Describe how you would prepare the following two solutions. Be sure to include the type of glassware which you would use and as much detail as necessary for someone to actually prepare the solution using good laboratory technique.
• 250 mLs of a 5% NaCl (w/v) from solid NaCl
• 250 mLs of 3 M HNO3 from concentrated nitric acid which is 15.8 M
To prepare a 250 mL solution of 5% NaCl (w/v) from solid NaCl, you would need the following:
1. Weighing scale: Use a balance or weighing scale accurate to at least 0.01 grams.
2. 250 mL volumetric flask: This is a flask with a long neck and a mark at exactly 250 mL. It ensures precise volume measurement.
3. Solid NaCl: Take the required amount based on the desired concentration.
Here are the steps to prepare the solution:
1. Calculate the amount of NaCl needed:
- Convert the desired concentration (5%) to a decimal fraction (0.05).
- Multiply the decimal fraction by the total volume of the solution (250 mL) to get the required grams of NaCl.
For example: 0.05 x 250 = 12.5 grams of NaCl
2. Weigh out the calculated amount of NaCl using the weighing scale. Make sure to use a clean and dry container.
3. Transfer the weighed NaCl into the 250 mL volumetric flask using a funnel or scoopula.
4. Add distilled water to the flask until it reaches the 250 mL mark. Be cautious and fill it up to the mark precisely. You can use a dropper to add water until it is very near the mark, and then use a wash bottle to finish the process, adding water drop by drop until the bottom of the meniscus touches the mark.
5. Close the flask with a stopper or a plastic cap, and mix the solution thoroughly by inverting the flask gently several times. This ensures uniform distribution of NaCl in the solution.
Voilà! You have prepared a 250 mL solution of 5% NaCl (w/v) from solid NaCl.
For the second solution, to prepare 250 mL of a 3 M HNO3 solution from concentrated nitric acid (15.8 M):
1. Concentrated nitric acid: Ensure that you are working in a well-ventilated area or under a fume hood due to the corrosive nature and release of fumes.
2. 250 mL volumetric flask: Same as above, a flask with a long neck and a mark at exactly 250 mL.
3. Distilled water: Needed to dilute the concentrated nitric acid.
Here are the steps to prepare the solution:
1. Calculate the volume of concentrated nitric acid required:
- Use the dilution formula: C1V1 = C2V2
- C1 = Concentration of concentrated nitric acid (15.8 M)
- V1 = Volume of concentrated nitric acid to be used
- C2 = Desired concentration (3 M)
- V2 = Final volume (250 mL)
Rearrange the formula to solve for V1:
V1 = (C2 x V2) / C1
For example: V1 = (3 x 250) / 15.8 = 47.47 mL
2. Using a graduated cylinder, measure the required volume of concentrated nitric acid. Ensure proper safety precautions like wearing gloves and eye protection.
3. Add the measured quantity of concentrated nitric acid carefully to the 250 mL volumetric flask. Rinse the graduated cylinder with distilled water, pouring the washings into the flask to ensure that all of the acid is transferred.
4. Add distilled water to the flask, gradually filling it up to the 250 mL mark. As mentioned earlier, ensure precision by using a dropper followed by a wash bottle to add water drop by drop until the bottom of the meniscus touches the mark.
5. Close the flask with a stopper or a plastic cap, and mix the solution thoroughly by inverting the flask gently several times.
Congratulations! You have successfully prepared a 250 mL solution of 3 M HNO3 from concentrated nitric acid. Remember to handle concentrated acids with caution and always follow proper laboratory safety protocols.