n(NaHCO₃)=1.680 g/(84 g/mol)=0.02mol
2 NaHCO₃------1 H₂SO₄
n(H₂SO₄)=0.01mol
c(H₂SO₄)=n/V=0.01mol/(20x10ˉ³L)=0.5mol/L