Pre- Lab Questions
1. Using your textbook or a handbook, look up the formula and structure of potassium hydrogen phthalate (KHP) used to standardize the solution of NaOH in this experiment. Calculate the Molar Mass of KHP. Molar Mass= 204.22 g/mol
2. Using your textbook or chemical dictionary, write the definition of indicator.
Indicator- a substance added at the beginning of the titration that changes color at (or very near) the equivalence point.
3. Suppose a sodium hydroxide solution were to be standardized against pure solid primary standard grade KHP. If 0.4538 g of KHP requires 44.12 mL of the sodium hydroxide to reach a phenolphthalein endpoint, what is the molarity of the NaOH solution?
Standardization of NaOH Titrant
| Sample 1| Sample 2 | Sample 3|
Weight of KHP taken| 0.80 g| 0.60 g| 0.70 g|
Initial NaOH buret reading| 1.80 mL| 2.10 mL| 1.64 mL|
Final NaOH buret reading| 42.40 mL| 33.20 mL| 37.50 mL| Volume NaOH used| 40.60 mL| 31.10 mL| 35.86 mL|
Moles of KHP present| .003917 mols| .002938 mols| .003428 mols| Molarity of NaOH solution| .09648 M| .09447 M| .09559 M| Mean Molarity of NaOHSolution and average deviation| 0.09551 M|
Analysis of Vinegar Solution
| Sample 1| Sample 2| Sample 3|
Quantity of Vinegar taken| 5.00 mL| 4.95 mL| 5.10 mL|
Initial NaOH buret reading| 4.00 mL| 0.00 mL| 1.55 mL|
Final NaOH buret reading| 47.5 mL| 41.00 mL| 47.40 mL|
Volume NaOH used| 43.50 mL| 41.00 mL| 45.85 mL|
Molarity of Vinegar| .831 M| .791 M| .859 M|
Mean molarity of Vinegar and average deviation| .827 M|
% by mass acetic acid present| 4.96%|
1. Commercial vinegar is generally 5.0 0.5 % acetic acid by weight. Assuming this to be the true value for your unknown, how much were you in error in your analysis?
2. The solid acids chosen for the analysis were typically...