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# need help!

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. While cleaning the toilet, 150 mL of disinfectant solution in poured into toilet containing 750 mL of water. If the initial concentration of the disinfectant was 3.40 mol/L, determine the new concentration of the solution.

Sep 27, 2014

#1
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. While cleaning the toilet, 150 mL of disinfectant solution in poured into toilet containing 750 mL of water. If the initial concentration of the disinfectant was 3.40 mol/L, determine the new concentration of the solution.

The first thing you do when you get a question like this on the lab is to write down what it is you want to calculate. Here you want to know the final concentration, so we write:

C(final) = ?

Then you write down everything you know:

V(initial) = 150 mL = 0,15 L

C(initial) = 3,4 mol/L

Here is where the actual thinking starts. You typically wanna know how many moles of something there are. Can we calculate that from these stats? Yup!

n(initial) = CV = 3,4 mol/L * 0,15 L = 0,51 mol

The number of moles of disinfectant does not change in this example:

n(final) = n(initial) = 0,51 mol

We once again look at the stats. Remember, we want to get the final concentration. What's concentration? It's amount of substance divided by volume. OK, guess we have to calculate the final volume:

V(final) = 150 mL + 750 mL = 900 mL = 0,9 L

Then, we follow our plan: To divide amount of substance by volume:

C(final) = n/V = 0,51 mol / 0,9 L = 0,5666... mol/L ≈ 0,57 mol/L

Sep 27, 2014

#1
+5

. While cleaning the toilet, 150 mL of disinfectant solution in poured into toilet containing 750 mL of water. If the initial concentration of the disinfectant was 3.40 mol/L, determine the new concentration of the solution.

The first thing you do when you get a question like this on the lab is to write down what it is you want to calculate. Here you want to know the final concentration, so we write:

C(final) = ?

Then you write down everything you know:

V(initial) = 150 mL = 0,15 L

C(initial) = 3,4 mol/L

Here is where the actual thinking starts. You typically wanna know how many moles of something there are. Can we calculate that from these stats? Yup!

n(initial) = CV = 3,4 mol/L * 0,15 L = 0,51 mol

The number of moles of disinfectant does not change in this example:

n(final) = n(initial) = 0,51 mol

We once again look at the stats. Remember, we want to get the final concentration. What's concentration? It's amount of substance divided by volume. OK, guess we have to calculate the final volume:

V(final) = 150 mL + 750 mL = 900 mL = 0,9 L

Then, we follow our plan: To divide amount of substance by volume:

C(final) = n/V = 0,51 mol / 0,9 L = 0,5666... mol/L ≈ 0,57 mol/L

Guest Sep 27, 2014