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>
Answer:
275g
Explanation:
Depending on the molar mass you are given, you can use that to solve this.
(I'm going based on my science class' molar mass of sulphur being 32.07g/mol)
Starting off, the formula for finding moles is
n=m/M (moles = mass / molar mass)
We can manipulate this equation to solve for mass.
m=Mn
now fill in what we now.
m = 32.07*8.56
mass = 274.5192
Now round for significant digits (if you are needed to do)
mass = 275g
Answer:
9
Explanation:
mass number = protons + neutrons
= 4 + 5 = 9
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