Solubility of Inorganic Compounds in Water

Some chemical compounds such as NaCl dissolve in water very well. But some are not. They are deposited as a precipitate at the bottom of the solution. However every compound has a limit to dissolve in water.

Example

Solubility of NaCl or KCl at 25⁰C

Compound	Solubility in water (g/100ml of water)
NaCl	36
KCl	35.5

• Maximum dissolving mass of NaCl in 100ml of water is 36g.
• Maximum dissolving mass of KCl in 100ml of water is 35.5g.

Solubility of silver chloride is much lower than solubility of sodium chloride in the water.

After that maximum limit, the compound does not dissolve in water furthermore and deposit on the bottom of the solution. You can see two separate parts in the aqueous solution.

Example: There is a 100 ml of distilled water. You add NaCl multiple times until see a precipitate.

Forming a precipitate

• Add 1 g of NaCl. All NaCl dissolves very well and no precipitate is formed.
• Add more 9g of NaCl to the solution. Again no precipitate is formed.
• Add more NaCl until total of 36g of NaCl. But no precipitate is given.
• Add 1g to the the aqueous solution. Now you see a white precipitate is deposited in the bottom of the solution.

In this tutorial, we are going to discuss followings.

1. Definition of solubility
2. Factors which can change solubility
3. Solubility explanations of s, p, d blocks elements
4. Solubility values of inorganic compounds listed by according to the anion and cation at different temperatures.

Solubility units

Solubility is expressed as maximum dissolving mass in unit volume of water.

• g/l
• mg/dm³

Effect of temperature on solubility of solid compound

When temperature increases dissolving amount (solubility) increases.

Solubility definition

Maximum amount of mass of the compound which can dissolve in a unit volume of solvent. Usually we express solubility as grams per 100ml of water (g/100ml).

Solubility of s block elements compounds

S block contains alkali metals and alkali earth metals. Alkali earth metals form more insoluble compounds than alkali metals.

Alkali metals

Most of the s block metals' compounds are soluble in water. Lithium forms some insoluble compounds. Lithium carbonate, lithium fluoride and lithium phosphate are insoluble in water.

Solubility of NaHCO₃ is low when compared to KHCO₃. This phenomenon is used in solvay process to manufacture sodium carbonate.

Alkali earth metals

Alkali earth metals form insoluble and soluble compounds.

Precipitates - alkali earth metals

• Carbonates of all alkali earth metals are insoluble.
• Sulfate of strontium and barium are precipitates. Calcium sulfate is a precipitate in higher concentrations of calcium and hydroxyl ion.
• All phosphates are insoluble.

Solubility of anions

According to the anion, solubility is changed. This is very important in qualitative analysis of inorganic compounds.

Silver nitrate is a soluble compound and silver chloride is a white precipitate.

Nitrate and nitrite

All metal nitrates and nitrites are soluble in water. NaNO₃, Al(NO₃)₃, Fe(NO₃)₃, NaNO₂ are some example nitrate and nitrite compounds which dissolve very well in water.

Sulfate ion

All alkali metal sulfate compounds are soluble. But in alkali earth metals, SrSO₄ and BaSO₄ are precipitates.

Some sulfate of 3d metal ions are soluble in water.

PbSO₄ is also a white precipitate and does not dissolve in water.

Solubility of 3d metal sulfate compounds

3d Metal Sulfate	Solubility in water
Cr2(SO4)3	Practically insoluble in water
MnSO4	52 g/100 cm3 at 50C
FeSO4	Soluble in water.
Fe2(SO4)3	Slowly sol in water;
NiSO4	29.3 g/100 cm3 at 00C 83.7 g/100 cm3 at 100 0C
CuSO4	Very soluble in hot water, soluble in cold water 243 g/l at 00C 75.4 g/100 cm3 at 1000C
ZnSO4	57.7 g/100 g water at 250C 101 g/100 g of water at 700C

Carbonate ion

Only lithium carbonate is the insoluble carbonate in the alkali metal carbonates. All alkali earth metal carbonates are insoluble in the water.

3d metal carbonates are also insoluble in water.

Solubility of metal carbonates can be used to identify metals by determining the compound is a aqueous solution or precipitate.

Solubility of metal carbonate compounds

Metal Carbonate	Solubility in water
Li2CO3	Solubility is low. Following solubility are expressed as w/w%. 1.52 at 00C 1.31 at 200C 1.16 at 400C 1.00 at 600C 0.84 at 800C 0.71 at 1000C
Na2CO3	30.7 g/100 g of water at 250C
K2CO3	105.5 at 0C 108.0 at 100C 110.5 at 200C 113.7 at 300C 155.7 at 1000C

Halide ion

Some metal halides such as NaCl, NaBr or KCl have a high solubility in water. But some metals such as lead or silver will make precipitates with halide ion. These behaviors can be used to identify halide ions compounds.

Precipitates of metal halides

Metal Chloride	Solubility in water
AgCl	0.520 mg/100 g at 500C - Insoluble in water
AgBr	0.14 mg/l at 200C - insoluble in water
AgI	3*10−7g/100 ml of water at 200C
PbCl2	Insoluble in water 0.673 g/100 ml water at 00C 0.99 g/100 ml water at 200C 3.34 g/100 ml water at 1000C
PbBr2	0.455 g/100 ml at 00C 0.973 g/100 ml at 200C 4.41 g/100 ml at 1000C
PbI2	0.044 g/100 ml at 00C 0.0756 g/100 ml 200C) 0.41 g/100 ml 1000C

Metal sulfide solubility

All alkali metal sulfide compounds and alkali earth metal sulfide are soluble in water. But some metal sulfide compounds' solubility is low and have colours too. These colours are very useful in qualitative analysis of identify sulfide anion.

Solubility of alkali metal sulfide and alkali earth metal sulfide

Metal Sulfide	Solubility in water
Na2S	soluble in water 18.6 g/100 g of water at 200C 29.0 g/100 g of water at 400C 35.7 g/100 g of water at 480C 39.0 g/100 g of water at 500C

Metal Hydroxides

Alkali metals

You know NaOH or KOH are very strong bases and dissolve very well in the water. But all metal hydroxides are not soluble in water and not strong bases too.

Alkali earth metals

Alkali metal hydroxide are soluble in water and strong bases. But, from alkali earth metal hydroxides, only strontium hydroxide and barium hydroxide are soluble and strong bases.

3d metals

All 3d metal hydroxides are insoluble in water and have less solubility. Special thing is most of the that hydroxides have colours.

Solubility calculation

Example: Maximum 22.7g of solid compound A dissolve in 250ml of water.

1. What is the solubility of A. Express it as g/100m
2. How much sugar will dissolve in 1l of water

1. solubility = 22.7 * (100/250)
2. solubility = 9.08g/100ml of water
   
3. dissolving mass in 1 liter = solubility * 1000/100
4. dissolving mass in 1 liter = 9.08g/100ml * 1000/100
5. dissolving mass in 1 liter = 90.8g

References

1. O'Neil, M.J. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Cambridge, UK: Royal Society of Chemistry, 2013., p. 397
2. Carr DS et al; Kirk-Othmer Encyclopedia of Chemical Technology. (2001). NY, NY: John Wiley & Sons; Lead Compounds. Online Posting Date: June 18, 2004.
3. Haynes, W.M. (ed.). CRC Handbook of Chemistry and Physics. 95th Edition. CRC Press LLC, Boca Raton: FL 2014-2015, p. 4-89

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