Práctica I-A: Instrumentación Básica del Laboratorio PDF

# Práctica I-A: Instrumentación Básica del Laboratorio ## Objetivo General * Identificar usos de los instrumentos y cristalería de laboratorio. ## Objetivos Específicos * Identificar los instrumentos más usados en el laboratorio. * Reconocer el uso de los instrumentos de laboratorio. * Identific...

# Práctica I-A: Instrumentación Básica del Laboratorio ## Objetivo General * Identificar usos de los instrumentos y cristalería de laboratorio. ## Objetivos Específicos * Identificar los instrumentos más usados en el laboratorio. * Reconocer el uso de los instrumentos de laboratorio. * Identificar la cristalería para medir volúmenes con mayor precisión. ## 1.1 Fundamentos Teóricos En los laboratorios de Química se utilizan instrumentos que deben ser reconocidos por los alumnos, tanto por su nombre, uso y manejo for a better performance in carrying out the practices. Below are detailed instruments and materials that are most frequently used in the laboratory. * **Tubo de ensayo**: Heat substances and carry out experiments. * **Probeta**: Measure volumes that do not require much precision. * **Pipeta**: Measure volumes of liquids with greater precision, with volumetric ones being more precise than graduated ones. * **Bureta**: Measure the volume of liquids used in volumetric analysis with great precision. * **Erlenmeyer flask**: Heat and observe chemical changes in titrations and in violent chemical reactions. * **Beaker**: Used to prepare, dissolve or heat directly on hot plates or heating plates. * **Funnel**: Used as an aid in the filtration process and to pass liquids. * **Balance**: To determine masses. * **Thermometer**: To measure temperature. * **Watch glass**: Cover a vessel and aid in weighing solids. * **Test tube rack**: To hold test tubes. * **Spatula**: Handling solids. * **Volumetric flask**: For the preparation of solutions. * **Bunsen burner**: Heat source. * **Hydrometer**: Measure the density of liquids. * **Clamps**: To hold items (test tubes, crucibles). * **Universal stand**: Hold objects (burets, thermometers, among others). * **Mortar and pestle**: Crush substances and grind. * **Tripod**: Hold objects. * **Wire gauze**: Hold a vessel during heating. * **Crucible**: Heat solids to high temperatures. * **pH-meter**: Measure pH. * **Flat-bottom flask**: For heating. * **Wash bottle**: Store distilled water. * **Separatory funnel**: Separate immiscible liquids. ## 1.2 Procedure for Identifying Laboratory Instruments Based on the explanations and demonstrations of the teacher, students will relate the images to the materials and instruments available in the laboratory, highlighting the name and corresponding use of each. ## 1.3 Materials Materials available in the laboratory: * Distillation flask * Beaker * Volumetric flask * Graduated cylinder * Erlenmeyer flask * Test tube Figure 1.1 Basic instruments for laboratory work. * Spatula * Mortar * Crucible * Tripod * Stirrer Figure 1.2 Basic instruments for laboratory work. * Buchner funnel * Graduated cylinder * Thermometer * Separatory funnel * Funnel * Graduated pipette * Volumetric pipette Figure 1.3 Basic Instruments for laboratory work. * Watch glass * Support for masses * Arm * Index of Fidelity (Calibration Line) * Base Figure 1.4 Manual balance. # Práctica I-B: Bunsen Burner and Combustion ## Objetivo General * Analyze the combustion process. ## Objectives Specifics * Operate the Bunsen burner correctly. * Compare complete and incomplete combustion * Identify flame zones. ## 1.4 Fundamentals of Theory. The Bunsen burner is a heat energy source used in chemical laboratories. It is named after the German chemist and physicist Robert Wilhelm Bunsen. It **consists of three parts**: A vertical tube with a hole for air inlet; a ring that regulates the air inlet; and a base through which the fuel enters. To light it, a lit match is held at the top of the vertical tube and the valve that allows gas to flow is carefully opened, regulating the flow. **Flame zones**: There are three zones: the cold or bluish zone, which corresponds to the inner part; the intermediate zone, which is luminous and yellow and corresponds to the ring that is lighter; and the zone with high temperature and light blue, which corresponds to the outer zone, which is slightly bluish. The characteristics of the flame in the Bunsen burner vary depending on whether the ring that regulates the air inlet is open or closed. The outermost part of the flame and the tip are hotter, indicating that the gas has entered completely. **Combustion**: The flame that is produced in the Bunsen burner is due to the combustion of propane gas with the oxygen in the air. Combustion is defined as a chemical reaction in which light and heat are produced. For this to be possible, three factors must intervene: * **Combustible**: The substance that burns in combustion. * **Combustion agent**: Keeps or activates the combustion. * **Ignition temperature**: The minimum temperature required for a combustible to ignite. When the fuel contains carbon and the combustion agent is oxygen, the combustion can be complete or incomplete. * **Complete combustion**: Occurs when all the carbon in the fuel combines with the oxygen and produces carbon dioxide and water, with the release of energy. * **Incomplete combustion**: Occurs when not all the carbon in the fuel combines with oxygen; some of it is deposited as solid carbon. This carbon is called soot or smoke. The complete combustion of propane gas is expressed by the following equation: $C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O + energy$ The incomplete combustion is expressed by the following equation: $C_3H_8 + 3O_2 \rightarrow C + 2CO + 4H_2O + energy$ ## 1.5 Materials and Reagents *Materials*: Test tubes, test tube tongs, test tube rack, stopwatch, matches, graduated cylinder, Bunsen burner. *Reagents*: Water, propane gas. ## 1.6 Procedure to Analyze the Combustion Process. * **1.6.1 Show the parts of the Bunsen burner.** With teacher supervision, the students will light the burner. * **1.6.2 Identify the zones in the flame.** With the burner lit, compare the characteristics of the flame with the inlet of the open and closed ring. Observe the color, size, and shape. * **1.6.3 Difference between complete and incomplete combustion.** Place the same amount of water in two identical test tubes. Place one of the test tubes in the burner flame with the air inlet open. * Determine the time it takes to boil and observe the exterior of the tube. * Repeat the steps above, with the air inlet closed. ## 1.7 The Bunsen Burner and its parts Figure 1.5 The Bunsen burner and its parts. * Hose * Outer cone * Inner cone * Tube * Ring * Base # Práctica II: Temperature and Density Measurements ## Objective General * Measure the temperature and density of various substances. ## Objectives Specifics * Use the balance correctly. * Measure the volume of solids and liquids * Determine the density of liquids and solids. * Measure the temperature of water under different conditions. * Calculate the temperature in various units. ## 2.1 Fundamentals of Theory. Figure 2.1 Density measurement. **Density**: Density is an intensive property (does not change with mass) of matter that is defined as the relationship that exists between the mass and volume occupied by that mass. The mathematical expression is: $D = \frac{M}{V}$, where M is mass and V is volume. Density is often expressed in grams per cubic centimeter ($g/cm^3$) for solids and liquids and in grams per liter ($g/L$ ) for gases. To determine the density it is necessary to know the value of the mass and the volume. The mass of the substances is measured on a balance (See fig.2.1). This can be done directly or indirectly. * **Direct measurement**: It is possible when the object is placed directly on the balance pan. * **Indirect measurement**: To measure the mass of granulated solids or liquids, you have to measure the container that holds them. By subtracting the masses, the mass of the substance is obtained. Solids can be regular and irregular. The volume of a regular solid is the same as the geometric volume of the solid. The volume of a regular solid is determined indirectly using Archimedes' principle, which states: When a solid is submerged in a fluid, it occupies a volume equal to the volume of the displaced fluid. The **hydrometer**, or **densimeter**, is the instrument used to directly measure the density of liquids. The relationship that exists between the density of a substance and the density of water at the same temperature is called **specific gravity**. **Temperature**: Temperature is the measure of the intensity (not quantity) of heat in a body. Temperature can be directly measured with a thermometer. Its units are: Celsius or Centigrade, Fahrenheit, Kelvin, and Rankine. To convert $^\circ C$ to $K$ there is: $K = ^\circ C + 273.15$ Equation to convert Celsius to Fahrenheit: $ ^\circ F = 1.8 \times ^\circ C + 32$ $R= ^\circ F + 460$ $ ^\circ C = \frac{( ^\circ F - 32 ) \times 5}{9}$ ## 2.2: Materials and Reagents *Materials*: Graduated cylinders, beakers, thermometers, tripods, wire gauze, clamps, Bunsen burner, and paper. *Reagents*: Water, zinc granules. ## 2.3: Procedures for Mass, Density, and Temperature Measurement. * **2.3.1 Know how to use the balance.** The teacher will show the parts of the balance and how to make direct and indirect measurements of different objects and substances. * **2.3.2 Students will perform measurements on objects and substances.** # Práctica III: Physical Changes and Chemical Phenomena ## Objective General * Differentiate between physical and chemical phenomena. ## Objectives Specifics * Identify physical and chemical phenomena. * Show chemical phenomena through equations. * Distinguish between reactants and products. ## 3.1 Fundamentals of Theory. Matter can present two kinds of modifications or phenomena. When the structure or composition of the matter does not changes, it is said that a physical phenomenon occurs. For example: Breaking a test tube; although its shape has changed, the resulting pieces of glass are still glass, meaning the chemical composition hasn’t changed. On the contrary, when there is a change in the chemical composition of matter, a chemical phenomenon is said to have occurred. For example, when heating a magnesium ribbon (see Fig. 3.1), the atoms separate and oxygen reacts easily, forming magnesium oxide. ## 3.1 Oxidation of Magnesium # Práctica IV: Study of Chemical Reactions ## Objective General * Analyze different reactions based on their reactants and products. ## Objectives Specifics * Identify reactions based on their manifestations. * Classify different types of reactions. * Conceptualize the precipitation process. ## 4.1 Fundamentals of Theory. When two or more substances are in contact they can form new substances that were not present before, with physical and different chemical properties from the ones that originated them. In this case, it is said that a chemical reaction occurs. For this to happen, the molecules must break down and the atoms rearrange to form new molecules. The substances that react are called *reactants* and the ones that are formed are called *products*. To describe a chemical reaction, symbols and formulas are used. Symbols represent elements while formulas represent compounds or chemical substances. The chemical reaction must fulfill the Law of Conservation of Mass, therefore it must be balanced. A chemical reaction can be identified by: * A color change * The release of a gas * The appearance of a precipitate ## 4.1.1 Classification of Chemical Reactions. * **Synthesis or combination**: Occur when two or more reactants interact to yield a single product. $A + B \rightarrow AB$ $2Hg + O_2 \rightarrow 2HgO$ * **Analysis or decomposition**: Occur when a single reactant yields two or more products: $AB \rightarrow A + B$ $2HgO \rightarrow 2Hg + O_2$ * **Substitution or displacement**: Occur when a more reactive element displaces a less reactive element from a compound. $A + BC \rightarrow AC + B$ $2KI + Cl_2 \rightarrow 2KCI + I_2$ * **Double substitution or double displacement**: Occur when one of the new products is insoluble in water after the displacement between metals.* $AB + CD \rightarrow AC + BD$ $2KCl + H_2SO_4 \rightarrow K_2SO_4 + 2HCl$ * **Neutralization**: Occurs when an acid and a base react to form a salt and water. $KOH + HCl \rightarrow KCl + H_2O$ ## 4.2 Materials and Reactors *Materials*: Test tubes, tongs, racks, Bunsen burner, matches. *Reactors*: Water, phenolphthalein (indicator), $Zn$, $C_{12}H_{22}O_{11}$, solutions of: $CuSO_4$, $BaCl_2$, $Na_2SO_4$, copper foil. # Práctica V: Relationship between Chemical Bonding and the Properties of Substances ## Objetive General * Relate the properties of substances to the chemical bonding. ## Objectives Specifics * Verify the relationship between polarity and solubility of different substances. * Differentiate between electrolytic and non-electrolytic substances. * Describe examples of applications of the properties of substances based on the type of bonding. ## 5.1 Fundamentals of Theory Figure 5.1 Ionic solute. Chemical bonds hold atoms together to form molecules. There are two types: ionic and covalent. Covalent bonds can be polar and nonpolar, the latter is also referred to as pure covalent bonds: * **Ionic compounds**: Formed by electron transfer from the metal to the nonmetal, so when dissolved in water, the ions separate (which is why these compounds are electrolytes). * **Covalent compounds**: Formed by sharing of electrons between two nonmetals. Polar covalent compounds are soluble in water and electrolytes, while nonpolar covalent compounds are insoluble in water and are non-electrolytes. The ionic or covalent nature of a bond can be determined using formulas derived from the difference in electronegativity between the elements that form the bonding. Electronegativity is the force by which an atom attracts electrons in a bond. Electronegativity increases from left to right and from bottom to top in the periodic table. Therefore, the most electronegative element is fluorine, followed by oxygen, then nitrogen, and chlorine. The latter two have the same electronegativity. Figure 5.2 Nonpolar solute. **Nonpolar covalent compounds**: Present elements with a difference in electronegativity of zero. Most organic compounds are nonpolar, which explains their low or nonexistent solubility in water.