9) Extra eredit (10 pts) During nanofabrication dioxide Tro\'n wafers However, c

Question

9) Extra eredit (10 pts) During nanofabrication dioxide Tro'n wafers However, concentrated processes, hydrofiuorie acid (HF) is used to reT Owe water) etches silicon water) and 1 L HF at 25°C. HP (typically 49 wt % HF in dioxide too quickly. Therefore, controllable etching. It comprises a 6 L NH4F solution (40 wt% NH solution (49 wt % HF in water). At 25°C, K. of HF is 6.6% 10.mtion at 250. NH4F and 1·15g/mL for HF. Calculate thepH of this buffered solution a buffered oxide etch solution is commonly used for more

Explanation / Answer

Mass of NH4F in the solution = Density*Volume = 1.11*6000 = 6660 g

Moles of NH4F in the buffer = Mass/MW = 6660/37 = 180

Mass of HF in the solution = Density*Volume = 1.15*1000 = 1150 g

Moles of HF in the buffer = Mass/MW = 1150/20 = 57.5

For HF, pKa = 4-log(6.6) = 3.18

Using Henderson Hasselbach equation:

pH = pKa + log(moles of salt/moles of acid)

Putting values:

pH = 3.18 + log(180/57.5) = 3.675

Hope this helps !

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