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I/GCSE Chemistry- Water of crystallization (2/2)

Equation formula example

· igcse chemistry

This I/GCSE Chemistry blogpost will look at an example of how to complete an equation for water of crystallization, let's go!

Heating Hydrated Magnesium Sulfate, MgSO4.XH2O, in a crucible forms anhydrous magnesium sulfate, MgSO4. Use the experimental data below to find the value of x and write the formula of the hydrated salt. 

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Mass of the empty crucible=42.000g

Mass of the crucible+MgSO4.XH2O=45.210g

Mass of the crucible+MgSO4=43.567g

Step 1-Work out the mass of MgSO4.XH2O and MgSO4 you have

  • Mass of MgSO4.XH2O = 45.210-42.000=3.210g
  • Mass of MgSO4= 43.567-42.000=1.567

Step 2-Calculate the number of moles of water lost 

  • Mass of water lost= 3.210-1.567=1.643g
  • Number of moles of water lost= Mass/relative atomic mass= 1.643g/ (H2O= 2x1+16)18=0.0913moles

Step 3-Calculate the number of moles of anhydrous salt made

  • Molar mass of MgSO4: 24+32+ 94x16) =120g/mol
  • Number of moles of MgSO4: mass/relative atomic mass= 1.567/120=0.0131 moles

Step 4-Work out the ratio of moles of anhydrous salt to moles of water

  • 0.0131 moles of salt : 0.0913 moles of water
  • so 1 moles of salt: 0.0913/0.0131= 6.97 moles of  water

Step 5-Round of your result to get a whole number 

6.97 moles of water+ 7 moles of water 

So the formula of hydrated salt is MgSO4. 7H2O  

That is it !

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References:

https://www.google.com/url?sa=i&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FMagnesium_sulfate&psig=AOvVaw0KtUiZWF4_B2SW3pShvjmy&ust=1629219041015000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCNDymIWAtvICFQAAAAAdAAAAABAD

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