Estimating the % purity of marble by back titration method Free Essay Example

The worths for the % purity of marble that I have actually calculated depend on a close variety, nevertheless there is a significant distinction, of 4.74% in the purity estimated in between the 2 specific values. Nevertheless, the deviation is covered by the uncertainty of ï ¿ 1/2 4.84%. However, specific mistakes have taken place that have actually caused this variance in the outcomes.

REASONS FOR VARIANCE

Random Errors

1. Loss of marble after weighing: After weighing out the marble, there is a small loss in mass in moving the mass from the butter paper used for weighing as a small quantity of the fine powdered marble sticks to the butter paper and does not react with the HCl at all.

Also, while moving the crushed CaCO3 some particles could have likewise been blown away by the wind. Hence the disparity in the masses utilized could represent the different worths gotten.

2. HCl left in the pipette: being a manual instrument, there is no guaranteed method of ensuring that each and every drop of the acid that was measured has been moved to the conical flask, this reduces the volume of acid used and such a modification in any one of the reading will straight impact the value of the % pureness.

3. Air bubbles in pipette dispenser: For this experiment, due to the destructive nature of the concentrated acid, a pipette dispenser was utilized to ration the HCl. Nevertheless there were some air bubbles that were caught that trigger a mistake in the volume of HCl that is not represented by the absolute uncertainty of the pipette.

Methodical Errors

1. Unevenly crushed marble: The CaCO3 supplied was not uniformly squashed; some was still in larger portions while the rest was finer granules. This non-uniformity in the texture of CaCO3 likewise produces a various surface location for the acid to react with and this can be the reason for the varying values of pureness.

2. Excess NaOH added in titration: While titrating the HCl and the HCl + CaCO3 services the usage of the phenolphthalein sign triggers an error in the quantity of alkali included as the titration is only stopped once the colour modifications to a pale pink, this firstly is a really qualitative and subjective instruction and likewise the indicator on turning pink suggest a slight alkalinity. Hence, the real neutralization point was left 1-2 hang back.

3. Unevenly distributed impurities: CaCO3 is found naturally as marble in the earth. Thus, being a natural stone the impurity that it will contain will be randomly distributed and due to this unevenness, the purity will vary with every sample.

IMPROVEMENTS TO PREVENT AFOREMENTIONED ERRORS

1. Keep fans and windows shut and cover CaCO3 while transporting: By doing this one can minimize the loss of particles and thus reducing the uncertainty.

2. Carefully using apparatus to avoid human errors: By practice and careful usage one can eliminate the errors caused by the air bubbles in the pipette, errors in transfer and parallax.

3. Marble should be crushed evenly: the CaCO3 should all be of the same texture so that the surface area is kept controlled and this will reduce the disparity in the purity values that have been caused by the differing surface areas.

4. Using another indicator that prevents uncertainty in the exact point of neutralization: If a solution like Universal Indicator is used then the exact point when the titration is complete can be easily identified and thus by eradicating this error, one can aim to reduce the disparity observed in the readings.

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