How Do You Calculate the Molarity of Chemical Solutions?

[pencil_4]

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.

 

[chemisttree]

Write out the definition of molarity and go from there.

 

[Blueshift5]

Molarity is a measure of the concentration of a chemical solution, specifically the number of moles of solute per liter of solution. It is calculated by dividing the number of moles of solute by the volume of the solution in liters.

In the first example, the molarity of Cu+2 can be calculated by first finding the number of moles of Cu+2 produced by the reaction. This can be done by converting the mass of copper metal to moles, using the molar mass of copper, and then dividing by the total volume of the solution in liters. This will give you the molarity of Cu+2 in the solution.

In the second example, you can use the same method to find the molar concentration of the ions present in the solution. For the .1 mol of Ca(NO3)2 in 100 mL of solution, you can first find the number of moles of Ca(NO3)2, and then use the coefficients in the balanced chemical equation to determine the number of moles of Ca+2 and NO3- ions. Finally, divide the moles of each ion by the total volume of the solution in liters to find the molarity of each ion.

For the solution containing 1 g of K3PO4 in 250 mL, you can use the same process to find the molarity of K+, PO4-3, and H+ ions, since K3PO4 is a strong electrolyte and will dissociate completely in solution.

It's important to remember that molarity is a measure of concentration, and can be calculated for solutions containing different substances, as long as the number of moles of solute and the volume of the solution are known. With some practice and understanding of the concept, these calculations will become easier for you. Good luck in your studies!