KHP mass measurements Titration of KHP with NaOH Initial (g) Final (g) Total (g) Initial NaOH...

KHP mass measurements			Titration of KHP with NaOH
Initial (g)	Final (g)	Total (g)	Initial NaOH vol. (mL)	Final NaOH vol. (mL)	Total NaOH sol’n (mL)	NaOH molarity (molarity)
73.9473	74.1675	0.2202	1.69	22.32	20.63	0.0523
97.6215	97.8296	0.2081	3.76	23.32	19.56	0.0521
95.8243	96.0261	0.2018	1.23	20.62	19.39	0.0510

From the sample volume and distances to the first and second equivalence points, calculate the molarities of hydrochloric and phosphoric acids in the sample. GIve uncertainties for the calculated molarities. How well do the replicated tritrations agree?

Expert Solution

Find out the average mass of KHP required for the titration.

x̅ = 1/3*(x₁ + x₂ + x₃) = 1/3*(0.2202 + 0.2081 + 0.2018) g = 0.2100 g.

Find out the standard deviation of the mass = √1/3[(x₁ - x̅)² + (x₂ - x̅)² + (x₃ - x̅)²] = √1/3*[(0.2202 – 0.2100)² + (0.2081 – 0.2100)² + (0.2018 – 0.2100)²] g = 0.007635 g.

Find out the average volume of NaOH required for the titration.

V̅ = 1/3*(V₁ + V₂ + V₃) = 1/3*(20.63 + 19.56 + 19.39) mL = 19.86 mL.

Find out the standard deviation of volume = √1/3*[(V₁ - V̅)² + (V₂ - V̅)² + (V₃ - V̅)²] = √1/3*[(20.63 – 19.86)² + (19.56 – 19.86)² + (19.39 – 19.86)²] mL = 0.548878 mL.

Find out the average molarity = 1/3*(0.0523 + 0.0521 + 0.0510) M = 0.0518 M.

Use propagation of errors to find the relative uncertainty in molarity = √[(uncertainty in mass/mass)² + (uncertainty in volume/volume)²] = √[(0.007635 g/0.2100 g)² + (0.548878 mL/19.86 mL)²] = √(0.00208566) = 0.045669

Find out the uncertainty in the molarity of NaOH as (relative uncertainty)*(average molarity) = (0.045669)*(0.0518 M) = 0.0023656 M ≈ 0.00236 M.

Report the molarity of NaOH as 0.0518 0.00236 M (ans).

queen_honey_blossom answered 2 years ago

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