Determine the mass of Co(NO3)2 X 6H2O to prepare 250mL of a .50M stock solution.

How many moles do you need?

M x L = moles
moles = grams/molar mass
Solve for grams,.

To determine the mass of Co(NO3)2 • 6H2O needed to prepare a 250 mL 0.50M stock solution, we need to follow these steps:

Step 1: Understand the problem.
We are given the desired concentration of the solution (0.50M) and the volume of the solution (250 mL). We need to find the mass of the compound Co(NO3)2 • 6H2O.

Step 2: Understand the formula and molar mass.
The formula Co(NO3)2 • 6H2O represents cobalt(II) nitrate hexahydrate. To find the molar mass, we add up the atomic masses of all the elements in the formula.
Cobalt (Co) has an atomic mass of 58.93 g/mol.
Nitrogen (N) has an atomic mass of 14.01 g/mol.
Oxygen (O) has an atomic mass of 16.00 g/mol.
Hydrogen (H) has an atomic mass of 1.01 g/mol.
There are two nitrate ions (NO3-) in the formula, so we multiply their molar mass by 2.
There are also six water molecules (H2O) in the formula, so we multiply their molar mass by 6.

Step 3: Calculate the molar mass.
Molar mass = (Co atomic mass) + (2 x N atomic mass) + (6 x O atomic mass) + (12 x H atomic mass) + (6 x water molar mass)
Molar mass = (58.93 g/mol) + (2 x 14.01 g/mol) + (6 x 16.00 g/mol) + (12 x 1.01 g/mol) + (6 x 18.02 g/mol)
Molar mass = 58.93 g/mol + 28.02 g/mol + 96.00 g/mol + 12.12 g/mol + 108.12 g/mol
Molar mass ≈ 303.19 g/mol

Step 4: Use the formula to calculate the mass of the compound.
To find the mass of the compound needed, we can use the formula:
Mass (g) = (Volume (L) x Molarity (mol/L) x Molar mass (g/mol))
First, we need to convert the volume from milliliters (mL) to liters (L).
Volume (L) = 250 mL ÷ 1000 mL/L
Volume (L) = 0.250 L

Now, we can calculate the mass of the compound:
Mass (g) = 0.250 L x 0.50 mol/L x 303.19 g/mol
Mass (g) = 37.90 g

Therefore, the mass of Co(NO3)2 • 6H2O needed to prepare a 250 mL 0.50M stock solution is approximately 37.90 grams.