Question

What is the mass of a sample of NH₃ containing 7.20 x 10²⁴ molecules of NH₃? a. 203 grams b. 161 grams c. 214 grams d. 187 grams

Answer 1

Option a. 203 grams

Step-by-step explanation:

By definition, 1 mole = 6.02 x 10^23 of anything.

7.20 x 10²⁴ molecules of NH₃ can be converted into moles NH3 by dividing by (6.02 x 10^23 NH3 molecules/mole).

(7.20 x 10²⁴ molecules of NH₃)/(6.02 x 10^23 NH3 molecules/mole)

NH3 molecules cancel and moles moves to the top, leaving:

(7.20 x 10²⁴/(6.02 x 10^23) moles

(7.20/6.02)*(10²⁴/10^23) moles

(1.196)*(
`10^(1)`) = 11.96 moles of NH3

Convert this to grams NH3 by multiplying by the molar mass of 17.0 grams/mole NH3.

(11.96 moles of NH3)*(17.0 grams/mole NH3) = 203.3 grams NH3

Round to 3 sig figs give us 203 grams.

Option a. 203 grams