solubility rule

Solubility rule of Salts: What is the general solubility rule of salts?

There is a need for students to understand the general solubility rule of salts.

Have you wondered while some ionic salts though polar do not still dissolve in water whereas other ionic salts dissolve? Whether you’re a student delving into the intricacies of chemistry or a curious mind seeking to comprehend the world at the molecular level, this exploration promises to illuminate the fascinating realm of salt solubility. For example, from the kitchen to the laboratory, the ability to predict whether a salt will dissolve or form a precipitate is indispensable and the solubility rules – a set of guidelines that offer clarity amidst the complexity of ionic interactions seem to be our easy pave way to this.

To help demystify the solubility rules of salts in chemistry. We’ll explore the principles behind these rules, uncover common patterns, and equip you with the knowledge to decipher the solubility behavior of various salts.

In Chemistry, there are different types of salts and memorizing their solubility per salt might be very grueling and that’s why we developed a smart way of recognizing soluble and insoluble salts.

It is important to also remember that covalent compounds generally do not dissolve in water though we have few exceptions.

But what exactly is solubility?

Solubility is the amount of solute in moles or grams that will dissolve in I dm3 of the solvent.

Yes, there are factors responsible for the dissolution of salts in water but we are actually looking at the summary of soluble and insoluble salts.

Why do I need to know much about the solubility of salts?

The knowledge of the solubility rule will make your journey in chemistry smooth and will help you determine precipitates and even predict both ionic equations.

It is relevant to remember that most covalent compounds are insoluble while most ionic compounds are soluble.

when we talk about salts, we mean both nitrates, chlorides, sulphates , carbonates.

10 Solubility Rules for Salts

At its core, solubility refers to the ability of a substance, known as the solute, to dissolve in a solvent to form a homogeneous mixture, typically a solution.

The driving force behind solubility lies in the concept of energetics. When a salt dissolves, the attractive forces between the solute ions and the solvent molecules overcome the forces holding the ions together in the solid lattice. This process, known as dissolution, involves the hydration or solvation of ions, wherein water molecules surround and stabilize the separated ions in solution.

However, not all salts exhibit the same propensity to dissolve. Enter the solubility rules – a set of empirical guidelines derived from experimental observations, which elucidate the solubility behavior of various salts. These rules serve as invaluable tools for predicting whether a salt will dissolve, form a precipitate, or remain insoluble under specific conditions.

Deciphering the Solubility Rules: Patterns and Principles

The solubility rules, though seemingly daunting at first glance, stem from discernible patterns rooted in the properties of ions and their interactions. While exceptions exist, these rules provide a reliable framework for making solubility predictions in many cases.

Let’s explore some key tenets of the solubility rules:

1.All salts of group one elements and ammonium are soluble.

Group one elements are Lithium, Sodium, Potassium, Caesium, Francium and Rubidium. Examples of salts of Group one include Lithium Chloride ( LiCl), Sodium Bromide( (NaBr), Potassium Sulphate (K2SO4), Caesium Flouride (CsF).

2. All nitrates are soluble

Examples of nitrates include sodium nitrate (NaNO3), Potassium nitrate (KNO3), Calcium nitrate (Ca(NO3)2.

3.All halides (except fluorides) are soluble except halides of silver and lead.

By halides, we mean salts ending with halogens e.g Chlorine, Bromine, and Iodine.

The insoluble halide are AgCl, AgBr, AgI, PbCl2, PbBr2, PbI2

4.All carbonates are insoluble except carbonates of group one elements.

Soluble carbonates are Na2CO3, K2CO3, Li2CO3, Cs2CO3 etc

5.All sulphates are soluble except Barium Sulphate, Lead II Sulphate and Calcium Sulphate

Though Calcium Sulphate is partly soluble in water.

6. All Phosphates are soluble except calcium phosphate Ca3(PO4)2 and Silver phosphate


7. All chromates are insoluble except lead chromate (PbCrO4) and Barium chromate (BaCrO4)

8.All hydroxides are insoluble except group 1 metals  hydroxides and ammonium hydroxides examples are NaOH, KOH etc

9. Most fluorides are soluble except Barium Fluoride BaF2, Magnesium Fluoride MgF2, Lead II fluoride PbF2

Most sulphides of all transition metals are insoluble

11. All salts of sodium, Potassium, Ammonium are soluble in water

Before I finally leave the solubility of salts, I would love you to remember that there are factors that affect the degree of solubility of salts.

The main factor is temperature, For example, have you ever wondered why a cube of sugar will dissolve more in hot or warm water than in cold water?

Why do we use hot water to make coffee or tea?

The answer is simple, sats will dissolve better when the temperature of the solvent is high.

If you use cold water, the coffee will be underextracted.

Also, salts will crystallize out i.e become insoluble in the solvent when the temperature of the solvent is low.

in conclusion, it is pertinent I mention again that apart from knowing the general solubility rule of salts still consider the factors affecting the degree of solubility.

Solubility rule for soluble and insoluble salts

Metal/saltsNitrates (NO3)Sulphates  (SO42)Chlorides   (Cl)Carbonates  (CO32- )Sulphides     (S2-)Chlorates (ClO3)Dichromate   ( Cr2O72- )
Potassium (K+) Sodium (Na+ Ammonium  (NH42+)KNO3 NaNO3 NH4NO3 SolubleK2SO4 Na2SO4 (NH4)2SO4 SolubleKCl NaCl NH4Cl SolubleK2CO3 Na2CO3 (NH4)2CO3 SolubleK2S Na2S (NH4)2S SolubleKClO3 NaClO3 NH4ClO3 SolubleK2Cr2O7 Na2Cr2O7 (NH4) 2Cr2O7 Soluble
Lead (Pb2+)Pb(NO3)2 SolublePbSO4 InsolublePbCl2 InsolublePbCO3 InsolublePbS InsolublePb(ClO3)2 SolublePbCr2O7 Insoluble
Zinc (Zn2+)Zn(NO3 SolubleZnSO4 SolubleZnCl2 SolubleZnCO3 InsolubleZnS InsolubleZn(ClO3)2 solubleZnCr2O7 Insoluble
Calcium (Ca2+)Ca(NO3)2 SolubleCaSO4 Partially insolubleCaCl2 SolubleCaCO3 insolubleCaS Sparingly solubleCa(ClO3)2 SolubleCaCr2O7 insoluble
Magnesiuum (Mg2+)  Mg(NO3)2 SolubleMgSO4 solubleMgCl2 SolubleMgCO3 InsolubleMgS Sparingly solubleMg(ClO3)2 SolubleCaCr2O7 Soluble
Aluminium (Al3+)Al(NO3)3 SolubleAl2(SO4)3 SolubleAlCl3 SolubleAl2(CO3)3 InsolubleAl2S3 InsolubleAl(ClO3)3 insolubleAl2(Cr2O7)3
Silver (Ag+)AgNO3 SolubleAg2SO4 SolubleAgCl InolubleAg2CO3 SolubleAg2S SolubleAgClO3 SolubleAg2Cr2O7   Soluble
Iron Fe2+Fe(NO3)2 Soluble  FeSO4 solubleFeCl2 SolubleFeCO3 InsolubleFeS Sparingly solubleFe(ClO3)2 SolubleFeCr2O7 Soluble
Iron Fe3+Fe(NO3)3 SolubleFe2(SO4)3 SolubleFeCl3 SolubleFe2(CO3)3 InsolubleFe2S3 InsolubleFe(ClO3)3 insolubleFe2(Cr2O7)3
Cu(NO3)2 SolubleCuSO4 solubleCuCl2 SolubleCuCO3 InsolubleCuS Sparingly solubleCu(ClO3)2 SolubleCuCr2O7 Soluble
Ba(NO3)2 SolubleBaSO4 solubleBaCl2 SolubleBaCO3 InsolubleBaS Sparingly solubleBa(ClO3)2 SolubleBaCr2O7 Soluble
 Nitrates (NO3)Sulphates  (SO42)Chlorides   (Cl)Carbonates  (CO32- )Sulphides     (S2-)Chlorates (ClO3)Chromates    (CrO42-) Dichromate   ( Cr2O72- )

Solubility chart of some other salts and compounds  

Metal/saltsChromates    (CrO42-)  Phosphates   (PO43-)Flourides (F)Iodidies (I)Oxides (O2-)thiocyanates (CNS)Acetates
Potassium (K+) Sodium (Na+ Ammonium  (NH42+)K2CrO4 Na2CrO4 (NH4)3CrO4 SolubleK3PO4 Na3PO4 (NH4)3PO4 SolubleKF NaF NH4F SolubleKI NaI NH4I SolubleK2O Na2O SolubleKSCN NaSCN NH4SCN SolubleCH3COOK CH3COONa CH3COONH4 soluble
Lead (Pb2+)PbCrO4 InsolublePb3 (PO4)2 InsolublePbF2 InsolublePbI2 InsolublePbO InsolublePb(SCN)2 Insoluble(CH3COO)2Pb Soluble
Zinc (Zn2+)ZnCrO4 InsolubleZn3 (PO4)2 InsolubleZnF2 SolubleZnI2 SolubleZnO InsolubleZn(SCN)2 Soluble(CH3COO)2Zn Soluble
Calcium (Ca2+)CaCrO4 InsolubleCa3(PO4)2 InsolubleCaF2 SolubleCaI2 SolubleCaO Slightly solubleCa(SCN)2 Soluble(CH3COO)2Ca Soluble
Magnesium (Mg2+)  MgCrO4 InsolubleZn3 (PO4)2 InsolubleMgF2 SolubleMgI2 SolubleMgO InsolubleMg(SCN)2 Soluble(CH3COO)2Mg Soluble
Aluminium (Al3+)Al2(CrO4)3 InsolubleAlPO4 InsolubleAlF3 SolubleAlI3 SolubleAl2O3 InsolubleAl(SCN)3 Soluble(CH3COO)3Al Soluble
Silver (Ag+)Ag2CrO4 InsolubleAg3PO4 InsolubleAgF InsolubleAgI InsolubleAg2O InsolubleAgSCN InsolubleCH3COOAg Soluble
Iron Fe2+  FeCrO4 InsolubleFe3 (PO4)2 InsolubleFeF2 SolubleFeI2 SolubleFeO InsolubleFe(SCN)2 Soluble(CH3COO)2Fe soluble
Fe3+Fe2(CrO4)3 InsolubleFePO4 InsolubleFeF3 SolubleFeI3 SolubleFe2O3 InsolubleFe(SCN)3 Soluble(CH3COO)3Fe soluble
Copper Cu2+CuCrO4 InsolubleCu3 (PO4)2 InsolubleCuCl2 SolubleCuI2 SolubleCuO InsolubleCu(SCN)2 Soluble(CH3COO)2Cu soluble
Barium Ba2+BaCrO4 InsolubleBa3 (PO4)2 InsolubleBaCl2 SolubleBaI2 SolubleBaO SolubleBa(SCN)2 Soluble(CH3COO)2Ba soluble

If you are wondering how I figured out the formula of these salts, you need to know that a compound is formed by exchange of valencies.

A second Solubility chart of the soluble salts and insoluble salts

NitratesAll nitrates are solubleNo exception
SulphatesAll sulphates are solubleExcept BaSO4, PbSO4
CarbonatesExcept K2CO3,Na2CO3, (NH4)2CO3All other carbonates are insoluble
ChloridesAll chlorides are solubleExcept PbCl2, AgCl,
IodidesAll iodides are solubleExcept PbI, AgI
FluoridesAll fluorides are solubleExcept PbF, AgF
ChloratesAll chlorates are solubleNo exceptions
DichromatesExcept Na2Cr2O7, K2Cr2O7All dichromates are insoluble
AcetatesAll acetates are soluble 

Hydration energy vs lattice energy

The solubility of salts is also influenced by the lattice energy and Hydration energy comparison.

Latice energy and hydration energy are two important properties of ionic solids on which their melting point, boiling point and solubility depends on.

Lattice energy and hydration energy are two important properties of ionic solids on which their melting point, boiling point and solubility depend.

lattice energy is the energy change that occurs when a compound is formed from its ion.

on the other hand, Hydration energy is the energy change when one mole of a gaseous ion is diluted in water.

A substance is water soluble when the Hydration energy is equal or greater than the lattice energy but insoluble when the Hydration energy is less than the lattice energy.

Hint on lattice and hydration energy

1.Lattice energy increases as the charge on the ion increases and the size decreases.

2.Hydration energy increases as the size of the ion decreases and charges on it increases.

3.Hyration energy of alkali metal salts are much lesser than those of corresponding alkaline earth metal salts.

How will you determine the solubility of a sparingly soluble salt?

Actually in chemistry, salts could be termed very soluble, partially soluble , sparingly soluble and insoluble.

what do sparingly soluble mean?

For sparingly soluble salts we mean the measure or degree of the mass of the salt that can dissolve in the solvent

Actually, if 1g of a salt that can dissolve in 100ml of a solvent, then the salt is considered sparingly soluble.

Most insoluble salts are actually sparingly soluble and and the solubility of sparingly salts can be determined using solubility product constant.

So to be able to measure the degree of solubility, we need to know how to calculate the solubility product constant of sparingly soluble salts.

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