Lab 6: Acid-Base Titration Flashcards

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Questions and Answers

What is the purpose of this lab?

Determine molecular weight of an unknown acid by reacting the acid with standardized sodium hydroxide.

What does 'monoprotic' mean?

Can generate one $H^+$ per molecule (correct)

Can generate two $H^+$ per molecule

Can generate multiple $H^+$ per molecule

Can generate three $H^+$ per molecule

What does 'diprotic' refer to?

Can generate three $H^+$ per molecule

Cannot generate $H^+$

Can generate one $H^+$ per molecule

Can generate two $H^+$ per molecule (correct)

What does 'triprotic' indicate?

Can generate three $H^+$ per molecule Signup and view all the answers

What is titration?

A process for ascertaining the exact volume of a solution that reacts stoichiometrically with a given volume of a second solution. Signup and view all the answers

What is the endpoint in a titration?

Occurs when stoichiometric quantities of acid and base have been mixed. Signup and view all the answers

What role does phenolphthalein play in titrations?

It is an indicator used to signal the endpoint, turning from colorless in acidic solutions to pink in basic solutions. Signup and view all the answers

What is the objective of the procedure?

Determine the actual concentration of NaOH solution for calculations in Part B. Signup and view all the answers

What is the procedure for Part A?

Prepare dilute NaOH solution and standardize it using oxalic acid. Signup and view all the answers

What does Part B of the procedure entail?

Using the NaOH solution to determine the molecular weight of the unknown acid. Signup and view all the answers

Calculate the number of moles of oxalic acid that can neutralize 25 mL of NaOH with a molarity of 0.12 M.

Calculate using the stoichiometric equation and molarity conversion. Signup and view all the answers

What calculations are required for the standardization of NaOH solution?

Find moles of H2C2O4*2H2O used and determine available protons for reaction. Signup and view all the answers

How do you calculate the molecular weight of unknown acid?

Find moles of NaOH reacting with unknown acid, then use mass and moles for calculation. Signup and view all the answers

What is the precise density calculation for your standardized NaOH solution?

Use the moles of NaOH and its molarity to find the density in g/mL. Signup and view all the answers

Study Notes

Purpose of Lab

Aims to determine the molecular weight of an unknown acid.
Reacts the acid with standardized sodium hydroxide (NaOH).

Acid Types

Monoprotic Acids: Produce one H+ ion per molecule (e.g., HCl, HNO3).
Diprotic Acids: Produce two H+ ions per molecule (e.g., H2SO4, H2C2O4).
Triprotic Acids: Produce three H+ ions per molecule (e.g., H3PO4).

Titration Process

Titration assesses the exact volume of a solution needed to react stoichiometrically with another solution.
One reagent is added from a burette until reaching the endpoint.

Endpoint

Achieved when stoichiometric quantities of acid and base have been mixed, indicated by [H+] = [OH-].

Indicator

Phenolphthalein: Used to indicate the endpoint in strong acid-base titrations.
Colorless in acidic solution, turns pink in basic solution.

Objective of Procedure

To determine the actual concentration of NaOH solution for calculations in Part B.

Part A: Standardization of NaOH Solution

Prepare dilute NaOH, standardize using oxalic acid through titration.
Endpoint indicated by a faint pink color change.
pH of clear oxalic acid solution is 8.
Use 2 drops of phenolphthalein in the Erlenmeyer flask containing approx. 0.5 grams of oxalic acid.

Part B: Determination of Molecular Weight of Unknown Acid

Utilize NaOH solution from Part A to find the molecular weight of the unknown acid.
Weigh 0.2 - 0.25 grams of the unknown acid.
Titrate in three flasks similarly to Part A, determining the number of reactive protons from the teacher's assistant.

Calculating Moles and Grams of Oxalic Acid

Given a NaOH molarity of 0.12 M, use the balanced equation for neutralization.
Calculate moles of NaOH using Molarity equation (moles = Molarity x Liters).
Convert moles of NaOH to moles of oxalic acid.
Convert moles of oxalic acid to grams.

Calculations A: Standardization of NaOH

Calculate moles of oxalic acid used by determining mass difference and applying molar mass.
Convert moles of oxalic acid to moles of H+ ions available for reaction.
Find moles of hydroxide ions (OH-) that reacted.
Calculate precise molarity of NaOH solution based on titration data volumes.

Calculations B: Molecular Weight of Unknown Acid

Calculate moles of NaOH that reacted with the unknown acid using molarity and volume.
Determine moles of unknown acid using the appropriate chemical reaction equation.
Calculate the molecular weight of the unknown acid from mass used and moles calculated.

Density of Standardized NaOH Solution

Find mol of NaOH and convert to grams using molar mass.
Convert grams to moles and perform volume calculations in liters.
Convert liters to milliliters to find density (grams per mL).

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Description

This quiz focuses on the key concepts of Acid-Base Titration from Lab 6. Learn the definitions of monoprotic, diprotic, and triprotic acids, as well as the purpose of the lab in determining the molecular weight of an unknown acid. Test your knowledge of these important chemistry terms and processes.