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Category: Wet Lab Experiments

Wet laboratories are laboratories where chemicals, drugs, or other material or biological matter are handled in liquid solutions or volatile phases, requiring direct ventilation, and specialized piped utilities (typically water and various gases).

The enthalpy change for a reaction between a strong acid and a strong alkali

Aim / Objective: 

To determine the enthalpy change for a reaction between a strong acid and a strong alkali.

Introduction:  Enthalpy is defined as the total energy in a system.  The change in energy ∆H can be positive in heat absorbing (endothermic reactions) or negative in heat releasing (exothermic reactions). This experiment focuses on one form of enthalpy change which is enthalpy of neutralization (∆Hn).  Enthalpy of Neutralization is the enthalpy change observed when one mole of water is formed when a base reacts with an acid in a thermodynamic system.

The literature standard enthalpy for a strong acid-base reaction is -57.1kJ/mol. For weak acids and bases the heat of neutralization is different as they are not fully dissociated and hence some heat will be absorbed.

Materials/ Apparatus:

1.0M HCl solution, 1.0M NaOH solution, 2 measuring cylinders, 2 Styrofoam cups, 2 beakers, 1 thermometer, 1 glass stirring rod.

Method / Procedure:

  1. Use a measuring cylinder to measure 50cm3 of sodium hydroxide (NaOH) and pour into a Styrofoam cup.
  2. Use a thermometer to measure the temperature of the NaOH. Record the reading.
  3. Use a measuring cylinder to measure 50cm3 of hydrochloric acid (HCl) and pour into a Styrofoam cup.
  4. Use a thermometer to measure the temperature of the HCl. Record the reading.
  5. Mix the contents of both cups in a beaker and stir the contents using the glass stirring rod.
  6. Take the temperature after stirring the mixture then record the reading.
  7. Repeat steps 1 to 6 TWO times and then tabulate the results.

Suggested Results:

Experiment numberInitial temperature / °CFinal temperature / °C
NaOHHClNaOH+ HCl
13233.546
23030.546
33030.546

Discussion / Calculations:

Heat released = mcΔT

  1. Calculate mass

1000g = 1kg

1000g ÷1000

x = 1kg

50cm3 of acid and 50cm3 alkali = 100cm3 = 1kg

  1. Average temperature = (32+30+30+33.5+30.5+30.5) / 6

= 186.5/6

= 31.08°C

  1. Change in temperature (ΔT) = final temperature – initial temperature

= (46 – 31.08) °C

= 14.92°C

Change °C to K = 14.92 + 273 =287.92

  1. Specific heat capacity = 4.187JK-1kg-1
  2. Heat energy released = mcΔT

= 1kg x 4.187JK-1kg-1 x 287.92K

= 1205.52104J

  1. Enthalpy change = mcΔT / number of moles

50cm3 of acid & base contains (2/1000) x 50

=0.1 moles

0.1 moles H20 = 727.92J

1.0 moles H2O = 727.92J / 0.1 moles

= 7279.2J

Change from J to kJ

7279.2J / 1000 = 7.279kJ

Write the molecular and ionic equation for the reaction

NaOH(aq)   +  HCL(aq)                NaCl(aq) +  H2O(l)

H+(aq)   +    OH(aq)                 H2O(l)

Explain whether the reaction was exothermic or endothermic?

Heat was lost from the mixture to the environment can be said to be exothermic.

What was the use of the Styrofoam cups?

They were used to minimize heat loss of the mixture to the environment.

Chromatographic Methods of separation of substances of a mixture

Chromatography is used to analyze small quantities of a mixture of substances which are chemically similar to each other. It involves the partition of the components of the mixture between a stationary phase and a mobile phase. The mixture to be separated is introduced on the stationary phase which stays still. The mobile phase is then allowed to move over the stationary phase for separation. Partition depends on the different solubilities of the components in the mobile phase and the different adsorption forces of the components with the stationary phase. Adsorption is the temporary attraction of molecules of a gas or liquid to a solid surface. Components with greater solubilities will dissolve into the mobile phase and move along with it readily. Components with stronger adsorption forces will be held on the stationary phase and not move along readily with the mobile phase. The differences in solubilities and adsorption bring about separation.

Paper Chromatography

In paper chromatography, a piece of filter paper or chromatography paper is used which consists of stationary water molecules embedded in a cellulose matrix. The water molecules act as the stationary phase. The mobile phase consists of a suitable solvent that travels up the stationary phase. The mixture to be separated is spotted a short distance from one end of the paper (the base line). The end below the spot is placed in the solvent. As the solvent moves along the paper it carries the mixture with it. The distance the solvent moves from the baseline is called the solvent front. Components of the mixture will separate readily according to how strongly they adsorb on the stationary phase and how readily they dissolve in the mobile phase. If the separated components are colorless, then a visualizing agent can be used to convert them into colored spots. The positions of certain substances can also be determined by fluorescing under a UV lamp. The ratio of the distance moved by a component of the mixture to the distance moved by the solvent is called retention factor. Rf = distance moved by a component distance moved by solvent Each component has a characteristic Rf value for a given solvent under controlled conditions. Thus Rf values of known substances can be used to identify components of a mixture. Paper chromatography is used to analyze mixtures such as dyes in ink, coloring in food additives and amino acids from protein hydrolysis. A visualizing agent such as ninhydrin is used to detect amino acids and amines.

Thin Layer Chromatography (TLC)

This method is similar to paper chromatography. The stationary phase is a thin layer of powered alumna or silica gel which s fixed on to a glass or plastic plate. Plates can be coated with a slurry of the powered adsorbent and then oven – dried. The mixture to be analyzed is spotted near the bottom of the plate. The end below the spot s placed in a suitable solvent. This solvent is the mobile phase and moves up the plate causing the components of the moving solvent. The separated components may be recovered for further analysis by scraping spots off the plate. Thin layer chromatography has the advantage that a variety of adsorbents can be used for separation. It is commonly used to separate amino acids in blood samples and for analysis of food dyes.

Column Chromatography

This method is similar to thin layer chromatography however the stationary phase is packed into a vertical glass column (diameter 1- 2cm) instead of being coated on a plate. A slurry of silica gel or alumina is commonly used for column chromatography. The mobile phase is a suitable solvent which is added to the top of the loaded column. The solvent flows down the column under gravity causing the components of the mixture to partition between the adsorbent and solvent. Each component emerges from the column at different times and can be collected separately. The time between addition of the sample at the top of the column and the emergence of a component at the bottom of the column is called the retention time of that component. Identical substances will have the same retention time under the same conditions thus retention times can be used to identify substances. Column chromatography has the advantage that larger quantities can be separated and therefore can be used to prepare compounds in addition to analyzing them. This method is used in biochemical research and in hospitals to identify amino acids, peptides and nucleotides.

High Performance Liquid Chromatography (HPLC)

This technique is similar to column chromatography however instead of gravity feed, high pressure is used to force the solvent through the column. Columns are smaller than those used in column chromatography, some being 10cm to 30cm long and 4mm in diameter. Retention times are shorter thus rapid analysis of substances can be made. HPLC s used n the industry and hospitals. It is also used to identify suspected stimulants, doping and drugs that may be present in athletes and racehorses.

Gas – Liquid Chromatography (GLC)

GLC uses a longer column than HPLC. It is usually packed with the stationary phase which is an inert powder coated with an non-volatile oil. The column is maintained at a constant, preset temperature in an oven. The mobile phase is an un-reactive gas. The sample to be analyzed has to be in the vapor state at the temperature at which the column is operated. The vaporized sample is carried through the column by the mobile phase. The sample is partitioned between the oil and the carrier gas A detector records each component as it leaves the column at different times. Emerging components can also be fed directly into a mass spectrometer for identification. GLC method of analysis is very sensitive and can be used in forensic testing, to monitor air and water pollution, to detect and identify traces of pesticides or agricultural chemicals in foodstuff and to check dosage of drugs in blood or urine samples.

Saponification

Saponification can be defined as a “hydration reaction where free hydroxide breaks the ester bonds between the fatty acids and glycerol of a triglyceride, resulting in free fatty acids and glycerol,” which are each soluble in aqueous solutions.

Aim / Objective:

To produce soap using a base-catalyzed saponification of triglycerides.

Introduction:

Soap molecules are the conjugate bases of fatty acids.  Vegetable oils and animal fats are the main materials that are “saponified”. These fats are in fact tri-esters of a glycerol molecule. In the traditional one-step process, the triglyceride is treated with a strong base (e.g., lye), which accelerates cleavage of the ester bond and releases the fatty acid in its conjugate base form, and glycerol.

A General Reaction is as follows:

Saponification Reaction

Saponification using triglycerides

Different alkyl (R) groups are found in different fats and oils.  Depending on which triglyceride (tri-ester) you choose, your soap will have different properties.  For example, some oils make soft or liquid soaps, and some fats make hard soap.

Materials/Apparatus:

Tripod stand, wire gauze, spatula, breaker, 2 measuring cylinder, glass stirring rod, filter funnel, filter paper, Bunsen burner, 2 test tubes with bungs, test tube rack, evaporating dish, castor oil, concentrated sodium hydroxide (NaOH), distilled water, perfume, dye, saturated solution of sodium Chloride (NaCl)

Method / Procedure:

  1. Half fill a beaker with tap water and set to boil.
  2. Place 2cmcastor oil into evaporating dish. Use a measuring cylinder to pour 10cm3 of concentrated NaOH into the castor oil
  3. Place the evaporating dish atop the beaker of boiling water
  4. Stir the mixture of oil and alkali with a glass stirring rod for 10-15 minutes
  5. Add 10cm3 of the saturated salt solution to the basin and stir the mixture
  6. Turn the Bunsen burner off and leave to cool for 2-3 hours
  7. Use a spatula to scrape the crust of soap which is formed on the side of the evaporating dish
  8. Put this material in a beaker
  9. Add water to the material in the beaker and heat the beaker.
  10. Add a few drops of dye and perfume to the beaker

Discussion:

1. What is the name given to this process?

>>> Saponification

2. Write the word equation for this reaction

>>> Fat/Oil + NaOH        =         Glycerol + Soap (Sodium Salt of Acid)

3. Why is the product of saponification called a salt?

>>> This experiment is the hydrolysis of a fatty acid, usually from lye and fats. The process produces a carboxylate which is a sodium salt.

4. Why was ethanol added to the mixture of fat and base?

>>> Ethanol (ethyl alcohol) is added to the mixture to make the soap transparent. Transparent soap is also known as glycerin.

5. How does soap emulsify fats and oils?

>>> Grease and oil are nonpolar and insoluble in water. When soap is mixed with oils and fats  the nonpolar hydrocarbon portion of the micelles of the soap break up the nonpolar oil molecules. A different type of micelle then forms, with nonpolar oils and fats molecules in the center. Therefore, grease and oil and the ‘dirt’ attached to them are caught inside the micelle and can be rinsed away.

6. Explain the difference in “hard water” and “soft water”

Hard water is any water containing a great quantity of dissolved minerals while soft water is treated water in which the only cation (positively charged ion) is sodium.

7.  Explain which water is better to use with soap

>>>Soap is less effective in hard water as it will react with the ions in the water to form the calcium or magnesium salt of the organic acid of the soap. These salts are insoluble and form grayish soap scum, but no cleansing lather.

Separating a mixture of oil and water using a separating funnel

Aim / Objective:

To separate a mixture of cooking oil and water.

Abstract:

In this experiment, an immiscible mixture of oil and water was separated using a separating funnel.

Materials/ Apparatus:

measuring cylinder, retort stand, beaker, clamp, separating funnel, conical flask, cooking oil and water,

Method / Procedure:

  1. Use a measuring cylinder to measure 10cm3 of cooking oil and pour it into the conical flask.
  2. Use another measuring cylinder to measure 10cm3 of water and add to the conical flask with the oil.
  3. Mix both liquids by shaking the flask vigorously.
  4. Use a clamp to attach the separating funnel to a retort stand. Ensure that the separating funnel is in the closed position and pour in the mixture of oil and water.
  5. Allow the mixture to settle for a few minutes. Place a beaker under the mouth of the separating funnel and allow the mixture of water to run off in the beaker slowly.
  6. Collect the remaining portions of water and oil and then the pure oil.

Diagram of apparatus showing the separation of a mixture of oil and water using a separating funnel

Suggested Results:

When the water was added to the cooking oil, it was seen to be the more dense liquid hence the water settled on top of it. Also in between the layer of pure oil and the layer of pure water, there was a layer consisting of a mixture of oil.

Diagram of apparatus showing the separation of a mixture of oil and water using a separating funnel

Discussion:

1.What type of mixture is the separating funnel generally used to separate?

>>>The separating funnel is generally used to separate a mixture of immiscible liquids. Immiscible meaning that the liquids do not mix but separate into distinct layers

2. Explain why this technique was suitable in separating the oil from the water.

>>>This technique was ideal for the experiment for when water is mixed with oil, it is known to be immiscible. It forms a total of three layers, a layer of pure oil, pure water and a layer of both water and oil mixed together.

3. Explain the chemical principle underlying the type of mixture formed by oil and water

>>>Pure oil doesn’t mix with water because water is polar solvent and oil is non-polar and like dissolves like. But in between the layer of pure oil and pure water there was a layer of both oil and water. This type of technique can be said to be an emulsion.

4.To what position should the top of the funnel be turned when opening it?

>>>The top should be vertical to allow the water to run out and must be closed before the oil reaches the bottom of the funnel

5.Can separating funnel be used to separate a mixture of ethanol and water? Explain your answer

>>>No. A separating funnel cannot be used to separate ethanol and water because ethanol will dissolve in the water due to polarity hence being classified as miscible liquids. So in order to separate a mixture of ethanol and water, one would have to use fractional distillation.

Source of Error/ Limitations/ Assumptions: 

–  Improper technique of decanting, thus allowing for the layers that were collected to be not entirely pure.

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