Experiment 1: Viscosity

Objectives: a. To determine the viscosity of various fluids using the Ostwald viscometerb. To determine the relationship of viscosity and temperature for various fluids

TheoryViscosity is a property of a fluid that resists change in formation or

movement of adjacent layers in the fluid. It refers to opposition of flow of the fluid. It is the ratio of shear stress to shear rate and is constant for a fluid at a given temperature. The viscosity of liquids decreases as temperature increases while the viscosity of gases increases as temperature increases. Thus, liquids flow more easily at high temperature while gases flow slowly.

Ostwald viscometer is an instrument used in determining the liquid viscosity by measuring the time the liquid flows. It is a glass capillary viscometer which is in the shape of U. The liquid is allowed to flow to its capillary and the time of flow of the liquid between two marks is noted. The flow rate of the liquid can be expressed through Hagen-Poiseuille’s equation:

Vt = πPt r

2

8 µL (1)

A volume of the liquid V, with a viscosity of µ, passes through the viscometer of radius r and length L in time t. The pressure P is constant over the time interval and is the difference in pressure between the inlet and the outlet of the viscometer. Equation 1 can be rewritten as µ = πPt r

4

8VL (2)

If two liquids use the same viscometer under similar conditions, the ratio of

the two viscosities µ1µ2

can be used. The values for volume, radius, length and

pressure can be cancelled. The pressure acting on the liquids is a function of density, gravitational constant and height. The equation can be further simplified as

µ1µ2

= ρ1t 1ρ2t 2

(3)

The equation is used when the viscosity of a given liquid is being measured with respect to another liquid whose viscosity is known. Water is usually used as the standard liquid whose viscosity is known at different temperatures. Materials and Methods

1

Ostwald viscometer Graduated cylinderIron stand and clamp Top loading balanceBeakers SugarHeating plate SaltThermometer Cooking oilStopwatch Distilled waterPipetteAspirator

1. The viscometer was cleaned first by rinsing it with distilled water and it was aspirated to dryness. The viscometer was then safely clamped on a stand in a vertical position.

2. The group was assigned to record the time of flow for distilled water at the following temperatures: 10OC, ambient temperature and 50OC. While two members of the group were assigned to record the time of flow of distilled water at the given temperatures, the other members cooled the distilled water to 10OC and heated it to 50OC.

3. Temperature of 10OC was obtained by submerging a beaker of distilled water in to a cold bath while 50OC was obtained by heating a beaker of distilled water using the heating plate.

4. The time of flow for distilled water at ambient temperature was first determined. Before the distilled water was poured unto the viscometer, the temperature of the liquid was measured twice inorder to get the mean ambient temperature.

5. Water was allowed to flow at the inside walls of the viscometer to avoid trapping bubbles.

6. With a volume of 3.5mL, the water was able to reach point C of the viscometer.

7. The water was forced to reach above point A by using the aspirator. It was released to allow it to flow down. By using a stopwatch, the time was recorded as the lower meniscus of the fluid reached point B from point A.

8. The same procedure was used in determining the time of flow for distilled water at 10OC and 50OC. The procedure was also repeated for the other fluids.

9. One member of the group was assigned to measure the mass and volume of the distilled water at the three given temperatures. Graduated cylinder was used for measuring the volume and the top loading balance for the mass.

Results and Discussion Table1. Distilled water

2

Temperature (°C)

Time (s) Mass (g)

Volume (mL)

Density (g/mL)

Viscosity

9.9 91.975 6.22 6.25 0.995227.95 91.375 10.015 10 1.0015

58.385.975

4.075 4.20.970238095

2

Table2. 20% Sugar solutionTemperature

(°C)Time (s) Mass

(g)Volume

(mL)Density (g/mL) Viscosity

10.3162.45

2.4 2.950.813559322 1.443872

276

28.65157.53

4.195 3.91.075641026 1.851621

81

50.95147.015

4.8 4.71.021276596 1.799925

462

Table3. 25% Sugar solution Temperature

(°C)Time (s) Mass

(g)Volume

(mL)Density (g/mL) Viscosity

10187.175

10.14 101.014 2.073507

607

30.4190.485

21.095 201.05475 2.195492

575

49.8183.745

10.245 101.0245 2.256716

403

Table5. 30% Sugar Solution Temperature

(°C)Time (s) Mass

(g)Volume

(mL)Density (g/mL) Viscosity

10.2257.815

10.975 101.0975 3.0912387

34

30.5264.2

11.085 9.951.114070352 3.2163780

27

51.3249.91

11.055 9.9751.108270677 3.3203125

74

Table4. 20% Salt solution Temperature

(°C)Time (s) Mass

(g)Volume

(mL)Density (g/mL)

Viscosity

9.75120.36

10.795 11.10.972522522

51.2787972

19

30.3112.5

11.615 12.10.959917355

41.180070687

51.5108.55

11.045 111.004090909 1.3066291

89

3

Annexes Tabe1. Distilled Water

Temperature (°C) Time (s) Mass (g) Volume (mL)Trial 1 Trial 2

9.8 10 91.55 92.64 6.20 6.24 6.20 6.3028 27.9 91 91.75 10.05 9.98 10 10

58.8 57.8 85.8 86.15 4.0 4.15 4.1 4.3

Table2. 20% Sugar SolutionTemperature

(°C)Time (s) Mass (g) Volume (mL)

Trial 1 Trial 210.1 10.5 162.45 --- 1.76 3.04 2.7 3.228.6 28.7 154.39 160.67 3.71 4.68 3.4 4.450.6 51.3 145.69 148.34 4.52 5.08 4.7 4.7

Table3. 25% Sugar SolutionTemperature

(°C)Time (s) Mass (g) Volume (mL)

Trial 1 Trial 2

10 10 183.78 190.57 10.1210.1

610 10

30.4 30.4 190.48 190.49 20.99 21.2 20 20

49.8 49.8 184.05 183.44 10.2510.2

410 10

Table5. 30% Sugar SolutionTemperature

(°C)Time of flow (s) Mass (g) Volume (mL)

Trial 1 Trial 2

10.1 10.3 255.6 260.03 10.9111.0

410 10

30 31 263.07 265.33 11.111.0

79.9 10

51.4 51.2 247.19 252.63 11.0511.0

69.95 10

Table4. 20% Salt SolutionTemperature

(°C)Time (s) Mass (g) Volume (mL)

Trial 1 Trial 2

4

10 9.5 120.36 10.810.7

911.2 11

30 30.6 112 113 11.6511.5

812.2 12

52 51 108.1 109 11.0511.0

411 11

5 10 15 20 25 30 35 40 45 50 550

0.5

1

1.5

2

2.5

1.443872276

1.85162181 1.799925462

2.0735076072.195492575 2.256716403

Y-Values

Y-Values

Axis Title

Axis Title

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