More Molarity

Here are some more examples of Molarity, getting trickier and trickier!

 

100 mL of 0.250 M Iron (II) Chloride reacts with excess copper. How many grams of Iron are produced?

Now, what do we ALWAYS do first?
Free body diagram!
Just kidding. Balanced Equation!
FeCl2 + Cu -> CuCl2  + Fe
 

0.250 mol   x   0.100 L  x  1   x   55.8 g  =  1.40 g
      L                                    1        1 mol    

Use the numbers given to you: the Molarity and volume, and then use the mole ratio and molar mass to get the end product! Remember, what you need over what you have!

ex 2. A 3.00 g piece of Iron is added to a beaker containing 100 mL of 0.750 M AgNO3. Determine the LR
Fe + 2AgNO3 -> Fe(NO3)2 + 2Ag

0.100 L   x   0.750 mol   x   1  x   55.8 g  =  2.09 g of Fe needed

                          1 L               2       1 mol 

Remember to convert mL to L and be consistent in your units!
To find the LR, as taught before, just convert one of your reactants' numbers to the number (it can be either mass, volume, moles) of your other reactant, to see if you have enough or not!
In this case, the AgNO3 is the LR

ex. 3 A beaker contains 100 mL  of 1.5 M HCl. Excess Zinc is added to the beaker. Determine how many litres of Hydrogen gas should be produced.

2HCl + Zn -> ZnCl2 + H2

0.100 L   x   1.5 mol   x   1   x  22.4 L  =  1.68 L

                      1 L              2        1 mol

Simply use mole ratio to convert to Hydrogen gas, and remember, in this case, because Hydrogen is a gas, you can use the volume at STP (22.4 L)!

Here's a link to website that explains it quite well, too!

http://dl.clackamas.cc.or.us/ch105-04/molarity.htm