Acid base titration example | Chemistry | Khan Academy

Khan Academy
15 Oct 201012:31
EducationalLearning
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TLDRThe video script describes a chemistry problem involving the determination of the mass and mass percent of oxalic acid in a sample. The problem is solved using stoichiometry, with the balanced chemical equation and molar masses of the reactants and products taken into account. The calculation reveals that the impure oxalic acid sample contains 72.7% oxalic acid by mass.

Takeaways
  • 🧪 The problem is derived from a chemistry textbook, specifically Chapter 4 of 'Chemistry & Chemical Reactivity' by Kotz, Treichel, and Townsend.
  • 🧬 An impure sample of oxalic acid weighing 1.034 grams is dissolved in water and titrated with sodium hydroxide solution to determine its mass and mass percent.
  • 🌟 Oxalic acid has the ability to donate two protons, which is unique and important for the titration process.
  • 📈 The balanced chemical equation for the reaction shows that two moles of hydroxide ions (from sodium hydroxide) are needed to neutralize one mole of oxalic acid.
  • 🔢 34.47 mL of 0.485 M sodium hydroxide solution is used to reach the equivalence point, indicating the amount of sodium hydroxide that reacted with the oxalic acid.
  • 📐 Calculations involve converting milliliters to liters, finding the moles of sodium hydroxide, and then determining the moles of oxalic acid based on the stoichiometry of the reaction.
  • 🔍 The molar mass of oxalic acid (H2C2O4) is determined to be 90 grams per mole by adding the atomic masses of its constituent elements (hydrogen, carbon, and oxygen).
  • 📝 From the moles of oxalic acid and its molar mass, the mass of oxalic acid in the sample is calculated to be 0.752 grams.
  • 🎯 The mass percent of oxalic acid in the impure sample is found to be 72.7%, which is derived by dividing the mass of oxalic acid by the total mass of the sample and multiplying by 100.
  • 🧠 The process requires understanding of titration, stoichiometry, and molar mass calculations, which are fundamental concepts in chemistry.
  • 📚 The example serves as a practical application of chemistry principles, showcasing the importance of accurate measurements and calculations in determining the composition of substances.
Q & A

  • What is the chemical formula of oxalic acid?

    -The chemical formula of oxalic acid is H2C2O4.

  • How many protons can oxalic acid donate?

    -Oxalic acid can donate two protons.

  • What is the significance of the double bond in the oxalic acid molecule?

    -The double bond in the oxalic acid molecule indicates the presence of two carbonyl groups, each with a carbon atom double-bonded to an oxygen atom.

  • How much sodium hydroxide is required to reach the equivalence point with the impure oxalic acid sample?

    -34.47 milliliters of 0.485 molar sodium hydroxide is required to reach the equivalence point with the impure oxalic acid sample.

  • What is the balanced chemical equation for the reaction between oxalic acid and sodium hydroxide?

    -The balanced chemical equation is: H2C2O4 (aq) + 2 NaOH (aq) → C2O4^2- (aq) + 2 H2O (l) + 2 Na+ (aq).

  • How many moles of sodium hydroxide are present in 34.47 milliliters of a 0.485 molar solution?

    -There are 0.0167 moles of sodium hydroxide in 34.47 milliliters of a 0.485 molar solution.

  • What is the molar mass of oxalic acid?

    -The molar mass of oxalic acid is 90 grams per mole.

  • How many grams of oxalic acid are in the 1.034 gram sample?

    -There are 0.752 grams of oxalic acid in the 1.034 gram sample.

  • What is the mass percent of oxalic acid in the impure sample?

    -The mass percent of oxalic acid in the impure sample is 72.7%.

  • How does the mass of oxalic acid in the sample compare to the total mass of the sample?

    -The mass of oxalic acid (0.752 grams) makes up 72.7% of the total mass of the impure sample (1.034 grams).

  • What is the role of the acid-base indicator in this experiment?

    -The acid-base indicator is used to determine the equivalence point in the titration process, which is when the reaction between the acid (oxalic acid) and the base (sodium hydroxide) is complete.

  • Why is it necessary to convert milliliters to liters in the calculations?

    -Converting milliliters to liters is necessary to match the units with the molarity, which is expressed in moles per liter, allowing for easier calculation and understanding of the solution's concentration.

Outlines
00:00
📚 Introduction to Oxalic Acid and Problem Statement

This paragraph introduces the source of the problem, which is a question from the book 'Chemistry & Chemical Reactivity' by Kotz, Treichel, and Townsend. The problem involves calculating the mass and mass percent of oxalic acid in a sample based on its reaction with sodium hydroxide. The paragraph sets the stage for the chemical analysis by describing the chemical structure of oxalic acid, its ability to donate two protons, and the role of sodium hydroxide in the reaction. The balanced chemical equation is also introduced, highlighting the need for two hydroxide ions to neutralize one molecule of oxalic acid.

05:01
🧪 Calculation of Moles of Sodium Hydroxide

In this paragraph, the video script focuses on calculating the actual number of sodium hydroxide molecules in the given solution. The concentration of the sodium hydroxide solution is known (0.485 molar), and the volume of the solution used in the reaction is given (34.47 milliliters). The calculation involves converting the volume to liters and then determining the moles of sodium hydroxide present. The result is 0.0167 moles of sodium hydroxide, which is a crucial step in the overall calculation process.

10:02
📊 Determining Moles and Mass of Oxalic Acid

The final paragraph of the script details the calculation of the moles and mass of oxalic acid. It starts by establishing the relationship between the moles of sodium hydroxide and oxalic acid, which is a 2:1 ratio. Using the previously calculated 0.0167 moles of sodium hydroxide, the moles of oxalic acid are determined to be 0.00835. The molar mass of oxalic acid is then used to calculate the mass of oxalic acid in the sample, which is found to be 0.752 grams. Finally, the mass percent of oxalic acid in the impure sample is calculated to be 72.7%, providing a clear answer to the problem presented.

Mindmap
Keywords
💡Oxalic Acid
Oxalic acid is a chemical compound with the formula C2H2O4, consisting of two carboxylic acid groups joined together. In the video, it is mentioned as the substance being analyzed, which can donate two protons and is interesting due to its ability to form a negatively charged ion after losing these protons. The mass of oxalic acid in the sample is one of the key calculations performed in the video.
💡Acid-Base Indicator
An acid-base indicator is a substance that changes color depending on the pH level of a solution, indicating whether the solution is acidic or basic. In the context of the video, an acid-base indicator is added to the oxalic acid solution to signal when the reaction with sodium hydroxide has reached the equivalence point, which is when the acid and base have reacted completely.
💡Equivalence Point
The equivalence point in a titration is the point at which the amount of titrant added equals the amount of analyte present in the solution, signifying the completion of the reaction. In the video, the equivalence point is reached when 34.47 milliliters of sodium hydroxide solution is added to the oxalic acid, indicating that all the oxalic acid has reacted with the sodium hydroxide.
💡Molarity
Molarity is a measure of concentration in moles of solute per liter of solution. It is used in the video to describe the concentration of the sodium hydroxide solution, which is 0.485 molar. This information is crucial for calculating the amount of substance in moles and ultimately determining the mass of oxalic acid in the sample.
💡Sodium Hydroxide
Sodium hydroxide, commonly known as lye or caustic soda, is a strong base that is used in the video as the titrant to neutralize the oxalic acid. It reacts with the acid by accepting protons, and its molarity and volume are used to calculate the moles of oxalic acid present in the sample.
💡Moles
A mole is a unit of measurement used in chemistry to represent the amount of substance. It is defined as the amount of substance that contains as many elementary entities (such as atoms or molecules) as there are atoms in 12 grams of carbon-12. In the video, the number of moles of sodium hydroxide is calculated from its molarity and volume, which is then used to determine the moles of oxalic acid based on the stoichiometry of the reaction.
💡Molar Mass
Molar mass is the mass of one mole of a substance, measured in grams per mole (g/mol). It is calculated by summing the atomic masses of all the atoms in a molecule. In the video, the molar mass of oxalic acid is determined by adding the atomic masses of its constituent elements (hydrogen, carbon, and oxygen) to find out how much one mole of oxalic acid weighs.
💡Stoichiometry
Stoichiometry is the study of the quantitative relationships between reactants and products in a chemical reaction. It is used in the video to determine the ratio of moles of sodium hydroxide to moles of oxalic acid, which is essential for calculating the mass of oxalic acid in the sample based on the balanced chemical equation.
💡Impure Sample
An impure sample refers to a sample that contains the substance of interest mixed with other substances. In the video, the oxalic acid sample is described as impure, meaning it contains not only oxalic acid but also other unknown substances. The goal of the analysis is to determine the mass percentage of oxalic acid in the sample.
💡Mass Percent
Mass percent is a measure of the mass of a particular substance in a sample, expressed as a percentage of the total mass of the sample. In the video, after calculating the mass of oxalic acid, the mass percent is determined by dividing the mass of oxalic acid by the total mass of the impure sample and multiplying by 100.
💡Chemical Reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. In the video, the chemical reaction involves oxalic acid donating protons to sodium hydroxide, resulting in the formation of a negatively charged oxalate ion and water. The balanced equation for this reaction is used to calculate the amount of oxalic acid present in the sample.
Highlights

The problem is derived from a Chemistry textbook by Kotz, Treichel, and Townsend, focusing on oxalic acid.

A 1.034 gram sample of impure oxalic acid is used in the experiment, dissolved in water with an acid-base indicator.

The titration requires 34.47 milliliters of 0.485 molar sodium hydroxide to reach the equivalence point.

Oxalic acid has the ability to donate two protons, making it an interesting acid for study.

Each molecule of sodium hydroxide can nab one hydrogen proton, and two are needed to fully neutralize oxalic acid.

The balanced chemical equation for the reaction between oxalic acid and sodium hydroxide is provided, showing the formation of water and sodium oxalate.

The molarity of the sodium hydroxide solution is 0.485 molar, which is used to calculate the moles of sodium hydroxide present.

To find the moles of sodium hydroxide, the volume in milliliters is converted to liters and then multiplied by the molarity.

The moles of oxalic acid are determined by dividing the moles of sodium hydroxide by two, as the reaction requires two moles of sodium hydroxide per mole of oxalic acid.

The molar mass of oxalic acid is calculated to be 90 grams per mole, based on the atomic weights of hydrogen, carbon, and oxygen.

The mass of oxalic acid in the sample is calculated to be 0.752 grams.

The mass percent of oxalic acid in the sample is found to be 72.7%.

The process involves understanding the stoichiometry of the acid-base reaction and applying it to determine the composition of the sample.

The experiment demonstrates the use of titration as a method to determine the concentration and purity of a substance.

The theoretical background of the reaction, including the properties of oxalic acid and its ability to donate protons, is explained.

The practical application of the experiment is in determining the mass percent of a compound in a sample, which is a common task in analytical chemistry.

The step-by-step calculation is detailed, providing a clear methodology for solving similar problems in chemistry.

The experiment's results are applicable to various fields, including pharmaceuticals, environmental science, and materials research, where the purity of chemicals is crucial.

Transcripts

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Chemical ReactionOxalic AcidSodium HydroxideNeutralizationMolarityMolar MassMass CalculationChemistry TutorialEducational ContentScientific AnalysisAcid-Base Indicator