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Applied Science BTEC: Unit 2 - Aim B
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This is my coursework in Applied science unit 2 learning aim B. I received a Distinction for this coursework. Hope it helps!
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Unit 2: Practical Scientific Procedures and TechniquesKeeping up the standards
Learning Aim B: Undertake colorimetry to study cooling curves
Introduction
In this report I am going to be looking at distinct types of thermometers like analogue (liquid)
and digital, and how they are used to gain accurate readings. I will check the calibration of
thermometers by using ice and boiling water. I will also be focusing on how to construct and
interpret cooling curves using data from my practical's: cooling of paraffin wax and cooling
of stearic acid. I will also give a thorough method for my practical's and make an equipment
list; I will also add a risk assessment and write what improvements I should make to my
practical so that it becomes more accurate and reliable. I will also be looking at the theory
behind thermometers.
Types of thermometers
Thermometers are tools to measure temperature, how hot or cold something is, thermometers
can be measured in degree Celsius (°C), Fahrenheit (F) or Kelvin (K). There are various types
of thermometers such as mercury thermometers, alcohol thermometers, infra-red
thermometers, probe thermometer and so on; all are divided into 2 categories, liquid or
analogue and digital or electric. Although inaccurate the first ever liquid thermometer
produced was in 1654, after this more people were invested in it till it eventually in 1709
became accurate and had gotten a scale, and they are like the ones we use today. Digital
thermometers were first created in 1867, so more than a whole century had passed from when
liquid thermometers were accurately created.
Liquid thermometers are a thin glass capillary tube which contains a type of liquid such as
mercury or alcohol, the way it works is that the bulb contains a large volume of the liquid,
and it expands (moves up) with the increase of temperature. This means that the thermometer
expands linearly with the temperature, there is also a scale on the side of the thermometer to
measure the temperature by how far up the liquid goes. A liquid thermometer takes time to
give the reading – however it may not be accurate as liquid thermometers will need to be read
by someone at eye level as the liquid will reach a certain line on the scale, factors which
could affect the way someone would read the thermometer are: poor eye sight, not reading it
at eye level as reading it from a different angle will show different results – to tackle this
problem and get a more accurate result you would take 3 readings and each time you would
read the thermometer at eye level then take the 3 readings and calculate the mean. For liquid
thermometers most of them contain alcohol-based liquid like ethanol and this is because
mercury is toxic. Mercury is safe within the thermometer however if the thermometer breaks
and the glass shatters the poisonous liquid will be exposed – this is a hazard, therefore the
alcohol thermometer is safer. Also, the alcohol thermometer has a lower freezing point than
mercury (it is –114°C whilst mercury is –40°C), so alcohol thermometers can be used to
measure lower temperatures.
Digital or thermometers come in different forms - they’re not all the same as they all have
different uses, like for example infra-red thermometers are mainly used to measure
temperature from a distance, so it is more commonly used in an industrial environment, and
, Unit 2: Practical Scientific Procedures and Techniques
probe thermometers are used to measure internal food temperatures. But all digital
thermometers require batteries which need to be changed periodically. How a digital
thermometer works is that by using heat sensors it figures out the temperature but an
electronic thermometer works a bit differently as it has a metal probe it will put a voltage
across the probe and that will measure how much current is running through it and there is a
microchip within the electronic thermometer and this will measure the resistance and convert
it into temperature measurements, a feature all digital thermometers have is that the reading is
displayed on a digital screen. As digital thermometers were made after liquid thermometers,
we could say that it is more modern and because it is more modern it is also more accurate,
the reason for this is that it displays the reading on a digital screen. Unlike the liquid
thermometer, a person will not need to read where the liquid has expanded to at eye level to
get the reading, by doing that it could result in inaccurate results because of the different
factors listed above in the second paragraph. Digital thermometers take away this inaccuracy
by allowing the reading to be read on the digital screen, it also gives faster results than liquid
thermometers and is safer as well. Although, a limitation is that it usually fluctuates a lot so
you may not get an exact result, when the battery is low the results would be inaccurate, but
we would not know when the battery needs replacing which makes it harder to know whether
our result is accurate or not. This is the reason we calibrate the thermometers by using ice and
boiling water.
Relationship between heat and temperature
But before going into calibration and cooling curves we first need to understand the
relationship between heat and temperature. Temperature is measured in degree Celsius (°C)
and Fahrenheit (F) whilst heat is measured in joules (J). Heat is thermal energy which is
transferred between systems (solid, liquid or gas) with different temperatures, like for
example from a high temperature system to a cooler temperature system. Temperature is the
measure of kinetic energy of the atoms in a system (solid, liquid or gas), this basically means
that temperature measures how much kinetic energy is in the system or object - if the atoms
in the system or object are vibrating fast (this is kinetic energy) this means that the system or
object has a high temperature, this could also cause a change in state - to a solid or a liquid.
Heat is an extensive property this means that heat depends on the amount of atoms that is
present. However, unlike heat, temperature is an intensive property which means that
temperature does not depend on the amount of substance that is present. This means that
temperature stays the same even when there is a change in size or amount of the substance.
Cooling curves
A cooling curve is a line graph that shows the changes in states. The independent variable is
the X-axis which is the time measured in seconds. The dependant variable is the Y-axis and
that is the temperature measure in degree Celsius.
I will be using a cooling curve to show my results of stearic acid and paraffin wax.
Calibration of thermometers
The reason we calibrate thermometers is so that we can make sure our thermometer is
accurate, to find this out we will let our thermometer measure the temperatures of substances
we know this will be crushed ice which should have a freezing point of 0°C and boiling water
which should have a boiling point of 100°C. The methods are described below.
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