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Calculate The Formula for The Following Hydrate Composed of 76.9

Reviewed by Calculator Editorial Team

This calculator helps determine the chemical formula of a hydrate containing 76.9% water by weight. A hydrate is a compound that contains water molecules as part of its crystal structure. The formula determination process involves calculating the ratio of water molecules to the anhydrous (water-free) compound.

How to Use This Calculator

To determine the formula of a hydrate containing 76.9% water:

  1. Enter the molar mass of the anhydrous compound (the compound without water)
  2. Enter the molar mass of the hydrate (the compound with water)
  3. Click "Calculate" to determine the formula

The calculator will show you the formula in the form Xa(H2O)b, where X is the anhydrous compound, a is the number of X units, and b is the number of water molecules.

Determining the Hydrate Formula

The formula of a hydrate can be determined using the following steps:

  1. Calculate the mass of water in the hydrate sample
  2. Determine the mass of the anhydrous compound
  3. Calculate the moles of water and anhydrous compound
  4. Find the simplest whole number ratio between them

Formula Used

The formula for determining the hydrate formula is:

Xa(H2O)b = (mass of anhydrous compound × molar mass of hydrate) / (mass of water × molar mass of anhydrous compound)

The molar mass of water (H2O) is always 18 g/mol. The molar mass of the anhydrous compound and hydrate must be known or measured.

Worked Example

Let's determine the formula for a hydrate containing 76.9% water with the following data:

  • Molar mass of anhydrous compound: 100 g/mol
  • Molar mass of hydrate: 118 g/mol
  1. Calculate the mass of water in 100 g of hydrate:

    Mass of water = 76.9% of 100 g = 76.9 g

  2. Calculate the mass of anhydrous compound:

    Mass of anhydrous = 100 g - 76.9 g = 23.1 g

  3. Calculate moles of water and anhydrous compound:

    Moles of water = 76.9 g / 18 g/mol = 4.27 moles

    Moles of anhydrous = 23.1 g / 100 g/mol = 0.231 moles

  4. Find the ratio between moles:

    Ratio = 0.231 / 4.27 ≈ 0.054

    To get whole numbers, multiply by 18.5 (approximately):

    • 0.231 × 18.5 ≈ 4.27
    • 4.27 × 18.5 ≈ 78.5

  5. Simplify the ratio to get the formula:

    X4(H2O)18

Note: The actual formula may vary slightly depending on the specific compound and experimental conditions. This example uses approximate values for illustration.

Frequently Asked Questions

What is a hydrate?
A hydrate is a chemical compound that contains water molecules as part of its crystalline structure. The water molecules are not chemically bonded to the main compound but are held in the crystal lattice.
How do I determine the percentage of water in a hydrate?
The percentage of water in a hydrate can be determined by heating the compound to drive off the water and measuring the mass loss. The formula is: (mass loss / original mass) × 100 = % water.
What factors affect hydrate formula determination?
Several factors can affect the accuracy of hydrate formula determination, including sample purity, heating conditions, and the presence of other volatile compounds. Proper experimental techniques and controls are essential.
Can this calculator be used for any hydrate?
This calculator provides a general method for determining hydrate formulas. The actual formula may vary depending on the specific compound and experimental conditions. Always verify results with laboratory data.