Homework Help: Another buffer problem

1. Sep 17, 2011

vande060

1. The problem statement, all variables and given/known data
Prepare 500ml of a reaction buffer containing .82% MgCl2, 62.5 mM glucose, 950 ATP, and 100mM Tris -Cl, pH 7.8 Use the stock solutions you have prepared

we had to prepare in previous problems:

500ml 1.75M glucose
25mL 2.5% glucose
2L of 1.8 Tris, pH 8.5

2. Relevant equations
C1V1 = C2V2
Pka Tris = 8.1
glucose mol mass = 180.16
ATP mol mass = 507.8

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3. The attempt at a solution

my calculation for MgCl2:

.82% = .82g/100ml = 8.2g/L
15% = 15g/100ml = 150g/L

C1V1=C2V2

150*x = 8.2*500

x = 28mL stck 15% MgCl2

My calculation for glucose

1.75M glucose = 315g/L
62.5mM = 11.2 g/L

C1V1=C2V2

11.2*500 = 315*x

x = 17.7 ml 1.75M glucose stock

Here is my calculation for ATP

5mM ATP = 3g/L
950nM ATP = .00048g/L

C1V1=C2V2

3*x = .00048*500

x =.08ml of stocK 5mM ATP

My calculation for the Tris I am not sure about, can I use my original pH 8.5 solution the prof asked me to prepare, or do I have to start over with the Tris acid and base components and use henderson H equation? does this all look right so far?

2. Sep 17, 2011

Staff: Mentor

C1V1 = C2V2 works for molar concentrations as well, you don't have to convert them to g/L.

My guess is you should prepare new buffer from HH equation.

3. Sep 17, 2011

vande060

is the rest of it right?

4. Sep 17, 2011

Staff: Mentor

Looks OK, but I just skimmed.