Tuesday, May 17, 2011

Chemistry Review Questions

3.         Which two forms of compounds (ionic, covalent, metallic) can conduct electricity? Under what conditions can they conduct electricity and why?

Ionic and metallic bonds can conduct electricity.

Ionic compounds can conduct electricity when in a molten state or if dissolved. They can conduct electricity in these states because the electrons can move throughout the molten compound or in the solution formed. They cannot conduct when solid unless they are under the influence of an electric field.

Metallic compounds can conduct electricity only when they are molten or dissolved in a solution. When molten or dissolved the compounds’ electrons are free to move around and are able to conduct in these states. Electricity is able then to pass through the free electrons in the molten or dissolved substance.

31. CH.9 Test Review: Change in pH, how to find the grams needed to increase the pH of a solution.  (Thought this problem was a little hard at first, but once explained it can be very simple.)
9) How many grams of NaOH would be needed to make the pH of a solution increase from 10.000 to 12.000 using 500.0mL of the solution.


pH1 10.000 -> pOH 4.000
pH2 12.000 -> pOH 2.000
V .500 L

Solve for molarity of OH-:
pOH -> M OH+ (10^-pOH)

pOH1 = 1.000x10^-4 M OH-
pOH2 = 1.000x10^-2 M OH-

Solve for the moles of OH- of each:
mol = MV

mol OH1- = 5x10^-5
mol OH2- = .00500

Find the change of the # of moles:

(mol OH1-) - (mol OH2-) = .00495 mol OH-

Moles of OH- in NaOH is 1 mol OH-

.00495 mol OH- x 40g NaOH/1 mol OH- = 
.198g NaOH