How do I do this problem?
1. A student did an alkalinity determination correctly, except that the sample titrated had a volume of 90.0 mL. Volume A was found to be 4.50 mL and Volume B was 7.00 mL.
a) Calculate the alkalinity value from these data and then calculate the correct value.
I got this far: A=(2A-B)
A=(2(4.50)-7.00)= 2 mL^-1
Now what do I do?
You say "except that the sample titrated had a volume of 90.0 mL." What should it have been? If you titrated two 90.0 mL samples and found one 4.50 mL to the end point and another 7.00 mL to the end point, just calculate the alkalinity normally. The two won't agree of course, they won't even come close, but that's just poor precision.
Based on the information given, it seems like you made a mistake while calculating the alkalinity value.
Here's the correct method to calculate the alkalinity value:
1. Start by using the formula A = 2A - B, where A represents Volume A and B represents Volume B.
A = 2(4.50 mL) - 7.00 mL
A = 9.00 mL - 7.00 mL
A = 2.00 mL
2. Determine the alkalinity value by dividing the result from step 1 by the volume of the sample titrated, which should be 90.0 mL.
Alkalinity = A / Volume of Sample
Alkalinity = 2.00 mL / 90.0 mL
Alkalinity = 0.0222 mL^-1
However, please note the statement "except that the sample titrated had a volume of 90.0 mL" is unclear. If the sample titrated was supposed to have a different volume, please provide that information to accurately calculate the correct value.