Determination Liquid viscosity determination at different temperatures

Determination Liquid viscosity determination at different temperatures

Abstract: to understand the principle of the thermostatic bath, structure and function of each component, learn to adjust the thermostat. Understand the significance of liquid viscosity and the principle and method of measuring viscosity. Determination of viscosity of ethanol at different temperatures by Ubbelohde viscometer, calculate the activation energy of ethanol flow.

1.      Constant temperature technology:

A thermostatic bath commonly used in laboratory is a common temperature control device. The basic principle is that when the bath temperature is lower than the set temperature, it heating automatically; when the bath bath temperature is higher than the set temperature, stop heating automatically, and automatically depending on the situation. As a result, the temperature fluctuates in a small range, and the system is confined to the required temperature at very small intervals under the constant temperature water.

2. Determination of liquid viscosity:

All the liquid have viscosity, it can be represented by a viscous coefficient η. η has the relationship with the molecular size, shape, and composition of liquid molecular force. In this experiment, the viscosity of liquid is measured by capillary outflow method. Under certain temperature by Poiseuille formula PI ETA = r4pt/ (8LV). The international system of η units is ETA Pa * s, 1P=0.1Pa * s. Usually use two kinds of liquid viscosity formula for doing business. That is η2=η1×p2t2/p1t1

The temperature changes of the intermolecular force , viscosity also changed.The relationship are η=Aexp(Evis/RT) or Inη=InA+Evis/RT.
 Among them, Evis is called liquid flow activation energy, to In on the 1/T map in a straight line, the slope of S=Evis/R,so Evis=SR.

Operation procedure of viscosity test:

1. Switch on the constant temperature sink power supply, turn on the switch, set the temperature for the experiment temperature, wait for the water temperature to the set temperature and keep stable.

2. Determination of 25 degree ethanol through Ubbelohde viscometer capillary time. Clamp the tube on the C tube with a clamp to absorb the gas. Draw the ethanol from the D ball, capillary, and E ball to the G ball. Step B tube of latex tube, remove the C tube clip, at this time, D ball part of ethanol flow back to the F ball, D ball through the C tube and atmospheric communication, capillary end that the atmosphere. The B pipe clamp is removed and the ethanol falls in the B tube. When the liquid level flows through the scale a, the stopwatch is started and the time is stopped when the liquid level drops to B. This time is the time between the AB and the volume of V ethanol flowing through the capillary tube ta. Repeat operation 2~3 times, each difference is not more than 0.5s, take the average.

3. Increase the temperature 3 degrees, ibid., the 2 step, determine the temperature of ethanol flow through the capillary tube, so measured 4~5 data.

4. After measuring, turn off the thermostat, the switch and the agitation tank switch, disconnect the power supply, and return the instrument, ear ball and stopwatch.

Experimental raw data

Number	1		2		3		4
T/℃	28		31		34		37
ρ/g×cm-3	0.78267		0.78		0.77756		0.775
t/s	a	b	a	b	a	b	a	b
	306.44	306.68	294.47	296.9	275.18	277.87	266.25	265.5

When T = 28 ° C, the viscosity of ethanol is η1 = 1.015 mPa × s

The activation energy of anhydrous ethanol was found to be 13.40 kj / mol

Experimental Data Processing and Results Discussion:

From the formula η1 / η2 = p1t1 / p2t2, and the viscosity of ethanol η1 = 1.015mPa × s can be obtained at different temperatures viscosity, as shown in the table below:

1/(T/K-1)	3.32×10-3	3.28×10-3	3.26×10-3	3.22×10-3
In(η/mPa×s)	0.0149	-0.0243	-0.0943	-0.138

Make Inη—1/T chart

Takes on the straight line A (0.00331, -0.001), B (0.00324, -0.109) two points, find the slope S = (0.001-0.109) / (0.00324-0.00331) = 1.54 × 103K

             Evis = RS = 8.31 x 1.54 x 103 KJ / mol = 12.80 KJ / mol

   The relative error E = | Evis-Evis true | / Evis true × 100% = | (12.8-13.4) /13.4|×100%=4.47%

Experimental error analysis:

1. viscometer can not be guaranteed when placed completely straight, resulting in a certain error;

2. with a stopwatch time, because the stopwatch itself is not accurate enough, will cause some error, and in the stopwatch may appear even when the phenomenon, so that measurement is not allowed;

3. because in the observation of the liquid surface, in the a and b line to determine the standard can not be exactly the same, resulting in a certain error.

Note:

1. viscometer must be placed as far as possible;

2. with the suction ball to absorb the liquid, the liquid may not be mixed with bubbles, or should be exhausted in order to be able to experiment;

3. if the operation to contact B tube or C tube should be particularly careful, because the B tube or C tube has a longer arm, the force is small but the formation of a larger torque, easy to break at the interface between the tube;

4. viscometer can not water, should ensure that the purity of the tube ethanol.

Kent Yuan (Mr.) Hangzhou Zhongwang Technology Co., LTD.

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