Question

1) Fill in the blanks with either less or more.

Consider two acids - HF and NH3. Fluorine is________ electronegative than N and therefore HF will be__________ acidic than NH3.

2) Consider a 1.55 x 10^-2M solution of H₂CO_{3 where} Ka₁ = 4.5 x 10^-7 and Ka₂ = 4.7 x 10^-11.

The concentration of CO₃^2- is ______ x 10^_________

Note: Is there is not exponent then answer 10^0.

3).Buffer solutions with a pH of 10 can be prepared using sodium carbonate (Na₂CO₃) and sodium hydrogen carbonate (NaHCO₃). What is the pH of a solution prepared by dissolving 10.0 g each of these two salts in enough water to make 0.250 L of solution? (pKb for Na₂CO₃ is 3.67)

4) Match the acid with it's correct pKa

H₃PO₄

H₂PO₄^-

HPO₄^2-

PO₄^3-

options:

A.	12.32
B.	7.21
C.	N/A
D.	2.16

Answer 1

1) Consider two acids - HF and NH3. Fluorine is more electronegative than N and therefore HF will be more acidic than NH3.

4) More the pK_a value, lesser is the acididc strength and vice versa

Thus, H₃PO₄ = NA

H₂PO₄^- = 2.16

HPO₄^2- = 7.21

PO₄^3- = 12.32

3) Molar mass of Na₂CO₃ = 106 g/mole

Thus, moles of Na₂CO₃ in 10 g of it = mass/molar mass = 10/106 = 0.0943

molar mass of NaHCO₃ = 84 g/mole

Thus, moles of NaHCO₃ in 10 g of it = mass/molar mass = 10/84 = 0.119

Now, as per Henderson's equation

pOH = pK_b + log{[salt]/[base]} = 3.67 + log(0.0943/0.119) = 3.57

Thus, pH = 14 - pOH = 10.43