338 ❯ STEP 5. Build Your Test-Taking Confidence(iv) Carefully add sodium hydroxide solution from the buret until the indicator indicates the
endpoint.
(v) Record the final volume of sodium hydroxide solution in the buret.
(vi) The difference in the initial volume and final volume from the buret gives the quantity of
sodium hydroxide solution added.
(vii) Use the recorded data and the concentration of the sodium hydroxide solution to determine
the moles of acid.
(viii) The mass of the acid divided by the moles of acid gives the molar mass of the acid.
The above steps are worth 1 point.
(c) (i) Weigh a small quantity of unknown acid into a beaker and add sufficient water to dissolve the
solid.
(ii) Using the mass of the acid and the molar mass calculated above determine the volume of standard
sodium hydroxide solution necessary to neutralize one-half of the acid in the beaker.
(iii) Fill the buret with sodium hydroxide solution and record the initial volume.
(iv) Carefully add sodium hydroxide solution from the buret until the calculated volume has been
added.
(v) Measure the pH of the half-titrated solution with the pH meter provided.
(vi) The pH of the half-titrated solution is equal to the pKa of the acid and Ka = 10 –pK.
The above steps are worth 1 point.
Total your points. There are 4 possible points.Question 5(a) Regardless of the value of x, it is the same in each half-reaction; therefore it is only necessary to add the
two half-reactions together.
x LiC 6 (s) → x Li+ + x e– + x C 6
Li1–xCoO 2 + x Li+ + x e– → LiCoO 2
Li1–xCoO 2 + x LiC 6 (s) → LiCoO 2 + x C 6
You get 1 point for the correct equation.
(b) Lithium metal will react with water.
You get 1 point for this explanation.
(c) The oxidation state of cobalt is +3. This is determined by assuming the oxidation states of lithium and
oxygen are +1 and –2, respectively. This leads to Li + Co + 2 (O) = 0 or (+1) + Co + 2 (–2) = 0.
The ground state electron configuration of Co^3 + is 1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 or [Ar]3d^6.
You get 1 point for the correct oxidation state of cobalt and 1 point for the correct electron configura-
tion. If you did not get the correct oxidation state, you can still get the second point if you give the
correct electron configuration of the ion predicted to be present. Note that no reasonable ion will have
any 4s electrons present.
Total your points; there are 4 points possible.20-Moore_PE01_p307-340.indd 338 31/05/18 1:58 pm