posted by Kris on .
The cola sample is 50. mL, the equivalence point volume is 13.4 mL, and the NaOH solution concentration is 0.025 M, what mass of H3PO4 was in the sample?
If done right, the titration of H3PO4 with NaOH has three equivalence points. Which equivalence point is the 13.4 mL?
1. Write the equation and balance it.
2. moles NaOH = M x L
3. Use the balanced equation to determine moles H3PO4. moles NaOH x (?moles H3PO4/moles NaOH) = moles H3PO4.
4. grams H3PO4 = moles x molar mass.
This question is a pre-lab assignment, therefore we have not done the titrations yet.
thank you for the the set up of the problem
The third H is almost impossible to titrate so it must be the first or second equivalence point. Judging from the volume my best guess it's the first one. The indicator can tell us which H is titrated. Do you have an indicator listed? Methyl Orange? phenolphthalein?
yes we have a list - it ranges from 2.2 to 12.0
2.2 – 4.2
bromocresol green (BG)
3.8 – 5.4
methyl red (MR)
4.8 – 6.0
bromothymol blue (BB)
6.0 – 7.6
thymol blue (TB)
8.0 – 9.2
alizarin yellow (AY)
10.1 – 12.0
You have six indicators listed. Probably one of the questions on your pre-lab assignment is to identify the proper indicator to use; therefore, the list doesn't help me.
what if the equation is H3PO4 + OH --> H2PO4 + H2O