In hydrated copper sulfate, the chemical formula is CuSO4.5H2O, while that of hydrated cobalt(II) chloride is CoCl2.6H2O. I want to ask how to determine the number of moles of water is needed to hydrate any salt. Is there a pattern or formula?
Often, but not always, it is twice the charge on the metal ion; i.e., for Cu that is +4 and for Co that is +6. For many ions it is +6 regardless. Mostly it's a case of remembering which is which. For Cu, the hydrate for Cu(H2O)4^2+ ion is 4. The extra H2O molecule is associated with the crystal structure as a whole to make it 5 H2O total.
To determine the number of moles of water needed to hydrate any salt, you need to examine the chemical formula of the hydrated salt. In general, a hydrated salt can be represented by the formula MxSy.nH2O, where M is the metal ion, S is the non-metal ion (also called the anion), and n is the number of water molecules associated with each formula unit of the salt.
To find the number of moles of water in a particular hydrated salt, you can follow these steps:
Step 1: Identify the anion and the cation in the hydrated salt. In your example of hydrated copper sulfate (CuSO4.5H2O), the cation is Cu^2+ and the anion is SO4^2-.
Step 2: Determine the number of water molecules in the formula. The number of water molecules is indicated by the coefficient next to H2O in the formula. In this case, there are 5 water molecules associated with each formula unit of copper sulfate.
Step 3: Determine the number of moles of water. The number of moles of water can be calculated by multiplying the coefficient of water by the molar mass of water (H2O), which is approximately 18 g/mol.
For example, to calculate the number of moles of water in hydrated copper sulfate:
Number of moles of water = 5 (coefficient) × 18 g/mol (molar mass of water) = 90 g/mol
So, in 1 mole of hydrated copper sulfate, there are 90 moles of water.
Repeat these steps for other hydrated salts like hydrated cobalt(II) chloride (CoCl2.6H2O). In this case, the number of moles of water in one mole of the hydrated salt is 6.
Therefore, by examining the chemical formula of a hydrated salt and following these steps, you can determine the number of moles of water required to hydrate any salt.