How Do You Calculate the Molarity of Chemical Solutions?

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SUMMARY

The calculation of molarity involves determining the number of moles of solute per liter of solution. In the provided example, to calculate the molarity of Cu2+ ions from a 0.1025 gram sample of copper dissolved in 200 mL of solution, first convert grams to moles using the molar mass of copper (63.55 g/mol), resulting in approximately 0.00161 moles. The molarity is then calculated as moles divided by liters, yielding a molarity of 0.00805 M. For the strong electrolytes, the concentration of ions in 0.1 mol of Ca(NO3)2 in 100 mL results in 0.2 M for Ca2+ and 0.4 M for NO3-, while 1 g of K3PO4 in 250 mL gives a concentration of 0.1 M for K+ and 0.033 M for PO43-.

PREREQUISITES
  • Understanding of molar mass calculations
  • Familiarity with the concept of moles
  • Knowledge of solution volume conversions (mL to L)
  • Basic principles of strong electrolytes and ion dissociation
NEXT STEPS
  • Study the definition and formula for molarity in detail
  • Practice converting grams to moles using molar mass
  • Learn about ion dissociation in strong electrolytes
  • Explore examples of molarity calculations with different solutes
USEFUL FOR

High school chemistry students, particularly those in AP Chemistry, educators seeking to clarify molarity concepts, and anyone needing assistance with solution concentration calculations.

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This is probably an incredibly easy one for you, but it's frying me. I'm in AP Chem, and since I'm involved in a lot (excuses, excuses...tsk tsk...), my brain is fried and it's having trouble clicking. My teacher is unhelpful, even hostile, and the book provides no explanations. For example:

A 0.1025 gram sample of copper metal is dissolved in 35 mL of concentrated HNO(subscript 3) to form Cu+2 ions and then water is added to make a total volume of 200 mL. (Calculate the molarity of Cu+2.)

Why isn't this clicking? Maybe a short answer and an explanation would be helpful.

Also this:

Calculate the concentration of all ions present in each of the following solutions of strong electrolytes:

.1 mol of Ca(NO3)2 in 100 mL of solution

&

1 g of K3PO4 in 250 mL of solution.

Thank you for any help.
 
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Write out the definition of molarity and go from there.
 

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