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7 chemistry labs (simple)

In chemistry laboratories there is space and materials necessary to develop even practices related to microbiology and biology in general. There are available reagents, glass materials, counters, funnels, solvents, distilled water, rubber hoses, extractor hoods, vacuum valves and gases for proper filtration and bunsen burners.

Basic chemistry laboratory. Source: Allan Cao / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Many practices require supervision by experienced teachers as well as student trainers, a clear awareness of the toxicology of the reagents being handled, and a mastery of techniques expected of an analyst. This is so at the university level.

At the secondary level, the experiments are generally simple and risk-free. And those that do are carried out by the teacher himself, as a demonstration, for the students to take data and then discuss the results.

Bacterial growth

Petri dish with Escherichia coli culture

In this practice, a growth graph of a non-pathogenic strain of Escherichia coli bacteria will be made . To do this, you will receive a bacterial suspension from your teacher.

100 mL of culture medium are inoculated, placed in an Erlenmeyer flask with 10 mL of a bacterial suspension of E. coli. The Erlenmeyer must be in a temperature regulated bath. The inoculated medium is shaken and a 5 mL sample is taken in sterile form, to obtain the zero time of the growth curve.

At the same time, the student will determine the optical density of this sample on a spectrophotometer. This procedure should be followed with the samples taken at the different incubation times, constructing the growth curve with the optical density values.

The student must discuss the shape of the growth curve, identifying the different phases of the curve made with the experimental data.

Target

The objective of the practice is to make a yogurt with a widely used procedure. In addition, we will try to see the effect of some types of sugars on the consistency of yogurt and its pH.

Materials

-Full liquid milk

-Full milk powder

-Saccharose

-Glucose

-Lactose

-Thermometer

-Universal indicator on tape

-4 glass jars with screw cap

Process

There are several ways to prepare yogurt. In this practice, the following procedure will be followed:

-Heat 1 liter of milk at 85ºC for 30 minutes.

-Turn off the heat and let the milk cool until it is lukewarm (60 ºC).

-Separate the milk into 4 portions of 250 mL, which will be placed in labeled jars, adding 1 tablespoon of whole milk to each one.

-Place in 3 different sugar jars. A bottle that serves as a control does not receive sugar.

-Immediately measure the pH of the 4 flasks using a pH indicator tape.

-When the temperature of the jars is around 44 ºC, add 0.5 tablespoons of a commercial yogurt to the 4 jars.

-Cover the jars and leave them in a place with a warm temperature overnight.

-The next day, examine the consistency of the yogurt in each of the 4 jars, as well as their pH.

-Note the results and have a discussion about them.

Hooke’s law

This law states that there is a relationship between the force applied to a spring and the degree of its stretch:

F = KX

Where F is the applied force, K the spring constant of the spring, and X the magnitude of the deformation of the spring by the applied force.

Although this practice has nothing to do with chemistry, it is still one of the simplest and safest that can be done at any level of education.

Process

The spring is suspended from a clamp, mounted on a universal bracket. Meanwhile, the different weights used in practice will be placed at the free end.

Initially, the initial length of the spring is carefully measured with a ruler, that is, without the application of any weight , and the pertinent annotation is made. Based on the characteristics of the spring, the teacher will indicate which weights should be used in practice.

The smallest weight is placed and the length of the spring is measured. By subtracting the length of the spring in the absence of weight, the stretching of the spring due to the applied force is obtained. In the same way, proceed with the other applied forces.

Then the student will proceed to transform the applied weight into Newton, since this is the unit of force. One kilogram of weight equals 9.8 Newton and one gram of weight is 0.0098 Newton.

With the data obtained, he will make a graph of Force (Newton) in the ordinate (y) Vs stretch of the spring in meters on the axis of the abscissa (x). The student will be able to obtain from the graph the constant of the stretch of the spring, since it will be the slope of the line.

Gas laws

Experiment A

A plastic bottle is taken and a light rubber ball attached to it is placed in the mouth of the bottle. When you squeeze the plastic bottle with one hand, the ball is ejected from the mouth of the bottle.

Questions

How is the observed behavior explained? What law is illustrated by the experiment? What is the formula of the law? Importance of the law.

Experiment B

The experimental design is the same as Experiment A, but in this case the bottle is not squeezed, but is placed in a hot water bath. The ball is expelled as in the previous experiment.

Questions

The same from the previous experiment.

Experiment C

Take two rubber balloons of equal volume , filled with air, and immerse one in cold water and the other in moderately hot water. The volumes of the balloons are compared at the end, noting the difference observed.

Questions

The same as in the previous experiments.

Preparation of solutions

In this practice, the student must prepare a mass / volume solution expressed as a percentage (%). In this case, 0.5 liter of a 5% (m / v) potassium chloride solution should be prepared.

Process

-The student must calculate the mass of solute that must be weighed to make the solution.

-The student will weigh the calculated mass of potassium chloride on the scale, carefully following the instructions given for the use of the scale.

-Once the potassium chloride has been weighed, it must be placed in a 1-liter beaker and a volume of water is added, so that the volume of the potassium chloride-water mixture does not exceed 0.5 L.

-After solubilizing the potassium chloride, it will be completed to 0.5 L by using a volumetric flask.

Crystallization

Crystallization is a routine procedure used in the purification of reagents.

To proceed to solubilize the sodium chloride, the quantity to be dissolved is placed in a beaker with 250 mL of water, adding with continuous stirring at the same time as the solution is heated.

This procedure produces a supersaturated sodium chloride solution, due to the heating of the solution, which dissolves any crystals that may remain intact. If there is a portion of solute that does not dissolve, it could be a contaminant that can be removed by hot filtration.

The sodium chloride solution is then allowed to cool. The excess of the salt that was dissolved by heating precipitates in the form of well defined crystals. Another way to produce crystallization is by slow and gradual evaporation of the solvent.

Hardness of water

The hardness of water is due to the concentration of dissolved calcium and magnesium ions. In this practice, its concentration will be determined following the complexometry method, by using a standardized solution of 0.01 M EDTA-disodium. The hardness of the water is expressed as mg of CaCO 3 / L (calcium carbonate).

Process

50 mL of the test water are placed in a 250 mL Enlenmeyer and 2 mL of a buffer solution (NH 4 Cl-NH 4 OH) pH 10.0 are added, and an amount of 0.1 – 0.2 g of the known indicator as eriotochrome T black (NET), producing a reddish coloration of the solution.

Next, the test solution is titrated by adding a 0.01 M EDTA-disodium solution, placed in a burette. The EDTA should be added slowly to the test solution with continuous stirring, visualizing a change in color of the titrated solution.

For a certain volume of EDTA added, it is observed that the titrated solution changes from a reddish tone to a blue tone, the volume of EDTA that produced the color change is noted.

The hardness of the water (expressed in mg of CaCO 3 / L) will be determined by applying the following formula:

mg CaCO 3 / L = (V EDTA · M EDTA / V sample) · 100.091

Coming 100,091 from:

100.091 g / mol (CaCO 3 MW ) 1,000 mg / g

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