Formula Units

[halle young 4A]

(a) Determine the number of KNO3 formula units in 0.750 mol KNO3 (b) what is the mass (in milligrams) of 2.39 x 10^20 formula units of Ag2SO4? (c) Estimate the number of NaHCO2 formula units in 3.429 g of NaHCO2, sodium formate, which is used in dyeing and printing fabrics.

[aphung1E]

A) to turn moles into formula units/atoms i used the equation from the textbook Number of object=amount in moles x avagadro's constant so you multiply 0.750 mol KNO3 x (6.022x10^23) and get 4.52x10^23 formula units.

B) They're asking us for the mass so we will need to find the moles. With the formula units given, you divide the formula units by avagadro's constant then multiply by the molar mass of Ag2SO4 but after you will need multiply it by 1000 since our answer is in grams and they want milligrams. 2.39x10^20 Ag2SO4 x(1 mol/6.022x10^23) x (311.8 g/1 mol) x (1000 mg/g)= 123.75 mg


C) You would multiply the mass of the sample 3.429g x(1mol/67.998g NaHCO2)=0.0504279538 moles then to convert it into formula units you will need to multiply by avagadro's constant giving you 3.04x10^22.

[AKatukota]

So formula units just means atoms?

[Anne Tsai 1F]

So formula units just means atoms?

It depends on the problem; formula units is used to describe the mass per mole of an ionic compound, while atoms is used to describe the mass per mole of an element.