How can you change a solution's concentration keeping the moles of the chemical the same?I'm doing a lab report on "Preparation of a Solution and Diluton" and that's one of the questions. Help me...

How can you change a solution's concentration keeping the moles of the chemical the same?

I'm doing a lab report on "Preparation of a Solution and Diluton" and that's one of the questions. Help me please!

Asked on by robl2874

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bandmanjoe's profile pic

bandmanjoe | Middle School Teacher | (Level 2) Senior Educator

Posted on

By simply removing the aqueous, or water concentration of the solution.  When you have a chemical that is mixed with water, and there are so many moles of that chemical mixed in with the water, if you remove some of the water, the number of moles of chemical will remain the same. 

It's kind of like this:  if you pour yourself a drink of your favorite soda over ice, but let it sit on the counter for about two or three hours, long enough for the ice to melt, and then come back to drink it, you would probably throw it out, claiming "the drink is watered down".  When you introduce water with another chemical, you are diluting it, or making the concentration weaker.  The number of moles of the substance stays the same, but the strength of the solution is determined by how many moles of solute are mixed with solvent.

Many cultures, to this day, get their salt for their cooking and food by placing sea water in large, shallow, evaporating pools.  The water evaporates away, over a period of days, leaving behind the salt that was dissolved in the sea water.  Remove the water, the moles of the chemical remain behind.

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