NaOH Standardization and Titration: Key Concepts and Procedures

What is the purpose of standardizing a NaOH solution?

To determine the concentration of a not accurately known NaOH solution.

What is the first step in the dilution of the NaOH solution?

Transfer 25 mL of the supposedly 1.0 M NaOH solution to a 250 mL volumetric flask and bring it up to volume with deionized water.

How should the volumetric flask be mixed after dilution?

Invert the volumetric flask 20 times to ensure thorough mixing.

What is the balanced equation for the reaction between NaOH and CO2?

2 NaOH (s or l) + CO2 (g) → Na2CO3 (aq) + H2O (l)

Why is it important to minimize CO2 absorption in NaOH solutions?

CO2 uptake can change the concentration of the NaOH solution by forming Na2CO3.

What is the molarity of the diluted NaOH solution prepared for titration?

Approximately 0.1 M after diluting the 1 M NaOH solution 10 times.

What is the endpoint indicator used in the titration with KHP?

Phenolphthalein.

How do you know when you have reached the endpoint of the titration?

The pink color does not disappear after 15 seconds of swirling.

What should be done with the burette before use?

Rinse it with distilled water and then with the NaOH solution.

What is the precision of volume readings for the 50 mL burets used in the titration?

Volume readings can be made with a precision of 0.02 mL.

What is the significance of weighing KHP before the titration?

To know the exact amount of KHP used for calculating moles and determining the concentration of NaOH.

What is the expected relationship between the molarity of the diluted NaOH and the original NaOH?

The original NaOH solution should be about 10 times more concentrated than the diluted solution.

How should NaOH be added during the titration process?

Initially, add about 1 mL at a time, then decrease to just a drop or two near the endpoint.

What is the role of KHP in the titration process?

KHP acts as a primary standard to determine the concentration of NaOH.

What is the maximum weight of KHP to be used in the experiment?

Between 0.300 ± 0.10 g.

What should be done if the results of the titration trials are not sufficiently close?

Repeat the titration a third time.

What is the importance of swirling the flask during titration?

To ensure proper mixing of the NaOH solution with KHP for accurate endpoint determination.

What is the effect of moisture on sodium hydroxide?

Moisture absorption leads to the formation of Na2CO3, affecting the NaOH concentration.

What is the final step after determining the molarity of the NaOH solution?

Report the average molarity of the base after repeating the standardization.

What is the purpose of standardizing a sodium hydroxide solution in titration?

To determine the concentration of the NaOH solution using a primary standard, potassium hydrogen phthalate (KHP).

What is titration?

An analytical method used to determine the concentration of a solution through a reaction with a solution of known concentration.

What is the role of a burette in a titration experiment?

To dispense measured increments of one solution into a known volume of another solution.

What indicator is used in this experiment and what color change indicates the endpoint?

Phenolphthalein; it turns pink in basic solutions and remains colorless in acidic or neutral solutions.

What is the endpoint of a titration?

The point where the indicator changes color, indicating that the reaction is complete.

What is the equivalence point in an acid-base reaction?

The point at which equal amounts of acid and base have reacted, meaning moles of H+ ions equal moles of OH- ions.

What is the titration error?

The difference between the equivalence point and the endpoint, usually because the endpoint is slightly after the equivalence point.

Why can't solid sodium hydroxide be used directly in titrations?

It is hygroscopic and absorbs moisture from the air, making it impure.

What is potassium hydrogen phthalate (KHP) used for in this experiment?

It is a primary standard used to accurately determine the concentration of the NaOH solution.

What is the molar mass of potassium hydrogen phthalate (KHP)?

204.22 g/mol.

What is the balanced chemical reaction when potassium hydrogen phthalate is dissolved in water?

KHC8H4O4 (s) → K+ (aq) + HC8H4O4- (aq).

How do you calculate the number of moles of KHP from its mass?

Moles = mass (g) / molar mass (g/mol).

What factors can lead to an increase in titration error?

1) Misreading the burette/not reading the meniscus correctly; 2) Incorrect solution concentration; 3) Leftover substances/water in glassware.

What is the formula for calculating molarity?

Molarity = moles of solute / volume of solution (L).

What is the molarity of NaOH if 0.002 moles are used in 15.5 mL of solution?

Molarity = 0.002 moles / 0.0155 L = 0.129 M.

What is the average molarity of the NaOH solution from the trials?

0.195 M.

What is the initial burette reading in Trial 1?

15.5 mL.

What is the volume of NaOH used in Trial 2?

15.2 mL.

How do you determine the moles of NaOH used in a titration?

By using the molarity of NaOH and the volume used in the titration.