Experiment 6 Titration II – Acid Dissociation Constant
Figure 4 Titration curve of weak diprotic acid by NaOH(aq) Pre-Lab Notebook: Provide a title, purpose, CH3COOH / NaOH reaction, brief summary of the procedure, and table of reagents (NaOH and CH3COOH) UCCS Chem 106 Laboratory Manual Experiment 6
Acid-Base Titration Curves Using a pH Meter
1) hydrochloric acid, HCl(aq) with sodium hydroxide, NaOH(aq); 2) acetic acid, CH 3 COOH(aq) with sodium hydroxide, NaOH(aq) The recorded volume and pH values will generate titration curves that will be used to compare features of the strong acid curve versus the weak acid curve You will determine the equivalence point volume and pH for both
FINDING THE UNKNOWN MOLARITY OF ETHANOIC ACID IN VINEGAR
Through this equation, we can say that the molarity of NaOH and the molarity of CH3OON is equal since their ration is 1:1 Since the NaOH is a standard solution, it reacts with the Acetic Acid (CH3COOH) The formula to find the moles and the molarity: This means that 1M of NaOH means that there is 1 mole in the NaOH/L Tjia 3
We discussed strong acid-strong base titrations last semester
the NaOH so, how much NaOH was added? 0 013 L NaOH soln x 0 01 mol NaOH = 0 0013 mol NaOH 1 L NaOH soln one mole CH 3CO 2H consumed and one mole of CH 3CO 2– formed for every mole of OH– added CH 3CO 2H OH– CH 3CO 2– start 0 0025 0 0013 0 rxn – 0 0013 – 0 0013 + 0 0013 after rxn 0 0012 ~ 0 0 0013
E17 Acid Ionisation Constant of Acetic Acid from Titration
addition of some NaOH, the +curve is relatively flat where [H (aq)] is given by equation (2) Near the equivalence point, the pH rises sharply At the equivalence point, all of the CH 3 COOH has reacted and the solution contains CH 3 CO 2 The pH at this point is greater than 7 as the acetate ion is a weak base and undergoes hydrolysis
Acids and Bases - University of Sydney
• Common strong bases are: NaOH, KOH, Ca(OH)2, Ba(OH)2 Weak indicates an equilibrium exists between the ions and the undissociated compound in solution with, very often, the undissociated compound dominating The pH of this solution may only be calculated if the equilibrium constant, K, as well as the concentration of the starting material is
Buffer Solutions - Cal State LA We Are LA
6 Buffer Solutions ν Let’s go back to problem of adding HCl to buffer solution: ν We can use H-H eqn to make the calculations much easier [CH3COOH] = 0 100 + [HCl]added [CH3COO-] = 0 100 – [HCl]
Acid-Base Chemistry
3O+] in a 0 053 M NaOH solution Step 1: since NaOH is a strong base, dissociation is complete ∴ [OH-] = 0 053 M Step 2: Use K w to calculate [H 3O+] K w = [H 3 O +][OH-] = 1 0 x 10-14 [H 3 O +] = K w [OH-] = 1 0 x 10-14 0 053-13= 1 9 x 10 M
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Sample report (Quantitative)
E17 Acid Ionisation Constant of Acetic Acid from Titration CurveAbstract
The acid ionisation constant for acetic acid has been determined by titration with NaOH. The pKa value
is found to be 4.6 in good agreement with the literature value.Introduction
When weak acids such as acetic acid dissolve in water, they only dissociate to a small extent. For acetic acid, CH3COOH, the dissociation reaction is:CH3COOH(aq)CH3COO(aq) + H+(aq) (1)
For this reaction, the equilibrium constant is also known as the acid ionisation constant, Ka:The aim of this experiment is to determine the value of Ka for acetic acid and to evaluate the accuracy
of titrations in measuring it. It is commonly tabulated using the pKa where: pKa = -log10Ka (3)Equation (2) can be re-arranged to give:
If a dilute solution of acetic acid is titrated with a dilute solution of sodium hydroxide, the following
reaction occurs:CH3COOH(aq) + OH(aq) AE CH3COO(aq) + H2O(l) (5)
During the titration, [CH3COOH(aq)] decreases and [CH3CO2(aq)] increases. From equation (3), thisleads to a continuously decreasing value of [H+(aq)]. This can be measured through the increase in the
pH. At the point when enough NaOH has been added that [CH3COOH(aq)] = [CH3COO-(aq)], all of the acetic acid. [CH3COOH(aq)] = [CH3CO2(aq)] occurs when half of this volume has beenadded. It is called the half-equivalence point. The pH at this point should equal the pKa value for acetic
acid. A plot of pH against the amount of added NaOH is called a titration curve.Method
The method in the laboratory handbook1 on pages E17-6 to E17-10 was followed.Results
Figure 1 shows the titration curve obtained in this experiment.The equivalence point is the mid-point on the vertical part of the curve. It corresponds to a volume of
NaOH of 26 mL and a pH of 8.57. The half equivalence point corresponds to a volume of 13 mL and a pH of 4.6. The value of Ka from the titration is 4.6. Figure 1. Titration curve showing the changes in pH when 0.1 M NaOH is added to 50 mL of a 0.05 M acetic acid solution.Discussion
The titration curve follows that expected for the titration of a weak acid with a strong base2. The initial
pH is 2.95 and is significantly higher than that for a strong acid of the same concentration. Afteraddition of some NaOH, the curve is relatively flat where [H+(aq)] is given by equation (2). Near the
equivalence point, the pH rises sharply. At the equivalence point, all of the CH3COOH has reacted and
the solution contains CH3CO2. The pH at this point is greater than 7 as the acetate ion is a weak base
and undergoes hydrolysis. curve gives the value of 4.6. The experimental value is in reasonably good agreement with the literature value3 of 4.76. The experimental value is slightly lower, perhaps because the exactequivalence point was missed during the titration. It is also possible that the solution was slightly more
acidic than expected due to dissolved CO2. To improve the result, the experiment could be repeated a number of times to find a better value for the equivalence point and the water could be boiled to remove dissolved CO2.Conclusions
From the titration of acetic acid with NaOH, its pKa value is 4.6. This is in reasonable agreement with
the literature value of 4.76. This indicates that titration curves are a good method of determining acid
dissociation constants.