Aim 32 How can we use a base

Aim # 32: How can we use a base to determine the concentration of an acid? H. W. # 32 Study pp. 524 -527 p. 521 Complete handout sheet

I Acid-Base neutralization Acid + Base → Salt + Water e. g. HCl(aq) + Na. OH(aq) → Na. Cl(aq) + H 2 O(l) II Acid-Base Titration The molarity of an acid can be determined by slowly adding a base of known molarity (a standard solution) to it until neutralization is achieved (endpoint). Standard Solution- a solution whose concentration is known exactly. End Point- the point in a titration when neutralization is achieved.

moles H+ = moles OHMa. Va = Mb. Vb (Ref. Table T) and Ma = Mb. Vb/Va III Solving titration problems Problem: A drop of phenolphthalein solution is added to a 25. 0 m. L solution of HCl, and the solution is titrated with 0. 1 M Na. OH. If the solution turns pink after the addition of 30. 0 m. L of the Na. OH, what was the concentration of the original HCl solution?

Ans: step 1. Write the balanced equation for the neutralization reaction. HCl(aq) + Na. OH(aq) → Na. Cl(aq) + H 2 O(l) 1 mol number of moles of base needed = number of moles of acid step 2. Calculate the concentration of the acid from the equation Ma. Va = Mb. Vb. Ma = Mb. Vb/Va = (0. 1 M)(30. 0 m. L) (25. 0 m. L) Ma = 0. 12 M HCl

Problem: 20. 0 m. L of H 2 SO 4(aq) is completely neutralized with 10. 0 m. L of 0. 50 M Na. OH solution. What is the molarity of the original acid solution? Ans: 1. Write the balanced neutralization equation. H 2 SO 4(aq) + 2 Na. OH(aq) → Na 2 SO 4(aq) + 2 H 2 O(l) 1 mol 2 mol number of moles = 2 x number of moles of base needed of acid 2 Ma. Va = Mb. Vb Ma = Mb. Vb = (0. 50 M)(10. 0 m. L) 2 Va 2(20. 0 m. L) Ma = 0. 125 M H 2 SO 4

Problem: Find the concentration of a 40. 0 m. L sample of of HNO 3(aq) that was titrated to the endpoint with 30. 5 m. L of a 2. 0 M Na. OH(aq) standard solution. Problem: What volume of 0. 50 M Ca(OH)2 solution is required to titrate 20. 0 m. L of 0. 20 M HCl to the endpoint?