Calculate the amount of Na2HPO4*7H2O in grams needed to make 50 mL of a 0.40 M solution. I think this is dealing with molarity but i cant figure it all out for some reason? Help would be greatly appreciated.

just steps is all i really need i think i need the molecular weights first then just simple molarity am i correct?

I got 0.02 g is this right?

Use the Henderson-Hasselbalch equation.

To calculate the amount of Na2HPO4·7H2O (sodium phosphate dibasic heptahydrate) needed to make a 0.40 M (mol per liter) solution, you need to follow these steps:

Step 1: Determine the molar mass of Na2HPO4·7H2O.
The molar mass of Na2HPO4 is:
(2 × atomic mass of Na) + atomic mass of P + (4 × atomic mass of O)
Simplifying this gives:
(2 × 22.99 g/mol) + 30.97 g/mol + (4 × 16.00 g/mol) = 141.96 g/mol

The molar mass of 7H2O (heptahydrate) is:
7 × (2 × 1.01 g/mol + 16.00 g/mol) = 126.18 g/mol

Total molar mass of Na2HPO4·7H2O:
141.96 g/mol + 126.18 g/mol = 268.14 g/mol

Step 2: Convert the given volume (50 mL) to liters.
Since the molarity is given in moles per liter, the volume needs to be in liters. Divide the volume in milliliters by 1000 to convert it to liters:
50 mL ÷ 1000 mL/L = 0.05 L

Step 3: Use the formula for calculating moles from molarity and volume.
The formula is:
moles = molarity × volume

Rearrange the formula to solve for moles:
moles = molarity × volume
moles = 0.40 mol/L × 0.05 L
moles = 0.02 mol

Step 4: Use the moles calculated to find the mass.
Multiply the moles by the molar mass of Na2HPO4·7H2O:
mass = moles × molar mass
mass = 0.02 mol × 268.14 g/mol
mass = 5.36 g

Therefore, you would need 5.36 grams of Na2HPO4·7H2O to make a 0.40 M solution with a volume of 50 mL.