Stoichiometry, concentration of solutions: Ba(OH)2 and H3PO4

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Discussion Overview

The discussion revolves around a stoichiometry problem involving the reaction between barium hydroxide (Ba(OH)2) and phosphoric acid (H3PO4). Participants are analyzing the required volume of Ba(OH)2 to completely react with a given volume of H3PO4, considering the triprotic nature of the acid.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant presents a balanced chemical equation for the reaction: 3Ba(OH)2 + 2H3PO4 → Ba3(PO4)2 + 6H2O.
  • The same participant calculates the moles of H3PO4 based on its concentration and volume, arriving at 3.45 moles.
  • They then apply the mole ratio to determine the moles of Ba(OH)2 needed, initially calculating 10.36 moles, which they later recognize as incorrect.
  • Another participant points out that the calculated answer is twice too large, suggesting a mistake in the mole ratio application.
  • A later reply acknowledges the error in the mole ratio, confirming it should be 3/2 instead of the previously used ratio.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct calculation initially, but there is agreement on the correction of the mole ratio from 3 to 2.

Contextual Notes

The discussion highlights potential confusion regarding stoichiometric calculations and the importance of accurately applying mole ratios in chemical reactions.

9781133886563
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Homework Statement



What volume of 0.0521 M Ba(OH)2 is required to react completely with 24.50 mL of 0.141 M H3PO4? Phosphoric acid is a triprotic acid.

Answer: volume of 0.0521 M Ba(OH)2 required = 99.5 mL

2. The attempt at a solution
1. I begin by balancing the equation: 3Ba(OH)2 + 2H3PO4 → Ba3(PO4)2 + 6H2O

2. I use M = Molarity = mol solute / L solution to find the mols of H3PO4... mol = 0.141 × 24.50 mL = 3.45 mol

3. According to the mole ratio... 3 × 3.45 mol of Ba(OH)2 = 10.36 mol of Ba(OH)2 needed.

4. M = mol/L ... mL = 10.36 mol / .0521 M = 199.0 mL of Ba(OH)2 needed, which is a wrong answer.

These are the steps I am taking. I must be making a mistake since I know that the answer is 99.5 mL.
 
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9781133886563 said:
3. According to the mole ratio... 3 × 3.45 mol of Ba(OH)2 = 10.36 mol of Ba(OH)2 needed.

Check this again.
 
Note that your answer is exactly twice too large (which points in exactly the same direction Pranav-Arora alredy signaled).
 
I see it now. The mole ratio is 3/2.

Thank you both.
 

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