A.) how would you prepare .250 l of a 0.300 m phosphate buffer at ph=3 (h3po4: pka1 = 2.12, pka2 = 7.21, pka = 12.32) using the appropriate weak acid and conjugate salt. b.) how would you prepare the assigned buffer (given in question #1a) if using combining the weak acid and 0.400 m naoh? c.) how would you prepare the assigned buffer (given in question #1a) if using combining the weak acid and 0.400 m hcl?

a) 0,857 g of H₃PO₄ with 9,016 g of KH₂PO₄

b) 166 mL of 0,400M NaOH

c) 22 mL of 0,400M HCl

Explanation:

a) The appropriate weak acid and conjugate salt are:

H₃PO₄ ⇄ H₂PO₄⁻ + H⁺ where pka = 2,12

Henderson–Hasselbalch equation finding pH = 3:

3 = 2,12 + log₁₀

7,59 =  (1)

If buffer concentration is 0,300M:

0,300 M = [H₃PO₄] + [H₂PO₄⁻] (2)

Replacing (2) in (1):

[H₃PO₄] = 0,035 M

Thus:

[H₂PO₄⁻] = 0,265 M

Thus, to prepare this buffer you need weight:

0,035 M × 0,250 L = 8,75x10⁻³ moles × = 0,857 g of H₃PO₄

And:

0,265 M × 0,250 L = 6,63x10⁻² moles × = 9,016 g of KH₂PO₄

b) Using 0,400 M NaOH the equilibrium is:

H₃PO₄ + NaOH ⇄ H₂PO₄⁻ + H₂O

Knowing the equilibrium concentrations are:

[H₃PO₄] = 0,035 M = 0,300 M - x -Because in the first all 0,300 M must be of H₃PO₄-

[H₂PO₄⁻] = 0,265 M

Thus, x = 0,265 M are NaOH needed to obtain the desire pH. Those are obtained thus:

0,265 mol/ L × 0,250L × = 0,166 L ≡ 166 mL of 0,400M NaOH

c) Using 0,400 M HCl the equilibrium is:

H₃PO₄ ⇄ H₂PO₄⁻ + HCl

Knowing the equilibrium concentrations are:

[H₃PO₄] = 0,035 M

[H₂PO₄⁻] = 0,265 M = 0,300 M - x -Because in the first all 0,300 M must be of H₂PO₄-

Thus, x = 0,035 M are HCl needed to obtain the desire pH. Those are obtained thus:

0,035 mol/ L × 0,250L × = 0,022 L ≡ 22 mL of 0,400M HCl

I hope it helps!

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6

pie chart because it is in percents ( % )