Gravimetric Determination of Calcium as Ca C2O4. H2O PDF

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Gravimetric Determination of Calcium as CaC2O4. H2O Argelia Ramirez Date: October 28, 2020 Objective: To determine the concentration of an unknown solution of CaC2O4 by gravimetric analysis method. As well as to learn how to use the process to find the amount of calcium. This accurate method will help is to determine the concentration of the unknown by the mass of the known precipitate. Introduction: Gravimetric analysis is a laboratory technique that is used to determine the mass the mass concentration of a substance by measuring the change in the mass, in this case by applying heat. Gravimetric analysis is a method in which the application of precipitation, a reaction in which an insoluble product is formed by two soluble substances reacting (Kan Wu and Mousavi, 2017). Conventional gravimetric methods are high accuracy, up to tenths of rel. % (Shneider, Alekseeva, and Karpov, 2014).This method can be time consuming and laborious but this procedure remain indispensable in the analysis of rich materials like, alloys, salt, preconcentrates, technological solutions, and others (Shneider, Alekseeva, and Karpov, 2014). Gravimetric analysis is not only use in a chemical laboratory. This method is also use in the food industry for the determination of packaging residues in feed (Giuseppina, at el, 2017). It is also use for the determination of hardness in water. This method is useful because it only needs simple stoichiometry to find the amount of reactant from a reaction that was used to make a product from the weight of product received. This process is an essay way to precise analysis of the product or element wanted and it has very little instrumental error. In this experiment the use of gravimetric analysis will help us to determine the molarity of Calcium from the precipitation of an aqueous of ammonium oxalate and urea. Materials and Method: The procedure was given by the TA’s through blackboard. It is going to be attach in this section. 1. Dry three medium-porosity, sintered-glass funnels for 1–2 h at 105 WC. Cool them in a desiccator for 30 min and weigh them. Repeat the procedure with 30-min heating periods until successive weighings agree to within 0.3 mg. Use a paper towel or tongs, not your fingers, to handle the funnels. Alternatively, a 900-W kitchen microwave oven dries the crucible to constant mass in two heating periods of 4 min and 2 min (with 15 min allowed for cooldown after each cycle). You will need to experiment with your oven to find appropriate heating times. 2.Use a few small portions of unknown to rinse a 25-mL transfer pipet, and discard the washings. Use a rubber bulb, not your mouth, to provide suction. Transfer exactly 25 mL of unknown to

each of three 250- to 400-mL beakers, and dilute each with ~75 mL of 0.1 M HCl. Add 5 drops of methyl red indicator solution to each beaker. This indicator is red below pH 4.8 and yellow above pH 6.0. 3.Add ~25 mL of ammonium oxalate solution to each beaker while stirring with a glass rod. Remove the rod and rinse it into the beaker with small portions of distilled water. Add ~15 g of solid urea to each sample, cover it with a watchglass, and boil gently for ~30 min until the indicator turns yellow. 4.Filter each hot solution through a weighed funnel, using suction (Figure 2-17 in the textbook). Add ~3 mL of ice-cold water to the beaker and use a rubber policeman to help transfer the remaining solid to the funnel. Repeat this procedure with small portions of ice-cold water until all of the precipitate has been transferred to the funnel. Finally, use two 10-mL portions of icecold water to rinse each beaker, and pour the washings over the precipitate. 5.Dry the precipitate, first with aspirator suction for 1 min, then in an oven at 105 WC for 1–2 h. Bring each filter to constant mass. The product is somewhat hygroscopic, so only one filter at a time should be removed from the desiccator, and weighings should be done rapidly. Alternatively, the precipitate can be dried in a microwave oven once for 4 min, followed by several 2-min periods, with cooling for 15 min before weighing. This drying procedure does not remove the water of crystallization. The chemical that were use in this laboratory are the following: Ammonium oxalate solution; Is an oxalate salt with ammonium. It is a colorless to white salt under standard conditions, odorless and non-volatile. It is usually use in pesticides as a inert ingredient for preventing, destroying or mitigating pests. In it monohydrate for it has a purity of 98 – 100.5%. It is harmful if it has contact with skin, swallowed, and cause serious irritation, can cause irritation or severe burns. In case of ingestion or excessive inhalation of dust causes systematic poisoning, some possible symptoms are pain in throat, esophagus and stomach. As well as mucous membrane turn white, vomiting, sever purging, weak pulse, cardiovascular collapse, and neuromuscular symptoms. It is soluble in water. Chemical Formula: (NH4)2C2O4 Structure:

Molecular weight: 124.1 g/mol

Density: 1.5 at 65.3 C

Methyl red indicator: Is a pH indicator is red at a pH under 4.4, yellow in pH over 6.2, and orange in between. It has a pKa of 5.1. It is an azo dye consisting of benzoic acid substitute at position 2 by 4- diazinyl group. It has a role as a dye. It is a member of azobenzenes, a monocarboxylic acid and a tertiar amino compound. It is a conjugate acid of a methyl red. It has a dark red color It is crystalline powder. Products used outside the home (includes outdoor toys such as sandboxes, canopies and shelters, garden statues, outdoor lighting and seating, outdoor power equipment, etc. Suspected of causing cancer, toxic to aquatic life with long lasting effects. It is hazardous to the aquatic environment, and it is a long-term hazard. It is soluble in very hot acetone, benzene, and chloroform. Almost insoluble in water. Chemical Fórmula: C15H15N3O2 Density: .791 g/cm3

Molecular Weight: 269.3 g/mol

Melting point:183 C

Structure:

Chloridric Acid: Hydrochloric acid, also known as HCl or hydrochloride, belongs to the class of inorganic compounds known as halogen hydrides. Hydrochloric acid is a potentially toxic compound. It is a colorless watery liquid with a sharp, irritating odor solution. It has many uses, including cleaning, pickling, electroplating metals, tanning leather, and refining and producing a wide variety of products. Hydrogen chloride can be formed during the burning of many plastics. Upon contact with water, it forms hydrochloric acid. Both hydrogen chloride and hydrochloric acid are corrosive. It is soluble in water and ethanol. It is not flammable. Hydrochloric acid is used in the production of chlorides, for refining ore in the production of tin and tantalum, for pickling and cleaning of metal products, in electroplating, or the neutralization of basic systems, as a laboratory reagent, as a catalyst and solvent in organic syntheses, in the manufacture of fertilizers and dyes, as well as the food industry. Causes severe skin burns and eye damage, is toxic if it is inhale. Inhalation of fumes results in coughing and choking sensation, and irritation of nose and lungs. Liquid causes burns.

Chemical Formula: HCl

Molecular Weight: 36.46 g/mol

Density: 1.00045 g/l

Structure:

Urea: is a nitrogenous compound containing a carbonyl group attached to two amine groups with osmotic diuretic activity. In vivo, urea is formed in the liver via the urea cycle from ammonia and is the final end product of protein metabolism. Administration of urea elevates blood plasma osmolality, resulting in enhanced flow of water from tissues, including the brain, cerebrospinal fluid and eye, into interstitial fluid and plasma, thereby decreasing pressure in those tissues and increasing urine outflow. Urea appears as solid odorless white crystals or pellets. It is soluble in water and ethanol. It is not flammable. It has therapeutic uses, as well as food additive, and in agriculture. GHS hazard statements has not classified. It causes redness and irritation of skin and eyes. It melts and decomposes, generating ammonia. Chemical Formula: NH2CONH2

Structure:

Unknown solution.

Molecular Weight: 60.056 g/mol Density 1.335: g /cc.

Results and Discussion: The data give it by the TA’s is the following: Experiment 1 Experiment 2 Experiment 3 Mass of funnel 31.6427g 32.1529g 31.8112g Mass of funnel + CaC2O2xH2O 38.7612g 39.2712g 38.8712g

Average of CaCO3 = 7.1185+7.1183+ 7.06 / 3 = 7.099g Weight Percent = 7.099g/ 40.079 = 17.71%

Precipitated Molarity of CaC2O4 Average molarity of Ca2+

Experiment 1 7.1185g .556 M .554 M

Experiment 2 7.1183g .556 M

Experiment 3 7.06g .551 M

To determine the molarity of calcium in the unknown solution and be more accurate the experiment was performed three times. From this different performance we took the average of the molarity to determine the calcium concentration from the CaC2O4 precipitate. The average concertation of calcium was .554M, with a 17.71% of weight percent. We also took the standard deviation of the molarity which is 5.27x10 -3. The experiment was done for the TA and then she reports the result to us so we can make the calculations. Conclusion After the performance of this experiment and the results present, we learn the following; For the conversion of mass it is necessary to know the stoichiometry of the reactions. We also know that an insoluble compound forms when the precipitating reagent is added to a solution containing the analyte. Even though it is a long process it is very accurate and effective. Gravimetric analysis determination is the primary method as the final analytical signal is weight of substance for the measurement of which high precision primary standard are available and it has an accuracy of u to .0001g and higher ( Alekseeca and Karpov, 2014).

References Amato G, Desiato R, Giovannini T, et al. Gravimetric quantitative determination of packaging residues in feed from former food. Food Additives & Contaminants Part A: Chemistry, Analysis, Control, Exposure & Risk Assessment. 2017;34(8):1446-1450. doi:10.1080/19440049.2017.1337277 Ferreira D, Barros M, Oliveira CM, da Silva RJNB. Quantification of the uncertainty of the visual detection of the end-point of a titration: Determination of total hardness in water. Microchemical Journal. 2019;146:856-863. doi:10.1016/j.microc.2019.01.069 Shneider B, Alekseeva T, Karpov Y. Application of atomic emission spectroscopy to the correction of the results of the gravimetric determination of platinum and palladium in materials of complex composition. Journal of Analytical Chemistry. 2015;70(10):1236-1242. doi:10.1134/S1061934815100147 Wu LK, Mousavi A. Determination of thiosulfate concentrations by gravimetric analysis: A desirable experiment for chemical education. Phosphorus, Sulfur & Silicon & the Related Elements. 2017;192(9):1074-1077. doi:10.1080/10426507.2017.1330828 Chemicals information and image retrieved from: “PubChem.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, pubchem.ncbi.nlm.nih.gov/.

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