Calcium levels in blood can be determined by adding oxa-late ion to precipitate calcium oxalate, CaC2O4, followed by dissolving the precipitate in aqueous acid and titrating the resulting oxalic acid (H2C2O4) with KMnO4:
How many milligrams of Ca2+ are present in 10.0 mL of blood if 21.08 mL of 0.000 988 M KMnO4 solution is needed for the titration?
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1
Determine the moles of KMnO_4 used in the titration by multiplying the volume of KMnO_4 solution (in liters) by its molarity.
Write the balanced chemical equation for the reaction between KMnO_4 and H_2C_2O_4. Use this equation to find the stoichiometric ratio between KMnO_4 and H_2C_2O_4.
Calculate the moles of H_2C_2O_4 that reacted using the stoichiometric ratio from the balanced equation.
Since the moles of H_2C_2O_4 are equal to the moles of CaC_2O_4, determine the moles of Ca^2+ present, as each mole of CaC_2O_4 contains one mole of Ca^2+.
Convert the moles of Ca^2+ to milligrams using the molar mass of calcium (Ca).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Precipitation Reactions
Precipitation reactions occur when two soluble reactants form an insoluble product, or precipitate. In this case, calcium ions (Ca2+) react with oxalate ions (C2O4^2-) to form calcium oxalate (CaC2O4), which can be separated from the solution. Understanding this concept is crucial for determining the amount of calcium in the blood, as it sets the stage for subsequent analysis.
Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. In this scenario, the oxalic acid produced from the dissolved calcium oxalate is titrated with a potassium permanganate (KMnO4) solution. The endpoint of the titration indicates that all the oxalic acid has reacted, allowing for the calculation of the original calcium concentration based on the volume and molarity of the KMnO4 used.
Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. In this problem, stoichiometry is essential for relating the amount of KMnO4 used in the titration to the amount of oxalic acid produced, and subsequently to the amount of calcium ions in the original blood sample. This allows for the conversion of titration data into a meaningful measurement of calcium concentration.
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