- Weighing Khp Preparing Naoh Titration 2 Goal A Solution Of Sodium Hydroxide Naoh Is Standardised Against The Titrimet 1 (155.12 KiB) Viewed 130 times
- Weighing Khp Preparing Naoh Titration 2 Goal A Solution Of Sodium Hydroxide Naoh Is Standardised Against The Titrimet 2 (48.31 KiB) Viewed 130 times
Purity of KHP (PHP) PkHp is 100.00% + 0.05%. The supplier gives no further information concerning the uncertainty in the catalogue. (a) Calculate for the standard uncertainty associated with the purity of the primary standard. Mass (mkHP) The relevant weighings are: container and KHP: 60.5450 g (observed) container less KHP: 60.1562 g (observed) KHP 0.3888 g (calculated) Because of the combined repeatability term identified above, there is no need to take into account the weighing repeatability. Any systematic offset across the scale will also cancel. The uncertainty therefore arises solely from the balance linearity uncertainty. Linearity: The calibration certificate of the balance quotes +0.15 mg for the linearity. This value is the maximum difference between the actual mass on the pan and the reading of the scale. The balance manufacturer's own uncertainty evaluation recommends the use of a rectangular distribution to convert the linearity contribution to a standard uncertainty. (b) Calculate for the standard uncertainty associated with the mass weighings.
0 Molar mass (MX) From the IUPAC table current at the time of measurement, the atomic weights and listed uncertainties for the constituent elements of KHP (CH3O.K) were: Atomic Quoted Element weight uncertainty с 12.0107 +0.0008 H 1.00794 20.00007 15.9994 10.0003 K 39.0983 +0.0001 For each element, the standard uncertainty is found by treating the IUPAC quoted uncertainty as forming the bounds of a rectangular distribution. (c) Calculate the standard uncertainties associated with the rectangular distribution of the quoted uncertainties for each element. (d) Calculate for the combined uncertainty associated with the molar mass of KHP. Repeatability (rep) The method validation shows a repeatability for the titration experiment of 0.05 %. This value can be directly used for the calculation of the combined standard uncertainty. Also, the rep factor has a nominal value of 1.0, which will not affect the value of the measurand. Titrant volume (V) Calibration: The limits of accuracy of the delivered volume are indicated by the manufacturer as at figure. For a 20 mL piston burette this number is typically +0.03 mL. le) Calculate the standard uncertainty associated with the buret calibration. Temperature: The uncertainty due to the lack of temperature control is calculated in the same way as in the previous example, but this time taking a possible temperature variation of 13 °C (with a 95 % confidence). (coefficient of volume expansion for water as 2.1x10**cº) of Calculate the standard uncertainty associated with the temperature.
Bias of the end-point detection: The titration is performed under a layer of Argon to exclude any bias due to the absorption of CO2 in the titration solution. This approach follows the principle that it is better to prevent any bias than to correct for it. There are no other indications that the end-point determined from the shape of the pH-curve does not correspond to the equivalence-point, because a strong acid is titrated with a strong base. Therefore, it is assumed that the bias of the end-point detection and its uncertainty are negligible. Vr is found to be 18.64 mL. (g) Calculate for the combined uncertainty associated with the volume of the titrant. Standard concentration of the titrant (CNH) (h) Calculate for the concentration and the combined uncertainty associated with the concentration of the NaOH standard solution. (i) Calculate for the expanded uncertainty at 95% confidence limit.