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Using solutions calculator for making small amounts of solutions of hydrates

Hello! Can someone please explain making solutions involving chemicals in hydrate form? I am using a calculator which has worked well for all chemicals except hydrates.

When using this calculator, I obtain different values for making a 1.0 molar solution of CuSO4 pentahydrate than the Flinn Scientific solutions cheat sheet has.

Solution Preparation Calculator

For example, to make a liter of solution, the Flinn Scientific sheet says this:

Copper(II) sulfate1.0 M249.7 g

The calculator says this:

Use 145.6358 grams to prepare: 1000 mL of 1.0 M CuSO4.5H2O

Can someone please clarify?

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Contributor III

Re: Using solutions calculator for making small amounts of solutions of hydrates

Dear Dawn and Educators,

The FIRST rule of computational devices is to KNOW their limitations!  Other than a quick list for stockroom preparations I do not really see the value of any package solution calculator for instructional purposes!  Start with the chemical principles and work out the answers.

It is obvious from the formula, and backed up by any number of references, that the molecular weight of Copper (II) Sulfate Pentahydrate is 249.7g/mol.  SO, any other value from any source - especially a packaged calculator or program! - should be checked manually, not just compared to some other list.  In this case, as stated, the molecular weight agrees with that in the Flinn list, and you should have checked it yourself with the atomic weights of the elements in the first place.

Finally then, with the correct molecular weight of 249.7g/mol we know that a 1M solution would require that amount dissolved in 1L of water.   This post is made some time after the original post in case there are others out there running into difficulties because of an overdependence on technology solutions instead of chemical understanding.

Best regards,