See lease the Conclusions from the above answers & my questions based on them:
1- Due to CO2 abosrbtion & available some amount of NaOH: buffer NaHCO3/H2CO3 can be formed with pH close to 6.4 (not desired for our case).
2- If adding bicarbonate, at the beginning when sending the batch to storage : buffer of Na2CO3/H2CO3 can be formed with pH ~ 7.4 (desired for our case).
1-When adding Na2CO3: Would the formed H2CO3 convert some of this bicarbonate to become NaHCO3?
2- What would be the pH value after adding Na2CO3? This question is because, as I know, at pH<9-10 you do not have carbonate ion, but rather bicarbonate ion (HCO3-) !!
3-If the facts in questions no.1 & 2 take place: What buffer would have the prevailing effect: NaHCO3/H2CO3 with pH ~6.4 or Na2CO3/H2CO3 with pH ~7.4 ?
Thanks for your response & assistance