Separating the compenents of a mixture

ACCESS CHEMISTRY

UNIT A

Practical Assignment – Separating the components of a mixture

Introduction

Aim:

The Aim of this experiment is to separate two compounds in a mixture of Silicon dioxide (sand) and Sodium chloride (salt).

Separating and recovering components of a mixture are challenging yet necessary in scientific research and for industrial use.

Separation processes, for example, are important in the oil industry as the components of crude oil (including diesel fuel, gasoline, jet fuel, and lubrication oil amongst others) are valuable and in high demand.

It is therefore important to understand how to separate components of mixtures.

Distilled water is used throughout the experiment due to the nature of the water. Distilled water is treated by a process of distillation and is thus purer than the original water or water from a tap as salt and other impurities do not evaporate with the water when treated and are therefore removed, this is important to this experiment as the total mass of salt is to be determined, had normal water been used, the results would be flawed.

Methods used in this experiment are as follows:

Filtration: A solid (sand) is separated from a liquid (salt solution) by use of a porous filter. This allows the solution to pass through but retains the solid.

Evaporation: The process of driving off a liquid so as to dry the required component and leave it behind.

Method

Risk Assessment:

Safety goggles were worn to protect the eyes from any hot particles spitting from the evaporating basin.
Students were instructed never to leave a Bunsen burner on a blue flame and unattended, but to turn the flame to a yellow flame so that it could be seen and no accidents could occur.
Students were not permitted to touch hot glass until cooled due to the risk of burning.
Students were advised to take care when stirring the mixture during the heating stage to avoid spillage and burns.

Equipment:

Safety glasses
500cm3 Beaker
Balance to weigh the sand/salt mixture
Distilled water
Bunsen burner
Tripod
Gauze
Glass rod for stirring
Filter paper
Filter funnel
Metal clamp stand
Watch glass
Oven
250cm3 evaporating basin
Pen and paper

The 50cm3 beaker was placed on the balance and a note was made of the mass.
10.01g of the mixture was weighed and poured into a 500cm3 beaker.
50cm3 of distilled water was poured into the beaker.
Gauze was placed on top of the tripod and the Bunsen burner lit, ...

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Equipment:

Safety glasses
500cm3 Beaker
Balance to weigh the sand/salt mixture
Distilled water
Bunsen burner
Tripod
Gauze
Glass rod for stirring
Filter paper
Filter funnel
Metal clamp stand
Watch glass
Oven
250cm3 evaporating basin
Pen and paper

The 50cm3 beaker was placed on the balance and a note was made of the mass.
10.01g of the mixture was weighed and poured into a 500cm3 beaker.
50cm3 of distilled water was poured into the beaker.
Gauze was placed on top of the tripod and the Bunsen burner lit, the 500cm3 beaker was then placed on the gauze and heated for about 1½ minutes.
The mixture was then stirred until the salt appeared to have dissolved completely in the distilled water.
Once the salt had dissolved, the Bunsen burner was turned to a yellow flame and set aside.
A filter paper was folded into quarters and placed inside the filter funnel.
An empty evaporating basin was placed on the balance and a note was made of its mass, it was then returned to the bench for use in the next step.
The filter funnel was then clamped using the metal clamp stand above the 250cm3 evaporating basin.
The mixture in the 500cm3 beaker was then poured through the filter into the evaporating basin.

The above diagram demonstrates how the sand was separated using filtration. Taken from

A small amount of distilled water was used to rinse out the final grains of sand from the 500cm3 beaker and poured into the filter.
The filter paper was then removed and placed on the watch glass, each student wrote their initials on the paper and put the watch glass with filter paper in the oven to dry it.
Whilst the filter paper and contents were drying in the oven, the Bunsen burner was turned to a blue flame and the 250cm3 evaporating basin was placed on the gauze and heated until nearly half of the contents of the evaporating basin container had evaporated.

The above diagram shows how evaporation took place and how the equipment was arranged to achieve this. Taken from

When the water had almost all evaporated, the Bunsen burner was turned to a yellow flame and set to one side and the water was allowed to evaporate by itself.
When the filter paper with sand had dried it was removed from the oven.
An empty filter paper was placed on the balance and a note was made of its mass.
The dried filter paper with the sand was then placed on the balance and the mass was recorded.
The evaporating basin containing the salt was then placed on the balance and its mass was recorded.
All masses were then recorded in a table of results. Using the recorded masses of the empty equipment, calculations were made of the mass of the sand and salt.

Results

Table:

To calculate the mass of salt, the following equation was used:

Evaporating basin and Salt – Evaporating basin = Salt

To calculate the mass of sand, the following equation was used:

Filter paper and Sand – Filter paper with Sand removed = Sand

To calculate the percentage loss of the original mixture, the following equation was used:

( (Initial Mass – Final Mass) / Initial Mass ) X 100

A note was also made of the mass of a new filter paper that had not been used.

Conclusion

The percentage loss of the mixture was calculated to be 5.59%. Observations were made of errors that could have contributed to this percentage loss and are listed overleaf.

Errors:

Whilst heating the salt and distilled water mixture, some salt particles were seen to jump out of the evaporating dish and were unable to be retrieved. A quantity of salt was lost in this manner.
Some sand particles were left inside the beaker upon rinsing out with distilled water.
When the filter paper containing the filtered sand was scraped clean, some sand remained in the filter paper and was difficult to remove.
Not all salt may have dissolved in the water and therefore there could be a small amount left with the sand particles when filtered.
Manufacturers of balances state that the mass of an object is accurate to ± a certain figure (often 0.01g), the more measurements that are taken, the more times this error occurs.

Should the experiment be repeated, these errors could be minimised by the following methods:

Whilst the salt is heating, a cover could be placed over the evaporating dish with a hole and some kind of tubing to allow the steam to escape but prevent loss of salt.
The sand particles in the beaker could be further washed out by distilled water; however there would still be a margin or error that could not be avoided.
Careful scraping of the sand from the filter paper using a spatula could minimise the percentage loss of sand that remained ingrained into the filter paper but again, there would still be a margin of error that could not be avoided.
A larger volume of distilled water could be used and it heated for longer to ensure that the salt had dissolved into the water.
Measurements could be made three times and an average reading taken to reduce errors, the number of measurements made should also be minimised so as not to add the errors together such as weighing sand then sand and paper, then sand and paper and watch glass etc. In this case, even with the minimum number of measurements made and averages taken, a margin of error will still be there. It is best to use a balance with the smallest margin of error quoted by manufacturers.