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# acid base titration

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13. A hydrocholoric acid solution is standardinzed by titrating 0.4541 g of primary stardard tris(hydroxymethyl)aminomethane. If 35.37 mL is required for the titration, what is the molarity of the acid?

15. A sodium hydroxide solution is standardized by titrating 0.8592 g of primary standard potassium acid phthalate to a phenolphthalein end point, requiring 32.67 mL. What is the molarity of the base solution?

18. Calculate the pH at 0, 10.0, 25.0, and 30.0 mL of titrant in the titration of 50.0 mL of 0.100 M NaoH with 0.200 M HCl.

https://brainmass.com/chemistry/physical-chemistry/acid-base-titration-104983

#### Solution Preview

13. The molar weight of TRIS is 121.14 g/mol. So the moles of 0.4541 g of TRIS is

At the end of the titration, the moles of the two chemicals are equal to each other.
So the molarity of HCl is

The molarity of HCl is 0.10526 M.

15. The molar weight of KHP is 204.2g/mole.
So the moles of 0.8592 g of KHP is

At the end ...

#### Solution Summary

If provides examples of finding the molarity and pH of the solution during the titration process.

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## Titration of Strong and Weak Acids. Determination and assessment of equivalence points. Calculation of molarity. Estimation of acid/base equilibrium constant, pKa

Procedure 1
Add 25 mL HCl (of unknown concentration) to the flask. Add 2 drops of phenolphthalein to the flask. Fill a burette with 50 mL of 1M NaOH solution. Record this initial volume (50mL). Record the pH of the solution in the flask. (0.22). Continue to add NaOH in 1 mL increments. Record the pH for each milliliter added.(0.27; 0.32; 0.37; 0.42; 0.48; 0.54; 0.60; 0.67; 0.75; 0.84; 0.95; 1.09; 1.28; 1.59; 7.00; 12.39=purple) The pink color will appear in flask all at once when the endpoint is either reached or crossed. Record the burette volume and pH at which this occurs. (34mL; 12.39)
Continue to add 5 more increments of 1 mL and record the pH at each point. (12.68; 12.84; 12.95; 13.05; 13.12)

Take a new flask and add 25 mL of HCl and 2 drops of phenolphthalein to the flask. Refill the burette to 50 mL NaOH. Based on the results of the previous titration, add enough NaOH solution - all at once - to get to 1 mL BEFORE the endpoint. (15mL/7.00 pH). Add NaOH DROP-WISE into the flask. Record the pH and volume until the endpoint is reached and several drops after it is reached. (at first 0.05mL it turned pink with a pH 11.10; after I added 4 more drops of 0.05 mL each with the following pH: 11.4; 11.57; 11.7; 11.79).

Assignment (Procedure 1)
1. Find the equivalence point from the graph. 15mL
2. At what point did your solution turn pink? 15.05 mL with 11.10pH
3. What is the pH at the equivalence point? (is the equivalence point the same as when it turned pink?... if yes then is 11.10 pH)
4. What is the equivalence point volume of NaOH? 15.05mL
5. Calculate the molarity of the HCl from the volumes of acid and base at the equivalence point and the molarity of the NaOH.
6. What is the pH at the half-equivalence point?

Procedure 2
In this procedure you will titrate a weak acid, acetic acid (CH3COOH), to see the difference in the titration curve of a weak acid as opposed to a strong acid. Take a clean flask and add 5 mL of acetic acid (of unknown concentration), 20 mL water and 2 drops of phenolphthalein to the flask. Refill the burette with the NaOH solution, and record the initial volume. (50mL) Record the initial pH of the flask solution. (2.78 pH) Add NaOH in 1 mL increments and record the pH for each milliliter added.(4.28; 4.76; 5.23; 8.95=turned pink) The pink color will appear all at once as the endpoint is either reached or crossed. Note the burette volume and pH at which this occurs. (46mL) Continue to add 5 more 1 mL increments of NaOH into the flask. Record the pH after each increment. (12.52; 12.81; 12.97; 13.08; 13.17)

Take a new flask and add 5 mL of acetic acid, 20 mL water, and 2 drops of phenolphthalein to the flask. Refill the burette to 50 mL NaOH. Based on the results of the previous titration, add enough NaOH solution - all at once - to get to 1 mL BEFORE the endpoint. (3mL/5.23pH) Add NaOH DROP-WISE into the flask (in 0.05mL increments). Record the pH and volume until the endpoint is reached and several drops after it is reached.(5.26; 5.29; 5.33; 5.36; 5.39; 5.43; 5.47; 5.51; 5.55; 5.60; 5.65; 5.71; 5.78; 5.85; 5.93; 6.04; 6.17; 6.35; 6.65; 8.95=pink)

Assignment (Procedure 2)

1. At what pH did your solution turn pink? 8.95
2. What is the pH at the equivalence point?
3. What is the equivalence point volume of NaOH?
4. What is the pH at the half equivalence point?
5. Calculate the molarity of the acetic acid from the volumes of acid and base at the equivalence point and the molarity of the NaOH.
6. Calculate the value of Ka of the acetic acid.
7. Look up the accepted value for the Ka of acetic acid on the internet. Calculate the percent error between the experimental and accepted values according to:
% error = |experimental Ka - accepted Ka| / accepted Ka * 100%

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