Since HEPES is a zwitterionic organic chemical buffering agent. At pH<7.0 it exists as cation (a positive ion , as negative charge is compensated by H+ present in the solution) to bring its pH to 7.45 (basic region) we must add NaOH. pH will increase when [H+] decreases. To decrease [H+] we must add NaOH ( a base). Solution Since HEPES is a zwitterionic organic chemical buffering agent. At pH<7.0 it exists as cation (a positive ion , as negative charge is compensated by H+ present in the solution) to bring its pH to 7.45 (basic region) we must add NaOH. pH will increase when [H+] decreases. To decrease [H+] we must add NaOH ( a base)..