BS Practicals

Experiment No. 1: Polarimeter | How polarimeter works | optical activity | polarimetry

A polarimeter is an instrument used in chemistry, physics, and other scientific fields to measure the optical properties of substances, specifically their ability to rotate the plane of polarized light. Polarimetry is the science and technique used to perform these measurements, while optical activity is a specific property of substances that causes them to interact with polarized light in a unique way.

Here’s how a polarimeter works and definitions of key terms:

1. Polarimeter:
   A polarimeter typically consists of the following components:
   a. Light Source: It emits unpolarized light, which means the light waves vibrate in all directions perpendicular to the direction of propagation.
   b. Polarizer: This component filters the unpolarized light and allows only light waves vibrating in a specific direction to pass through. This results in linearly polarized light.
   c. Sample Cell: The substance to be analyzed is placed in a sample cell or tube, which is positioned between the polarizer and the analyzer.
   d. Analyzer: The analyzer is another polarizing element that is rotated to a specific angle relative to the polarizer. It is used to detect the change in polarization caused by the sample.
   e. Detector: A light detector measures the intensity of light emerging from the analyzer.
2. How it works:
   When unpolarized light passes through the polarizer, it becomes linearly polarized. As this polarized light travels through the sample, some substances have the property of optical activity. Optical activity is the ability of a substance to rotate the plane of polarization of linearly polarized light as it passes through. This rotation is typically measured in degrees and is specific to the substance and its concentration. The analyzer is then rotated to an angle where the intensity of light reaching the detector is either maximized or minimized, depending on the direction of rotation. The difference in the angle of rotation between the polarizer and the analyzer provides information about the degree of optical activity of the sample.
3. Polarimetry:
   Polarimetry is the scientific technique used to measure the degree of optical activity of substances. It quantifies how much a substance can rotate the plane of polarized light, allowing researchers to determine the concentration and specific optical activity of a substance in a sample.
4. Optical Activity:
   Optical activity is a property of certain chiral (non-superimposable mirror-image) substances that cause them to interact with polarized light in a way that rotates the plane of polarization. Chirality refers to molecules that exist in two mirror-image forms called enantiomers. Optical activity is a valuable tool in chemistry for identifying and characterizing chiral compounds, such as sugars and certain drugs, as it helps determine their purity and concentration.

In summary, a polarimeter is an instrument used for polarimetry (BS Practicals), which measures the optical activity of substances by analyzing how they rotate the plane of polarized light. Optical activity is a property that plays a crucial role in the study of chiral molecules and has important applications in fields such as chemistry, pharmacology, and food science.

Experiment 2: Heat of Neutralization Experiment. | BS Practicals

The Heat of Neutralization experiment measures the heat energy released when an acid and a base react to form water and salt. This experiment helps us understand the heat changes that occur during chemical reactions.

Here’s how the experiment works:

1. Materials: You will need a calorimeter (a container that insulates heat), a thermometer, a known amount of acid and base, and a stirring rod.
2. Procedure:
   a. Measure equal amounts of acid and base.
   b. Place them in the calorimeter.
   c. Stir the mixture and record the initial temperature.
   d. Observe the temperature change as the reaction occurs.
   e. Record the highest temperature reached.
3. Calculation:
   a. Find the temperature change (final – initial temperature).
   b. Use the formula: Heat (q) = mass x specific heat capacity x temperature change.
4. Importance:

• Understanding Heat Changes: It helps us understand how much heat is produced or absorbed during a chemical reaction.
• Thermodynamics: This experiment is a part of thermodynamics, which is crucial in chemistry and engineering.
• Industrial Processes: Knowledge of heat changes is important in various industrial processes to control reactions and save energy.
• Environmental Impact: Helps us design processes with minimal environmental impact by optimizing energy usage.

In summary, the Heat of Neutralization experiment (BS Practicals) helps us measure heat changes in chemical reactions, which is important for understanding chemical processes and their practical applications in various industries.

Experiment No. 3: Determine the heat of the solution of KNO₃ by an experiment.

An experiment on the heat of a solution of potassium nitrate measures how much heat is absorbed or released when potassium nitrate dissolves in water. This helps us understand the energy changes involved in the process.

To conduct this experiment, you will need a few key instruments:

1. Potassium Nitrate (KNO3): This is the substance you want to dissolve.
2. Water: You’ll need a specific amount of water to mix with the potassium nitrate.
3. Calorimeter: This is a special container that can measure changes in temperature. It’s usually made of a material that doesn’t conduct heat well, like Styrofoam.
4. Thermometer: To measure the temperature of the solution accurately.

Here’s how the experiment works:

1. Initial Temperature: Measure the initial temperature of the water in the calorimeter. This is the starting point of the experiment.
2. Add Potassium Nitrate: Slowly add a known amount of potassium nitrate to the water in the calorimeter. Stir the solution gently until all the potassium nitrate dissolves. This step represents the dissolution of potassium nitrate in water.
3. Temperature Change: After the potassium nitrate has completely dissolved, measure the final temperature of the solution. The temperature change from the initial to the final temperature will indicate whether the process absorbed or released heat.
4. Calculating Heat: To calculate the heat of solution, you can use the formula: Heat of Solution (q) = mass of water (m) x specific heat of water (c) x change in temperature (ΔT) Specific heat of water (c) is usually around 4.18 J/g°C.
5. Analysis: A negative value for q indicates that heat was released during the dissolution, while a positive value means heat was absorbed. This information tells you about the energy changes in the process.

In summary, this experiment allows you to measure how much heat is involved when potassium nitrate dissolves in water, helping you understand the heat exchange that occurs during this chemical process.

Experiment No. 4: Determine Viscosity, Rheochore and percentage composition of Unknown mixtures. | BS Practicals

Experimental Procedure to Determine Viscosity, Rheochore, and Percentage Composition of an Unknown Mixture:

Instrumentation: (BS Practicals)

1. Viscometer
2. Stopwatches
3. Weighing balance
4. Thermometer
5. Graduated cylinders
6. Unknown mixture sample
7. Newtonian standard fluid (known viscosity)
8. Water bath

Procedure:

1. Calibration of the Viscometer:

• Fill the viscometer with the Newtonian standard fluid.
• Measure the time it takes for the fluid to flow a known distance through the viscometer. Record this time as ‘t_standard.’
• Repeat this process at least three times and calculate the average time.

1. Preparation of the Unknown Mixture:

• Weigh a sample of the unknown mixture using the weighing balance and record the mass as ‘m_unknown.’
• Place the unknown mixture in a graduated cylinder and measure its volume, recording it as ‘V_unknown.’
• Calculate the density of the unknown mixture as ‘ρ_unknown = m_unknown / V_unknown.’

1. Viscosity Measurement:

• Clean the viscometer thoroughly and fill it with the unknown mixture.
• Record the time it takes for the unknown mixture to flow the same known distance as in the calibration step. Record this time as ‘t_unknown.’
• Repeat the measurement at least three times and calculate the average time.

1. Calculations:

• Calculate the viscosity of the unknown mixture using the formula:
  Viscosity (η_unknown) = (t_unknown / t_standard) * Viscosity of standard fluid
• Calculate the rheochore (reciprocal of the viscosity) of the unknown mixture as ‘R_unknown = 1 / η_unknown.’

1. Determination of Percentage Composition: (BS Practicals)

• Calculate the percentage composition of the unknown mixture based on the densities:
  Percentage of component A = (Density of component A / Density of the mixture) * 100%
  Percentage of component B = (Density of component B / Density of the mixture) * 100%
  (Assuming the mixture consists of two components, A and B)

Example Readings:

• Newtonian Standard Fluid (for calibration):
• t_standard = 45 seconds (average time)
• Unknown Mixture:
• m_unknown = 25 grams
• V_unknown = 30 mL
• ρ_unknown = 25 g / 30 mL = 0.833 g/mL
• Viscosity Measurement:
• t_unknown = 60 seconds (average time)
• Calculations:
• η_unknown = (60 s / 45 s) * Viscosity of standard fluid
• R_unknown = 1 / η_unknown
• Percentage Composition (Assuming a binary mixture):
• Calculate the densities of components A and B based on their known densities and the density of the mixture.
• Calculate the percentages of each component using the densities.

Please note that this is a simplified procedure, and in practice, factors like temperature control, calibration precision, and choice of standard fluid can impact the accuracy of the results.

Experiment No. 5. Refractometry. Use of refractometer to determine refractive index. | BS Practicals

Experimental Procedure to Determine Refractive Index by a Refractometer:

1. Gather Equipment:

• Obtain a refractometer, a clean glass sample plate, and a light source.

1. Prepare Sample:

• Ensure the sample to be tested is clean and free from any contaminants or bubbles.

1. Calibrate the Refractometer:

• Turn on the refractometer and let it warm up for a few minutes.
• Open the prism cover and place a few drops of distilled water on the prism.
• Close the cover gently and adjust the calibration to read 0 with distilled water.

1. Prepare the Sample Plate:

• Clean the glass sample plate and place it on a flat surface.
• Add a small amount of the liquid sample onto the sample plate.

1. Measurement:

• Open the prism cover again and place the sample plate carefully on the prism.
• Close the cover gently, ensuring there are no air bubbles between the prism and the sample.

1. Read the Refractive Index:

• Look through the eyepiece or digital display of the refractometer.
• The scale will show the refractive index (nD) of the sample.

1. Record the Result:

• Take note of the refractive index reading.

1. Clean Up:

• Remove the sample plate and clean it thoroughly.
• Turn off the refractometer.

Refractometry is the science of measuring the refractive index of substances, which quantifies how much a substance bends light.

Instrumentation: A refractometer typically consists of a light source, a prism, an eyepiece or digital display, and a calibration adjustment. The sample is placed on the prism, and the refractive index is determined by measuring the angle at which light is bent as it passes through the sample. This bending of light is directly related to the refractive index of the substance.

Simple Structure of a Refractometer: It usually comprises a sturdy base with an eyepiece or digital readout, a prism, and a cover. The prism is the critical component, where the sample is placed for measurement. Light from the source passes through the prism and the sample, and the resulting angle of light deviation is used to calculate the refractive index of the sample.

Experiment No. 6: Sublimation Process. | BS Practicals

Experimental Procedure of Sublimation: (BS Practicals)

1. Materials Needed:

• Sublimate (solid substance that undergoes sublimation)
• Sublimend (container for collecting the sublimate)
• Heating apparatus (e.g., Bunsen burner or electric hot plate)
• Thermometer
• Glass funnel
• Watch glass or cold surface (for condensing the sublimate)

1. Setup:

• Place the sublimate inside a Sublimend container.
• Set up the heating apparatus.

1. Instrumentation:

• Sublimate: The substance you want to sublimate.
• Sublimend: A container used to collect the sublimate.
• Heating apparatus: A heat source like a Bunsen burner or electric hot plate.
• Thermometer: To monitor the temperature.
• Glass funnel: Helps direct the sublimate vapor to the Sublimend.
• Watch glass or cold surface: For condensing and collecting the sublimate.

1. Procedure:

• Place the sublimate inside the Sublimend container.
• Position the Sublimend with the sublimate on the heating apparatus.
• Heat the sublimate gently by gradually increasing the temperature. Observe the temperature using the thermometer.
• As the sublimate heats up, it will turn into vapor without melting. The vapor will rise.
• Use a glass funnel to direct the vapor towards the cold surface (watch glass or cold surface) where it will condense back into a solid form.
• This solid form collected on the cold surface is the sublimate.

1. Working:

• Sublimation is the process of changing a substance directly from a solid to a vapor without going through the liquid phase.
• When the sublimate is heated, it absorbs heat energy, causing its particles to gain enough energy to break away from the solid and become vapor.
• The vapor is collected and condensed back into solid form on a cold surface, resulting in the formation of the sublimate.

1. Definition:

• Sublimate: A sublimate is a solid substance that undergoes sublimation, changing from a solid directly to a vapor upon heating.
• Sublimend: The Sublimend is a container used to collect the sublimate during the sublimation process.

In summary, sublimation is a process where a solid changes directly into a vapor upon heating. The sublimate is the solid substance undergoing this change, and it is collected using a Sublimend container. The setup involves heating the sublimate and directing the vapor to a cold surface where it condenses back into a solid form.