# Measuring The Ph And Concentration Of The Citric Acid

453 Words2 Pages
The purpose of this lab was to estimate and calculate the pH and concentration of the citric acid being used, in this case lemon juice. To measure the pH of the citric acid using the pH paper, a piece of pH paper is placed into the citric acid, changing the color of the paper. This is then compared to a chart that has average colors of paper of different pHs. To calculate the pH of the Citric Acid through titration a buret was used to dispense the base, NaOH, in to the acid H3C6H5O7. Since acids donate protons to solutions and bases accept these donated protons, a moment of equilibrium occurs. To recognize this moment of equilibrium, a color changing solution was added to the acid. Phenolthalein, which is colorless in acids and pink in bases, was mixed in with the citric acid.…show more content…
When the pink remained longer in the solution, this means that the solution is getting closer to equilibrium. Once the solution become neutral during the titration, the originally clear mixture become a light peach. The volume of base resulting in the equilibrium was measured. Once the average volume of base required to cause equilibrium with the acid was found, the moles of Sodium Hydroxide (NaOH) can be calculated. This is done by dividing the molarity of the NaOH by the volume of NaOH. Once this is found, the moles of Citric Acid can be calculated by multiplying the moles of NaOH by the molar ratio, which in this case was one mole H3C6H5O7 to 3 moles NaOH. To find the concentration of the Citric Acid, the moles of Citric Acid is divided by the volume of the Citric Acid in liters. Since Citric Acid is Polyprotic, which means that it can donate three proton to the solution, the quotient is then multiplied by three to get the concentration. From the concentration, the pH can be calculated. This is found by taking the negative log of the concentration of the