium iodide and nitric acid containing lead were liquid. When the potassium iodide was added in the beaker containing lead and nitric acid, an aqueous component is formed (lead iodide). ...read more.

Conclusion

0.129 6.23 1:1.7 Average 0.144 1.13 0.144 6.95 1:1.6 Conclusion: The ratios of the mole of lead to Iodine were calculated and are 1: 1.6. We can assume that the compound is lead iodide PbI2 since the oxidation status of lead is either 2 or 4. Therefore, the theoretical ratio of iodine to lead is 1:2. Compared to the ratio in this experiment, the iodine in the theoretical ratio is greater by 0.4 than that of obtained calculation from our experiment. Moreover, the percentage error of each calculation is below 5%, thus, the results are acceptable. If the percentage error is larger than 5%, the experiment is not valid. Evaluation: However, the result 1:1.6 obtained is slightly different from the theoretical possible ratio 1:2. Hence, the component was not completely gathered. The product may have escaped when the watch glass was lifted, lost during filtration, or left on the wall of the beaker containing lead iodide. Furthermore, the purity of lead will influence the ratio. The lead used might not be pure. If the lead was impure, other product apart from lead iodide would be formed. To further improve the experiment, we must avoid lead iodide to escape, avoid lead iodide on the funnel, and filter all the lead iodide in the beaker. These would give greater ratio of iodine to lead. Reference: - http://en.wikipedia.org/wiki/Lead_iodide ?? ?? ?? ?? European International School Manila Page 1 of 5 ...read more.

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