Chapter 24. General Chemistry Experiment
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1. Experimental Apparatus
2. Experimental Equipment
⑴ Atomic Force Microscope (AFM)
① Measurement possible down to fractions of atomic diameters
② Usable even in atmospheric conditions
⑵ Elemental Analyzer
① Determines the amounts (%) of C, H, N, S, O
② Combusts the sample under O2 in the precise amount to ionize constituent elements (C, H, N, S, O).
③ Oxidizes to H2O, CO, CO2, N2, NO, NO2, SO2, SO3 in the oxidation reactor
④ Reduces NO and NO2 to N2, SO3 to SO2, and oxidizes CO to CO2 in the reduction reactor
⑤ Measure the amount of CO2 finally produced after undergoing a pyrolysis process in the absence of oxygen during oxygen measurement.
⑥ Other generated gases are separated using an adsorption trap.
⑦ Analyze the final generated gases using GC chromatography under helium to calculate the content of each gas.
⑶ Energy Dispersive X-ray Spectroscopy (EDS)
① Utilizes characteristic x-rays
② Characteristic X-ray: X-rays are generated when an electron from the K-shell is ejected by ionizing radiation, and an electron from the L-shell moves to the K-shell.
Figure 1. The Principle of Characteristic X-rays
○ K: Electron shell with n = 1.
○ L: Electron shell with n = 2.
○ M: Electron shell with n = 3.
③ The term “characteristic” is used to indicate that a common peak is observed regardless of the type of scintillating material.
④ These X-rays can be applied to Single Photon Emission Computed Tomography (SPECT).
⑷ Gas Chromatography (GC)
① Definition: The method in which the evaporated sample components are separated by being distributed between the stationary phase in the column and the mobile gas phase.
② Inert gases like helium, hydrogen, nitrogen, argon are commonly used as carrier gases. Helium is mainly used as the gas phase.
○ Reason 1: Lighter gas molecules like H2, He have higher diffusion coefficients, leading to faster separation
○ Reason 2: Lighter gas molecules like H2, He have higher thermal conductivity, reducing preheating time
○ Reason 3: Gases like H2, O2 can react with the sample
③ Advantages: High resolution
④ Disadvantages: Analyzing non-volatile compounds is challenging; suitable for small molecular weights (typically 100 - 103)
⑤ Application 1: Gas-Liquid Chromatography (GLC) and Gas-Solid Chromatography (GSC)
⑥ Application 2: Measuring molecular weights through gas chromatography: using correlation between retention time and molecular weight
⑦ Application 3: Gas Chromatography Mass Spectrography (GC-MS)
○ 1st Step: Separated substances from gas chromatography are electronically ionized or chemically ionized for mass-dependent classification
○ 2nd Step: Separated substances form unique mass spectra
○ 3rd Step: Structure information is obtained by comparing with accumulated library data or quantitative analysis
○ Can also be used for quantifying trace components by selecting 1st ions and performing 2nd ionization
⑸ High-Performance Liquid Chromatography (HPLC)
① Measures presence and molecular weight of trace substances using the difference in movement distance on a stationary phase in chromatography
② Molecular weight conditions: 6 × 101 ~ 104
③ Comprises solvent, pump, injector, column, detector, recorder
④ Most common detector in HPLC is UV detector
⑤ Refractive Index (RI) detector is sensitive to environmental changes like pressure and temperature, but not very sensitive to solutes
⑹ Inductively Coupled Plasma (ICP)
① ICP: Introduces the sample into argon plasma formed by high-frequency induction coil, measures emitted spectral lines and intensity at 6000 ~ 8000 K when atoms in ground state move to excited state
② Electrons move to ground state within 10-7 ~ 10-8 seconds
③ The sample emits light corresponding to the energy difference, which is then spectrally analyzed using a diffraction grating spectrometer, and the intensity of light is measured for each wavelength.
④ Application 1: ICP-MS
⑺ Scanning Electron Microscope (SEM)
① Mainly obtains surface information of samples
② Depth of focus is over twice that of optical microscopes
⑻ Vibrating Sample Magnetometer (VSM)
① Principle: Magnetic Hysteresis
⑼ X-ray Diffraction (XRD)
① Principle: Bragg Diffraction
⑽ X-ray Photoelectron Spectroscopy (XPS)
① Principle: Photoelectric Effect
3. Experimental Reagents
4. Experimental Techniques
⑴ Fundamentals of Chemical Experiments
① Experiments with toxic gases are conducted in a hood
② Dilute sulfuric acid is prepared by adding water to a beaker before adding concentrated sulfuric acid
③ When transferring concentrated hydrochloric acid, use a glass rod to guide the acid along the beaker wall
④ Due to sodium hydroxide’s high moisture absorption, accurate weighing is challenging
⑤ The produced NaOH solution is not stored in glass containers for long periods
⑥ If a mercury thermometer breaks, sprinkle sufficient sulfur to absorb the mercury vapor and collect it after a day
⑵ Volumetric Analysis and Standardization of Solutions
① Volumetric analysis: Experimental method to determine the amount of unknown sample
○ Burette: Instrument for measuring volumes
○ Add a solution of known concentration until
the sample is completely consumed using a burette
○ Utilize reactions that can immediately conclude when solution is added with the burette
② Standardization
○ Primary Standard Substance: Substance with a specific concentration of solution that can be accurately prepared and used
○ Condition 1: Obtainable in pure state (constant composition)
○ Condition 2: Easy to purify
○ Condition 3: High molecular weight for accurate mass measurement
○ Standard Solution: Solution that undergoes standardization using primary standard substance for volumetric analysis
○ Standardization Process: Using the solution of primary standard substance to accurately measure the concentration of the solution for volumetric analysis
○ Example: Using a solution of primary standard substance potassium hydrogen phthalate (KHP) to measure the concentration of NaOH(aq), where NaOH is the standard solution
⑶ Direct and Indirect Titration
① Direct Titration: Method of directly determining the amount of analyte
○ Condition 1: Rapid reaction between analyte and standard solution
○ Condition 2: Complete reaction
○ Condition 3: Suitable indicator available at equivalence point
○ Example 1: Measuring the concentration of acetic acid using NaOH standard solution
CH3COOH + OH- → CH3COO- + H2O
○ Example 2: Measuring the concentration of Cl- using AgNO3 standard solution
Ag+ + Cl- → AgCl
② Indirect Titration: Used when direct titration conditions are not met
○ Substitution Titration: Adding excess of a solution that reacts with the interfering substance to remove it
○ Example: Quantification of metal cations using EDTA
○ Step 1: Add magnesium’s EDTA chelate compound (MgY2-) to a solution containing metal cation Mn+
MgY2- + Mn+ → MYn-4 + Mg2+
○ Step 2: Titrate the resulting excess Mg2+ with EDTA
○ Eriochrome Black T or Calmagite can be used as indicators
○ The molar amount of Mg2+ measured in Step 2 equals the molar amount of Mn+ present in the original solution
○ Back Titration: Adding excess standard solution and titrating the remaining substance
○ Used when direct reaction between analyte and standard solution is slow
○ Example 1: Quantification of Ni2+ using back titration
○ Step 1: Add excess EDTA standard solution to the sample solution containing Ni2+ ions
Ni2+ + Y4- → NiY2-
○ Step 2: After the reaction is complete, titrate the remaining EDTA to quantify the concentration of Ni2+
Mg2+ + Y4- → MgY2-
○ Step 3: Mg2+ forms a complex with Eriochrome Black T indicator, changing color from blue to violet
○ The molar amount of Ni2+ in the initial solution is the difference between the molar amount of EDTA added in Step 1 and the molar amount of EDTA measured in Step 2
○ Example 2: DNP Method (2,4-dinitrophenyl hydrazine colorimetric method)
○ Step 1: Under sulfuric acid, oxidation substance and DNP undergo dehydration reaction to form bi-2,4-dinitrophenyl hydrazone
○ Step 2: Quantify oxidizing substance by colorimetrically measuring bi-2,4-dinitrophenyl hydrazone of matching color
⑷ Removal of Interfering Substances
① Masking Agent: Substance that prevents unwanted reactions (side reactions) from occurring
② Induces reactions to remove substances participating in side reactions
○ Example: Quantification of copper in steel samples
○ Main reaction for quantification: Cu2+ + 2I- → Cu + I2
○ Undesirable reaction: 2Fe3+ + 6I- → 2Fe + 3I2
○ Adding F- acts as masking agent, preventing the side reaction by forming FeF3(s)
③ Separation by Precipitation
④ Separation by Acid-Base Regulation
○ Solubility of hydroxides and acids varies with solution pH
○ Adjusting solution pH can dissolve hydroxides for separation
⑤ Separation Using Solvent Extraction
○ Chemical species distribute differently between immiscible solvents
○ One solvent can extract the substance from the other
Input : 2019-09-08 23:51
Modified : 2022-07-06 17:46