We have 10g of rock salt which has been given to us and we can use any method we want to extract the salt from it. WE then will be judged on the amount of salt that we produce and the how pure it is. This will be judged on how white it is.
When we were given this task the group that I was in wanted to use a dissolving and evaporating method to get the salt form the rock salt.
We are going to use the evaporation method. You grind up the rock salt and hen dissolvent into a solvent (water). Then you filter out the rock, and then you are left with a clear solution. You then pour the liquid in an evaporating basin and then heat it, leaving purified salt.
Apparatus
In this experiment we had to use:
Pestal and Mortar
Funnels
100ml beakers
Bunsen burner
Heat-proof mat
Evaporating basins
Flask
Stirring rod
Filter paper
Tripod
Gauze
Method
We first used a pestle and mortar to grind the rock salt as small as possible to dissolve into a solvent. Making these particles smaller would mean that it would be faster and easier to dissolve. This seemed the best thing to do seeing that we were also being timed to finish in a one hour period.
A solvent is a liquid that the solute (the rock salt) will dissolve in to. The way that we will purify is this. As we mix the crushed rock salt in to the solvent which is water in this case only the salt will dissolve because it is a soluble and rock is an insoluble. A soluble is substance that will dissolve into a solvent and an insoluble is a substance that will not. Then we will filter the solution using filter paper to get out all of the crushed rock. This is a way of separating mixtures. In the experiment that we are doing we use two different methods of separating mixtures for the same experiment.
We used filter paper into a funnel and then put the funnel in to a beaker. The solution that we had then was put into this set of apparatus and then all the rock was filtered out. We were then left with a clear solution which contains salt. You can not see the rock because it has filled the gaps of the water particles. First you can see all the particles, but as it dissolves it fits into the gaps of the particle which is your solvent. This is why so many solvents are only liquids. Once we have the solution of just salt we put it into an evaporating basin. This is where we extract the salt from the water.
We have a Bunsen burner, a tripod, a heat proof mat, and gauze. We placed the tripod on to the heat proof mat and the then put the Bunsen burner under the tripod. Then we put the gauze on the tripod and the gauze. Wearing our goggles we then lit the Bunsen burner. Then water then started to evaporate. This is explaining evaporation
Evaporation, is the change of a liquid into vapour at any temperature below its . For example, water, when placed in a shallow open container exposed to air, gradually disappears, evaporating at a rate that depends on the amount of surface exposed, the of the air, and the temperature. Evaporation occurs because among the molecules near the surface of the liquid there are always some with enough heat energy to overcome the cohesion of their neighbours and escape (see ; ). At higher temperatures the number of energetic molecules is greater, and evaporation is more rapid. Evaporation is also increased by increasing the surface area of the liquid or by increasing the air circulation, thus carrying away the energetic molecules leaving the liquid before they can be slowed enough by collisions with air molecules to be reabsorbed into the liquid. If the air is humid some water molecules from the air will pass back into the liquid, thus reducing the rate of evaporation. An increase in atmospheric pressure also reduces evaporation. The process of evaporation is always accompanied by a cooling effect. For example, when a liquid evaporates from the skin, a cooling sensation results. The reason for this is that only the most energetic molecules of liquid are lost by evaporation, so that the average energy of the remaining molecules decreases; the surface temperature, which is a measure of this average energy, decreases also. Many processes are based on this principle.
Results
When we had evaporated all the solution with a Bunsen burner, we were then left with salt left with some salt. But the salt in the Bunsen burner was “slushy”. This was because we didn’t have enough time to evaporate all of the water in the evaporating basin. For this reason we were given a lower mark. We were also given a low mark in purity of the salt because when you are evaporating the salt towards the end the salt starts to “spit” out of the basin. We were very desperate for as much salt as we could get al we scraped that salt off the table and heat proof mat to get as much salt as possible.
This is what we were trying to get.
Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids. It forms small, transparent, and colourless to white cubic crystals. Sodium chloride is odourless but has a characteristic taste. It is an ionic compound, being made up of equal numbers of positively charged sodium and negatively charged chloride . When it is melted or dissolved in water the ions can move about freely, so that dissolved or molten sodium chloride is a conductor of electricity; it can be decomposed into sodium and chlorine by passing an electrical current through it.
Nearly all chemical compounds that contain either sodium or chlorine are ultimately derived from salt. Salt is widely and abundantly distributed in nature. It makes up nearly 80% of the dissolved material in seawater, and is the greater part of dissolved matter in the Dead Sea, the Great Salt Lake, and in salt wells in various parts of the world. It is also widely distributed in solid form. The mineral halite is pure salt. Rock, or mineral, salt is usually less pure; it is found in large deposits in the United States, notably in New York, Michigan, Ohio, Kansas, Texas, and Louisiana, and also in Great Britain, France, Germany, Russia, China, and India. The manufacture and use of salt is one of the oldest chemical industries. Salt is mined from deposits or is obtained as brine by introducing water into the deposits to dissolve the salt and then pumping the solution to the surface. Salt is also obtained by evaporation of seawater, usually in shallow basins warmed by sunlight; salt so obtained was formerly called bay salt, and is now often called solar salt. Most salt for table use is obtained from seawater; it is usually not pure sodium chloride, small amounts of other substances (e.g., magnesium carbonate, hydrated calcium silicate, or tricalcium phosphate) being added to it to prevent lumping.
This is what salt is and what it is used for.
We collected our salt into a 100 ml beaker. We use a spatula to scrap the salt out of the evaporating basin so that we could measure how much we had produced. I first measured a 100ml beaker that was empty to see much that it weighed. Then I measured our beaker with the salt in it. The scales that we used were accurate to 100th of a gram and were sensitive enough to be forced down when we breathed. For this reason we the person that I measured the beaker with and I had to stand back and wait for the scale to settle to find out exactly how much the beakers weighed. I then had to subtract the beaker with no salt in it and the beaker with salt in it to find out how much salt we had produced. We had produced 4.01 grams of salt which is a 40.1% yield. WE had predicted to get a 50 percent yield so I think that our prediction was quite good.
Compared with the other groups though we had produced a very low yield. The highest yield was 96.5%.
Here is a table with the results of the other groups and where our group placed on that.
The group that I was in is Group B. We came second to last in the graph because we had the second lowest yield. So since we had this low yield and purity we came second.
Analysis
This experiment has showed that we have gathered a smaller yield for many different lessons. W were all given the same amount of rock salt, but the rock salt that we were given could have contain much less salt then the group with the most. This graph demonstrates how much rock, sand; grit and salt were in the rock salt that we were given.
Our group
Group C
From this you can see that we might have had a much lower yield compared to Group C and the groups with a higher yield because they had much more salt in there rock salt then our group’s rock salt. This is also far because each group got 10g of rock salt each. This could be because when rock salt forms it is formed in huge an area which is then covered over by marine sediments. When out rock salt was gather is could have been taken from the top of the deposit and more sediments (sand, rock, grit) could have been gathered along with a small amount of actually rock salt.
Our prediction was correct in a way seeing that we thought that we had less salt then most of the groups but we got 10% less yield then we expected to get.
The pie chart that I have made supports our prediction. Since we had a low amount of salt in our rock salt the result of having a low yield is correct.
Evaluation
I think that our group could have produced much better salt. We did not get very pure salt because it spat out of evaporating dish when we were evaporating the solution, so all the bits of salt that came out we put in to our container. This meant that we could have less salt then we were supposed to have because we were not able to get all of it. But it could also mean that we have particles in the salt which are not salt so we could have said we got more salt then we actually had. WE could have also not as got as pure salt as the other groups because we only filter the salt solution once. Some of the very fine pieces of sand could have gotten through the filter paper. But we still think that for reason we didn’t get as much salt as we were meant to.
We could have not dissolved all of our rock salt when we dissolving it. When we thought that we were done dissolving the rock salt some of the salt which was not dissolved could have been caught in the filter paper, thus leaving less salt for us.
We also towards the end of the experiment used two sets of Bunsen burners and evaporating basins to try to evaporate as much solution as possible. Doing this means that we could lose more salt when were trying to scrape it out of the evaporating basins. We should have filled the evaporating basins with water and then dissolved the remaining salt in them. Then added the two together into one evaporation basin, then heated them again to get more salt.
When we were evaporating we did not evaporating it fully so the salt was
“slushy”. This meant that there was still water in the salt. So when we weighed the salt we did not take into account the water. This meant that we had another problem with the weight. We had less salt then what we said original said. To avoid this we should have let the water evaporate naturally. We did not want to heat it any more with a Bunsen burner because it heated the salt to much. IT would then cause the salt to spit up to 6ft, we wanted to not be harmed so we did not heat it any more. We also would have lost salt when it “spat” the salt.
