Calculating Benzoic Acid Moles & Percent Purity

In summary, the conversation is about a chemistry question regarding a sample of monoprotic benzoic acid dissolved in water and titrated with a sodium hydroxide solution. The first part of the question asks for the number of moles of benzoic acid that were titrated, which can be solved using the formula n1v1=n2v2. The second part asks if the sample is pure, and the solution involves using the molarity=normality equation to determine the number of moles and then using the molecular formula to calculate the weight of the sample. If the weight equals the given sample weight, then the sample is 100% pure, otherwise the percentage of purity can be calculated. The conversation ends with
  • #1
feelau
61
0
chem question please help

Homework Statement


Ok, so there's .9734 g sample which contained monoprotic benzoic acid C6H5COOH and it's dissolved in 75 mL of water and titrated to the equivalence point with 31.78 mL of .09251 M NaOH solution. a) how many moles of benzoic acid were titrated b) Was this a pure sample of benzoic acid? c) If the sample is no, Calculate its percent purity.

The attempt at a solution
ok so for the first problem part a is pretty easy but then I have no idea how to determine if this sample is pure and how to calculate percent of purity.
 
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  • #2
In this case, for both the acid and base, normality equals molarity. Hence you can use n1v1=n2v2.

You know for sure the 31.78ml of .09251M soln were used. You are unsure of the weight of benzoic acid. Hence, N*75=31.78*.09251. From this you can calculate N. This much in any case you've figured out... right?

Now, molarity=normality, therefore you know the number of moles. You have the formula for benzoic acid so you know the weight of benzoic acid. You know the number of moles, so you can find the weight of the sample of benzoic acid titrated. If that weight equals .9743 grams, then the sample is 100% pure, else (weight/.9734)*100 is your percentage.

If you don't know the weight of 1 mol of carbon/oxygen/hydrogen:

C=12gms
0=16gms
H=1gm
 
  • #3
Thank you so much. I've never seen any problems with this question so I had no clue. Thanks!
 

1. How do I calculate the number of moles of benzoic acid in a sample?

The number of moles of benzoic acid can be calculated by dividing the mass of the sample by its molar mass. The molar mass of benzoic acid is 122.12 g/mol. Therefore, to calculate the moles, divide the mass of the sample (in grams) by 122.12 g/mol.

2. What is the formula for calculating the percent purity of benzoic acid?

The formula for calculating the percent purity of benzoic acid is: (moles of pure benzoic acid/total moles of benzoic acid) x 100%. This formula compares the amount of pure benzoic acid (determined through titration or other methods) to the total amount of benzoic acid in the sample.

3. Can I use the percent purity of benzoic acid to determine its mass in a sample?

Yes, you can use the percent purity of benzoic acid to determine its mass in a sample. Simply multiply the percent purity (in decimal form) by the total mass of the sample to find the mass of pure benzoic acid present.

4. How do I convert moles of benzoic acid to grams?

To convert moles of benzoic acid to grams, multiply the number of moles by its molar mass. The molar mass of benzoic acid is 122.12 g/mol. Therefore, to convert moles to grams, multiply the number of moles by 122.12 g/mol.

5. Can I use the percent purity of benzoic acid to determine its concentration in a solution?

Yes, you can use the percent purity of benzoic acid to determine its concentration in a solution. First, calculate the moles of pure benzoic acid present in the sample. Then, use this number of moles and the volume of the solution to calculate the concentration in units of moles per liter (M).

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