A 150 milliliters sample of hydrochloric acid HCl completely reacted with 60 point 0 milliliters of a 0 point 1 0 0 cap m NaOH solution. The equation for the reaction is given. HCl plus NaOH rightarrow NaCl plus cap h sub 2 cap o What was the original concentration of the HCl solution?

The balanced reaction has a 1:1 ratio of HCl to NaOH, so the HCl amount equals the NaOH amount. The NaOH contains 0.100 mol/L × 0.0600 L = 0.00600 mol. Dividing by the HCl volume, 0.150 L, gives 0.00600 mol ÷ 0.150 L = 0.0400 mol/L, or 0.040 M. The correct choice is 0.040 M.

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