Question

In: Chemistry

Phosphoric acid is a triprotic acid, so H3PO4, H2PO4 -, and HPO4 2- are all acids....

Phosphoric acid is a triprotic acid, so H3PO4, H2PO4 ^-, and HPO4 ^2- are all acids. Which of the solutions below would have the lowest pH?

0.1 M NaH2PO4
0.1 M Na2HPO4
0.1 M Na3PO4

Expert Solution

answer : 0.1 M NaH2PO4 solution has lowest pH value

pH orders : 0.1 M NaH2PO4 < 0.1 M Na2HPO4 < 0.1 M Na3PO4

detailed solution :

Ka1 = 7.1 x 10^-3 pKa1 = 2.15.

Ka2 = 6.3 x 10^-8 , pKa 2 = 7.20.

Ka3 = 4.5 x 10^-¹³ , pKa3 = 12.35

(a) 0.1 M NaH2PO4

H2PO4- -------------------> HPO4-2 + H+

0.1 0 0 ---------------> initial

0.1-x x x

Ka2 = [HPO4-2][H+]/[H2PO4-]

Ka2 = x^2 / (0.1-x)

6.3 x 10^-8 = x^2 / (0.1-x)

x^2 + 6.3 x 10^-8 x - 6.3 x 10^-9= 0

x = 7.93 x 10^-5

[H+] = x = 7.93 x 10^-5 M

pH = -log[H+]

pH = -log (7.93 x 10^-5 )

pH = 4.1-------------------------------------------(1)

(b) 0.1 M Na2HPO4

39. Phosphoric acid (H3PO4) is a triprotic weak acid. Calculate the pH, [H3PO4], [H2PO4 -], [HPO4...

39. Phosphoric acid (H3PO4) is a triprotic weak acid. Calculate the pH, [H3PO4], [H2PO4 -], [HPO4 2-], and [PO4 3-] of a 4.5 M H3PO4 aqueous solution. H3PO4 (aq) + H2O (l) ⇌ H3PO4 - (aq) + H3O+ (aq) Ka1 = 7.5 × 10-3 H3PO4 - (aq) + H2O (l) ⇌ HPO4 2- (aq) + H3O+ (aq) Ka2 = 6.2 × 10-8 HPO4 2- (aq) + H2O (l) ⇌ PO4 3- (aq) + H3O+ (aq) Ka3 = 4.2 × 10-13

2. Phosphoric acid (H3PO4) is a triprotic acid with the following pKa values: pKa1 = 2.15...

2. Phosphoric acid (H3PO4) is a triprotic acid with the following pKa values: pKa1 = 2.15 pKa2 = 7.20 pKa3 = 12.35 a). You wish to prepare a 1.000 L of a 0.0450 M phosphate buffer at pH 6.8. Which of the following salts do you use (PICK 2) and what mass of each salt will you add to the mixture? H3PO4 (M.W.= 97.995) KH2PO4 (M.W.=136.086) Na2HPO4 (M.W.=141.959) AlPO4 (M.W.=121.953) 2 b). A concentrated phosphate buffer known as “phosphate buffered...

Phosphoric acid, H3PO4(aq), is a triprotic acid. Calculate the pH and concentrations of H3O + (aq),...

Phosphoric acid, H3PO4(aq), is a triprotic acid. Calculate the pH and concentrations of H3O + (aq), H3PO4(aq), H2PO4 − (aq), HPO4 2− (aq), PO4 3− (aq), and OH− (aq) in a 0.100-M phosphoric acid solution at 25°C.

Phosphoric Acid, H3PO4(aq) is a triprotic acid, meaning that one molecule of the acid has three...

Phosphoric Acid, H3PO4(aq) is a triprotic acid, meaning that one molecule of the acid has three acidic protons. Estimate the pH and the concentrations(M) of all species in a 0.300 M phosphoric acid solution. pKa1= 2.16 pKa2=7.21 pKa3=12.32 [H3PO4]= [H2PO4-]= [HPO4^2-]= [PO4^3-] [H+]= [OH-]= pH=

Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three...

Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three acidic protons. Estimate the pH, and the concentrations of all species in a 0.500 M phosphoric acid solution. pKa1= 2.16 pKa2=7.21 pKa3= 12.32 What's: H3PO4, H2PO4-, HPO4-2, PO4-3, H, OH, and pH -Thanks!

For a 0.110 M H3PO4 solution, find the equilibrium concentrations of H3PO4, H2PO4-, HPO4^2-, PO4^3-, and...

For a 0.110 M H3PO4 solution, find the equilibrium concentrations of H3PO4, H2PO4-, HPO4^2-, PO4^3-, and H3O+. For H3PO4: Ka1= 7.5x10^-3, Ka2= 6.2x10^-8, Ka3= 4.2x10^-13

Phosphoric acid, H 3 PO 4 ( aq ) , is a triprotic acid, meaning that...

Phosphoric acid, H 3 PO 4 ( aq ) , is a triprotic acid, meaning that one molecule of the acid has three acidic protons. Estimate the pH and the concentrations of all species in a 0.500 M phosphoric acid solution. [ H 3 PO 4 ] = [ H + ] = [ H 2 PO − 4 ] = [ OH − ] = [ HPO 2 − 4 ] = [ PO 3 − 4 ] =

Phosphoric acid is a triprotic acid, and the Ka values are given below. Calculate pH, pOH,...

Phosphoric acid is a triprotic acid, and the Ka values are given below. Calculate pH, pOH, [H3PO4], [H2PO4 2- ], [HPO4 - ], and [PO4 3- ] at equilibrium for a 5.00 M phosphoric acid solution. Ka1 = 7.5 x 10-3 Ka2 = 6.2 x 10-8 Ka3 = 4.2 x 10

Let’s consider the dissociation of phosphoric acid H3PO4. All four possible protonation states, with H number...

Let’s consider the dissociation of phosphoric acid H3PO4. All four possible protonation states, with H number from zero to three, must co-exist in equilibrium. H3PO4 <-> H2PO4- <-> HPO42- <-> PO43- pK1=2 pK2=7 pK3=12 Find relative populations of all four states at the pH of the human blood, ~7.4.

Phosphoric acid is a triprotic acid. Calculate the [PO4^3-] if you start out with 5.00 M...

Phosphoric acid is a triprotic acid. Calculate the [PO4^3-] if you start out with 5.00 M phosphoric acid.