Chem問題...急急急急!!!pls help!!

Question

35.0mL of 1.00M H2SO4 reacts with 175mL 0.250M NaOH, calculate the concentration of the excess acid....
pls help...thank you so mch!!!

Answer 1

2NaOH + H2SO4 → Na2SO4 + 2H2O
Mole ratio NaOH : H2SO4 = 2 : 1

No. of moles of H2­SO4 added = MV = 1 x (35/1000) = 0.035 mol
No. of moles of NaOH added = MV = 0.25 x (175/1000) = 0.04375 mol

When NaOH is completely reacted, 0.04375/2 = 0.02188 mol of H2SO4 is needed.
NaOH is the limiting reactant, and H2SO4 is in excess.

No. of moles of excess H2SO4 = 0.035 – 0.02188 = 0.01312 mol
Total volume = 35 + 175 = 210 mL = 0.21 L
Concentration of excess acid = (mol/vol) = (0.01312/0.21) = 0.06248 M