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 salt?
Have you wondered while some ionic salts though polar do not still dissolve in water whereas other ionic salts dissolve?
In Chemistry, there are different types of salts and mememorising their solubility per salt might be very gruelling and that’s why we developed a smart way of re ogixing soluble dnd 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 and Hydroxides
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
Ag3PO4
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/salts | Nitrates (NO3–) | Sulphates (SO42)– | Chlorides (Cl–) | Carbonates (CO32- ) | Sulphides (S2-) | Chlorates (ClO3–) | Dichromate ( Cr2O72- ) |
| Potassium (K+) Sodium (Na+) Ammonium (NH42+) | KNO3 NaNO3 NH4NO3 Soluble | K2SO4 Na2SO4 (NH4)2SO4 Soluble | KCl NaCl NH4Cl Soluble | K2CO3 Na2CO3 (NH4)2CO3 Soluble | K2S Na2S (NH4)2S Soluble | KClO3 NaClO3 NH4ClO3 Soluble | K2Cr2O7 Na2Cr2O7 (NH4) 2Cr2O7 Soluble |
| Lead (Pb2+) | Pb(NO3)2 Soluble | PbSO4 Insoluble | PbCl2 Insoluble | PbCO3 Insoluble | PbS Insoluble | Pb(ClO3)2 Soluble | PbCr2O7 Insoluble |
| Zinc (Zn2+) | Zn(NO3 Soluble | ZnSO4 Soluble | ZnCl2 Soluble | ZnCO3 Insoluble | ZnS Insoluble | Zn(ClO3)2 soluble | ZnCr2O7 Insoluble |
| Calcium (Ca2+) | Ca(NO3)2 Soluble | CaSO4 Partially insoluble | CaCl2 Soluble | CaCO3 insoluble | CaS Sparingly soluble | Ca(ClO3)2 Soluble | CaCr2O7 insoluble |
| Magnesiuum (Mg2+) | Mg(NO3)2 Soluble | MgSO4 soluble | MgCl2 Soluble | MgCO3 Insoluble | MgS Sparingly soluble | Mg(ClO3)2 Soluble | CaCr2O7 Soluble |
| Aluminium (Al3+) | Al(NO3) | Al2(SO4)3 Soluble | AlCl3 Soluble | Al2(CO3)3 Insoluble | Al2S3 Insoluble | Al(ClO3)3 insoluble | Al2(Cr2O7)3 |
| Silver (Ag+) | AgNO3 Soluble | Ag2SO4 Soluble | AgCl Inoluble | Ag2CO3 Soluble | Ag2S Soluble | AgClO3 Soluble | Ag2Cr2O7 Soluble |
| Iron Fe2+ | Fe(NO3)2 Soluble | FeSO4 soluble | FeCl2 Soluble | FeCO3 Insoluble | FeS Sparingly soluble | Fe(ClO3)2 Soluble | FeCr2O7 Soluble |
| Iron Fe3+ | Fe(NO3) | Fe2(SO4)3 Soluble | FeCl3 Soluble | Fe2(CO3)3 Insoluble | Fe2S3 Insoluble | Fe(ClO3)3 insoluble | Fe2(Cr2O7)3 |
| Copper Cu2+ | Cu(NO3)2 Soluble | CuSO4 soluble | CuCl2 Soluble | CuCO3 Insoluble | CuS Sparingly soluble | Cu(ClO3)2 Soluble | CuCr2O7 Soluble |
| Barium Ba2+ | Ba(NO3)2 Soluble | BaSO4 soluble | BaCl2 Soluble | BaCO3 Insoluble | BaS Sparingly soluble | Ba(ClO3)2 Soluble | BaCr2O7 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/salts | Chromates (CrO42-) | Phosphates (PO43-) | Flourides (F–) | Iodidies (I–) | Oxides (O2-) | thiocyanates (CNS–) | Acetates |
| Potassium (K+) Sodium (Na+) Ammonium (NH42+) | K2CrO4 Na2CrO4 (NH4)3CrO4 Soluble | K3PO4 Na3PO4 (NH4)3PO4 Soluble | KF NaF NH4F Soluble | KI NaI NH4I Soluble | K2O Na2O Soluble | KSCN NaSCN NH4SCN Soluble | CH3COOK CH3COONa CH3COONH4 soluble |
| Lead (Pb2+) | PbCrO4 Insoluble | Pb3 (PO4)2 Insoluble | PbF2 Insoluble | PbI2 Insoluble | PbO Insoluble | Pb(SCN)2 Insoluble | (CH3COO)2Pb Soluble |
| Zinc (Zn2+) | ZnCrO4 Insoluble | Zn3 (PO4)2 Insoluble | ZnF2 Soluble | ZnI2 Soluble | ZnO Insoluble | Zn(SCN)2 Soluble | (CH3COO)2Zn Soluble |
| Calcium (Ca2+) | CaCrO4 Insoluble | Ca3(PO4)2 Insoluble | CaF2 Soluble | CaI2 Soluble | CaO Slightly soluble | Ca(SCN)2 Soluble | (CH3COO)2Ca Soluble |
| Magnesium (Mg2+) | MgCrO4 Insoluble | Zn3 (PO4)2 Insoluble | MgF2 Soluble | MgI2 Soluble | MgO Insoluble | Mg(SCN)2 Soluble | (CH3COO)2Mg Soluble |
| Aluminium (Al3+) | Al2(CrO4)3 Insoluble | AlPO4 Insoluble | AlF3 Soluble | AlI3 Soluble | Al2O3 Insoluble | Al(SCN)3 Soluble | (CH3COO)3Al Soluble |
| Silver (Ag+) | Ag2CrO4 Insoluble | Ag3PO4 Insoluble | AgF Insoluble | AgI Insoluble | Ag2O Insoluble | AgSCN Insoluble | CH3COOAg Soluble |
| Iron Fe2+ | FeCrO4 Insoluble | Fe3 (PO4)2 Insoluble | FeF2 Soluble | FeI2 Soluble | FeO Insoluble | Fe(SCN)2 Soluble | (CH3COO)2Fe soluble |
| Fe3+ | Fe2(CrO4)3 Insoluble | FePO4 Insoluble | FeF3 Soluble | FeI3 Soluble | Fe2O3 Insoluble | Fe(SCN)3 Soluble | (CH3COO)3Fe soluble |
| Copper Cu2+ | CuCrO4 Insoluble | Cu3 (PO4)2 Insoluble | CuCl2 Soluble | CuI2 Soluble | CuO Insoluble | Cu(SCN)2 Soluble | (CH3COO)2Cu soluble |
| Barium Ba2+ | BaCrO4 Insoluble | Ba3 (PO4)2 Insoluble | BaCl2 Soluble | BaI2 Soluble | BaO Soluble | Ba(SCN)2 Soluble | (CH3COO)2Ba soluble |
| Chromates | Phosphates | Chlorides | Iodides | Oxides | Thiocyannate | Acetates |
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
| Salts | Soluble | Insoluble |
| Nitrates | All nitrates are soluble | No exception |
| Sulphates | All sulphates are soluble | Except BaSO4, PbSO4 |
| Carbonates | Except K2CO3,Na2CO3, (NH4)2CO3 | All other carbonates are insoluble |
| Chlorides | All chlorides are soluble | Except PbCl2 |
| Iodides | All iodides are soluble | Except PbI, AgI |
| Fluorides | All fluorides are soluble | Except PbF, AgF |
| Chlorates | All chlorates are soluble | No exceptions |
| Dichromates | Except Na2Cr2O7, K2Cr2O7 | All dichromates are insoluble |
| Acetates | All 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.
