help!! how do i do this?

Question

how many moles of sodium cations, Na+, are dissolved in a 1.0L sample of:

0.10M NaCl

3.0M Na2SO4

0.30M Na3PO4

Answer 1

In terms of a formula: n_i = M_iV or moles = molarity * volume

This gives you the moles of solute, not the moles of a particular ion. These salts dissociate completely, so the moles of a particular ion per more of formula unit is just the subscript of the ion:

There is a little bit of a problem with the question in that these solutions are not actually mixed together in any proportion. We have to make the assumptions that we added enough solid salts to some water to reach the molarity of the salt given we added enough water at the end to get 1 liter of solution.

1 liter (.1 moles NaCl/ 1 liter) (1 mole Na⁺/mole NaCl) = .1 moles Na⁺

1liter(3.0 moles Na₂SO₄/ 1 liter) (2 moles Na⁺/mole of Na₂SO₄) = 6 moles Na⁺

I'll leave the last one for you. Then add up the moles of Na⁺ contributed by each salt.

Answer 2

You can figure out why fraction of Na is in each concentration, when you figure out what portion Na takes up for each molecule you can then use this to figure out the moles of Na or Sodium per solution.

For example:

The 1st one says you have NaCl, sodium chloride.

The equation is:

M= mol/L

. molarity is equal to the moles of solution over Liters of solution.

0.1M= mol/1L.

When you solve for moles of solution you get:

mol= 0.1*1 = 0.1.

So now you know that your moles for the solution is 0.1. what fraction of this is Na?

NaCl atomic weight is: 58.44276g/mol.

To figure out what portion this is of sodium, put the atomic weight of sodium over that of entire NaCl or sodium chloride:

22.98976/58.44276 = 0.39337. This is how much it is if sodium.

Now multiply this by the moles you solved for the solution, 0.1

0.1*0.39337= 0.039337 or 0.040 moles of Na for the first solution you were given of 0.1M for the NaCl.

You can repeat this process for the following concentration solutions

Of 3.0M for Na2SO4

And

0.3M for Na3PO4

First find out what the fraction of Na is for each molecule and multiply this by the moles you find for each solution.

Remember, M=mol/L