116 . T, T, CE
An indicator is a chemical substance used in low concentration during a titration reaction. It
will change color over a certain pH range. The color change, which occurs as the indicator
undergoes a dissociation reaction, is used to identify the end point of a titration reaction.
117. Part C
24 . B
To answer this question, you need to write the Lewis dot diagrams and then use any one of
several formulas to find the formal charge. One such formula is formal charge = valence
electrons – [number of bonds + number of nonbonding electrons]. The Lewis dot structure of
HNO 3 shows that nitrogen is double bonded to one oxygen, single bonded to another oxygen,
and single bonded to another oxygen that is single bonded to a hydrogen—there are no lone
electron pairs on the nitrogen. Using the formula, formal charge is equal to the valence
electrons of nitrogen (5) minus the sum of the number of bonds and the number of
nonbonding electrons, which in this case is 4. So, the formal charge on the nitrogen is 5 minus
4, or 1.
25 . D
In a solution, HCl contributes 1 mol of H+ ions per mol of HCl. NaOH also contributes 1 mol of
OH– ions per mol of NaOH. Therefore, to neutralize the 80 mL of a 0.5M NaOH solution, you
must have the same number of moles of HCl. The number of moles of NaOH you have is:
(0.80 L)(0.5 mol/L) = 0.04 mol of NaOH
and therefore 0.04 mol of OH– ions.
To calculate the volume of a 1M solution of HCl, you will need to get 0.04 mol, perform the
following calculation:
26 . D
An electrolyte is a substance that ionizes to yield an electrically conducting solution. A strong
