[FightinTexasAggie]

Hi all, I was working on my chem II work and I got stuck on three problems. Would anyone be willing to explain how to work these problems? Nothing we have done in class are like these. I got every other problem, but for some reason when I look at these three I am completely lost. Thanks a bunch.

1. Calculate the maximum volume in mL of 0.15 M HCl that each of the following ant-acid formulations would be expected to neutralize. Assume complete neutralization.

a) A tablet containing 250 mg Al(OH)3, and 150 mg Mg(OH)2.
b) A tablet containing 850 mg of CaCO3

2. Calculate the pH of 0.280 L of a 0.475 NaHSO3 - 0.305 M Na2SO3 buffer before and after the addition of the following substances.

a) Calculate the initial pH
b) Calculate the pH after the addition of 5.0 mL of 0.200 M HCl
c) Calculate the pH after the addition of 5.0 mL of 0.130 M NaOH

3. A particular saturated solution of Ca3(PO4)2 has [Ca^2+] = [PO4^3-] = 2.9 x 10^-7 M.

a) What is the value of ksp for Ca3(PO4)2?
b) What is [Ca^2+] in a saturated solution of Ca3(PO4)2 that has [PO4^3-] = 1.4 x 10^2 M?
c) What is [PO4^3-] in a saturated solution that has [Ca^2+] = 1.4 x 10^-2 M?

[UG]

1. Calculate the maximum volume in mL of 0.15 M HCl that each of the following ant-acid formulations would be expected to neutralize. Assume complete neutralization.

a) A tablet containing 250 mg Al(OH)3, and 150 mg Mg(OH)2.
b) A tablet containing 850 mg of CaCO3

a) Calculate the amount of moles of aluminium hydroxide and magnesium hydroxide, for every one mole of Al(OH)3 there are 3 moles of OH^- and for every mole of Mg(OH)2 there are 2 moles of OH^-, calculate the total number of moles of OH^-, this will be neutralised by the HCl, which is 0.15M, the volume(L) of HCl = number of moles of H⁺ / concentration (0.15M).
b)Same thing here, calculate moles (n) of CaCO3, n = mass/Molar mass. This will be neutralised by the HCl, CaCO3 + 2HCl  CaCl2 + CO2 + H2O, just be careful here because the ratio is 1:2 so the number of mole of HCl will be double that of the number of moles of CaCO3. Then calculate the volume of HCl, same formula, V = n/C

2. Calculate the pH of 0.280 L of a 0.475 NaHSO3 - 0.305 M Na2SO3 buffer before and after the addition of the following substances.

a) Calculate the initial pH
b) Calculate the pH after the addition of 5.0 mL of 0.200 M HCl
c) Calculate the pH after the addition of 5.0 mL of 0.130 M NaOH

You got the k_a or pK_a values there? You're going to need them.

3. A particular saturated solution of Ca3(PO4)2 has [Ca^2+] = [PO4^3-] = 2.9 x 10^-7 M.

a) What is the value of ksp for Ca3(PO4)2?
b) What is [Ca^2+] in a saturated solution of Ca3(PO4)2 that has [PO4^3-] = 1.4 x 10^2 M?
c) What is [PO4^3-] in a saturated solution that has [Ca^2+] = 1.4 x 10^-2 M?

K_sp = [Ca²⁺]³[PO₄^3-]²
plug the numbers in.
b) once you have the K_sp value, substitute 1.4 x 10^2 M into [PO4^3-] and then calculate [Ca²⁺]

c) same thing as b)

[FightinTexasAggie]

That is what threw me off about number 2. There is no Ka or pKa. That is every bit of information that was given.

[Borek]

So you have to find them - check if there is no table in your book.