Please read to the bottom - This help was wonderful and absolutely correct, I'm asking a bit more regarding the same question, please read below.
Imagine that you have been asked to prepare 500ml of a 0.25 mol L solution of Sodium Hydroxide, NaOH. Describe how you would prepare this solution. Include any calculations that you would perform.
chemistry - DrBob222, Thursday, October 14, 2010 at 9:00pm
I assume you meant 0.25 moles/L.
M = moles/L
0.25 = moles/0.500 L
moles = 0.125 moles.
Then moles = grams/molar mass
molar mass NaoH = 40 g/mole
grams = 0.125 x 40 = ??
So you want to place ?? g NaoH in a 500 mL volumetric flask, dissolve in some water, then make to the mark with distilled water.
chemistry - Dexter, Friday, October 15, 2010 at 7:34pm
amazing help - this is what I got too however they also want me to explain the steps I would take to prepare this solution. I'm using a graduated cylinder to measure the sodium hydroxide and need to convert the 5 grams to ml. I'm not sure the steps to take. Do I use the dilute solution formula with Vi x 0.125 mol/L = .500L x 0.25 mol/L ? Doing this doesn't seem right to me because I get the answer 1 L. Please let me know. Thank you so much for your help, it really was appreciated and helped me verify my work.
I'm a little confused at this point. You need a balance to weigh out 5.00 g NaOH. You place that in a 500 mL volumetric flask, add enough water to dissolve the solid NaOH, (swirl until all of the solid is dissolved), then add water to the volumetric flask to the mark. YOu will then have prepared 500 mL of a 0.25 M solution. (Technically, this is not a very good procedure BECAUSE NaOH is not pure enough to use as a primary standard; however, it will come close to being 0.25 M. (If you are using a graduated cylinder, perhaps you aren't familiar with the volumetric flask. The 500 mL volumetric flask looks like a Florence flask BUT the neck of the flask is a long one with a mark etched into the glass exactly at the 500 mL mark. Thus, adding water to the mark makes it exactly 500 mL. That is much more accurate than using a graduated cylinder.)
To prepare a 500 ml solution of a 0.25 mol/L Sodium Hydroxide (NaOH), you will need to follow these steps:
1. Calculate the number of moles required:
- Given that the concentration is 0.25 mol/L, and the volume is 0.500 L, we can use the formula M = moles/L to find the number of moles.
- Substituting the values, we have 0.25 mol/L = moles/0.500 L. Solving this equation gives us 0.125 moles.
2. Convert the moles into grams:
- The molar mass of NaOH is 40 g/mol, so we multiply the number of moles by the molar mass to get the mass of NaOH required.
- 0.125 moles x 40 g/mol = 5 g of NaOH.
3. Measure the mass of NaOH:
- Using a balance or a scale, measure out 5 g of NaOH.
4. Convert the mass of NaOH to milliliters (ml):
- To convert grams to milliliters, we need to know the density of NaOH, which is the mass per unit volume.
- However, since the density of NaOH is not given, we cannot directly convert grams to milliliters.
- In this case, it is best to use a graduated cylinder to measure the volume directly rather than trying to convert the mass to volume.
5. Dissolve NaOH in water:
- Add the 5 g of NaOH into a clean, dry, and labeled 500 ml volumetric flask.
- Fill the flask with distilled water until approximately 2/3 full.
6. Mix and make to the mark:
- Use a glass stirring rod to dissolve the NaOH completely in the water, ensuring a uniform solution.
- After the NaOH is fully dissolved, fill the flask up to the mark with distilled water.
- Cap the flask and invert it several times to ensure thorough mixing.
You should now have a 500 ml solution of 0.25 mol/L NaOH prepared.