4. How would you prepare a solution containing 50mM NaCl (mwt = 58.5g/mol) and 10mM Na2HPO4 (358.057 g/mol) in a final volume of 250ml?
How many millimoles of NaCl do you need? That's mL x M = 250 mL x 0.050 M = 12.5 millimoles or 0.0125 moles NaCl.
How many millimoles of Na2HPO4 do you need? That's 250 mL x 0.010 M = 2.50 millimoles or 0.00250 mols Na2HPO4.
Convert moles to grams. g = mols x molar mass = ? g for NaCl and ? g for Na2HPO4. Weigh these amounts of NaCl and Na2HPO4, place those weighed amounts in a 250 mL volumetric flask, add some DI water, swirl until all is dissolved, add DI water to the mark on the flask, stopper, mix thoroughly, label.
To prepare a solution containing 50mM NaCl and 10mM Na2HPO4 in a final volume of 250ml, you will need to follow these steps:
1. Calculate the amount of NaCl needed:
- Molarity (M) = moles/volume (L)
- Moles = Molarity x Volume (L)
- Moles NaCl = 50mM x 0.250L = 12.5 mmol
- Convert moles to grams:
- Grams NaCl = moles NaCl x molar mass NaCl
- Grams NaCl = 12.5 mmol x 58.5 g/mol = 731.25 mg
2. Calculate the amount of Na2HPO4 needed:
- Moles Na2HPO4 = 10mM x 0.250L = 2.5 mmol
- Convert moles to grams:
- Grams Na2HPO4 = moles Na2HPO4 x molar mass Na2HPO4
- Grams Na2HPO4 = 2.5 mmol x 358.057 g/mol = 895.14 mg
3. Add the calculated amounts of NaCl and Na2HPO4 to a container (such as a beaker).
4. Add distilled water to the container to bring the final volume to 250ml. This will ensure that the concentrations of NaCl and Na2HPO4 are accurate.
5. Mix the solution thoroughly until all the salts are dissolved.
Note: It is important to measure the volume accurately and use a precise measuring instrument to achieve the desired concentrations.