General Chemistry Laboratory Manual For

1st Year Students College Of Pharmacy

2019-2020

Laboratory Reports

1- Lab Preparation Write-ups (Pre-Labs): It is necessary that you study the experiment that you are to do prior to arriving to the laboratory. You should read the lab manual carefully and try to understand the overall content and purpose. 2- Report Format: Reports will be written down in a laboratory notebook

)A) Experiment Number and Title: Name: Last Name, First Name Lab Number : Date: Lab Partner’s Name:

(B) Procedural Outline: Include a short summary of the overall experimental plan you are going to run. If the experiment involves an organic reaction, you need to draw the structures of the reactants and products in full. Also, a table should be set up listing the following for each compound to be used: physical properties (bp, mp, density). You should also note any hazards involved with the experiment.

(c) Observations/Data: Accurately record what you do and what you observe. (d) Discussions/Conclusions: Write your conclusions, lessons, and comments. (e) Answers to Questions: Provide answers to the questions at the end of each experiment. The questions are usually related to practical elements of the experiments and you should try to look at them during the laboratory sessions and talk your ideas over with your Instructor or TA.

List of Glassware and Equipment

Reagent bottle Test tubes Test tube racks

Washing bottle Conical flasks

Pipette

Stirrer Volumetric flasks Dropper

Stand and Clamp Fume Hood Burette

Beakers Petri dish Graduated Cylinders Funnel

Oven Hot plate Water bath Sensitive balance

Filter paper Tong Capillary tube

Thermometer Spatula Watch glass pH paper

Round bottom flask

Criteria Theory 25% Practical laboratory 25% Report 5 point Quiz 5 point Seminar 5 point Midterm Exam 5 Point Final Course Exam 5 Point

1- 0rganic Experiments Seventh Edition Louis F. Fieser Late Professor Emeritus Harvard University Kenneth L Williamson Mount Holyoke College

References

2- A Textbook of Practical Organic chemistry by VOGELS Fifth edition Revised by former and current members of the school of chemistry Thames polytechnic .London BrianS.Furniss Antony J.Hannaford Peter W.G.Smith Austin R.Tatchell

3- Laboratory Experiment For General Organic and Biochemistry Fourth Edition Bettelheim and Landesberg

Experiments NO. (1) Determination Of Melting Point Of Solid Organic Compounds

Purpose The purpose of this experiment is to determine the melting points of various organic compounds and to use these to identify unknowns. Equipment/Materials known Organic compounds ( Benzoic Acid,Benzophenone, Salicylic Acid )

Thermometer Capillary tubes Mortar and pestle (optional) Watch glass Stand and clamp Oil bath Bunsen burner

• The melting point of a substance is the temperature at which the material changes from a solid to a liquid state at atmospheric pressure. While the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point

• Determining the melting point of a compound is one way to test if the substance is pure. A pure substance generally has a melting range (the difference between the temperature where the sample starts to melt and the temperature where melting is complete) of one or two degrees. For example, M.P. 142-144°C. However, a sample is impure if it has a melting point range that is lower and/or wider than that the literature value. More impurities increase this effect.

• A wide melting- point range (more than 2° C) usually indicates that the substance is impure; a narrow melting point range (0.5-2° C) usually indicates that the substance is fairly pure. However, there are some exceptions to both of these generalizations.

The melting or freezing point of a substance refers to the temperature at which the solid and liquid states are in equilibrium

The melting point is the temperature at equilibrium when starting in the solid state and going to the liquid state. The freezing point is the temperature at equilibrium when starting in the liquid state and going to the solid state.

Melting points of pure substances occur over a very narrow range and are usually quite sharp. The criteria for purity of a solid is the narrowness of the melting point range and the correspondence to the value found in the literature. Impurities will lower the melting point and cause a broadening of the range. For example, pure benzoic acid has a reported melting point of 122C benzoic acid with a melting point range of 121–122C is considered to be quite pure.

The melting point of solid is defined as the temperature at which the solid exists in equilibrium with its liquid under an external pressure of one atmosphere

Generally, melting points used by chemists for two reasons:

Determination of purity.

Identification of unknowns compounds.

Pure crystalline substances have a clear, sharply defined melting point.

Sample Preparation Any substance being loaded into a melting point capillary must be:

1. Fully dry

2. Homogeneous

3. In powdered form

A sample height between 2.0 mm and 3.0 mm is recommended for optimum results.

The rate of heating is the most important factor in obtaining accurate melting points. Heat no faster than 1°C per minute.

Preparation: 1-Place a sample of the compound into a capillary tube. a. Push the open end of a capillary tube into the powdered sample. b. Move the powder to the closed end of the capillary tube. Repeat until the powdered sample occupies 1-2 mm of the capillary tube end. 2-Fix the capillary tube to the thermometer by sticker. 3- Set up a ring stand with a Bunsen burner. 4- Place oil in to the beaker. 5- Use the Bunsen burner to heat the mineral oil slowly. 6-Record the temperature at which the solid in the capillary tube melts.

A Mel-Temp apparatus equipped with a digital thermometer is shown below

The Thiele tube is a glass tube designed to contain heating oil and a thermometer to which a capillary tube containing the sample is attached. The shape of the Thiele tube allows for formation of convection currents in the oil when it is heated. These currents maintain a fairly uniform temperature distribution throughout the oil in the tube. The side arm of the tube is designed to generate these convection currents and thus transfer the heat from the flame evenly and rapidly throughout the heating oil. The sample, packed in a capillary tube is attached to the thermometer, and held by means of a rubber band or a small slice of rubber tubing. It is important that this

rubber band be above the level of the oil (allowing for expansion of the oil on heating). Otherwise, the oil softens the rubber and allows the capillary tubing to fall into the oil.

• The Thiele tube is usually heated using a micro burner with a small flame but a Bunsen burner can also be used. When heating, the rate of temperature increase should be carefully controlled. Usually one holds the burner by its base and, using a small, gentle flame, moves the burner slowly back and forth along the bottom of the side arm of the Thiele tube. If the heating rate is too fast, the burner is removed for a few seconds before resuming the heating process. The rate of heating should be slow.

Q1 / Is benzoic acid harmful? benzoic acid is used in foods and medicines and is of low hazard at the concentrations

used. (It occurs naturally in plants, notably berries.) Its antimicrobial properties can protect against some biological hazards, and it has long been used as an antiseptic.

Draw out a capillary tube. Put some benzoic acid crystals in it. Fix the tube with rubber bands to a centigrade thermometer that goes up to 150 degrees at least. The crystals should be next to the bulb on the thermometer. Put the tube and thermometer in an oil bath. Heat gently with stirring. Watch the crystals when the temperature gets to about 115 deg. Continue raising the temperature slowly, watching for the temperature at which the crystals melt. Write down this temperature. Turn off the heat. Let the oil cool. Return it to its bottle. Wash the flask and thermometer put them back in their place.

Q2 / How can you determine the melting point of benzoic acid?

Q3/ What are the criteria for purity of a solid?

Q4 / A student did a melting point determination for a sample of acetanilide and found a melting point of 113–114C. What conclusion can the student draw about the sample?

The boiling point of a liquid is the temperature at which its vapor pressure is equal to the surrounding atmospheric pressure. The normal boiling point of a liquid is the temperature at which its vapor pressure is equal to one atmosphere (760 torr).

Factors That Affect the Boiling Point 1- Pressure: when the external pressure is: • less than one atmosphere, the boiling point of the liquid is lower than its

normal boiling point. • equal to one atmosphere, the boiling point of a liquid is called the normal

boiling point. • greater than one atmosphere, the boiling point of the liquid is greater than its

normal boiling point.

2- Types of Molecules: the types of molecules that make up a liquid determine its boiling point. If the intermolecular forces between molecules are: • relatively strong, the boiling point will be relatively high. • relatively weak, the boiling point will be relatively low.

EXP. NO. 2 A- Determination Of Boiling point B- Distillation

Question: At what temperature does water boil? What determines the boiling point of water?

Answer: The boiling point of water depends on the atmospheric pressure, which changes according to elevation. The boiling point of water is 100°C or 212° F at 1 atmosphere of pressure (sea level), but water boils at a lower temperature as you gain altitude (e.g., on a mountain) and boils at a higher temperature if you increase atmospheric pressure (lived below sea level).

The boiling point of water also depends on the purity of the water. Water which contains impurities (such as salted water) boils at a higher temperature than pure water. This phenomenon is called boiling point elevation.

• The boiling point of organic compounds can give important information about their physical properties and structural characteristics. Boiling point helps identify and characterize a compound. A liquid boils when its vapour pressure is equal to the atmospheric pressure. Vapour pressure is determined by the kinetic energy of a molecule.

• Kinetic energy depends on the temperature, mass and velocity of a molecule. When the temperature increases, the average kinetic energy of particles also increases. When the temperature reaches the boiling point, the average kinetic energy becomes sufficient to overcome the force of attraction between the liquid particles. As the force of attraction decreases, the molecules in the liquid state escape from the surface and turn into gas

• The boiling point of a liquid varies with the surrounding atmospheric pressure. A liquid at a higher pressure has a higher boiling point than when that liquid is at lower atmospheric pressure.

• The normal boiling point of a compound is an indicator of the volatility of that compound. The higher the boiling point, the less volatile is the compound. Conversely, the lower the boiling point, the more highly volatile is the compound. At a given temperature, if a compound’s normal boiling point is lower, then that compound will generally exist as a gas at atmospheric pressure. If the boiling point of the compound is higher, it then exists as a liquid

1. Strength of intermolecular forces

The relative strength of intermolecular forces such as ionic, hydrogen bonding, dipole-dipole interaction and Vander Waals dispersion force affects the boiling point of a compound. The influence of these forces depends on the functional group present. We can explain the effect of these forces on the boiling point of compounds with the help of some examples. Consider butane and its three derivatives such as diethyl ether, n- butanol and sodium n- butoxide.

n-butane (C4H10) contains no polar functional group. The only attraction between the butane molecules is weak Vander Waals dispersion forces. The result is that butane boils at a temperature at which water freezes, and is much lower than diethyl ether. In the case of diethyl ether, the molecules are held together by dipole-dipole interaction which arises due to the polarized C-O bond. Its boiling point is 35oC. Compare its boiling point with that of n- butanol. The boiling point of n- butanol is 117oC. The greatly increased boiling point is due to the fact that n- butanol contains hydroxyl group, which is capable of hydrogen bonding. But the boiling point of sodium butoxide is higher than that of butanol because the attractive force in sodium butoxide is very strong ionic bond. The intermolecular forces go in the order Ionic > Hydrogen Bonding > Dipole-Dipole > Van der Waals dispersion force.

What are the general trends that affect the boiling point?

2. Length of carbon-carbon chain As the number of carbon atoms increases or the length of carbon-carbon chain increases, the boiling point also increases. This is because the force of attraction between the molecules increases as the molecule gets longer and has more electrons. It takes more energy to overcome the force of attraction, and so the boiling point rises.

3. Branching decreases the boiling point

As the length of carbon chain increases, the surface area of the compound will also increase. Van der Waals dispersion force is proportional to the surface area. So the increase of surface area increases the ability of individual molecules to attract each other. Branching in molecules decreases the surface area thereby decreasing the attractive force between individual molecules. As a result, the boiling point decreases.

Consider the boiling point of n-pentane and neo-pentane (2,2-dimethyl propane). These are isomers having the same molecular formula (C5H12), but differ in their structures. The boiling point of neopentane is much lower than that of n-pentane.

4. Polarity Polarity of the molecule determines the force of attraction between the molecules in the liquid state. In polar compounds, the positive end of one molecule is attracted by the negative end of another molecule. That means polar molecules are attracted by opposite charge effect. The polarity of a molecule is determined by its functional group. The greater the polarity, the higher is the boiling point.

Boiling point of some common organic compounds

Procedure

B- Distillation Distillation is process involving the conversion of a liquid into vapor that is subsequently condensed back to liquid form. Distillation is a physical separation process, and not a chemical reaction

Distillation is a procedure that separates a mixture of liquids with different boiling points. Distillation is a useful technique in chemistry labs, where chemists use it to purify a compound, and also in industry, especially in the petrochemical , refining industry and in the manufacture of ethanol. It is for this last that distillation is most famous--alcoholic beverages are produced through a process of distillation. .Applications of distillation The application of distillation can roughly be divided in four groups: laboratory scale, industrial distillation, distillation of herbs for perfumery and medicinal (herbal distillate), and food processing. Commercially, distillation has a number of applications. It is used to separate crude oil into more fractions for specific uses such as transport, power generation and heating. Water is distilled to remove impurities, such as salt from seawater. Air is distilled to separate its components—notably oxygen, nitrogen, and argon— for industrial use.

Types of distillation

1. Simple distillation

2. Fractional distillation

3. Steam distillation

4. Vacuum distillation

Fractional Distillation Fractional distillation is similar to simple distillation, except the same process is repeated in successive cycles. Each cycle produces a mixture richer in the more volatile compound than the mixture before it. Fractional distillation is necessary when the boiling points of the liquids in the original mix are close enough to each other that simple distillation is not enough to purify either compound.

Simple Distillation If water is placed in a sealed container and allowed to evaporate, it will eventually reach an equilibrium such that the water vapor is condensing just as fast as the water is evaporating. The pressure of the vapor at this equilibrium is called the vapor pressure. Vapor pressure is different for different substances and varies with temperature. In a mixture of two liquids with different boiling points, the vapor will have more of the liquid that is more volatile, i.e., evaporates more readily. In simple distillation, the liquid mixture is heated and the vapor rises through a tube and is collected and recondensed. The recondensed liquid will have a higher concentration of the more volatile component than the original mix. If the two liquids in the original mix have widely different boiling points, a one-step evaporation and recondensation process is all that is necessary. This process is called simple distillation.

Steam Distillation

Steam distillation is used to separate heat-sensitive components. Steam is added to the mixture, causing some of it to vaporize. This vapor is cooled and condensed into two liquid fractions. Sometimes the fractions are collected separately, or they may have different density values, so they separate on their own. An example is steam distillation of flowers to yield essential oil and a water-based distillate.

Vacuum Distillation Vacuum distillation is used to separate components that have high boiling points. Lowering the pressure of the apparatus also lowers boiling points. Otherwise, the process is similar to other forms of distillation. Some liquids boil at such high temperatures that simple or fractional distillation using the process described above would be impractical or dangerous. Vacuum distillation, however, offers another alternative. The boiling point of a liquid falls when the pressure is reduced. The boiling point of water, for example, is lower at high altitude than at sea level. By reducing the pressure in the container, the boiling point of the liquids in the mixture can be reduced and the mixture distilled at a lower temperature. This technique is called vacuum distillation.

Simple Distillation

Fractional Distillation

Distillation Under Reduced Pressure

Boiling chips should be placed in the distillation flask for two reasons: they will prevent superheating of the liquid being distilled and they will cause a more controlled boil, eliminating the possibility that the liquid in the distillation flask will bump into the condenser.

Never add a boiling chip to a solvent which is already hot, because it can cause to solvent to boil over violently.

Boiling chips are small, insoluble, porous stones made of calcium carbonate or silicon carbide. These stones have pores inside which provide cavities both to trap air and to provide spaces where bubbles of solvent vapor can form. These bubbles ensure even boiling and prevent bumping and boiling over and loss of the solution. Always use a boiling chip when heating a solvent. Never add a boiling chip to a solvent which is already hot, because it can cause to solvent to boil over violently. If you forget to add a boiling chip before you begin, you must cool the solution before adding one to prevent product loss. Boiling chips cannot be re-used since the pores inside these stones become filled with liquid on cooling.

Boiling chips are typically made of a porous material, such as alumina, silicon carbide, calcium carbonate, calcium sulfate, porcelain or carbon. This ensures that the boiling chips will provide effective nucleation sites, yet are chemically inert. pieces of broken porcelain ware or glassware are often used.

Q1 / Which would be expected to have the higher boiling point, /-butyl

alcohol (2-methyl-2-propanol) or n-butyl alcohol (1-butanol)?

Question