Question

how much NaNO3 must be weighted out to make 50ml of aqueous sol. containing 70mg per
ml?

Answer 1

The concentration of Na is 70 mg / mL and you have 50 mL, soyou have 70 mg/mL * 50 mL = 3500 mg.
The atomic mass of Na is 23 g/mole.Calculate how many moles of Na you have in 3500 mg (3.g): 3,5/23 = 0.15 moles.
NaNO₃ dissociates into Na⁺ and NO₃^- so the moles of NaNO₃ is the same as molesof Na⁺. To get the mass of NaNO₃, we can multiply the moles of NaNO₃ by the molecular weight of NaNO₃: 0,15*85 = 12,75g.