Answer:
2.25g of NaF are needed to prepare the buffer of pH = 3.2
Explanation:
The mixture of a weak acid (HF) with its conjugate base (NaF), produce a buffer. To find the pH of a buffer we must use H-H equation:
pH = pKa + log [A-] / [HA]
<em>Where pH is the pH of the buffer that you want = 3.2, pKa is the pKa of HF = 3.17, and [] could be taken as the moles of A-, the conjugate base (NaF) and the weak acid, HA, (HF). </em>
The moles of HF are:
500mL = 0.500L * (0.100mol/L) = 0.0500 moles HF
Replacing:
3.2 = 3.17 + log [A-] / [0.0500moles]
0.03 = log [A-] / [0.0500moles]
1.017152 = [A-] / [0.0500moles]
[A-] = 0.0500mol * 1.017152
[A-] = 0.0536 moles NaF
The mass could be obtained using the molar mass of NaF (41.99g/mol):
0.0536 moles NaF * (41.99g/mol) =
<h3>2.25g of NaF are needed to prepare the buffer of pH = 3.2</h3>
The substance has a higher density than water
Answer:
Time = 0.929s = 0.93s (2 s.f)
Explanation:
Rate constant, k = 34.1 M^-1s^-1
Initial Concentration, [A]o = 0.100M
Time = ?
Final Concentration [A] = 0.0240M
The parameters are represented in the following equation as;
1/[A] = kt + 1/[A]o
kt = 1/[A] - 1/[A]o
kt = 1/0.0240 - 1/0.1
kt = 31.67
t = 31.67 / 34.1
t = 0.929s = 0.93s (2 s.f)
