Solving for a reactant

Question

Ammonium phosphate ((NH4)3PO4)is an important ingredient in many fertilizers. It can be made by reacting phosphoric acid (H3PO4)with ammonia (NH3).

What mass of ammonium phosphate is produced by the reaction of 6.9g of ammonia?

Be sure your answer has the correct number of significant digits.

Answer 1

Write an unbalanced chemical reaction equation to correspond to the word problem:

H₃PO₄ + NH₃ → (NH₄)₃PO₄

Balance the equation:

H₃PO₄ + 3NH₃ → (NH₄)₃PO₄

Calculate the number of moles in 6.9 g of NH₃ (ammonia) using the periodic table:

N: 14.007 x 1 = 14.007

H: 1.008 x 3 = 3.024

------------------------------

NH₃ = 17.031 g/mol

(6.9 g NH3)/(17.031 g/mol) = 0.40514 moles of NH₃

Using the molar ratios in the balanced chemical reaction equation, calculate the number of moles of (NH₄)₃PO₄ (ammonium phosphate):

The chemical reaction equation says it takes 3 moles of NH₃ to make 1 mole of (NH₄)₃PO₄ therefore 0.40514 moles of NH₃ will produce 0.13505 moles of (NH₄)₃PO₄ (divide 0.40514 by 3)

Calculate the molar mass of (NH₄)₃PO₄ using the periodic table

N: 14.007 x 3 = 42.021

H: 1.008 x 12 = 12.096

P: 30.974 x 1 = 30.974

O: 15.999 x 4 = 63.996

-------------------------------

(NH₄)₃PO₄ = 149.087 g/mol

(0.13505 moles of (NH₄)₃PO₄ )(149.087 g/mol) = 20.17 grams however, we start with 2 sig figs so we must use 2 sig figs in our answer so 2.0x10¹ grams of (NH₄)₃PO₄ is produced (or you could answer "20. grams" showing the decimal point)