Question

An order calls for 6 grams of magnesium sulfate added to 500mL of NS infused at a rate of 1 g/hr. You have available 50%w/v magnesium sulfate vials. How many total milliosmoles (mOsm) are in the compounded solution? (MW MgSO4•7H20= 246.47, MW NaCl = 58.44) Please round the final answer to the nearest whole number

Answer 1

50 % w/v means 50 g in 100 mL

Osmolality = no of osmoles/ L of solvent

For magnesium sulfate , no of species = 2

Concentration = 50 % w/v = 50 g in 100 mL

No of moles of magnesium sulfate = 50 g / 246.47 g = 0.2029 moles

Volume of solvent = 100 mL = 0.1 L

Concentration = 0.2029 / 0.1 = 2.029 moles/L

Osmolality = 2 * 2.029 = 4.058 osmol/L = 4058 mOsmol/L

so number of milliosmoles of magneium sulfate in the sompounded solution = 4058

certain points from the question ;

Weight of magnesium sulfate = 6 g

Volume of NS= 500 mL

Rate of infusion = 1 g/hr

Available formulation of magnesium sulfate = 50 % w/v

6 g in 500 ml = 1 g in 500/6 = 1 g in 83.33 mL

1 g / hour infusion rate = 83 ml in an hour