23 (0.5 pt) Data Table ll: Determination of Molar Mass of Unknown # #3 #2 #1 Tit

Question

23 (0.5 pt) Data Table ll: Determination of Molar Mass of Unknown # #3 #2 #1 Titration Mass of Sample (g) Final Buret Reading mL) Initial Buret Reading (mL) Volume Used (mL) o, 229 o. 2 4 3 o.53 36 5 0,5 2 Calculations attach it to this grade digits for Do the CAPA assignment to check your calculations. Print and sheet. Significant figures should be correct for reported values, but keep all further calculations. In other words, do not round until all calculations are complete. Part A: Calculated results for standardization of NaOH (0.5 pt) KHC8H404-2 ou 2 2 g mol-1 Molar Mass KHP (potassium hydrogen phthalate Mass of KHP Moles of KHP Volume of NaOH Molarity of NaOH Trial mol (mL)(mol/L) | o,781 #1 Average Molarity of NaOHElok Relative Standard Deviation If RSD > 5 ppt, then recalculate the average of the [NaOH) and RSD using the most precise data. New Average Molarity of NaOH- Relative Standard Deviation : 76

Explanation / Answer

Part A) Calculation for RSD of NaOH

average molarity of NaOH (X) = 0.1013 M

let individual molarities by x

then,

RSD = sq.rt.[(x-X)^2/2]

         = sq.rt.[(6.4 x 10^-7 + 1.2 x 10^-3 + 2.5 x 10^-7)/2]

         = 0.024

Determine the molar mass of unknown acid

Formulas,

molarity(M) = moles(mol)/volume(L)

moles (mol) = grams(g)/molar mass(g/mol)

molar mass(g/mol) = grams/moles

So,

Part B) molar mass of unknown acid

Trial    mass of acid(g)    NaOH (ml)     NaOH (mol)        molar mass (g/mol)

#1            0.243                   36.05             0.00365                   66.575

#2            0.243                   36.50              0.00370                   65.676

#3            0.229                   34.04              0.00345                   66.377

average molar mass of unknown acid (X) = 66.21 g/mol

all three values represented as x g/mol

RSD = sq.rt.[(x-X)^2/2]

         = sq.rt.[(0.133 + 0.285 + 0.028)/2]

         = 0.472 g/mol

which is less than 5 ppt.

sample calculation Tria#1

moles NaOH = 0.1013 M x 0.03605 L = 0.00365 mol

molar mass of unknown acid = 0.243 g/0.00365 mol = 66.575 g/mol

Discussion : possible sources of error are If incorrect weight of unknown acid is taken, this could lower or raise the calculated molar mass of the acid.

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