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Postby OwenSumter_2F » Mon Oct 05, 2020 9:03 am

I'm having trouble with how to approach this problem:

"A solution is prepared by dissolving 0.500 g of KCl, 0.500 g of K2S, and 0.500 g of K3PO4 in 500. mL of water. What is the concentration in the final solution of (a) potassium ions; (b) sulfide ions?"

How do I find the concentration of only parts of the solution?

Shrinidhy Srinivas 3L
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Re: G21

Postby Shrinidhy Srinivas 3L » Mon Oct 05, 2020 9:33 am

I attached my work for the problem. But, you need to be able to find the total moles of the ion you're looking for and divide it by the total volume to find the answer for each part. For instance, since each molecule has potassium in it, you would convert the grams of each product into moles of potassium ions as shown. Then, you add all the moles together and divide by 0.5 L (which is the total volume) to find the concentration of potassium ions (remember that concentration is moles solute/liters solution). Hope this helps!

Arezo Ahmadi 3J
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Re: G21

Postby Arezo Ahmadi 3J » Mon Oct 05, 2020 2:05 pm

In order to find only parts of the concentration, you'll need to look at each molecule that has that ion that you're looking for. So for part a, you'll notice that KCl, K2S, and K3PO4 all have the K+ ion, so we're going to have to use the masses we were given for each of them. Now, you are going to have to convert these masses that are in grams to moles, so find the molar mass of KCl, K2S, and K3PO4. For example, when you convert KCl, you will go from 0.500 g to an amount in moles by dividing 0.500 g by the molar mass. Now, you want to specifically find the moles of K+ in KCl, so you will have to use the ratio of K+ moles in KCl, and to do this, you can see that there is only one atom of K+ in KCl, so it will just be a 1:1 ratio.

Do this for K2S and K3PO4, and then make sure that you add up these moles and divide by the volume given which is 0.500 L, and you should get a molarity that is given in terms of the moles of K+ divided by the volume.

Then, make sure to repeat this process for the next part of the question. Hope this helps!

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