When 8.88 g of c6h10 were reacted with excess of o2, 18.9 g of co2 were recovered. given this information, what is the % yield of co2?

66.2% yield  
The balanced equation for the reaction is: 
2C6H10 + 17O2 ==> 12CO2 + 10H2O  
So for every 2 moles of C6H10 consumed, we should get 12 moles of CO2. Or to simplify, for each mole of C6H10, we should get 6 moles of CO2. Now let's calculate the molar mass of C6H10 and CO2 and then determine how many moles of each we really have.
 Atomic weight carbon = 12.0107 
 Atomic weight hydrogen = 1.00794 
 Atomic weight oxygen = 15.999
 Molar mass C6H10 = 6*12.0107 + 10*1.00794 = 82.1436 g/mol
 Molar mass CO2 = 12.0107 + 2*15.999 = 44.0087 g/mol 
 Moles C6H10 = 8.88 g / 82.1436 g/mol = 0.10810337 mol
 Moles CO2 = 18.9 g / 44.0087 g/mol = 0.429460538 mol 
 Since we had 0.10810337 moles of C6H10, we should have gotten
6*0.10810337 = 0.648620221 moles of CO2, but only got 0.429460538 moles. So let's divide the actual yield by the theoretical yield to get the percentage yield. 
0.429460538 / 0.648620221 = 0.662114014 = 66.2%

The answer to your question really depends on three things: how much water you have, how cold it is to start out, and how cold the things around it are. water actually freezes when it gets to 32 degrees fahrenheit (0 degrees celsius), but the time it takes to get there may be different.  let's start with the first. if you take two glasses, and fill one with a tiny bit of water, and the other about halfway, then put them both in the freezer, the one with less water will freeze first (you can try this at home, but i recommend using plastic cups and not glass ones).  now let's move on to the second part. let's say you have two glasses, and you fill one with really cold water that has been in the refrigerator, and the other with really hot water from the sink. if you put both of them in the freezer, the one that started out colder will freeze first.  for the third part, let's imagine that you have two glasses with the same amount of water in them, and the water is at the same temperature. imagine putting one outside on a really really cold day in georgia, and having a friend in alaska put one outside on the same day. since it would be so much colder in alaska, the glass of water there would freeze before yours.  so, if you took a tiny bit of really cold water in a glass, and put it outside on a cold day in alaska, it would freeze a lot faster than a big glass of hot water outside on a cold day in georgia. 

Use a magnet to separate iron, evaporate water, i'm not sure how to separate the other two i'm sorry but good luck