# Two, extra TOPIC 4 questions for my AP classes

September 29, 2008

Take a look at these BEFORE the test on Wed 10/1.

Question 1: It concerns silicon tetrachloride and can be found as part (b) on this page; http://www.drbateman.net/asa2sums/sum1.2/test1.2.htm

• 1cm3 = 1mL
• 1dm3 = 1L
• the equation for “neutralisation” that the questions refers to is;

HCl + NaOH ==> NaCl + H2O

• The correct answer is 91.8%

Question 2: This question has been adapted from an unkown source;

2.00 g of an impure copper ore that contains some undetermined amount of copper pyrites with the formula CuFeS2, is treated so that all of the copper ions are dissolved into exactly 100mL of solution. 20mL portions of this solution are treatd with excess KI and the reaction below takes place;

2Cu2+ + 4I ==> 2CuI + I2

The iodine that is produced in this reaction requires 18.3mL of 0.10M sodium thiosulfate to react completely according to the equation below;

2S2O32- + I2 ==> S4O62- + 2I

Calculate the % purity of the ore.

• The correct answer is 84%