Potassium Phosphate

Atomic Structure

Potassium Phosphate (K₃PO₄) is composed of three potassium atoms and one phosphate. Phosphate is a polyatomic ion composed of one phosphorus atom and four oxygen atoms.

Isotopes of Bonding Elements

Potassium has 3 naturally occurring isotopes: K39 (93.3%), K41 (6.7%), K40 (0.01%). Average mass is 39.1u.

Phosphorus has 1 naturally occurring isotope: P31 (100%) Average mass is 31u.

Oxygen has 3 naturally occurring isotopes: O16 (99.76%), O18 (0.20), O17 (0.04). Average mass is 16u.

Physical Characteristics of Bonding Elements

Potassium is a soft white metal with silvery lustre and a low melting point.

Phosphorus is a soft and waxy solid that is colourless and semitransparent and glows in the dark.

Oxygen is a colourless and odorless gas.

Electron Configuration and Electronegativity of Bonding Elements

Element	Electron Configuration	Electronegativity
Potassium	4s1	0.82
Phosphorus	3p3	2.19
Oxygen	2p4	3.44

Bohr-Rutherford and Lewis Dot Diagrams of Bonding Elements


Element	Bohr-Rutherford Diagram	Lewis Dot Diagram
Potassium
Phosphorus
Oxygen
	Compound Diagrams
Phosphate
Potassium Phosphate

Flame Test for Bonding Metal

Potassium burns with a light purple (lilac) colour.

The Compound

Names of the Compound

Chemical Formula	K₃PO₄
Classical	Potassium Phosphate
IUPAC	Tripotassium Phosphate

Hydrates

Potassium Phosphate has one existing hydrate.

Chemical Formula	K₃PO₄ • H₂O
Classical	Potassium Phosphate Monohydrate
IUPAC	Tripotassium Phosphate Monohydrate

Chemical Reactions

Potassium Phosphate can appear in decomposition, single displacement, and double displacement reactions.

Example of a Decomposition Reaction	K₃PO₄(s) + H₂O(L) → 3K(aq) + PO₄(aq)
Example of a Single Displacement Reaction	K₃PO₄(aq) + Au(s) → AuPO₄(s) + 3K(aq)
Example of a Double Displacement Reaction	K₃PO₄(aq) + 3AgNO₃(aq) → Ag₃PO₄(s) + 3KNO₃(aq)

Potassium Phosphate's solubility in water is 50.8g/100mL

The Mole

Potassium Molar Mass	39.10u	Phosphate Molar Mass	30.97u + 4(16.00u) = 94.97u
Phosphorus Molar Mass	30.97u	Potassium Phosphate Molar Mass	3(39.10u) + 94.97u = 212.27u
Oxygen Molar Mass	16.00u

Example of a Calculation using Avogadro's Number

212.27u x 6.022x10^23 = 1.27x10^26u is the mass of one mole of Potassium Phosphate.

Example of a Calculation using Mass

n x M = m

4 x 1.27x10^26u = 5.08x10^26g

There are 5.08x10^26g in 4 moles of K₃PO₄

Example of a Calculation of Percent Composition

100 ÷ 212.27u = 0.47

3(39.10u) x 0.47 = 55.131% Potassium

30.97u x 0.47 = 14.5559% Phosphorus

4(16.00u) x 0.47 = 30.08% Oxygen

55.131 + 14.5559 + 30.08 = 99.7669 = ~100% Potassium Phosphate

Empirical Formula

K₃PO₄

The empirical formula for potassium phosphate is exactly the same as the chemical formula.

Stoichiometry

Molar ratios in an equation:

2 moles of potassium phosphate react with 3 moles of gold.

K₃PO₄(aq) + Au(s) → AuPO₄(s) + 3K(aq)

1 : 1 : 1 : 3

2/1 3/1

2<3

K₃PO₄ is the limiting reagent.

Au is the excess reagent.

Properties of Solutions/Acids and Bases

Dissociation of K₃PO₄ in water:

K₃PO₄(s) + H₂O(L) → 3K⁺(aq) + PO₄⁻³(aq) + H₂O(L)

Example of K₃PO₄ being a product of a neutralization reaction:

H₃PO₄(aq) + KOH(aq) → K₃PO₄(aq) + H₂O(L)

Solubility and Reactions

The solubility curve of K₃PO₄ compared to K₂CO₃ and O₂: