Question

You report to the lab for the day and are told that you should replenish the buffers. You check and see that the 2L bottles for the following stock solutions are low:

2M NaCl

1M Tris buffer, pH 8.0

50% glucose

1) How much weight of NaCl (58.4g/mol) will you need to refill the 2L bottle?

2) How much weight of Tris buffer (157.6g/mol) will you need to refill the 2L bottle? The Tris buffer will need to have its pH adjusted. It starts at 10.7. What will you add to adjust to pH 8.0?

3) How much weight of glucose (180.2g/mol) will you need to refill the 2L bottle?

Answer 1

1) 2M NaCl:

Molarity = (grams of NaCl/mol.wt of NaCl)(1/volume in L)

we have mol.wt of NaCl = 58.4 g/mol and volume = 2L and molarity = 2M

therefore,
2 M = (g. of NaCl/58.4 g/mol)x (1/2L)

g. of NaCl = 233.6 g of NaCl

The weight of NaCl required is: 233.6 g

2) 1M Tris buffer, pH 8.0:

Molarity = (g. of Tris buffer/mol.wt of Tris) x (1/volume in L)
we have mol.wt of Tris = 157.6g/mol and volume = 2L and molarity = 1M

1 M = (g. of Tris buffer/157.6g/mol) x (1/2L)

g. of Tris buffer = 315.2 g

Dissolve the 315.2 grams of Tris buffer salt in approximately 1L. The resulting solution show pH about 10, then you slowly add few drops of
concentrated HCl solution to adjust the pH to 8.0. And finally, the total volume of the solution make up to 2L to get the desired solution.

3) 50% (mass/volume) glucose:

To make 2 L solution you need to weight = 1000g of glucose and slowly add water with constant stirring. Sometimes you need to warm the
solution to mix well. You should not boil the mixture. You should add water to make the final volume to 2L.

Therefore, the weight of glucose = 1000g and add water to make the final mixture volume to 2L. This will be your 50% (mass/volume) glucose.