EXPERIMENT 19 PRE-LABORATORY QUESTIONS 1. In Figure 19.1 the equivalence point i

Question

EXPERIMENT 19 PRE-LABORATORY QUESTIONS 1. In Figure 19.1 the equivalence point is at point D a. If 40.00 mL of C- 0.106 formic acid(HOOCH) is titrated with 0.212 M NaOH, what is the volume of titrant, NaOH, required to reach the equivalence point D. b. At point D, the trated solution is basic. Show the reaction that is responsible for the basic pH at the equivalence point D 2. Using the Ka for formic acid, calculate the pH at the equivalence point D. for the titration described in Question 1 3. Calculate the pH at the beginning of a titration of 50.00 of 0.005M HA (Ka = 2.0 x 10-2) with NaOH solution. If the quadratic equation is assumed to be accurate, what would the percent error in the pH if the simpler (square root) equation were used to calculate the pH instead. equation were used to calculate the pl instead. 4. According to Figure 19.1 at which point(s) A, B, C, D, on the titration curve does a buffer solution result?

Explanation / Answer

1a) Write down the balanced reaction:

HCOOH (aq) + NaOH (aq) -----> HCOO-Na+ (aq) + H2O (l) …..(1)

Moles NaOH added at the equivalence point = moles HCOOH titrated.

Moles HCOOH titrated = (40.00 mL)*(1 L/1000 mL)*(0.106 mol/L) = 0.00424 mol.

Therefore, moles NaOH added = 0.00424 mol (since there is 1:1 molar ratio).

Therefore, volume of NaOH required to reach the equivalence point = (moles NaOH added/concentration of NaOH in mol/L) = (0.00424 mol/0.212 mol/L) = 0.02 L = 20 mL (ans).

b) The neutralization reaction is shown in (1) above.

Sodium formate (HCOONa) is the conjugate base of the weak acid, HCOOH and re-establishes acid-base equilibrium by reacting with water as shown below:

HCOO-Na+ (aq) + H2O (l) ------> HCOOH (aq) + NaOH (aq)

Note that NaOH (strong base) is formed at the equivalence point and hence the solution is basic.

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