Chemistry Design IA Pre-IB Year 10 Term 2 How will changing the temperature of a liquid affect the height of the liquid in a capillary tube?
Spandan Gangopadhyay Teacher: Dr Natt Date: 13/05/2010
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Will increasing the temperature of water (H2O) increase its height in a capillary tube?
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Capillary Ac ion Capillarity is the tend ency of a liquid in a narrow tube or pore to
rise or fall as a result of certain variables such as surface tension of the liquid (Oxford, 2005). A key pro cess to de onstrate this concept is thecapillary tube.
When a capillary tube is placed in a liquid such as water a concave meniscus forms because of th e surface tension pulling the liquid column up until there is a suffi cient mass of liquid for gravity to overcom e the intermolecular force of the liquid. Capillarity acts on con cave menisci to pull th e liquid up, increasing the amount of favourable contact area between the liquid and the contain er. On conv ex menisci, however, capillarity acts to pull the liquid down, redu cing the amount of contact area (Tsokos, 2010). The diameter of the tube is in an inverse relation to the height of the liquid in the tube, as a liquid will rise higher in a narrow tube compared to a wid er tube (provided the liquid forms a concave meniscus for a liquid that forms a conv ex meniscus, the liquid will sink lower in a narrow tub e,
compared to a wider tube). The height of a liquid in a capillary tube is given by the formula,
Where:
is the liquid-air surface tensi on (energy/area)
is the contact angle of the liquid on the substance of the capillary tube
is the density of liquid (mass/volume)
g is acceleration due to gravity (length/time )
r is radius of the capillary tube (length).
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2 Pre-IB 2
1 2 2 Temperature Independent Variable
Temperature is a measure of the average kinetic energy of the pa rticles in a sample of matter, expressed in terms of units or deg rees designated on a standard scale (Oxford, 2005 Or basically, temperature is a way of measuring the heat on an
object. A higher temperature m eans that the m olecules of the object have more energy and thus move at a faster speed compared to molecules of an object with a lower temperature (about.com). Since the molecules move at a faster speed, their intermolecular force their attraction towards each other is also lower (Tsokos, 2010). This is because the intermolecular space increases when an object is heated,
thus things expand when heated. But e ven though an object expands when heated, its mass stays the sam e. The only difference occurs in its density. Density is simply a measurement of how densely t he molecules of an object are packed together. A higher density means the molecules of the object have a greater intermolecular force which in turn means that they also have smaller intermolecular spaces. Another thing temperature affects in a liquid is the surface tension. Surface tension is a property of liquids such that their surface behaves like a thin, elastic film. Surface tension is an effect of intermolecular attraction, in which molecules near the surface undergo a net attraction to the rest of the fluid, while molecules in the centre of the substance are attrac ted to other molecules equally in all directions and undergo no net attraction (Tsokos, 2010). Thus, by changing the temperature of the liquid one indirectly changes the density and surface tension of the liquid both of which are variables that t h o tica
affect the height of the liquid in a capillary tube (see 1. 2. 1).
Spandan Gangopadhyay Chemistry Design IA Term 2 Pre-IB
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1 3 Variables 1 3 1 Independent Variable and Dependent Variable !
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Independent Variable
Temperature of the water, measured using a o
thermometer with a maximum tolerance of 100 C o
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20 C (± 1 C) 30 C (± 1 C) 40 C (± 1 C) 50 C (± 1 C) 60 C (± 1 C) 70 C (± 1 C) 80 C (± 1 C) 90 C (± 1 C)
Dependent Variable
The height of water in a capillary tube, mea sured using the scale on the capillary tube.
1 3 2 Controlling Variables "
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Table 1: Variable and their Method of Control
Variable
Method of Control
Volume of water
100mL measured using a measuring cylinder (± 0.5mL)
Pressure
Kept constant at lab
Radius of Capillary Tube
Same capillary tube used
(diameter = 0.1cm) *Note: the diameter increased slightly when in contact with the hot water but the change was negligible. Angle of contact between capillary tube and
o
90
o
(± 1 ) measured using a L-square ruler
water Experimenter
Only one person will read the ruler and one will hold the capillary tube. This will keep the degree of error consistent.
Spandan Gangopadhyay Chemistry Design IA Term 2 Pre-IB
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1 4 Equipment and Procedure 1 4 1 Equipment #
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Thermometer Distilled Water 100mL Measuring Cylinder L-square ruler Clamp and Stand 100mL Beaker Capillary Tube with millimetre scale (diameter = 0. 1cm) Electric water heater/cooler capable of specific temperatures
1 4 2 Procedure $
$
1. The electric water heater/ cooler was used to get the distilled water to the o
desired temperature, 20 C. The temperature of the water was checked with the thermometer. 2. 100mL of wa ter was measured into the beaker using the measuring cylinder.
3. The L-square ruler was used to ensure that the capillary tube was perpendicular to the surface of the water. The L-square was placed along the edge of the beaker and the capillary tube was lowered into the water such that it touched the Lsquare. 4. The capillary tube was lowered into the water until it was exactly 1cm into the beaker; the scale on the ca pillary tube was used for exact measurements. It was then secured with the clamp and stand. 5. No action was taken
until the height of the liquid in the capillary tube w as stable for approximately 1 minute. 6.
The millimetre scale on the capillary tube was used to read the height which was then recorded (Table 2).
7.
Steps 1-6 were repeated 5 times to ensure reliable data.
8.
Steps 1-7 were repeated 7 times with the temperature of the water 30 C,
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40 C, 50 C, 60 C, 70 C, 80 C and 90 C respectively.
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Table 2: Height of water in a capillary tube with temperature of the water Temperature
Height of Water in the Capillary Tube (millimetres)
20oC 30oC 40oC 50oC 60oC 70oC 80oC 90oC
1 5 is Assessment Table 3: Risks, precautions and actions to take. %
is
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Hot Water
Precaution
Action to Ta e
Avoid contact with skin
Wash with room temperature
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water and then with cold water to prevent burn/s Fragile glassware
Handle with care
(capillary tubes)
Wash with water if bleeding; ensure no glass is left buried under the skin.
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2 0 Bibliography
od na ics. Retrieved may 9, 2010, from about.com. (n.d.). about ph ics: t h http://physics.about.com/od/thermodynamics/p/thermodynamics.htm '
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Oxford. (2005). Oxf o d Dicti ona 0
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11t h E di ti on. Oxford University Press.
Tsokos, K. A. (2010). Ca b i dg Ph sics f o t h IB Di p o a. Cambridge University Press. 2
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