[Marry]

How many grams of Na2CO3 to be mixed with 5.00 g of NaHCO3 to
produce 100 mL buffer with pH = 10.00?

[Marry]

H2CO3 + H2O -----> H3O(+) + HCO3(-) Keq1º = 4,45x10^-7

HCO3(-) + H2O -----> H3O(+) + CO3(2-) Keq2º = 4,84x10^-11

[H3O+]² = Ka (Ca - [H3O+]) / Cb + [H3O+]

This is the equation that I use?

As they step 5 grams to mol / L?

[Borek]

No, you need to use Henderson-Hasselbalch equation.

[Marry]

H2CO3 + H2O -----> H3O(+) + HCO3(-) Keq1º = 4,45x10^-7

HCO3(-) + H2O -----> H3O(+) + CO3(2-) Keq2º = 4,84x10^-11


10,00 =  10.31 + ( log [CO3(-)] / log [HCO3(-)]

?

[Borek]

10,00 =  10.31 + ( log [CO3(-)] / log [HCO3(-)]

Not bad, although you added a log into the equation.

Now it should be a matter of simple concentration calculations. [HCO₃^-] is given (not directly, but you shouldn't haver any problems calculating it).

[Marry]

10,00 =  10.31 + ( log [CO3(-)] / log [HCO3(-)]

Not bad, although you added a log into the equation.

Now it should be a matter of simple concentration calculations. [HCO₃^-] is given (not directly, but you shouldn't haver any problems calculating it).

H2CO3 + H2O -----> H3O(+) + HCO3(-) Keq1º = 4,45x10^-7

HCO3(-) + H2O -----> H3O(+) + CO3(2-) Keq2º = 4,84x10^-11


10,00 =  10.31 + ( log [CO3(-)] / [HCO3(-)]

Log [CO3(2-)] - Log [HCO3(-)] = 0,31
------------------------------------

HCO3 = 1+ 12+48 = 61g

1 mol-----> 61g
x---------> 5g

(12,2 mol)-???
--------------------------------
Log [CO3(2-)] - Log [12,2] = - 0,31

Log [CO3(2-)]= - 0,31 +1,08

Log [CO3(2-)] = 0,77


10^0,77= 5,88mol/L


5,88:10 = 0,58 mol


CO3---> 60g/L


1 mol --------------60
0,58----------------x

R- 34,8g?

[AWK]

Log [CO3(2-)] - Log [HCO3(-)] = 0,31

Something is missing on the right side
Note - mass of NaHCO₃ is given and you have to calculate mass of Na₂CO₃

Now convert ratio of concentrations into ratio of masses and take into account that one of them is 5.00 g.

[Borek]

HCO3 = 1+ 12+48 = 61g

1 mol-----> 61g
x---------> 5g

(12,2 mol)-???

There is something wrong with the math here. Looks like you are using a correct approach, but it gets twisted on the way. Besides, number of moles is NOT YET a concentration.

Log [CO3(2-)] - Log [12,2] = - 0,31

This is different from what you wrote above - sign on the right is different. Could be it was just a typo.