18. (Ch2) If a solution containing 4 g of NaOH is exactly neutralized by 80.00 mL of an aqueous HCl solution, the molarity of the HCl solution must have been a. 0.00137 b. 1.37 c. 0.00125 d. 1.25 e. none of these

To find the molarity of the HCl solution, we need to use the concept of stoichiometry and the balanced chemical equation for the reaction between NaOH and HCl.<br /><br />The balanced chemical equation for the reaction is:<br /><br />NaOH + HCl → NaCl + H2O<br /><br />From the balanced equation, we can see that one mole of NaOH reacts with one mole of HCl.<br /><br />First, we need to calculate the number of moles of NaOH in the solution. We can do this by using the molar mass of NaOH, which is 40.00 g/mol.<br /><br />Number of moles of NaOH = mass of NaOH / molar mass of NaOH<br />= 4 g / 40.00 g/mol<br />= 0.1 mol<br /><br />Since the reaction is a 1:1 ratio, the number of moles of HCl required to neutralize the NaOH is also 0.1 mol.<br /><br />Next, we need to calculate the molarity of the HCl solution. Molarity is defined as the number of moles of solute per liter of solution.<br /><br />Molarity of HCl = moles of HCl / volume of HCl solution in liters<br />= 0.1 mol / 0.08 L<br />= 1.25 M<br /><br />Therefore, the molarity of the HCl solution must have been 1.25 M. The correct answer is option d.