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A 64.0 mL portion of a 1.60 M solution is diluted to a total volume of 248 mL. A 124 mL portion of that solution is diluted by adding 195 mL of water. What is the final concentration? Assume the volumes are additive.

Sagot :

Explanation:

You can solve this problem by using the dilution factor,

DF

, which essentially tells you the factor by which the concentration of an initial solution decreased upon dilution.

The dilution factor is calculated by using either volumes or molarities

So, the dilution factor for the first dilution

58.0 mL

248 mL

will be

DF

1

=

248

mL

58.0

mL

=

4.276

The first solution was diluted by a factor of

4.276

, which means that its concentration decreased by a factor of

4.276

. Therefore, the concentration of the diluted solution will be

c

diluted

=

c

concentrated

DF

1

c

diluted

=

1.30 M

4.276

=

0.304 M

Now, you take a sample of

124 mL

of this diluted solution and add another

165 mL

of water. The final volume of the solution will be

V

final

=

124 mL

+

165 mL

=

289 mL

The concentration of the

124 mL

sample is equal to the concentration of the first diluted solution, i.e.

0.304 M

.

The dilution factor for the second dilution will be

DF

2

=

V

final

V

sample

DF

2

=

289

mL

124

mL

=

2.331

Therefore, the concentration of the final solution will be

c

final

=

c

sample

DF

2

c

final

=

0.304 M

2.331

=

¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

a

a

0.130 M

a

a

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