DETERMINATION OF VISCOSITY USING OSTWALD PDF

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Physical chemistry laboratory report for chem324...

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University of Science and Technology of Southern Philippines

Name: GERALDEZ, ALDRIN N. Section: 3H1 Date of Submission: November 6, 2021 Laboratory Report No: 3

DETERMINATION OF VISCOSITY USING OSTWALD VISCOMETER

I.

INTRODUCTION

The viscosity of liquid is a resistance to flow of a liquid. All liquids appear resistance to flow change from liquid to another, the water faster flow than glycerin, subsequently the viscosity of water less than glycerin at same temperature. Viscosity occurs as a result of contact liquid layers with each other. The viscosity is measuring by Ostwald viscometer. Relative Viscosity is the ratio of the absolute viscosity of the fluid on the viscosity of water at a certain temperature. Ostwald viscometer is a commonly used viscometer, which consists of a U-shaped glass tube held vertically. For more accurate measurements it is held in a controlled temperature bath. It is also known as a glass capillary viscometer. The result is typically expressed in centipoise (cP), which is the equivalent of 1 mPa’s (millipascal second). In one arm of the U is a vertical section of precise narrow bore (the capillary). Above there is a bulb, with it is another bulb lower down on the other arm. In use, liquid is drawn into the upper bulb by suction, and then allowed to flow down through the capillary into the lower bulb. Two marks (one above and one below the upper bulb) indicate a known volume. The method of determining viscosity with this instrument consists of measuring the time for a known volume of the liquid (the volume contained between the marks A and B) to flow through the capillary under the influence of gravity. The time taken for the level of the liquid to pass between these marks is proportional to the kinematic viscosity. The time required for the test liquid to flow through a

capillary of a known diameter of a certain factor between two marked points is measured. The instrument must first be calibrated with materials of known viscosity such as pure (deionized) water. Knowing the value of viscosity of one liquid, one can calculate the viscosity of other liquid.

𝑛2 =

𝑃2𝑡2 × 𝑛1 𝑝1𝑡1

where n1 and n2 are viscosity coefficients of the liquid and water, and p1 and p2 are the densities of liquid and water, respectively.

II.

OBJECTIVES

This experiment aims to achieve the following objectives; 1. To measure the viscosity of a sample liquid.

III.

MATERIALS AND METHODS

The chemicals and materials involved in this experiment Distilled water, Beaker, Ostwald viscometer, Pipette, Weighing machine, Stop watch, Sample liquid.

Initially, the viscometer was cleaned with water and ethanol. Then, dried it in Oven for 10-15 minutes at 50°C. Next, the bulb 1 was filled completely with fixed amount of water with the help of pipette. Through the rubber tube, the water was sucked to the level above the upper mark A. Then water is allowed to flow down. When water meniscus reaches the mark A, the stopwatch is started. When the meniscus reaches the mark B, the stopwatch is stopped. This time to flow the liquid from mark A to mark

B was recorded for water. Averages of three determinations were taken to measure the accurate value. The time of flow of sample liquid represents t1. Similarly the above procedure is repeated with the liquid sample. Averages of three determinations were taken to measure the accurate value. The time of flow of sample liquid represents t2. The densities of water and sample liquid are determined by using specific gravity bottle. The viscosity of sample liquid is determined by substituting the value in the equation given.

IV.

RESULTS

Table 1. Data for determination of liquid density

Weight of empty specific gravity bottle (W 1)

20.53 g

Weight of specific bottle + distilled water (W2)

55.59 g

Weight of specific gravity bottle + turpentine oil (W3)

50.39 g

Sample Calculations: Equation 1: density of liquid P2=

𝑊3−𝑊1 𝑊2−𝑊1

50.39−20.53

= 55.59−20.53 = 0.852 𝑔/𝑚𝐿

The density of turpentine oil (P2) is 0.852 g/mL (calculated) The density of water at room temperature (P1) = 0.997 (standard)

Table 2. Data for determination of liquid viscosity

Time of flow

Mean Time Density (p)

Viscosity (n)

g/mL

(Centipoise)

(t)

Liquid Sample 1

2

3 s

Distilled Water

21.94

21.37

21.13

t1 = 21.48

0.997 g/mL

0.8937cp

Turpentine Oil

26.33

25.91

25.75

t2 =25.99

0.852 g/mL

0.9240 cp

Equation 2: Viscosity of liquid 𝑛2 =

𝑃2𝑡2 (0.852)(25.99) × 𝑛1 = × 0.8937 = 0.9240 𝑐𝑝 𝑝1𝑡1 (0.997)(21.48)

The viscosity of water at room temperature (n1) = 0.8937 cp The viscosity of turpentine oil at room temperature is 0.9240 cp

V.

DISCUSSION

Though the analysis of the results, it can be observed that in able to generate the data, distilled water was used as a reference liquid since it can exist in a solid, liquid, and gaseous phase, therefore, making it the most versatile compound.

VI.

REFERENCES

•

VII.

Viscosity. (2020, August 16). https://chem.libretexts.org/@go/page/1512

APPENDIX

Images from experiment...