Equivalence Point- Concentration

In summary, the concentration of the stock HBr solution is 0.1262 M. The correct volume to use for the calculation is 20 mL instead of 50 mL, and the dilution calculations can be omitted. The correct number of moles of KOH used is 2.52322*10^-3 mol.
  • #1
a.a
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0

Homework Statement



A 20.00 ml stock sample of HBr is diluted to 50 mL. If 18.76 ml of 0.1345 M KOH was required to reach the equivalence point, what is the concentration of the stock HBr solution?

Homework Equations



KOH + HBr --> KBr + H20

M = conc. = mol./L

n = V * conc.

The Attempt at a Solution



n-KOH= V-KOH * conc. KOH = (18.76*10^-3 L) * (0.1345 mol./L) = (2.52322*10^-3 mol.)

=> n-HBr= (2.52322*10^-3 mol.)

V-HBr= 5.0*10^-4 L

conc. HBr = (2.52322*10^-3 mol.)/ (5.0*10^-4 L) = 5.04644 M

I don't think this the right answer but I seem to endup with the right units, can someone please tell me what I am doing wrong and how to go about this question the right way?
 
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  • #2
Generally you are on the right track, however:

a.a said:
V-HBr= 5.0*10^-4 L

that's not true. 5*10-4 L = 0.5 mL.

Also think whether you should use 20 mL or 50 mL. Question asks for the concentration of the stock solution. Note, that if you will not dilute your sample to 50, you will use exactly the same amount of KOH, so you can omit dilution calculations.
 
  • #3
Hi,

I did it over agian and used 20 ml and the answer i got was 0.1262 M

can you please verify?

btw, is there a thank you button on this fourm?
 
  • #4
a.a said:
I did it over agian and used 20 ml and the answer i got was 0.1262 M

OK

btw, is there a thank you button on this fourm?

I think there was once, but it was getting too hot of continuous pressing.
 

1. What is the equivalence point in a titration?

The equivalence point in a titration is the point at which the number of moles of the titrant (the solution being added) is equal to the number of moles of the analyte (the solution being titrated). This is when the reaction is complete and all of the analyte has been neutralized.

2. How is the equivalence point determined?

The equivalence point is determined by using an indicator or by monitoring the pH of the solution. Indicators change color at a specific pH, which can indicate when the equivalence point has been reached. The pH can also be monitored using a pH meter, and the equivalence point is reached when the pH levels off or no longer changes with the addition of more titrant.

3. Can the equivalence point be different for different titrations?

Yes, the equivalence point can be different for different titrations. It is dependent on the specific reaction being titrated and the strength of the solutions used. Different reactions and solutions will have different stoichiometric ratios, which will affect the equivalence point.

4. What is the relationship between concentration and equivalence point?

The relationship between concentration and equivalence point is that the concentration of the titrant at the equivalence point is equal to the concentration of the analyte. This is because the number of moles of each solution is equal at the equivalence point, and concentration is calculated by dividing the number of moles by the volume of the solution.

5. Why is the equivalence point important in a titration?

The equivalence point is important in a titration because it signifies when the reaction is complete and the correct amount of titrant has been added to neutralize the analyte. This information is crucial in determining the concentration of the analyte, which can have important implications in various fields such as medicine, environmental science, and food science.

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