The yield from an acid-carbonate reaction

Item

Weight (g)

Uncertainties (g)

Observations

Flask and contents

90.650

±0.001

Balance display fluctuating in the third decimal place. The reading varies between 90.649 and 90.651.

Watch glass

19.217

±0.001

Balance display fluctuating in the third decimal place. The reading varies between 19.216 and 19.218.

Watch glass with Na2CO3

20.128

±0.001

Some spillage on the balance plate

Watch glass with Na2CO3 residue

19.220

±0.001

Some spillage on the bench

Flask and contents after the reaction

91.257

±0.001

Some Na2CO3 stuck on the neck of the flask

Data

Weight (g)

Uncertainties (g)

Observations

Mass of Na2CO3 transferred

0.908

±0.001 + ± 0.001 = ± 0.002

Upon transfer there was vigorous effervescence with some spitting, indicating there was a gas formed. Heat was generated and sizzling sound as well was produced.

Total mass before the reaction

110.778

±0.001 + ± 0.001 = ± 0.002

Total mass after the reaction

110.477

±0.001 + ± 0.001 = ± 0.002

The flask was weighed when there was no visible bubbling.

Mass of CO2 released

0.301

±0.002 + ± 0.002 = ± 0.004

Calculation steps

Uncertainty Propagation

0.908 grams of Na2CO3(s) = 0.908g = 0.00857 moles ( rounded to 3 sif) 105.99g/mol

The uncertainty in 0.908g is ± 0.002

= (± 0.002/0.894) x 100 = 0.22%

0.22%

The uncertainty in 105.99g/mol is ± 0.01= (0.01/105.99) x 100 = 0.0000095% and so will be ignored.

-

Total uncertainty

0.22%

According to the mole ratio demonstrated in the equation, 0.00857 moles of Na2CO3(s) should produce 0.00857 moles of CO2(g)

0.00857 moles of CO2(g) = 0.00857mol x 44.01g/mol

= 0.377g (3sf)

The uncertainty in 0.00857 moles of CO2(g)

0.22%

The uncertainty in 44.01g/mol is ± 0.01

= (0.01/44.01) x 100 = 0.0000052% and so will be ignored

-

Final absolute uncertainty = (0.22/100) x 0.377 = 0.00083g

0.00083g

Errors

Random Errors

Systematic errors

Mistakes

This experiment includes random errors such as unreliable data due to the only trial being tested, fluctuation of the electronic balance and instrumental uncertainties. The processed data table has displayed all the uncertainty values. Additional random errors that may have been overlooked or underestimated may include:

Extent of fluctuation of the balance

The readings on the balance may show an extent of fluctuation over ±0.001, such as ±0.002, or even ±0.003.

Reading the electronic scales

Electronic scales were not read consistently. This would result in a false estimation of the true value and data would be recorded imprecisely.

Consideration of these additional random errors may account for a doubling or even tripling of the uncertainty to 0.66% but this is still a diminutive quantity of 20.2% discrepancy.

Systematic occurred during the experiment errors are listed below:

Incomplete reaction of carbon dioxide

An ideal of 100% reaction is impossible to be reached because not all carbon dioxide reacts. Thus the quantity of carbon dioxide produced (in gaseous state) would not be maximised. Also, it is difficult to determine whether a reaction is completed merely by observation. The reaction may be continued even if the solution is seemingly in a static state and weighing it before its completion would cause a shortfall in mass loss. However it would result in only about 2% of the errors since a very small amount of carbon dioxide does not react or continue to react.

Solubility of CO2

As hydrogen oxide molecules are produced during the reaction, carbon dioxide, due to its good solubility, will dissolve in water and hence reducing the amount volatilised in the air. This is mostly likely the major cause in discrepancy which would possibly contribute 10%-15% of the errors.

Electronic balance inaccuracy and inconsistency

Faulty calibration of electronic balance may have led to inaccurate results. The true mass could be higher or lower than the display on the balance and this may account for approximately 1%-2% of the errors.

Mistakes occurred were recorded in the Raw Data Table. Most listed can be associated with a reduction in mass loss.

Spillage of the sodium carbonate during weighing and transferring to the conical flask. The result affects an estimate of 1% of errors taking place.

Sodium carbonate was not thoroughly transferred into the flask. For example, it sticked to the neck of the flask and will not react with hydrochloric acid.

Improvements

Random Errors

Systematic errors

Mistakes

In order to reduce and minimise the Random Errors listed above, the following precautions can be taken:

Extent of fluctuation of the balance

Observe the display for a longer period of time and record the correct uncertainty until there is a stable extent of fluctuating data.

Reading the electronic scales

Since this error cannot be avoided but can only be minimised, several trials of reading should be taken and recorded, and the average reading should be calculated in order to increase the precision of the result.

The Systematic Errors can be rectified in the following way:

Incomplete reaction of carbon dioxide

This error can be theoretically corrected by increasing the concentration of hydrochloric acid to promote a more rapid and more violent reaction. Waiting for longer time for the reaction to complete is also suggested.

Solubility of CO2

By increasing the temperature for this experiment, the solubility of carbon dioxide gas could be reduced and therefore the gas released could increase and thus providing a more accurate result.

Electronic balance inaccuracy and inconsistency

Changing the apparatus to ensure that the balance has not been damaged over time - would possibly avoid error.

To avoid the Mistakes in future experiments the following modifications can be made:

A beaker and a funnel should be included in this experiment in order to prevent future mistakes because of sodium carbonate spillage.