The purity of a solid containing KHP is determined by titration with a standard

Question

The purity of a solid containing KHP is determined by titration with a standard sodium hydroxide solution. When a 0.4334(±0.0001)g sample is dissolved in water, it requires 13.42(±0.08) mL of 0.1166(±0.0002) M NaOH to reach the endpoint. The molar mass of KHP is 204.221(±0.007) g/mol.

(a) What is the mass percent KHP purity in the solid sample? What is the absolute uncertainty in the mass percent KHP purity? Report your answers to two significant figures in the uncertainty.
_____ (±  ) _____%
(b) Which measurement provides the greatest contribution to the overall uncertainty?
     ---Select One--- NaOH Concentration, Sample Mass, NaOH Volume, or KHP Molar Mass
(c) If only the uncertainty from the dominant factor is considered and all other measurement uncertainties are ignored, what is the calculated uncertainty in the mass percent KHP purity? Report your answer to two significant figures.

±______ %

Explanation / Answer

Purity of KHP solid

(a) moles of NaOH used for titration = 0.1166 M x 13.42 ml = 1.5648 mmol

maxima = 0.1168 M x 13.50 ml = 1.5768 mmol

minima = 0.1164 M x 13.34 ml = 1.5528 mmol

moles NaOH with uncertainty = 1.5648 +/- 0.0120 mmol

moles KHP = moles NaOH

mass% KHP in solid = 1.5648 x 204.221 x 100/1000 x 0.4334 = 73.7344%

maxima = 1.5768 x 204.228 x 100/1000 x 0.4335 = 74.2853%

minima = 1.5528 x 204.214 x 100/1000 x 0.4333 = 73.1834%

mass% KHP with uncertainty = 73.7344 +/- 0.5510 %

(b) Greatest contribution to the overall uncertainty is by NaOH concentration.

(c) New uncertainty in KHP purity,

moles of NaOH used for titration = 0.1166 M x 13.42 ml = 1.5648 mmol

maxima = 0.1168 M x 13.42 ml = 1.5674 mmol

minima = 0.1164 M x 13.42 ml = 1.5621 mmol

moles NaOH with uncertainty = 1.5648 +/- 0.0027 mmol

moles KHP = moles NaOH

mass% KHP in solid = 1.5648 x 204.221 x 100/1000 x 0.4334 = 73.7344%

maxima = 1.5675 x 204.221 x 100/1000 x 0.4334 = 73.8616%

minima = 1.5521 x 204.221 x 100/1000 x 0.4334 = 73.1360%

mass% KHP with uncertainty = 73.7344 +/- 0.3628 %

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