# Chemistry 12

posted by .

The value of Kb for HPO₄²- is?

A. 2.2*10^-13
B. 6.2*10^-8
C. 1.6*10^-7
D. 4.5*10^-2

I don't get how to solve this.

• Chemistry 12 -

If you are asking what is the dissociation constant (Kb) for HPO₄², you want be able to solve for it with the information given; you have to look up the Ka for HPO₄² in a book.

Ka for HPO₄²=4.2 x10^-13

Kw= Ka*Kb

Solving for Kb,

Kb=Kw/Ka= 1 x 10^-14/4.2 x10^-13 =2.40 x 10^-2

This answer is not one of your answer choices, so I'm a little stuck on this one.

• Chemistry 12 -

It's Kw/k2 for H3PO4.
I'm sure you remember Kw = 1E-14.

• Chemistry 12 -

How do you know which ka to use? There is one on the base side of the chart, and one of the acid side of the chart. For the one of the acid side of the chart, the Ka is 2.2*10^-13 And for the one on the base side of the chart, it is 6.2*10^-8.

• Chemistry 12 -

With that being said,

Kb=Kw/Ka= 1 x 10^-14/6.2 x10^-8 =1.6 x10^-7

• Chemistry 12 -

Thanks so much :) So if we were to find the Ka, then we would use the ka on the acid side of the chart?

• Chemistry 12 -

Correct me if I'm wrong but
HPO4^2- + HOH ==> H2PO4^- + OH^-

k3 for H3PO4= 4.2E-13 = (H^+)(PO4^3-)/(HPO4^-) and that doesn't contain the ions needed for HPO4^2- to act as a base. k2 for H3PO4 does.

k2 = (H^+)(HPO4^2-)/(H2PO4^-)
I think the answer is c.

• Chemistry 12 -

Yes, the way your reference is set-up. Remember, Kw= Ka*Kb. if you want to know the Kb, you need to know the Kw and Ka. If you want to know the Kb, you need to know the Ka and Kw.

• Chemistry 12 -

Its c, I used the wrong Ka value when I initially did it.

• Chemistry 12 -

Thanks soo much to both of you :)

## Similar Questions

1. ### Math

Solve the system by addition or substitution. 3x – 4y = 8 6x – 2y = 10 Please get me on the correct track for 3x -4y =8 x=4, y=1 for 6x - 2y =10 x= 2, y= 1 Solve one equation for x. 3x = 4y + 8 x = (4y + 8)/3 Insert that value …
2. ### Chemistry

Write equilibrium Constant expressions (k) for the following reactions: Ni(s)+ 4CO(g) <-> Ni(CO)₄ HF(aq) <-> H(aq) + F(aq) Cl₂(g)+2Br(aq) <-> Br₂(l) + 2Cl(aq)
3. ### Chemistry

I don't understand these two questions. Any help on how to figure this would be great. Thanks. 1. Write the equation for the decomposition of the hydrate, MgC*XH₂O 2. Write the equation for the decomposition of the hydrate, CuSO₄*XH₂O.
4. ### chemistry 2

which of the following has the highest bugger capacity?
5. ### chemistry

Consider Ba (NO₃)₂ + K₂SO₄ → BaSO₄ + 2KNO₃ (0.10 M) (0.10 M) (10.0 mL) (20.0 mL) Will the K₂SO₄ be sufficient to precipitate all the Ba⁺² ions in the Ba (NO₃)₂?
6. ### intro to chemistry

. Nitrogen is unique in that it forms no fewer than seven molecular oxides. The one of highest molar mass is dinitrogen pentoxide, N 2 O 5 , a crystalline, colorless solid made by the reaction of nitric acid (HNO 3 ) with P 4 O 10 …
7. ### linear algebra

use a computer software or graphing utility to solve the system of linear equation. x₁+0.5x₂+0.33x₃+0.25x₄=1.1 0.5x₁+0.33x₂+0.25x₃+0.21x₄=1.2 0.33x₁+0.25x₂+0.2x₃+0.17x₄=1.3 …
8. ### chemistry

how many moles are present in 2.45 x 10²³ molecules CH₄?
9. ### Chemistry check my answers

Please check my answers For each of the 7 reactions in this experiment, write a balanced equation and classify it as a synthesis, decomposition, single replacemnt, neutralization, or double replacement reaction. Reaction 1 1)Adjust …
10. ### Chemistry

Calculate the concentrations of Cd ⁺ ², [Cd (CN)₄-²] and CN at equilibrium when they dissolve mole of 0.42 Cd (in the ₃)²⁺ 2.50 M. Given: Kf = 7, 1 x 10 ^16

More Similar Questions