Two Factors Affect The Viscosity Of Magma

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Magma is molten material beneath or within the earth’s crust, from which igneous rock is formed. Magma can only be in places that are hot enough to melt rocks. When magma is formed it rises to the surface through the earth’s crust. When magma reaches the earth’s surface it is known as lava.

It can erupt on the earth’s surface, either on land or under the ocean, by a volcano or through a fissure. It solidifies into igneous rock that is also called lava. Before reaching the earth’s surface, the mixture of solid and liquid rock, and gases, is known as magma. Lava is composed chiefly of silica and the oxides of aluminium, iron, magnesium, calcium, sodium, and potassium.There are two types of magma granitic magma and basaltic magma.

Both of these types of magma contain SiO2 (sulphur dioxide). Granitic magma is very thick and contains 70% Sulphur Dioxide it has a temperature of about 750((. Basaltic magma is runny and contains 45% Sulphur Dioxide it has a temperature of 1100((. The more SiO2 bonds the stronger the magma is, also meaning it is thicker.My Experiment is on the viscosity of magma and how you would measure it. Factors that could affect the viscosity of magma are Temperature and composition. Composition because magma contains a certain amount of water and temperature because this will tell me how runny the magma is at different temperatures.

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The technical definition of Viscosity is; the property of resting alternation in position of its parts relative to each other, which simply means how runny a substance is. This is what I will be trying to find out and the substance is magma.Pre-TestsIn my experiment I unfortunately wont be able to use real magma as it is at such high temperatures, it would expensive and inconvenient to get hold of and is also toxic. So instead of Magma I will be using a substance called glycerol. I have looked into different substances and their advantages and disadvantages. I knew it had to be something that was still liquid in a freezer it also had to be a substance that can be diluted easily. I have looked into using syrup and decided it was a bad idea because it gets very messy and sticky when hot and is also tempting to eat. I also looked into using thick engine oil but this wasn’t very good either as you can only dilute it in white spirit, which could become dangerous and expensive. I have decided on Glycerol because it is cheap dissolves in water, it isn’t poisonous and has similar properties to magma.With the substance and the factors that could affect the viscosity of glycerol I had to find the easiest way to test them. Temperature I can vary by heating the glycerol and composition I can mix the glycerol with water I then had to find out what the affect of these factors was on the glycerol. I looked into a couple of ways to test the affect of temperature and composition. The first one I came up with was to dribble the glycerol along a set-up of gutters and time to see how long it takes to travel down the gutters and fill up a certain amount of the pot at the bottom. This is a diagram of how that experiment was set up:Through research I have discovered lots of problems with this method like by the time the glycerol has travelled along the gutter it will have cooled down, it is messy, it is hard to pour at a constant speed. The other method I came up with was to fill a measuring cylinder with glycerol then drop a marble in the top and time to see how long it takes to reach the bottom. There are also problems involved in this method like it is also messy, you have to make sure you use all of the same equipment, it is tricky to get the marble out, once it is at the bottom of the tube.MethodI have looked at my results from my pre tests and this method seems to be safe, easy and not too time consuming.Below is diagram of how I set up my equipment used to do my experiment. When I choose temperature as the variable I kept the volume of glycerol the same. I had to be very careful to make sure I used the exact same measuring cylinder, marble and stop watch. These are all things that needed to be taken into account if I want to make my experiment fair. The volume of glycerol used was 25cm(. To make sure I used the same equipment each time I labelled my measuring cylinder put the marble in it and pushed tissue in the top of it.I had to heat the glycerol to get it to the desired temperatures I did this using a water bath. My starting temperature was 20(C and rising by 10 each time. My maximum temperature was 70(C. Once the glycerol was at the desired temperature, I put 25cm( of it into my measuring cylinder and dropped my marble in the top of it timing it to see how long it took to reach the bottom. I repeated the experiment three times to make it a fair test.The second experiment was on composition this was a lot harder to carry out. I used the exact same equipment that I used for temperature. In this experiment composition is the variable and I kept the temperature constant at room temp. I used 25cm( of diluted glycerol. I diluted the glycerol by using the ratio 24glycerol: 1water, 23glycerol: 2water.I used the same method for this experiment as I did for temperature, for each of the ratio’s I repeated the experiment three times for each mix of glycerol and water. This helped to make sure that my results were reliable and fair.PredictionIn my experiment I had to use glycerol instead of magma but there are things that can be related to each one like that the more viscous a substance is the thicker it is. There are two factors that affect the viscosity of glycerol, which means there are probably two factors that affect the viscosity of magma. The higher the temperature of the glycerol the less viscous it is. Granitic magma is hotter than basaltic so it is likely that it basaltic will be thicker. The same kind of theory can be used for composition the greater the amount of water present the less viscous it is. There is a lot of water present in magma and so the same will happen the more water the less viscous.SafetyAlthough I have decided to use glycerol instead of magma there are still lab safety precautions that have to be followed.* Lab coats musty be worn at all times* Ties should be taken off* Long hair should be tied back* Safety goggles must worn at all times* We will be dealing with some high temperatures so caution must be taken when heating or carrying the glycerol* Bags should be kept out of the way* You shouldn’t sit down at any time throughout the experimentTable to show results for temperatureTemp((C)Time (seconds)123average20113112112112304947477484032303231502523252360131113127013111112Table to show results of compositionRatio of glycerol two waterTime (seconds)123Average24:13132333223:22931303022:32829272820:51110111115:10333310:1511110:250.90.70.80.8AnalysisMy graphs seem to back up my theory that as the temperature was increased the time it took for the marble to travel to the bottom of the tube reduced. In the second graph, which shows the results from the composition experiment, from this I can see that my prediction that as the amount of water added to the glycerol increased the time taken for the marble to travel to the bottom of the tube reduced. This proves that two factors that effect magma are temperature and composition.There were two experiments carried out so I will analyse each of them individually in the following paragraphs.The first experiment I carried out was on the effects of temperature on the viscosity of magma. It is obvious that the temperature has an affect on the viscosity of the glycerol. The reason for the loss in thickness is because as the temperature increases the kinetic energy of the molecules in the glycerol increased so their bonds weakened and broke there for the glycerol became less viscous. This would also happen in magma, as there are strong Si-O bonds, which as the temperature increased so would their kinetic energy and so weakening their bonds these are the bonds, which made the magma so thick.The second experiment I carried out was to test the effect of composition on the viscosity of magma. My results show that as the concentration of water in the glycerol increased the time taken for the marble to pass through the glycerol to the bottom of the tube increased as well. The glycerol became runnier because the more water bonds there are present the weaker the bonds between glycerol molecules become. This is also what would happen in magma as the water bonds would weaken the Si-O bonds in the magma and so making it runnier.By looking at my results and background work I have realised that, Basaltic magma is hotter so will be runnier than granitic magma because the kinetic energy in basaltic magma is higher so it has weaker bonds. With the composition basaltic magma has alt more water in it than granitic and so the Si-O bonds are weaker. From this I can predict that basaltic magma is more viscous and is runnier.EvaluationThe results I received backed up my prediction and I feel were very reliable. Although these results were good it would have been nearly impossible to get perfect results with the equipment we used. There are also two other main sources of error these are human error. When measuring out the ratios in the composition experiment I could of made some mistakes and not quite got the concentration correct. Another chance for human error would have been starting and stopping the stopwatch when the marble was dropped into the measuring cylinder and hit the bottom. It would have been impossible to get this exactly right unless we could use really high tech equipment, which could have been very expensive. The other type of possible error was to do with equipment.There was a lack of glycerol so for the composition experiment I had to use the glycerol from the temperature experiment this could have been a source of error. When heating the glycerol we had do it in a water bath which wasn’t very accurate as once it was at the right temperature I had to carry it back over to my desk were I was working, by this time it was already starting to cool down. The last source of error I could easily recognise was that the marble and the measuring cylinder was a very tight fit and I think the marble sometimes got stuck on the edge of the tube. Other than these possible causes of error I feel the experiment went ahead very smoothly without any injuries or major problems.