TITULAÇÃO ACIDO-BASE: Cálculos passo a passo (Ensino médio)

Summary

This video explains a titration experiment to determine the concentration of acetic acid in vinegar. Using a burette with a sodium hydroxide solution of known concentration, the vinegar's acetic acid content is titrated until the solution turns a faint pink, signaling neutralization. The process involves calculating molarity and converting it into mass percentage, ultimately showing the acetic acid percentage in vinegar is around 4.5%, slightly higher than the labeled value. The video covers the steps of neutralization reactions, formulas, and conversions necessary for determining the acid concentration and its mass percentage in the solution.

Takeaways

• 😀 The experiment involves a titration, where a known concentration solution (NaOH) is used to determine the concentration of an unknown solution (acetic acid in vinegar).
• 😀 A burette and an Erlenmeyer flask are used in the titration setup, where NaOH is added to the vinegar until the solution turns pink.
• 😀 The titrant used is a sodium hydroxide (NaOH) solution, and the goal is to determine how much NaOH is required to neutralize the acetic acid in vinegar.
• 😀 The neutralization reaction involves acetic acid (from vinegar) reacting with NaOH to produce sodium acetate and water.
• 😀 The endpoint of the titration is indicated when the solution turns slightly pink, showing that all the acetic acid has been neutralized.
• 😀 A volume of 15 ml of NaOH was required to neutralize 20 ml of vinegar in the experiment.
• 😀 The relationship between the concentration and volume of the titrant and the unknown solution is given by the equation: C1 * V1 = C2 * V2.
• 😀 The concentration of NaOH (C1) used in the experiment was 1 mol/L, and the volume of NaOH used was 15 ml (converted to 0.015 L).
• 😀 The concentration of acetic acid in the vinegar (C2) was calculated to be 0.75 mol/L using the equation from the titration.
• 😀 To find the mass percentage of acetic acid in vinegar, the molar mass of acetic acid (60 g/mol) is used to convert the concentration from mol/L to g/L, resulting in 45 g/L of acetic acid in the vinegar.
• 😀 Finally, the mass percentage of acetic acid is calculated to be 4.5%, which is slightly higher than the 4% stated on the vinegar label.

Q & A

What is the purpose of the titration experiment discussed in the transcript?

The purpose of the titration experiment is to determine the concentration of acetic acid in vinegar, which is typically unknown. The experiment uses a known concentration of sodium hydroxide (NaOH) as a titrant to neutralize the vinegar and calculate the acetic acid concentration.

What equipment was used in the titration experiment?

The titration experiment used a burette to dispense the titrant (NaOH solution), and a Wellen Mayer flask, which contained the vinegar solution.

What is the role of the sodium hydroxide (NaOH) solution in the experiment?

The sodium hydroxide (NaOH) solution serves as the titrant with a known concentration, used to neutralize the acetic acid in the vinegar. The volume of NaOH required to reach the endpoint allows for the calculation of the acetic acid concentration in the vinegar.

What reaction occurs during the titration process?

During the titration, an acid-base neutralization reaction occurs. The acetic acid in the vinegar (CH3COOH) reacts with the sodium hydroxide (NaOH), producing sodium acetate (CH3COONa) and water (H2O).

How is the endpoint of the titration experiment identified?

The endpoint is identified when the solution in the Wellen Mayer flask turns a faint pink color, indicating that all the acetic acid has been neutralized by the sodium hydroxide.

What formula is used to calculate the concentration of acetic acid in the vinegar?

The formula used is C1 × V1 = C2 × V2, where C1 is the concentration of NaOH, V1 is the volume of NaOH used, C2 is the concentration of acetic acid (which we want to determine), and V2 is the volume of vinegar.

How is the concentration of acetic acid in the vinegar calculated?

The concentration of acetic acid is calculated by rearranging the formula C1 × V1 = C2 × V2 to solve for C2. The known concentration of NaOH (C1) and the volume of NaOH used (V1) are substituted into the equation, along with the known volume of vinegar (V2), to determine the concentration of acetic acid (C2).

What is the molar mass of acetic acid (CH3COOH), and why is it important?

The molar mass of acetic acid is 60 grams per mole. This value is important because it allows us to convert the concentration of acetic acid from moles per liter (mol/L) to grams per liter (g/L), which is more understandable for practical purposes like determining percentage composition.

How is the percentage by mass of acetic acid in vinegar determined?

The percentage by mass of acetic acid is determined by first calculating its concentration in grams per liter (g/L). Then, the concentration in g/L is divided by 1000 (since the density of water is 1 g/mL) and multiplied by 100% to get the mass percentage.

What was the final result for the percentage of acetic acid in the vinegar sample, and how does it compare to the label?

The final result for the percentage of acetic acid in the vinegar was 4.5%. This is slightly higher than the 4% acetic acid concentration typically indicated on the vinegar's label, confirming the accuracy of the titration process.