WHAT IS THE MOLARITY OF A SOLUTION PREPARED BY DISSLOVING 4.92 GRAMS OF CALCIUM NITRATE, Ca(NO3)2 in 250 mL OF WATER?
Remember the definition.
M = #mols/L.
# mols = grams/molar mass.
Post your work if you get stuck.
Dr. Bob222 I'm not following. Would you please further explain?
Thanks
Plug in the numbers.
# mols = g/molar mass = 4.92/molar mass Ca(NO3)2 = xx mols Ca(NO3)2.
Then M = #mols/L = xxmols/0.250 L = ?? M.
Technically, the problem should have said in 250 mL of SOLUTION. There is a difference. Or the problem could have said dissolve in a little water and make to a final volume of 250 mL. Or they could have asked for the molality and given the density and calculated the molarity that way; however, I think, in the spirit of the problem that it means 250 mL solution.
To find the molarity of a solution, you need to know the amount of solute (in moles) and the volume of the solution (in liters).
Step 1: Convert the mass of calcium nitrate (Ca(NO3)2) to moles.
To do this, you'll need to know the molar mass of calcium nitrate, which can be calculated by adding up the atomic masses of calcium (Ca), nitrogen (N), and oxygen (O).
Ca: atomic mass = 40.08 g/mol
N: atomic mass = 14.01 g/mol
O: atomic mass = 16.00 g/mol
Calculating the molar mass:
(40.08 g/mol x 1 Ca) + (14.01 g/mol x 2 N) + (16.00 g/mol x 6 O) = 164.09 g/mol
Now, divide the mass of calcium nitrate (4.92 grams) by its molar mass (164.09 g/mol) to find the number of moles:
4.92 g / 164.09 g/mol = 0.030 moles
Step 2: Convert the volume of water from milliliters to liters.
Given volume: 250 mL
To convert to liters, divide by 1000:
250 mL / 1000 mL/L = 0.25 L
Now that we have the number of moles (0.030 moles) and the volume of the solution in liters (0.25 L), we can calculate the molarity.
Molarity (M) is defined as moles of solute per liter of solution.
Molarity = moles of solute / volume of solution in liters
Molarity = 0.030 moles / 0.25 L
Molarity ≈ 0.12 M
Therefore, the molarity of the calcium nitrate solution is approximately 0.12 M.