Taking into account the definition of dilution:
- you have to use 8.23 mL of a stock solution of 7.00 M HNO₃ to prepare 0.120 L of 0.480 M HNO₃.
- If you dilute 20.0 mL of the stock solution to a final volume of 0.270 L , the concentration of the diluted solution is 0.518 M.
<h3>Dilution</h3>
Dilution is the process of reducing the concentration of solute in solution, which is accomplished by simply adding more solvent to the solution at the same amount of solute.
In a dilution the amount of solute does not change, but as more solvent is added, the concentration of the solute decreases, as the volume (and weight) of the solution increases.
A dilution is mathematically expressed as:
Ci×Vi = Cf×Vf
where
- Ci: initial concentration
- Vi: initial volume
- Cf: final concentration
- Vf: final volume
<h3>Volume of stock solution</h3>
In this case, you know:
- Ci= 7 M
- Vi= ?
- Cf= 0.480 M
- Vf= 0.120 L
Replacing in the definition of dilution:
7 M× Vi= 0.480 M× 0.120 L
Solving:
Vi= (0.480 M× 0.120 L)÷ 7 M
<u><em>Vi= 0.00823 L= 8.23 mL</em></u> (being 1 L= 1000 mL)
Finally, you will need 8.23 mL of the stock solution.
<h3>Concentration of the diluted solution</h3>
In this case, you know:
- Ci= 7 M assuming the stock solution is 7.00 M HNO₃
- Vi= 20 mL= 0.02 L
- Cf= ?
- Vf= 0.270 L
Replacing in the definition of dilution:
7 M× 0.02 L= Cf× 0.270 L
Solving:
(7 M× 0.02 L)÷ 0.270 L= Cf
<u><em>0.518 M= Cf</em></u>
Finally, the concentration is 0.518 M.
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