Essay on Viscosity and Glass Slide

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Why do some liquids flow more freely than others?

The Hypothesis is that:
Liquids containing long or large molecules are more viscous (i.e. they do not flow so freely)
Prediction:
I think that some liquids flow more freely than others depending on a number of factors. I think that one of the major factors, which may affect viscosity of alcohols, is their hydrocarbon chain length. I believe that as the chain length increases then the viscosity will also increase.
Introduction:
The aim of this coursework is to investigate whether the hypothesis stated is correct or not. I will be investigating if long or larger molecules of liquid are more viscous. I will be checking if the liquid is denser or not. This would be due to the reluctance of the fluid.
Viscosity is due to the reluctance of a fluid (liquids or gas) to flow. A viscous fluid will be resistant to flow. Viscous means the flow of a liquid or gas or in simpler terms, viscous means thicker. Therefore the more viscous the liquid, the slower it runs down a slope. Viscosity is measured in milli-pascals seconds (mPas). Viscosity of a fluid is related to its density. There are many factors that affect viscosity of a fluid, such as chain lengths and temperatures. A shorter chain length would mean that the liquid would have low viscosity, therefore they would flow more freely. They also would have low attractive forces, which mean the bonds are less attracted and move freely. A long chain length would have a high attractive force hence the bonds would interact stronger and the molecules are held more tightly together. Furthermore, chains would be tangled together leading to having a high viscosity and being denser. The liquid would have a thicker consistency. If the liquid were at a low temperature, then the molecules would be tightly packed also the forces of attraction are intact. It would also have a high density and a high viscosity. However, if it had high temperature the molecules would be widely spread and the forces of attraction would be broken. Thus it would have low density and low viscosity.

There are three different methods were utilized to investigate viscosity.
Slide method: In this method, a drop or two were placed onto a glass slide. The fluid would go down the glass slide, and the time it takes to travel down the glass slide is recorded.
Ball method: In this method the use of cylinders were made. Each cylinder would contain a liquid in them. Then a ball is dropped in the cylinder and the time it takes for the ball to reach the bottom is what is being measured.
Capillary method: In this method a liquid is within a straw and is timed how long it takes for the liquid slide back down.
This times measured in the different methods can be used to calculate speed and give an indication of viscosity.
Method
Pros
Cons
Things to be aware of next time
Slide
Easy to use and observe. Accurate readings.
Correct angle
(Surface tension)
Correct angle each time. Repeats. Separate slides.
Ball
Good for an estimation of viscosity.
Liquids need to be colorless.
Same volumes, cylinders. Need to have colorless liquids.
Capillary
Quick method to estimate.
Difficult to get an accurate recording.
Need to make apparatus more accurate.

Looking at the table, the slide method was chosen. The slide method is a simple task to perform and is accurate, and more reliable than the other methods stated. However the Ball method is good for estimation and so is the Capillary method. Having accurate results makes the test more reliable. The advantages of the Slide Method over the other methods are that it is easy to use and to observe. However to get the correct angle all the time can be problematic since the slide would have to be removed to be cleansed. However the Ball method would require colorless liquids to see the ball go down, and have the same volumes and cylinder. In the Capillary method it would be hard to get an accurate recording
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