## Determination of viscosity of liquid using Ostwald’s viscometer

**BP407P Physical Pharmaceutics II Practical**

### Aim:

To determine the viscosity of the unknown liquid by using Ostwald’s viscometer

**REQUIREMENTS:**

Ostwald’s viscometer

Stop clock

Specific gravity bottle

Sample

Distilled water

### PRINCIPLE:

The force of friction with one part of a liquid offering to another part of the liquid is called viscosity. For measuring the viscosity coefficient Ostwald’s viscometer method is used which is based on poiseuilles’s law. According to this law, the rate of flow of liquid through a capillary tube having viscosity coefficient (n)

Where,

V= volume of liquid (ml)

T= flow of time in seconds through capillary (in second) R= radius of the capillary (cm)

ɳ= viscosity coefficient (poise)

p= hydrostatic pressure

Since the hydrostatic pressure (driving force) of the liquid is given by

ɳ= dgh

Where,

h= height of the column d= density of the liquid

### PROCEDURE:

Wash the relative density bottle with distilled water and dry.

Take the weight of the empty bottle and filled the given liquid

Clean and rinse the viscometer properly with distilled water

Fix the viscometer vertically in the stand and filled the specific amount of given unknown liquid in the viscometer

Time of flow recorded when the liquid starts to flow from the marks C and D above and below the bulb a. the experiment was repeated 3-4 times to get the viscosity of the given unknown liquid.

For more details about Viscometer: Click here

### Physical Pharmaceutics II Practical

- Determination of particle size, and particle size distribution using the sieving method
- Determination of particle size, and particle size distribution using the Microscopic method
- Determination of bulk density, true density and porosity
- Determine the angle of repose and the influence of lubricant on the angle of repose
- Determination of viscosity of liquid using Ostwald’s viscometer
- Determination of sedimentation volume with the effect of different suspending agent
- Determination of sedimentation volume with the effect of different concentrations of single suspending agent
- Determination of viscosity of semisolid by using Brookfield viscometer
- Determination of reaction rate constant first order.
- Determination of reaction rate constant second order
- Accelerated stability studies

**Frequently Asked Questions (FAQs)**

**What is an Ostwald viscometer?**An Ostwald viscometer is a glass capillary viscometer designed to measure the viscosity of a fluid by determining the time it takes for the fluid to flow through a narrow tube under the influence of gravity.

**How does an Ostwald viscometer work?**The Ostwald viscometer relies on the principle of viscous flow. A known volume of the liquid to be tested is drawn into the capillary tube, and the time it takes for the liquid to flow a specific distance is measured. The viscosity is then calculated using the known dimensions of the capillary tube and the time of flow.

**What are the components of an Ostwald viscometer?**An Ostwald viscometer typically consists of a U-shaped glass capillary tube, a reservoir bulb at one end to hold the liquid, and timing marks to measure the flow time.

**What is the significance of the U-shaped tube in an Ostwald viscometer?**The U-shaped tube allows for a more accurate measurement of viscosity because it minimizes the effect of the meniscus, which can affect the flow in a straight capillary tube.

**How is the viscosity calculated using an Ostwald viscometer?**The viscosity (η) of the liquid is calculated using the formula: η = K * ρ * t, where K is a constant specific to the instrument, ρ is the density of the liquid, and t is the flow time.

**What are the advantages of using an Ostwald viscometer?**Ostwald viscometers are relatively simple to use and provide a quick method for measuring the viscosity of liquids. They are especially useful for Newtonian fluids, where viscosity is constant regardless of shear rate.

**What types of fluids can be measured using an Ostwald viscometer?**Ostwald viscometers are suitable for measuring the viscosity of Newtonian fluids, which have a constant viscosity regardless of shear rate. Non-Newtonian fluids may require specialized viscometers.

**How does temperature affect viscosity measurements with an Ostwald viscometer?**Temperature can significantly impact viscosity. Ostwald viscometers may include temperature control features to ensure accurate measurements at a consistent temperature.

**Are there limitations to using Ostwald viscometers?**Ostwald viscometers may not be suitable for non-Newtonian fluids or fluids with high viscosity. Additionally, errors can arise from factors like meniscus effects and variations in gravitational force.

**How is calibration performed for an Ostwald viscometer?**Calibration is typically performed using reference fluids with known viscosities. By measuring the flow times of these fluids and comparing them to their known viscosities, the instrument’s constant (K) can be determined.

**What are the applications of Ostwald viscometers?**Ostwald viscometers are used in various fields, including chemical, pharmaceutical, and food industries, where precise viscosity measurements are essential for quality control and process optimization.

**Can an Ostwald viscometer be used for opaque or non-liquid samples?**Ostwald viscometers are specifically designed for liquid samples. Opaque or non-liquid samples may require alternative viscometer designs or measurement techniques.

**How accurate are viscosity measurements with an Ostwald viscometer?**The accuracy of viscosity measurements with an Ostwald viscometer depends on factors like instrument quality, proper calibration, and adherence to operating procedures. For high-precision applications, advanced viscometers may be preferred.

**Are there variations of Ostwald viscometers?**Yes, there are variations of Ostwald viscometers, including modified designs for specific applications. The Cannon-Fenske routine viscometer is one such example often used in laboratories.

**Can an Ostwald viscometer measure dynamic viscosity?**Yes, an Ostwald viscometer can measure dynamic viscosity, which is the ratio of shear stress to shear rate in a fluid. The dynamic viscosity can be calculated using the formula η = K * ρ * t, as mentioned earlier.

Ostwald viscometers provide a straightforward and practical method for measuring the viscosity of Newtonian fluids. While they have limitations, they remain a valuable tool for various industries that require quick and reliable viscosity measurements.

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