Buffers in Household Products: Part B
Buffers in Household Products
Jihyun Yoo
Integrating Content, Inquiry and Reasoning
A buffer is prepared using the conjugate acid-base pair acetic acid and acetate ions.
This is the chemical equations showing the reactions that take place when H+ and when OH- are added to the buffer.
The approximate concentration of a hydrochloric acid solution is 0.5 M. The exact concentration of this solution is to about determined by titration with 0.215 M sodium hydroxide solution.
A 10.00mL sample of the HCI solution was transferred by pipet to an Erlenmeyer flask and then diluted by adding about 40mL of distilled water.
Assume the approximate H3o+ concentration and pH of the solution in the flask before the titration begins.
Phenolphthalein indicator was added, and the solution in the flask was titrated with 0.215 M NaOH until the indicator just turned pink (pH = 8-9). The exact volume of NaOH required was 22.75 mL.
Use the following equation to calculate the concentration of HCI in the original 10.00 mL sample.
Mb x Vb = nMa x Va
Mb = molarity of standard base solution
Vb = volume of base added
n = mole ratio (number of moles of base that react with one mole of acid)
Ma = unknown molarity of acid solution
Va = unknown molarity of acid solution
One of student accidentally "overshot" the endpoint and added 23.90 mL of 0.215 M NaOH.
Is the calculated concentration of HCi likely to be too high or too low as a result of this error?
It would be calculated too high relative to the actual value.
The volume of NaOH and mL or whatever is used to determine the number of moles have been added to the solution, so as it increase and that is the equal to number of moles of acid in case so the number goes up but the volume of HCi is constant, so the beaker won't be affected by anything. The more volume that add, the bigger numerator will be in the calculation and bigger concentration.
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