Cliffs AP Chemistry, 3rd Edition

(d) Pure HCl is not an acid.

• An acid is measured by its concentration of H+(its pH).


• Pure HCl would not ionize; the sample would remain as molecular HCl (a gas).


• In order to ionize, a water solution of HCl is required:
  HCl(aq) →H+(aq) +Cl–(aq)

(e) HClO 4 is a stronger acid than HClO 3 , HSO 3 – , or H 2 SO 3.

• As the number of lone oxygen atoms (those not bonded to H) increases, the strength of the
  acid increases. Thus, HClO 4 is a stronger acid than HClO 3.


• As electronegativity of central atom increases, acid strength increases. Thus, Cl is more
  electronegative than S.


• Loss of H+by a neutral acid molecule (H 2 SO 3 ) reduces acid strength. Thus, H 2 SO 3 is a
  stronger acid than HSO 3 –.


• As effective nuclear charge (Zeff) on the central atom increases, acid strength is likewise
  increased. Thus, a larger nuclear charge draws the electrons closer to the nucleus and
  binds them more tightly.

Part B: Question 6

Question 6 might best be answered in the bullet format.

6. Restatement: Interpret using bonding principles.
   (a) Restatement: Compare carbon-to-carbon bond lengths in C 2 H 2 and C 2 H 6.

• Lewis structure of C 2 H 2 :


• Lewis structure of C 2 H 6 :

•C 2 H 2 has a triple bond, whereas C 2 H 6 consists only of single bonds.

• Triple bonds are shorter than single bonds since bond energy is larger for a multiple bond.
  The extra electron pairs strengthen the bond, making it more difficult to separate the
  bonded atoms from each other.

H

C

H

H

H

H C H

H C CH

Answers and Explanations for the Practice Test