Determining Molar Concentration of a Sodium Hydroxide Solution PDF

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Determining Molar Concentration of a Sodium Hydroxide Solution

Purpose of the lab: To determine the molar concentration of a sodium hydroxide (NaOH) solution by using the Titration Method. Fundamental principle or theory behind the experiment: In this lab we neutralized an acid with a base by using titration, and then using information collected figured out the molar concentration of the NaOH solution. All neutralization reactions in general work like this: Acid + Base  Salt + Water or in our case KHC₈H₄O₄ + NaOH  NaKC₈H₄O₄ + H₂O The brief procedure(s) or method(s) to reach the goal of the experiment: To start off we measured out 100mL of NaOH solution, and cleaned the buret first with water and then twice with 5mL of the NaOH. We covered the rest of our NaOH solution with paraffin and put it to the side. Next we weighed a sample of KHP which was 2.54g. Using this number we calculated the moles of KHP by using 204.2g per mole as the molar mass of KHP. The result was 0.0147moles. We then diluted this sample with 40mL of water, and added 3 drops of indicator (phenolphthalein) to this solution. Then we poured 50mL (to the 0 line) of our NaOH solution into the buret, and slowly started titrating the acid (KHP) with the base (NaOH). We titrated one drop at a time while constantly stirring the solution. With every drop the KHP solution would turn pink for a moment and then turn back to clear. When it finally turned pink and stayed that way we knew that the reaction was complete, and we stopped titrating, took the reading on the buret and noted that to be the volume of NaOH (22.8mL). Since we knew from our acid/base formula that the stoichiometric ratio of KHP to NaOH is 1:1, we knew that the amount of moles of NaOH used was the same as the moles of KHP calculated earlier. With this information and the volume we got from titration we easily calculated the molarity concentration of NaOH and found it to be 0.544M. We then repeated the entire experiment with a new sample of KHP (3.1g) and found the amount of moles to be 0.0152, the volume of NaOH used to titrate 25.7mL, and the molarity of NaOH 0.549M. Finally we took the average of our two results which was 0.5465M and that was our mean molarity. Please see attached Data Sheet for any findings and measurements. Discussion regarding possible experimental errors: There are a few errors that could have occurred:  

It was important to be very precise in all of our measurements (weight of initial sample of KHP, titration volume of NaOH, etc…) since our results are all based off of one another. It was also very important to clean the buret very carefully and to make sure no water was stuck to the sides. If water was stuck on the inside of the buret, our reading would be off since it would look like more NaOH was used.

Conclusion: Titration seems to be a very good way to calculate the molarity of an acid or a base. This information could then also be used to find the percent concentration of either solution.

Please see attached Calculations and Conclusions page for more detailed answers on the experiment....