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I am measuring the rate of reaction how fast a reaction takes of sodium thiosulphate and hydrochloric acid. There are different variables I could use to see the change in the rate of reaction. These include temperature, concentration or catalysts. I am going to do two experiments, one changing the temperature and one changing the concentration of the sodium thiosulphate. This is how they will be done. Planning Experimental Procedures Equipment Sodium thiosulphate Na S O of different concentrations Hydrochloric acid HCl Tile marked with a cross Measuring cylinder x2 Beaker x2 Bunsen Tripod Test tube x2 Stopwatch Thermometer As the diagrams show, firstly I will measure the right amount of sodium thiosulphate and hydrochloric acid into two separate test tubes. If it is needed, these will then be put into water and heated with a Bunsen burner and tripod until they are up to temperature, which will be measured with a thermometer in the water. They will then be put into the beaker. Firstly, the experiment will be done with the substances at room temperature. This means that the beaker will be filled with Na S O and HCl via two measuring cylinders and placed on the tile marked with a cross. The amount of Na S O and HCl being put in the beaker will be determined by prior tests, but they will only need to be quite small amounts. As soon as the two substances are mixed together, the stopwatch will start timing and it will stop when the cross is obscured. When the substances need to be heated, they will be put in separate test tubes and heated in a beaker of water as above. They will be mixed together when up to temperature. One of the experiments will show the difference temperature makes and the other will show the difference the concentration of the sodium thiosulphate makes. During the experiments, goggles and aprons will be worn at all times for safety. The tests will be made fair by the fact that only one thing will be changed each time "“ the temperature or concentration of the sodium thiosulphate. We presume that when the concentration of the Na S O is increased, the rate of reaction will be higher. This is because if there are more molecules, they are more likely to collide and react. However, the collision theory says that a very small percentage of these collisions results in a reaction. This is because of an energy barrier. Only those particles with enough energy to overcome the energy barrier will react when they collide. So, if the frequency of collisions is increased, the rate of reaction will increase. However, the percentage of successful collision will remain the same. The particles go through random collisions in which energy is transferred between the colliding particles and this leads to particles with differing energies. The distribution of the energies of a particle of gas is shown by the Maxwell-Boltzmann energy distribution curve, shown below. We would also presume that when the temperature is increased it will have the same effect. This is because the molecules will collide more often and with greater energy and so will be more likely to successfully react because their bonds break. For an average reaction a 10 C temperature rise doubles the rate of reaction because about twice as many particles possess the necessary activation energy. The next diagram shows Maxwell-Boltzmann distribution curves for a fixed mass of gas at two temperatures T and T where T is about 10 C higher than T . The total area under the curve remains the same since there is no change in the number of particles present. So, I predict that in the experiment were the temperature is varied, the rate of reaction will go up as the temperature goes up. In the experiment where the concentration of the thiosulphate is to be varied, I expect the rate of reaction to go up as the concentration goes up. If the concentration doubles, I would expect the rate of reaction to double and if the concentration is zero I would expect the rate of reaction to be zero. In the graph showing temperature compared to rate of reaction, I would expect there to be negative correlation and in the graph showing concentration compared to rate of reaction, I would expect there to be negative correlation. However, it remains to be seen if the results will follow this theory. Here are the results tables that will be used: Temperature 1st results 2nd results Average Rate Of Reaction C seconds seconds seconds seconds Room approx.20 30 40 50 60 70 This is for the first half of the experiment where everything will be kept the same except the temperature which will range from 20 C to 70 C. It is hoped that there will be sufficient time for two experiments and an average will be calculated afterwards. The concentration of the sodium thiosulphate used throughout will be 30g/dm. Concentration 1st results 2nd results Average Rate Of Reaction g/dm seconds seconds seconds seconds 15 20 25 30 35 40 This is the other section to the experiment where everything will be constant apart from the concentration of the sodium thiosulphate. It has been decided that a concentration of no less that 15g/dm will be tested because any less than this would probably take too long. The hydrochloric acid and the sodium thiosulphate will not be heated and the tests will be done at room temperature, usually around 20 C. The experiment will be done twice or three times if possible and the results will be made fair by the fact that only one thing will vary each time. Goggles and aprons will be worn at all times for safety. It has been decided that 5ml of HCl and 20ml of Na S O will be used. Obtaining Evidence These are the results of the experiments: Temperature 1st results 2nd results Average Rate Of Reaction C seconds seconds seconds secs Room approx.20 74.5 69.9 72.2 13.85 30 38.1 38.3 38.2 26.18 40 35.9 39.4 37.65 26.56 50 20.7 18.1 19.4 51.55 60 12.3 9.9 11.1 90.09 70 5.9 5.2 5.55 180.18 Concentration 1st results 2nd results Average Rate Of Reaction g/dm seconds seconds seconds secs 15 125.2 123.5 124.35 8.04 20 74.5 69.9 44.2 13.85 25 53.6 51.2 52.4 19.08 30 49.6 51.6 50.6 19.76 35 45.7 48.8 47.25 21.16 40 22.6 30.5 26.55 44.35 Analysing evidence and drawing conclusions All results have now been obtained and they seem to be quite good, all showing correlation. As was hoped at the start, a repeat was managed for each test and an average worked out from those figures. The results were recorded with decimal place and the averages and rate of reactions are to two decimal places. The rate of reaction is the key thing being looked at in this experiment and this is how it was calculated: 1 Time taken for cross to be obscured This figure was then multiplied by 1000 to make it easier to deal with. The figures have all been rounded to two decimal places. My predictions have been correct. When the concentration of the sodium thiosulphate has gone up, as the first part of the experiment shows, the rate of reaction goes up. When the temperature goes up, as the second results table shows, so does the rate of reaction. This is what was expected and therefore makes it highly unlikely that there have been any major mistakes, although all results are obviously not perfect. The next three pages are graphs. Graphs one and two relate to the first table of results and graph three relates to the second table. The reason there are two graphs for the first table is that one shows time taken for cross to be obscured and the other shows rate of reaction. Rate of reaction is what is being investigated and so only a rate of reaction graph was needed for table two. There are two graphs for the first results table to show the difference in time taken and rate of reaction i.e. the time taken for cross to be obscured shows negative correlation while graph two shows positive correlation. By drawing a line of best fit on the rate of reaction graphs, we can see that there are no results that are obviously completely wrong. With both graphs the last result is suprisingly high, and this can be seen on the results table as well. Evaluating Evidence The procedure used was good and produced good results but it could have been improved and these will be listed later. The results are mainly good, there are no odd results and everything came out as expected. This could mean that the experiment was done perfectly but it doesn't. Although all the average times and rates of reaction all conform to a pattern, they are not all evenly spaced and therefore are probably not perfect. As an example, in the first experiment, where the temperature was being varied, the rates of reaction of 30 C and 40 C were 26.18secs and 26.56secs respectively. This was only an increase of 0.38secs compared to an increase of 90.09secs for 60 C to 70 C from 90.09secs to 180.18secs . Clearly this is an enormous difference and disproportionate. The results could be correct but the results do appear to nearly double each time, except for in this instance. There are similar examples from the second experiment but they are not as obvious. Improvements that could be made if the experiment was repeated: When doing the results that took less time some took around five seconds, it would have been more accurate to have two people so one person could put the substances together while the other person started timing Obviously it would have been good to have done more repeats. Two tests were managed each time but if one had been wrong this could have dramatically changed the average time and therefore rate of reaction. Increasing the surface area of a reactant will increase the rate of a reaction. This is because the reacting particles can only collide with he surface of the solid and the particles within the solid cannot react until those on the surface have reacted and moved away. Powdered calcium carbonate has a much larger surface are than the same mass of marble chips and therefore will react more quickly. All in all I think this was a good experiment and the best that could have been done with the time and resources available. The results supported my predictions and they seem to be fairly reliable results. Aim : We did 4 experiments to find out how the rate of reaction changes with differing concentrations of Sodium Thiosulphate, Hydrochloric Acid and water. As an inert and stable liquid, water was used to alter concentration of Sodium Thiosulphate without changing the end amount of solution. All the atoms in a water molecule have a full outer shell, so they would not react with the other chemicals. WATER IS USED TO SLOW THE REACTION SO THAT IT IS EASIER TO TIME HOW LOG
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I am measuring the rate of reaction how fast a reaction takes of sodium thiosulphate and hydrochloric acid. There are different variables I could use to see the change in the rate of reaction. These include temperature, concentration or catalysts. I am going to do two experiments, one changing the temperature and one changing the concentration of the sodium thiosulphate. This is how they will be done. Planning Experimental Procedures Equipment Sodium thiosulphate Na S O of different concentrations Hydrochloric acid HCl Tile marked with a cross Measuring cylinder x2 Beaker...
supported my predictions and they seem to be fairly reliable results.

Aim : We did 4 experiments to find out how the rate of reaction changes with differing concentrations of Sodium Thiosulphate, Hydrochloric Acid and water. As an inert and stable liquid, water was used to alter concentration of Sodium Thiosulphate without changing the end amount of solution. All the atoms in a water molecule have a full outer shell, so they would not react with the other chemicals.

WATER IS USED TO SLOW THE REACTION SO THAT IT IS EASIER TO TIME HOW LOG

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Prediction I predict that the...Prediction I predict that the lower the concentration of the hydrochloric acid so there is fewer particles per cm3, the slower the rate of reaction will be. This is because there will be fewer particles in the Hydrochloric acid per cm3, and the solution will be more dilute so less successful collisions will be made due to fewer particles to react with each other. So I think if the Hydrochloric acid is very strong with no water to dilute the substance the cross on the paper will disappear the quickest as I think the most amount of sulpher will be created in the reaction. I think this will happen because there are more of the hydrochloric acids particles per cm3 so the chance of a successful reaction with a hydrochloric particle and a sodium thiosulfate particle is higher so the rate of reaction is faster which causes more sulphur to be given off. But if less reactions take place the rate of reaction will be slower so I think less sulphur will be given off because of this. Here is a Picture showing what I think will happen in a high concentration of sodium thiosulfate and also in a lower concentration. This is called the collision theory. I found these diagrams when I researched about rates of reaction I think reactions will happen faster due to the collision theory. This is where if two particles collide with each other with enough force a reaction takes place. So if there is more of the Hydrochloric acid more reactions take place as the chances of a head on collision which causes a reaction to take place is greater as there is more Hydrochloric acid per cm3 I also think that the reaction will happen in direct proportion. So if the amount of Hydrochloric acid is halved the amount of reactions will also half. I don't have any research to back this up but I think this will happen as it is logical. I also think this will happen because if the amount of Hydrochloric acid is doubled there is going to be double more Hydrochloric acid particles than what was in the solution before so in theory the time it takes for the cross to disappear should be halved and happen double as quick as the time before Here is a prediction graph of what I think is going to happen Method I am going to investigate how different concentrations of Hydrochloric acid and water affect the rate of reaction. As I have chosen to use different concentrations I am going to vary the amount of Hydrochloric acid in the solution. But to keep it a fair test and for the experiment to work I must keep the total volume the same. I am going to have the total volume 40 cm3. To make the experiment a fair test I will always have 20 cm3 of sodium thiosulfate. But I must always have 40 cm3 in the solution so if I have the Hydrochloric acid quite dilute at 10 cm3 I must have 10 cm3 of water to keep the experiment fair to make the total volume all the same. To also keep it a fair test I will also have to keep other variables the same. This is the temperature. To keep this fair I will do the experiment all in one room so there is no difference in temperature and away from windows so the sun can not affect my experiment. This along with always keeping the volume the same will make my experiment a fair test. In my experiment I am going to see how long it takes for different solutions of Hydrochloric acid to produce enough sulphur until a cross on a piece of paper disappears. I will explain how this works now. What I will be doing First of all I will get all of my apparatus which is listed below. I will then set up my experiment. To start this I will put a piece of paper with a thick cross done in pen underneath a beaker. This is what will tell me what the rate of reaction is like. Because if the cross disappears quickly the rate of reaction is high and lots of sulphur is given off because of this as more particles are reacting quicker. But if the rate of reaction is slower it will take longer for the sulphur to cover the cross so it could not be seen. This would mean less reactions were taking place and slower because not as much sulphur is being formed. So that is what I will use the cross for. I am going to keep the level of sodium thiosulfate the same in my experiment and every time at 20 cm3. So in a small measuring cylinder so I can measure the amount more accurately I will use a pippet and measure 20 cm3 into the measuring cylinder. I will then pour this amount into the beaker. After this in a new measuring cylinder so I don't get the two substances contaminated I will measure out the first amount of the hydrochloric acid which I will be using. I will be using the following amounts watercm3 hydrochloric acidcm3 0 20 5 15 All add up to 20cm3 10 10 15 5 17 3* *The last set I had to change as if I had it all water a reaction could not have taken place which was just realized because there would be no particles from hydrochloric acid to react and to cause a reaction. So if I was using 15 cm3 of hydrochloric acid I would measure this amount into a measuring cylinder using a pippet. I would also need 5 cm3 to make the whole solution up to 20 cm3. After adding the 5cm3 of water into the same measuring cylinder I would then add this is to the beaker with the sodium thiosulfate in. Once this is poured in I will use a stopwatch and wait, without stirring or touching the beaker or the solution. I will time how long it takes for the sulpher to fully make the cross on the piece of paper disappear. I will then stop the stopwatch when the cross has disappeared and write down the results in a table. I will then repeat the same procedure with different amounts of hydrochloric acid and water which are shown above. But on each of the different amounts 20cm3 of sodium thiosulfate will always be used. This will make every concentration I try 40cm3. This will help to make it a fair test. I am going to repeat each amount of hydrochloric acid and water 3 times. This will help make my experiment a fair test as I can then take averages and taken 3 results will show any abnormities which I could then repeat ,to try and get a better set of results. In the results table I will have to convert the times into seconds so I can work out averages. Here is a picture of the apparatus set up:- List of equipment Measuring cylinders Pippet Stop watch Beaker Paper cross Hydrochloric acid Sodium thiosulfate Water After finding all of my results for each concentration and making averages I could do a calculation to find the rate of reaction. . This calculation would give me the rate of reaction, which is measured in how many reactions there are per second as the more collisions of particles per second the faster the reaction will be and so the higher the number. To find this out I will first need to take averages from each concentration. After this I would take this number and divide it by 1. This will give me a very small number but will probably come up on my calculator with like 8.8454 with -03 at the top at the end of the number. I would have to change this to standard form. This would be done by moving the decimal place backwards 3 places as it is negative and replacing the digits behind with zeros. So the number would become 0.0088 Here is a example:- say a average is 127 seconds for the cross to disappear. So 1 divided by 127 is 7.8740 -03 so moving the decimal point back 3 spaces the number would become 0.0078. This would be the rate of reaction Water Hydrochloric Acid cm3 Sodium Thiosulphate cm3 Volume cm3 Seconds Time 1 Time 2 Time 3 avr RoR 0 20 20 40 115 113 109 112 0.0089 5 15 20 40 123 125 118 122 0.0082 10 10 20 40 138 135 137 137 0.0073 15 5 20 40 157 161 163-152* 157 0.0064 17 3 20 40 210 218 200 209 0.0048 results * With this result I think I had a abnormity so I decided to retake that result and I came out with 152 seconds which was more like what I had been looking for. I used this result to work out the average. Analysis From my results I have drawn 2 graphs from the results I have collated. In the first graph it shows the rate of reaction and also the concentrations of hydrochloric acid and water. The graph shows that at fully concentrated hydrochloric acid with no water the rate of reaction which happens with the amount of reactions per second that the most happen with 0.0089. At a quite strong concentration of 15 cm3 hydrochloric acid and 5 cm3 water the rate of reaction was also quite high but not as high as the highest concentration. This amount was 0.0082. From this amount it goes down to 0.0073 at a concentration of 10 cm3 acid and 10cm3 water. The next point is then at 0.0064 at 5 cm3 acid and 15 cm3 water. These 4 points go in a very steady line which is quite steep. This shows that the part in my prediction where I said I thought the results would go down in direct proportion is right. But after the 4th point the line on the graph gets even steeper going downwards. I think this is because we made a mistake with what concentrations to use so we used 3cm3 acid and 17 cm3 water so the concentration was a lot weaker than the others. I believe if we had started at 25cm3 hydrochloric acid and nothing of water and then 20cm3 acid and 5cm3 water all of the results would have continued the steady quite steep directly proportional line. ON this graph it also shows that as the concentration decreases of hydrochloric acid the rate of reaction in the solution falls. This is shown from the highest concentration of hydrochloric acid where the rate of reaction of successful collisions in one second was a high value of 0.0089 and at the lowest concentration it was 0.0048 showing the difference in the amount of successful collisions. On the second graph it shows how the change in concentration affects how long it took for the sulphur produced from the experiment to cover the cross so it could no longer be seen. The averages f the concentrations shows a gradual curved line starting at the lowest time for the cross to disappear at the highest concentration which took 113 seconds to the longest time at 210 seconds at the weakest concentration of acid. The graph goes up in a curve from the highest concentration to the weakest concentration. This shows that as the concentration of the hydrochloric acid increases the time it takes for the cross to disappear decreases. I think that it takes less time in higher concentrations for the sulphur to make the cross disappear and the rate of reaction goes up is because of the amounts of particles in the hydrochloric acid. I think that the rate of reaction is higher in the more concentration solutions because there are more hydrochloric acid particles in the solution per cubic centimetre. This means there is a higher chance of those particles colliding with a sodium thiosulphate particle and there being a successful collision because there are more of them. This is backed up with scientific research which I took from a chemistry book "The more concentrated acid has more acid particles per cubic centimetre so these particles will collide with the substance more often causing a reaction to take place if the collision is strong enough" This and my graphs back this up and also what I said in my prediction. I also think more sulphur is produced quicker with higher concentrations because of the collision theory. Because there are more successful reactions per second in higher concentrations due to increased hydrochloric acid particles per cm3 so more sulphur is produced as a waste gas after the reactions take place. So if there are more reactions per second the sulphur is given off more quickly due to this. This is why the sulphur makes the cross disappear more quickly with higher concentrations of acid and why there are more reactions per second with higher concentrations of acid. Here is a equation for the reaction:- HCl + sodium thiosulfate sodium chloride + sulfur dioxide + sulfur + water HClaq + Na2S2O3aq NaClaq + SO2g + Ss + H2Ol This reaction shows the hydrochloric acid and sodium thiosulfate reacting together to produce the other products of sodium chloride + sulfur dioxide + sulfur + water. This is where the sulphur comes from. Evaluation I think my experiment went well and there were good points to it and also bad points. The good points "“ I think I did well to keep all the variables the same except for the concentration, but only on the first day of the experiment. I managed to not let temperature affect the investigation by doing it in the centre of the room to avoid the sunlight. I also kept the beaker absolutely still whilst doing the experiment so I did not affect any other variables. I also think I did well when measuring amounts. For the lower concentrations I used small measuring cylinders so I could be more accurate on how much of the substance was in it. This was also useful when measuring the amount of water. Apart from these good things I feel the experiment could be done a lot better. The first major problem with how I did this experiment was that even though I kept all the other variables the same I took some results on a different day which unsettled my results. The first two results of each concentration were taken on the first day of the experiment and I was getting balanced results with 115 seconds and 113 seconds for the biggest concentration of the acid. But on the third attempt on the same concentration done on another day the time for the cross to disappear was less with 109 seconds. This was the same for all the results I took on the 2nd experiment day. I think the temperature affected the results and it was hotter on the 2nd day to speed up the reaction and act as a catalyst. I could not help this but if I did the experiment again I would try to get it all done on one day so different temperatures on different days could not affect the experiment. If I took all the results on one day it would make the experiment a lot fairer as natural weather effects over different days could not affect my experiment if it was all done on one day. But even with doing the experiment over two days my results kept mostly within 10% with each other. I worked this out by taking the biggest difference over three values of a given concentration and dividing the difference from the biggest and the smallest, so if I had 3 results of 123,127 and 125 the biggest difference is 4. This is then divided by the biggest number which is 127 and multiplied by 100 to turn it into a percentage. So the calculation would be 4/127 multiplied by 100 I don't think I had some within 10% of each other because the experiment was carried out on two different days. I think if the test had been carried out all on one day the results would be a lot more accurate. Another bad thing I thought about the experiment was having to use the naked eye to tell when the cross had fully disappeared. Sometimes I could not tell if the cross had fully disappeared as I could see little glimpses of it. This could affect timings by considerable amounts as I never really new when the cross had fully disappeared. I think this was a major problem with the experiment and how it was carried out. Another thing that added to this problem was that I used two different crosses on the different days, again showing how it should really be carried out on just one day to make it a fair test. If I was to do the experiment again with the same method I would make sure to use just one cross and stick to it. But I think there is another method available if I was to do this experiment again. I could use a realistic computer simulation. On this program it would allow me to change many variables mainly concentration and temperature. Either can be easily adjusted and is very simple to use. I think this would be a very good idea because it would completely be a fair test and no variables other than the one you want can affect it as it is a simulation. On the screen the variable can be changed and on the screen it shows how many reactions there have been. The data given after the experiment has been completed can then be easily put onto graphs and analysed. I think this would be a much better method as it would get rid of the slightly inaccurate method of seeing how long it takes for the sulphur to completely cover the cross. With the simulation it would get rid of all these hassles and I think the results would be a lot more accurate because all the other variables can be kept exactly the same as it is a simulation on the computer. Overall I think the experiment went quite well but the problems with doing the experiment on different days and using different crosses didn't make the experiment that viable or that fair. But even with these problems my results were quite accurate and reliable but I feel could have been made better by preferably using a computer simulation which would be very reliable and accurate   

Prediction I predict that the lower the concentration of the hydrochloric acid so there is fewer particles per cm3, the slower the rate of reaction will be. This is because there will be fewer particles in the Hydrochloric acid per cm3, and the solution will be more dilute so...

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HYPOTHESIS We can recognize four... HYPOTHESIS We can recognize four types of substances due to their structure: ionic, metallic, covalent, and molecular. If a given substance has a metallic luster, is malleable and ductile, is a good conductor of heat and electricity, and has high melting and boiling points, than it is supposed to be a giant metallic structure. If a given substance has low melting and boiling points and does not conduct electricity, it surely is a molecular structure. If a given substance is soluble in water and in other polar solvents, if it conducts electricity after being melted or dissolved, and if it has high melting and boiling points, we can predict that it is a giant ionic structure. So we will have to check which of these properties does a given substance have. APARATUS spatula stirring rod open electric circuit batteries, light bulb, electric wire with two dismantled endings two metal plates the first made of copper, the second made of zinc plastic wash bottle test tubes in amount of 4 watch glasses in amount of 5 Bunsen burner test-tube rack porcelain crucible crucible tongs triangle tripod I decided to use separate watch glass for each substance to avoid possible laboratory errors resulting from contamination with the previous one. CHEMICALS substance A "“ white, granulated powder substance E "“ silver nodules, apparent metallic luster substance C "“ tiny, white crystals substance D "“ a bit larger white crystals substance B "“ black powder distilled water SAFETY RULES Be careful while burning substances in a flame! Don't put your hand into water when the electric current flows "“ you can have your skin seriously damaged! Do not touch hot crucible with bare hand, use crucible tongs! PROCEDURE I put a few grams of each substance except for substance E, which I put into a watch glass using a spatula into separate test tubes, placed in a test tube rack. I put a hint of each substance into separate watch glass. I use open electric circuit in order to investigate electric conductivity of each substance in solid state. I pour a few droplets of water into each watch glass using plastic wash bottle. Then I mix each substance with a stirring rod in order to make process of dissolving faster and more effective. I put two metal plates into each watch glass, so they are partly sunk in the water or solution, if it was formed in the manner one ending of the electric wire sticks to the first plate, and the second ending sticks to the second plate, and it is important that plates do not touch each other. Then I observe whether the light bulb is shining. I take a hint of each substance one by one, using a spatula. I put each substance into a porcelain crucible. I put crucible on a triangle placed on a tripod above the Bunsen burner. Then I turn the burner on and wait up to a minute in order to check whether the melting point is low or high. To handle the crucible I use crucible tongs. Note: I carefully clean spatula before using it again and again, I do the same with the stirring rod and porcelain crucible. DATA COLLECTION A B C D E Conductivity in solid state - + - - + Conductivity after being dissolved - - + - - Solubility in water + - + - - Melting point low high high high high CONCLUSION Substance A is soft and granulated. This substance has low melting point, what indicates that the intermolecular forces are weak. It does not conduct electricity, because molecules are not charged. So substance A has undoubtedly molecular covalent structure. However, on contrary to other substances with molecular covalent structure, it is quite soluble in water, what means that its' molecules can form hydrogen bonds to the water to compensate for the water-water hydrogen bonds broken. Example of such molecules are sugar molecules, so this substance is probably sucrose. In the case of the substance E there is an apparent metallic luster, so it has the giant metallic structure. This metal has high melting point, because it takes a lot of energy to break up a lattice of ions in a sea of electrons with strong forces of attraction, called metallic bonds, between them. Metals are good conductors of electricity because the delocalized, free electrons can move through the lattice carrying charge, when a voltage is applied across the metal structure. The substance C is the only substance aqua solution of which conducts electricity, so it has to have giant ionic structure. It's because the water molecules, which are dipoles, can attract the ions away from the lattice. The ions move freely, surrounded by water molecules. Dissolved or melted ionic compound conducts electricity, because the lattice breaks up and the ions are free to move as charged particles. It can be assumed that substance D is a giant covalent structure, because it is insoluble, it is very hard, but brittle, it forms crystal lattice, and it has high melting point. In addition, this substance does not conduct electricity at all. Substance B is soft and brittle in touch - the sheets can slide over each other easily. It may indicate that this substance has a molecular structure, like the first one. But it has much higher melting point than molecular substances. Besides that, it conducts electricity in solid state, and it does not dissolve in water. This set of properties is very specific "“ it is a combination of single properties of different types of structures. The fact that this substance could well be used as a lubricant layers are easily rubbed off could indicate that this substance can be graphite. EVALUATION After an experiment was finished, our chemistry teacher wrote the names of substances that we were to determine structures of, on the blackboard, so we could verify if our findings were correct and propose improvements to the method in case they were not. And so: substance A appeared to be glucose, substance B "“ graphite, substance C "“ sodium chloride, substance D "“ silicon dioxide, and substance E "“ chromium metal. My predictions according to substance A appeared to be correct. In case of substance E, which is chromium metal, I also obtained correct results. I think that this substance, like it is in case of all metallic substances, has a structure very easy to determine experimentally, even, to say, with bare eye, because we know that metals are the only type of substances that perform a property called metallic luster. Other properties I observed also form a set of properties typical for metal, which is chromium in this case. I was right in case of substance C, which, as it appeared later, is sodium chloride, and sodium chloride is the most characteristic representative of ionic substances. My assumptions relating to substance D are also proved to be correct, since I know now that this substance was silicon dioxide, commonly occurring as quartz, being a good exemplification of properties connected with a giant covalent structure. In case of substance B, I was again right, due to the fact that this substance appeared to be graphite, as I have predicted. Graphite is another example of giant covalent structure, but, on contrary to silicon dioxide, it conducts electricity "“ this property is specific only for this particular substance.   

HYPOTHESIS We can recognize four types of substances due to their structure: ionic, metallic, covalent, and molecular. If a given substance has a metallic luster, is malleable and ductile, is a good conductor of heat and electricity, and has high melting and boiling points, than it is supposed to...

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