Molarity Problems Emergency!!!?

Question

Please, can anybody tell me how to figure out the problems that my teacher gave to my class to review for an AP chemistry Test shes giving us a in a couple of days and I have no clue how to solve these problems.

The following problems are:

1) A solution of hydrogen peroxide is 30% H2O2 by mass and has a density of 1.11 g/cm3. What is the molarity, if even possible

2) Calculate the molarity of C2H5OH in a water solution that is prepared by mixing 50 ml of C2H5OH with 100 ml of Hs0 at 20 degrees Celsius. The density of the C2H5OH is 0.789 g/ml at 20 degrees Celsius.

3)What is the molarity of a solution of 50 g of propanol (CH3CH2CH2OH) in 152 ml water, if the density of water is 1.0 g/ml.

4). A solution containing 296.6g of Mg(NO3)2 per liter has a density of 1.114 g/ml. The molarity of the solution is what?

Answer 1

Molarity = moles per liter of solution
1)
1 L of 30% H2O2 weighs 1110 gram (1.11 g/cm^3 x 1000 cm^3 = 1110 g)
30% of 1110 g = 333 grams
333 g / 34 g/mol = 9.79 moles
30% H2O2 is 9.79 molar

2)
50 mL x 0.789 g/mL = 39.45 g
50 mL + 100 mL = 150 mL
39.45 g / 46.07 g/mol = 0.856 mol
0.856 mol / 0.150 mL = 5.71 molar

Now yopu should have a "clue" as to how you can solve #3 and #4

Answer 2

whats up merely kno this one element and all ur doubts of molarity would be cleared. assume we are speaking approximately molarity of A then in a answer of quantity V then Molarity=Moles of A/V(in litres) and for pK element pK= -log (molarity of ok) comparable for Cl-

Answer 3

1) Atomic weights: H=1 O=16 H2O2=34 Let H2O2 be called HP. Let the solution be called S.

30gHP/100gS x 1.11gS/1mLS x 1molHP/34gHP x 1000mLS/1LS = 9.79 moles HP per L solution, which is molarity.

The rsst of them go pretty much the same way.