CHEM LAB 9-10
Calculate the concentration (in M) of acetate ion in a buffer solution made from 2.00 mL2.00 mL of 0.50 M acetic acid0.50 M acetic acid and 8.00 mL8.00 mL of 0.50 sodium acetate0.50 sodium acetate .
0.4 M 8.00 mL x 0.50 M/ 10.00 mL
If the pH at the half-titration point of a weak acid is 4.2, what is the Ka of the acid?
6.3 x 10^-5 Ka = 10^-4.2
If 0.75 g of a monoprotic weak acid required 22.50 mL of 0.510 M NaOH to titrate it, what is the molar mass of the acid?
65 g/mol 0.510 mol x 22.5 mL x 1/1000 mL = 0.011475 mol 0.75 g / 0.011475 mol = 65 g/mol
If a 1.00 mL sample of the reaction mixture for the equilibrium constant experiment required 32.40 mL of 0.258 M NaOH to titrate it, what is the acetic acid concentration in the mixture?
8.36 M 0.258 M x 32.40 mL/ 1000 L = 0.0083592 mol 0.0083592 mol/1000 mL = 8.36 M
An ammonia buffer solution contains 0.25 M NH4+NHX4X+ and 0.22 M NH3NHX3 . The pKa of ammonium is 9.24. What is the pH of the buffer?
9.18 pH = 9.24 + log 0.22/0.25
Consider the pictured titration curve of an unknown acid with sodium hydroxide. What is the best description of the unknown acid? What is the first pKa of the unknown acid? Report the answer to one decimal point. What is the second pKa of the unknown acid? Report the answer to one decimal point
A weak diprotic acid 2.3 7.0
When using a pH meter to monitor a stirring reaction mixture, where should you place the pH sensor electrode?
Between the stirring vortex and the side of the glassware
When taking pH measurements of solutions, why is it important to stir thoroughly after adding each reagent?
Mixing helps ensure that the measured pH is reflective of the entire solution.
The pKa of an acid can be determined through titration with a strong base. Gradually increase the volume of the base, stopping after the equivalence point is reached. The pKa of the acid is equal to the pH at the midway volume to the equivalence point.
The pKa of an acid can be determined through titration with a strong base. Gradually increase the volume of the base, stopping after the equivalence point is reached. The pKa of the acid is equal to the pH at the midway volume to the equivalence point.
How does the titration curve of a diprotic acid differ from that of a monoprotic acid?
There are two equivalence points.
At what times should a pH electrode be submerged in a solution?
When being stored in a storage cabinet When not being used between measurements When monitoring a reaction in a beaker
The equivalence point of any acid-base titration can be determined visually from a titration curve by finding the place where
the curve has the steepest slope.
A titration curve is a plot of titrant volume on the x-axis and pH on the y-axis.
titrant volume pH
A formic acid buffer solution contains 0.20 M HCOOHHCOOH and 0.25 M HCOO−HCOOX− . The pKa of formic acid is 3.75. What is the pH of the buffer?
3.85 pH = 3.75 + log 0.25/0.20
buffer capacity
the amount of acid or base a buffer solution can absorb without a significant change in pH
