To determine the volume of concentrated ammonium hydroxide solution needed to prepare a 500.0 mL solution of 0.250 M NH3, we can follow these steps:
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Calculate the number of moles of NH3 needed in 500.0 mL of a 0.250 M solution:
\[ \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{Liters of solution}} \]
Rearranging this gives us:
\[ \text{moles of NH3} = \text{Molarity (M)} \times \text{Liters of solution} \]
\[ \text{moles of NH3} = 0.250 , \text{mol/L} \times 0.500 , \text{L} = 0.125 , \text{mol} \]
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Determine the mass of NH3 needed: The molar mass of NH3 is approximately \( 14.01 , \text{g/mol (N)} + 3 \times 1.008 , \text{g/mol (H)} = 17.03 , \text{g/mol} \).
Therefore, the mass of NH3 required is:
\[ \text{mass of NH3} = \text{moles} \times \text{molar mass} = 0.125 , \text{mol} \times 17.03 , \text{g/mol} \approx 2.13 , \text{g} \]
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Calculate the mass of concentrated ammonium hydroxide: The concentrated ammonium hydroxide solution is 28.0 wt% NH3, which means that in 100 g of solution, there are 28.0 g of NH3. Let's use this to find out how much concentrated solution is needed to get 2.13 g of NH3.
The mass of the concentrated solution needed is:
\[ \text{mass of solution} = \frac{\text{mass of NH3}}{\text{wt%}} = \frac{2.13 , \text{g}}{0.280} \approx 7.589 , \text{g} \]
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Calculate the volume of concentrated ammonium hydroxide needed: Now we need to convert this mass of the solution to volume. We can use the density of the concentrated solution for this conversion.
The density of concentrated ammonium hydroxide is \(0.899 , \text{g/mL}\):
\[ \text{Volume} = \frac{\text{mass}}{\text{density}} = \frac{7.589 , \text{g}}{0.899 , \text{g/mL}} \approx 8.43 , \text{mL} \]
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Final Calculation and Measurement: To prepare 0.250 M NH3 solution, take approximately 8.43 mL of the concentrated ammonium hydroxide solution and dilute it in a volumetric flask or a graduated cylinder to a final volume of 500.0 mL with distilled water.
Detailed Preparation Steps:
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Gather the materials: You will need concentrated ammonium hydroxide, a 500.0 mL volumetric flask or graduated cylinder, a pipette or a graduated cylinder for measuring the 8.43 mL of the concentrated solution, and distilled water.
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Measure the concentrated ammonia: Use the pipette or graduated cylinder to accurately measure out 8.43 mL of the concentrated ammonium hydroxide solution.
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Dilute the solution:
- Pour the 8.43 mL of concentrated ammonium hydroxide into the 500.0 mL volumetric flask or graduated cylinder.
- Add distilled water slowly until the total volume reaches 500.0 mL. Make sure to mix the solution thoroughly by inverting the flask or stirring.
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Label the solution: Clearly label the flask or container with the concentration and content (0.250 M NH3 solution) for future reference.
By following these steps, you will successfully prepare a 500.0 mL solution of 0.250 M NH3.
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