Abstract
Chemistry
Published: Not Published
In the first part of the lab, you will use a 50% w/w solution of NaOH to prepare 500 mL of ~0.1 M. The 50% w/w NaOH is indicative of its weight ratio. For example, if the instructor prepared 150 mL of the 50% w/w NaOH solution, then 150 g of NaOH was dissolved in 150 g of water, and the total weight of the solution is 300 g.
Density of 50% w/w stock solution | 1.53 g/mL |
Molar massNaOH | 39.998 g/mol |
Mass of NaOH in 50% w/w stock solution (mg) | |
Total mass of 50% w/w stock solution | |
Volume of 50% w/w stock solution (mL) | |
Moles of NaOH in 50% w/w solution (mol) | |
Molarity of 50% w/w stock solution (M1) | |
Volume of 50% w/w solution needed (V1) |
After you have prepared 0.1 M NaOH, determine its exact concentration, or standardize it, using the acid-base titration method. In this technique, a base like NaOH is slowly added to an acid like potassium hydrogen phthalate (KHP). The chemical reaction that takes place in the flask is a neutralization reaction. In this neutralization reaction, one mole of base neutralizes one mole of acid, resulting in salt and water. This reaction is performed in the presence of the indicator phenolphthalein, which is colorless at the start of the reaction when the pH is acidic. The indicator turns pink as soon as enough NaOH is added to the flask to make the pH basic.
Molar massKHP = 204.23 g/mol | Flask A | Flask B | Flask C |
Mass of KHP (g) | |||
Volumeinitial NaOH(mL) | |||
Volumefinal NaOH (mL) | |||
VolumeNaOH (mL) | |||
Moles of KHP | |||
Moles of NaOH | |||
Molarity of NaOH | |||
Average molarity | |||
Standard deviation |
In this experiment, we will determine two of the three pKa values for the triprotic acid, phosphoric acid, using acid-base titration. In this neutralization reaction, phosphoric acid reacts with NaOH to form water and the salt, sodium phosphate.
Volume1st equivalence point (mL) | |
Volume1st half-equivalence point (mL) | |
Volume2nd equivalence point (mL) | |
Volume2nd half-equivalence point (mL) | |
1st pKameasured | |
1st pKatheoretical | 2.16 |
2nd pKameasured | |
2nd pKatheoretical | 7.21 |
Moles of NaOH | |
Moles of H3PO4 | |
Molarity of H3PO4 |
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