Titration Lab Before you begin the lab you should estimate how much 0.2M NaOH wi
ID: 1052987 • Letter: T
Question
Titration Lab
Before you begin the lab you should estimate how much 0.2M NaOH will be needed to titrate the 0.1 M acid solutions.
II. Experimental Procedure
Part 1: Standard solutions
A. Preparation
1) Label a 400-mL beaker “Waste”.
2) Label a 100-mL beaker “NaOH”. Take the beaker to the hood and pour about 50 m of 0.2M NaOH into it.
3) Set up the titration equipment as demonstrated by your lab instructor. Put a white paper towel on the base of the ring stand. This will help you see the color changes more easily.
4) Close the stopcock and use a plastic pipet to pour 1-2 mL NaOH into the buret. Open the stopcock and allow most of the NaOH to drain into the waste beaker.
5) Repeat the rinse. Add NaOH and allow most to drain out.
6) Carefully pour NaOH into the buret until it is mostly full. Move the waste beaker away from the buret.
B) Experimental
Follow the same procedure for 0.1 M HCl, 0.1 M acetic acid and 0.1 M citric acid.
1. Prepare the acid for titration
Label a clean, dry 50-mL beaker with the name of the acid.
Take the beaker to the hood and pour about 20 mL acid into the beaker.
Get a clean, dry 125-mL erlenmeyer flask. A beaker can be used if a flask is not available.
Measure 20.0 mL distilled water with a graduated cylinder. Pour it in to the flask.
Use a pipette to measure 10.0-mL acid. Add the acid to the flask.
Use pH paper to estimate the pH of the solution.
Add 2 drops phenolphthalein to the flask and mix it by swirling gently.
Record the color of the solution.
2) Perform the titration.
Record the initial volume of NaOH in the buret. Slowly add NaOH to the acid solution. Swirl the flask as the base is added to ensure complete mixing.
Stop periodically to check the color of the solution.
Record the buret volume when the color of the acid solution first starts to change color and the volume when the color persists after swirling.
Stop the titration when the color of the acid solution is no longer changing. Record the final volume of NaOH.
3) Change acids.
Pour the acid mixture into Waste. Rinse the flask and the graduated pipette with distilled water into Waste.
Follow the steps in parts 1 and 2 with another acid. If the level of NaOH in the buret drops below 20.0 mL, add more NaOH. If you have to add more NaOH during a titration, ask your lab instructor for help.
4) When you have titrated all three acids, calculate the concentration of each acid sample.
Part 2: Dilutions
Dilute the acid sample 1:2, 1:5 and 1:10 to create 20 mL of each dilution.
1:2
10mL water and 10mL of acid sample
1:5
16mL water and 4mL of acid sample
1:10
18mL water and 2mL of acid sample
3) Repeat the procedure in part B for the diluted samples.
4) Calculate the concentration of your samples based on your titrations for those samples you were able to titrate. Using your dilution factor, calculate the initial concentration of your samples.
HCL
Acetic Acid
Citric Acid
pH of diluted acid solution
1
4
3
Color of acid solution with phenolphthalein
pink
pink
pink
Amount of acid titrated (mL)
10.0
10.0
10.0
Initial volume of NaOH (mL)
0
6.8mL
0
Final volume of NaOH (mL)
6.8mL
12.6mL
15mL
Volume of NaOH (mL)
6.8mL
5.8mL
15mL
Amount of NaOH added (mmol)
1.36 mmol
1.16mmol
3.00mmol
Amount of acid (mmol)
1.36mmol
1.16mmol
3.00mmol
Concentration of acid titrated (M)
014M
0.12M
0.10M
Concentration of acid before dilution (M)
0.1M
0.1M
0.1M
Concentration of NaOH was 0.2M
Concentration of each acid (HCL, Acetic Acid, and Citric Acid) was 0.1M
30mL total of HCL
NaOH + HCl --> NaCl + H2O
Calculations for NaOH:
(0.1 M HCL) (0.0068L)= 0.0136 moles NaOH X 1000mmoles/1mole = 1.36mmol
NaOH and HCl are 1:1 ratio so the amount of NaOH added (mmol) and the amount of acid (mmol) are the same? That’s how it calculated the other two solutions.
Are my numbers for: Concentration of acid titrated (M) and Concentration of acid before dilution (M), seem, correct?
Unknown Acid:
Concentrated Solutions
1:2
1:5
1:10
pH of diluted acid solutions
1
1
1
Color of acid solution with phenolphthalein
pink
pink
pink
Amount of acid titrated (mL)
Initial volume of NaOH (mL)
2.6
13
16.9
Final Volume of Naoh (mL)
13
16.9
20.7
Volume of NaOH (mL)
10.4
3.9
3.8
Amount of NaOH added (mmol)
Amount of acid (mmol)
Concentration of acid titrated (M)
0.10M
0.098M
0.19M
Concentration of acid before dilution (M)
0.1M
0.1M
0.1M
Concentration of NaOH was 0.2M
Concentration of each acid (HCL, Acetic Acid, and Citric Acid) was 0.1M
20mL of each dilution
H2SO4 + 2NaOH -> Na2SO4 + 2H2O
I’m not sure how to calculate the concentration of acid titrated (M) and the Concentration of acid before dilution (M)?
Answer the following questions about your titrations.
a. Did you find a difference in pH between any of the samples? Given the definition of pH (pH=-log[H]), what is your conclusion about the reason for the differences.
b. How close did you get to the known concentration of the acid standards? What could you have done differently to make the titration more accurate.
c. Were you able to titrate all three dilutions of your concentrated sample? Why or why not?
HCL
Acetic Acid
Citric Acid
pH of diluted acid solution
1
4
3
Color of acid solution with phenolphthalein
pink
pink
pink
Amount of acid titrated (mL)
10.0
10.0
10.0
Initial volume of NaOH (mL)
0
6.8mL
0
Final volume of NaOH (mL)
6.8mL
12.6mL
15mL
Volume of NaOH (mL)
6.8mL
5.8mL
15mL
Amount of NaOH added (mmol)
1.36 mmol
1.16mmol
3.00mmol
Amount of acid (mmol)
1.36mmol
1.16mmol
3.00mmol
Concentration of acid titrated (M)
014M
0.12M
0.10M
Concentration of acid before dilution (M)
0.1M
0.1M
0.1M
Explanation / Answer
The above calculation looks correct.
concentration of acid titrated = moles of acid/volume of acid solution
moles of acid = moles of NaOH
concentration of acid titrated = 0.1 M
Now initial concentration before dilution
1 : 5 dilution
initial concentration = 0.1 x 20/10 = 0.2 M
1 : 5 silution
initial concentration = 0.1 x 20/16 = 0.125 M
1 : 10 dilution
initial concentration = 0.1 x 20/4 = 0.5 M
Solutions
a. The initial pH of the sa ples diferent from each other. The difference is due to dilution effect.
b. The concentration of acid solution thus calculated are close to theoretical value or expected value. The titration could have been perfomred slowly and with a proper indicator to get better results.
c. The titrations of all three samples were possible. With highly dilute solution the end point is carefully watced or error would be introduced due to fats addition of titrant.
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