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  1. Problems
  2. /Ammonium phosphate, a fertiliser, has the formula (NH₄)₃PO₄…
MediumChemistryHigh School (9–10)GeneralAtoms and Molecules › Molecules, Ions and FormulaeNumericalBoard Exam

Ammonium phosphate, a fertiliser, has the formula (NH₄)₃PO₄…

StemPy LabContributed by StemPy Lab

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

Ammonium phosphate, a fertiliser, has the formula (NH4)3PO4(\text{NH}_4)_3\text{PO}_4(NH4​)3​PO4​. How many atoms of each element are there in one formula unit? How many atoms are there in all?

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Work it out on paper, then type your number. The answer itself stays hidden.

Need a reminder? The key ideaShowHide

A molecule is a group of atoms joined together. Its atomicity is the number of atoms in it. A small number after a symbol counts atoms in one molecule; a number in front counts molecules; a number after a bracket multiplies everything inside.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

Step 1. The ammonium groups. Nitrogen 3×1=33 \times 1 = 33×1=3; hydrogen 3×4=123 \times 4 = 123×4=12.

Step 2. The phosphate group. Phosphorus 111; oxygen 444.

Step 3. All the atoms. 3+12+1+4=203 + 12 + 1 + 4 = 203+12+1+4=20.

Answer: 333 N, 121212 H, 111 P and 444 O: 202020 atoms.

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  1. Molecules and atomicityMolecules, Ions and Chemical Formulae

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