Concentration of Ions

[chemkink]

I need to know how to calculate the concentration of all of the ions in these solutions:

0.00200 mol of sodium phosphate in 10.0 mL of solution
0.300 mol of barium nitrate in 600.0 mL of solution
1.00 g of potassium chloride in 0.500 L of solution
132 g og ammonium sulfate in 1.50 L of solution

I have know idea how to do this and it isn't in my book, so I obviously need help.

Chemkink

[Paul Robbins]

Find concentration (units M) by dividing:

Number of moles / volume

Volume must be in liters.

Looking at your first example:

0.00200 mol of sodium phosphate in 10.0 mL of solution

You are given the number of moles = 0.00200.
You are given the volume = 10.0 ml. Convert ml to liters by dividing by 1000.

Volume = 0.0100 l.

Concentration = moles / volume

= 0.002 / 0.01

= 0.200 M

[Paul Robbins]

Now looking at your third example:

1.00 g of potassium chloride in 0.500 L of solution.

Again, we need to know number of moles and we need to know volume.

We are told we have 1.00 g of potassium chloride. We convert this into moles using the equation:

number of moles = mass in grams / molecular mass.


Molecular mass of potassium chloride = atomic mass potassium + atomic mass chlorine

= 39.0 + 35.5

= 74.5 g/mol

number of moles = 1.00 / 74.5

= 0.0134228

Then, same as in the first example:

Concentration = moles / volume

= 0.0134228/0.5

= 0.0268 M

[KathChem82]

you can express the concentration of the following by means of molarity.

since molarity is expressed in moles per liter (mol/L), you will have to identify your given. if you are given with moles in an mL of solution (example number 1) you will have to convert mL into liters (i'm assuming that you know how to convert measurements) and then perform the calculation by dividing the number of moles in volume of your solution (L).
if you are given with the mass of the solute, then you just have to convert it into moles in order to follow the equation mole of solute/Liter of solvent.
every problem will be an easy task as long as you stick and follow the units.
you can also express the concentration into mmol of solute/mL of solvent.