Summary

This page tabulates many important formulae of oxides, hydroxides, carbonates, and the salts chlorides, sulfates/sulfates, and nitrates. Solubility data for selected salts is given together with their solubility curves graphical representation and how to do simple solubility graph reading and mass of salt crystallising calculations.  Finally how to calculate the water of crystallisation from heating the salt i.e. from mass loss data.  These revision notes, data tables and solubility curve graphs of various compounds including salts, should prove useful for the new AQA chemistry, Edexcel chemistry & OCR chemistry GCSE (9–1, 9-5 & 5-1) science courses.

For GCSE students see the 8b. solubility summary - its all you need!

Other than the oxides, hydroxides and carbonates (1st column), the original acids are

hydrochloric acid HCl,   sulfuric acid H₂SO₄  and  nitric acid HNO₃

which give the salts (2nd column) when reacted with a metal, oxide, hydroxide or carbonate.

Note that salt preparations are described in section 6

The negative ions (anions):

O^2– oxide (O), OH^– hydroxide (OH),

CO₃^2– carbonate (CO₃),  HCO₃^– hydrogencarbonate (HCO₃),

Cl^– chloride (Cl), SO₄^2–  sulfate (SO₄), NO₃^– nitrate (NO₃)

Assume the compounds are soluble unless otherwise stated.

The 3rd right column shows what ion/metal can be 'substituted' into the formulae in the 1st/2nd columns.

QUITE SIMPLY YOU SUBSTITUTE M with the appropriate metal symbol TO GET THE FORMULA

The valency is the numerical chemical combing power of an atom or an ion.

How to work out formulae is explained on another web page

Note that salt preparations are described in section 6

• Interpretation of graph eg

  • Reading graph: at 38^oC the solubility of copper sulfate, CuSO₄, is 28g of anhydrous salt per 100g of water.

  • Reading graph: at 84^oC the solubility of potassium sulfate, K₂SO₄, is 22g per 100g of water.

  • Ex Q1: How much potassium nitrate will dissolve in 20g of water at 34^oC?

    • At 34^oC the solubility is 52g per 100g of water,

    • so scaling down, 52 x 20 / 100 = 10.4g will dissolve in 20g of water

  • Ex Q2: At 25^oC 6.9g of copper sulfate dissolved in 30g of water, what is its solubility in g/100cm³ of water?

    • Scaling up, 6.9 x 100 /30 = 23g/100g of water (check on graph, just less than 23g/100g water).

  • Ex Q3: 200 cm³ of saturated copper solution was prepared at a temperature of 90^oC. What mass of copper sulfate crystals form if the solution was cooled to 20^oC?

    • Solubility of copper sulfate at 90^oC is 67g/100g water, and 21g/100g water at 20^oC.

    • Therefore for mass of crystals formed = 67 – 21 = 46g (for 100 cm³ of solution).

    • However, 200 cm³ of solution was prepared,

    • so total mass of copper sulfate crystallised = 2 x 46 = 92g

• Note: The density of water is close to 1.0g/cm³ or ml, so for approximate purposes. the volume in cm³ or ml of just the water is numerically close to the value in g, i.e. 100 cm³ of water or solution is about 100g of water.

• How do we determine the water of crystallisation of a salt?

• Given data, how do calculate the water of crystallisation of a salt?

• Determination and calculation of salt formula containing 'water of crystallisation'.

  • Some salts, when crystallised from aqueous solution, incorporate water molecules into the structure. This is known as 'water of crystallisation', and the 'hydrated' form of the compound.

  • e.g. magnesium sulfate MgSO₄.7H₂O. The formula can be determined by a simple experiment (see the copper sulfate example below).

  • A known mass of the hydrated salt is gently heated in a crucible until no further water is driven off and the weight remains constant despite further heating. The mass of the anhydrous salt left is measured. The original mass of hydrated salt and the mass of the anhydrous salt residue can be worked out from the various weighings.

  • The % water of crystallisation and the formula of the salt are calculated as follows:

    • Suppose 6.25g of blue hydrated copper(II) sulfate, CuSO₄.xH₂O, (x unknown) was gently heated in a crucible until the mass remaining was 4.00g. This is the white anhydrous copper(II) sulfate.

    • The mass of anhydrous salt = 4.00g, mass of water (of crystallisation) driven off = 6.25–4.00 = 2.25g

    • The % water of crystallisation in the crystals  is 2.25 x 100 / 6.25 = 36%

    • [ A_r's Cu=64, S=32, O=16, H=1 ]

    • The mass ratio of CuSO₄ : H₂O is 4.00 : 2.25

    • To convert from mass ratio to mole ratio, you divide by the molecular mass of each 'species'

    • CuSO₄ = 64 + 32 + (4x18) = 160 and H₂O = 1+1+16 = 18

    • The mole ratio of CuSO₄ : H₂O is 4.00/160 : 2.25/18

    • which is 0.025 : 0.125 or 1 : 5, so the formula of the hydrated salt is CuSO₄.5H₂O

• All concentration calculations are covered on the on–line calculations page, especially sections 7. on molarity, 11. and 12. on molarity and acid–base (alkali) titrations, section 14.3 on dilutions.

Note that salt preparations are described in section 6