Chemistry Help?

[jessulkerz]

1- In the reaction Fe2O3 + 3 CO = 2 Fe + 3 CO2, what is the total number of moles of CO used to produce 112 grams of iron?
a) 1.0 b)2.0 c)3.0 d)4.0


2- Given the reaction:
4Al + 3O2 = 2Al2O3
How many moles of Al2O3 will be formed when 27 grams of Al reacts completely with O2?
a) 1.0 b)2.0 c)0.50 d)4.0


3- What is the molarity of a solution that contains 40 grams of NaOH in 0.50 liter of solution?
a) 1.0M b)2.0M c)0.25M d)0.50M


4- A 1-kilogram sample of water will have the highest freezing point when it contains
a) 1 x 10^23 dissolved particles
b) 1 x 10^21 dissolved particles
c) 1 x 10^19 dissolved particles
d) 1 x 10^17 dissolved particles


Please dont just tell me the answers, please explain as much as you can.
Thanks in advance

[Dr.A]

Moles Fe = 112 g / 55.847 g/mol =2.0
the ratio between CO and Fe is 3 : 2
3.0 moles CO needed

Moles Al = 27 g / 27 g/mol = 1 mole
the ratio between Al and Al2O3 is 4 : 2
moles Al2O3 produced = 1 x 2 / 4 = 0.5

Moles NaOH = 40 g / 40 g/mol = 1 mole
M = 1 mole / 0.50 =2.0 M

a) the greatest number