Purpose: To find the pH and concentration of acid

Materials:

• 50 mL water
• 5.70g of nerds (Malonic Acid)
• 30 mL of sample
• phenolphthalein
• Stir stick
• Graduated cylinder
• 3 funnels
• 3 filer sheets
• Erlenmeyer flask
• 3 beakers
• Ring stand and mixer
• 15 mL of 0.10 M NaOH

Procedure:

1. crush nerds into a fine powder. Measure mass and record.

2. Dissolve powdered nerds in 50 mL of water and mix with a stir stick.

3. Place filter sheets in the funnels and filter the acid solution.

4. Measure out 10 mL of the acid solution.

5. Add two drops of phenolphthalein to 10 mL of solution.

6. Titrate 10 mL of solution by adding 0.10 M NaOH.

7. Continue to add NaOH until ppt begins to turn pink, thus indicating the solution is neutral. Repeat 3 times.

8. Record how much of the basic solution was added.

Data:

Trial #	Volume of Acid (mL)	Volume of NaOH (base) (mL)
Trial 1	10 mL	5.40 mL
Trial 2	10 mL	4.60 mL
Trial 3	10 mL	4.60 mL
Average Volume		4.87 mL

Calculations:

since two of the trials had the same volume of NaOH used, we only wrote two equations.

Conclusion:

In conclusion, we found that acids are a recurring part of our daily lives. It was surprising to us that the candy had a fairly low amount of a strong acid. We found the concentration of our acid by diluting it in water and filtering it. We then used titration to help us find the pH of the candy. The phenolphthalein was an important aspect that informed us when our solution was neutral by turning pink. We used the M1V1 = M2V2 formula in order to find the concentration of hydronium ions, helping us find our final pH. Our final pH was between 1.45 and 2 which makes sense since the pOH of the base is about 13.

Part I:  Preparation of a standard absorption curve for FeSCN+2

Standard	0.20M Fe(NO3)3	0.0020 M KSCN	0.100M HNO3	[FeSCN+2]	Absorbance
A	10.0 mL	0.0 mL	15.0 mL	0	0
B	10.0 mL	1.0 mL	14.0 mL	M	0.343
C	10.0 mL	1.5 mL	13.5 mL	M	0.518
D	10.0 mL	2.0 mL	13.0 mL	M	0.706
E	10.0 mL	2.5 mL	12.5 mL	M	0.860
F	10.0 mL	3.0 mL	12.0 mL	M	1.130

 

EQUATION:

Y : 4572.1x – 0.0068 | 

 

Part 2: Measuring Equilibrium

Test Solution	0.0020 M Fe(NO3)3	0.0020 M KSCN	0.10 M HNO3	Initial [Fe+3]	Initial [SCN–]	Absorbance	Equilibrium [FeSCN+2]*
I	5.0 mL	0	5.0 mL	M	0	0	0
II	5.0 mL	1.0 mL	4.0 mL	M	M	0.174
III	5.0 mL	2.0 mL	3.0 mL	M	M	0.370
IV	5.0 mL	3.0 mL	2.0 mL	M	M	0.512
V	5.0 mL	4.0 mL	1.0 mL	M	M	0.696
VI	5.0 mL	5.0 mL	0.0 mL	M	M	0.836

 

ICE Charts

Test Solution Keq = 260	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

 

Test Solution Keq = 280	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

 

Test Solution Keq = 260	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

 

Test Solution Keq = 290	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

 

Test Solution Keq = 280	Fe3+               +                SCN–                    ⇄            FeSCN2+
I			0
C	–	–	+
E

CONCLUSION AND EVALUATION:

1. Comment on your Keq values.  Do your results convince you that Keq is a constant value regardless of the initial concentrations of the reactants?  Why or why not?The results of our Keq values convinced me that Keq is not a constant value. Our values jumped around between 260 and 290, leading us to the conclusion that Keq is not a constant value and will change if you alter any of the initial concentrations.
2. Calculate the average value of Keq from your five trials.  The actual value of Keq  for this reaction at 25oC is reported as 280.  Calculate (should you use all of your values?) the percent difference of your average value from the reported value:
   Actual Value: 280
   Experimental Value: 273.91
   % difference: (273.91 – 280) / 280 = 2.17%