Determine the mass of Co(NO3)2•6 H2O to prepare 250 mL of a 0.50 M stock solution.
How many mols do you want? That is M x L = ?
Then mols = grams/molar mass
Solve for grams.
To determine the mass of Co(NO3)2•6H2O needed to prepare 250 mL of a 0.50 M stock solution, we need to calculate the number of moles of Co(NO3)2•6H2O required.
The formula for the amount of a substance can be calculated using the equation:
Amount (in moles) = Concentration (in M) × Volume (in L)
Here, the concentration of the stock solution is given as 0.50 M, and the volume is given as 250 mL. However, we need to convert the volume from milliliters to liters:
Volume (in L) = 250 mL / 1000 mL/L
Volume (in L) = 0.250 L
Now, we can calculate the number of moles:
Amount (in moles) = 0.50 M × 0.250 L
Amount (in moles) = 0.125 moles
The formula for Co(NO3)2•6H2O indicates that it contains 1 mole of Co(NO3)2 for every 1 mole of Co(NO3)2•6H2O. Therefore, the number of moles of Co(NO3)2 is also 0.125 moles.
To determine the mass of Co(NO3)2, we need to know its molar mass. The molar mass of Co(NO3)2 can be calculated by adding the atomic masses of the constituent elements.
Atomic mass of Co (cobalt) = 58.93 g/mol
Atomic mass of N (nitrogen) = 14.01 g/mol
Atomic mass of O (oxygen) = 16.00 g/mol
The molar mass of one Co(NO3)2 unit is:
(1 × Atomic mass of Co) + (2 × Atomic mass of N) + (6 × Atomic mass of O)
= (1 × 58.93 g/mol) + (2 × 14.01 g/mol) + (6 × 16.00 g/mol)
= 58.93 g/mol + 28.02 g/mol + 96.00 g/mol
= 182.95 g/mol
Now, we can calculate the mass of Co(NO3)2:
Mass = Amount (in moles) × Molar mass
Mass = 0.125 moles × 182.95 g/mol
Mass = 22.87 grams
Therefore, you would need approximately 22.87 grams of Co(NO3)2•6H2O to prepare 250 mL of a 0.50 M stock solution.