Including water in molar mass for molarity?

In summary, when converting mol to grams for a 1M solution of potassium sodium tartrate, it is important to use the full formula weight, including water (KNaC4H4O6*4H2O). This is because each molecule carries 4 H2O, which requires taking more mass to get the same number of molecules.
  • #1
mishima
561
34
Hi, let's say I need 60 mL of a 1M solution of potassium sodium tartrate, I am looking for how many grams to measure out of my stock. So I need to convert mol to grams using molar mass. Do I use the full formula weight that includes water KNaC4H4O6*4H2O, or simply the KNaC4H4O6?
 
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  • #2
You need a specific number of molecules of your substance. If every molecule carries 4 H2O around, you have to take more mass to get the same number of molecules.
Use the full formula weight, including H2O.
 
  • #3
Thanks for that clarification.
 

1. What is molar mass?

Molar mass is the mass of one mole of a substance, expressed in grams per mole. It is also known as molecular weight.

2. Why is water included in molar mass for molarity?

Water is included in molar mass for molarity because it is a solvent that can affect the concentration of a solution. The mass of water molecules needs to be taken into account when calculating the molarity of a solution.

3. How is water's molar mass determined for molarity calculations?

Water's molar mass is determined by adding the mass of two hydrogen atoms (1.01 g/mol each) and one oxygen atom (16.00 g/mol), resulting in a molar mass of 18.01 g/mol.

4. Can water's molar mass vary in different solutions?

Yes, the molar mass of water can vary in different solutions depending on the concentration of solutes present. This is because the mass of the water molecules is affected by the dissolved solutes.

5. What are the units for molar mass and molarity?

Molar mass is measured in grams per mole (g/mol) and molarity is measured in moles per liter (mol/L).

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