Use the formula to calculate the ionic strength of: ?= (1/2)?(c)(z) 2 where c= t

Question

Use the formula to calculate the ionic strength of:

?= (1/2)?(c)(z)2

where c= the concentration of ions

z=the charge on each of those ions

a)0.1 M sodium chloride

b) 0.2 M potassium chloride

c)0.1 M calcium chloride

d)0.1 M sodium sulfate

e) 0.2 M magnesium chloride

f)10 mM trisodium ATP (assume the ATP has three negative charges)

g) a 50 mM buffer of monosodium dihydrogen phosphate and disodium monohydrogen phosphate at pH 7. The relevant pKa is 6.8. You'll have to figure out the concentrations of all the ionic species before computing the ionic strength.

Explanation / Answer

0.1M NaCl

1/2*(0.1+0.1) =0.1M

0.2M KCl

1/2*(0.2+0.2) = 0.4/2 = 0.2M

0.1MCaCl2

1/2(0.1*4+2*0.1) = 0.6/2 = 0.3M

0.1M Na2SO4

1/2(0.1*2+0.1*4)=0.6/2=0.3M

0.2M MgCl2

1/2(0.2*4+2*0.2) = 1.2/2=0.6M

10mM Na3ATP

1/2(3*10mM+10*9)=60mM

pH = pKa - (log charged / neutral)

7-6.8=0.2=-log (charged/neutral)

10-0.2 = charged/neutral

NaH2PO4/NaHPO4 = 10-0.2 =0.6309

NaH2PO4 = 0.63 * NaHPO4

NaHPO4 + 0.63 * NaHPO4 = 50mM

(1+0.63)* NaHPO4 = 50mM

NaHPO4 = 50/1.63 = 30.67mM

NaH2PO4 = 50-30.67 = 19.33mM

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