Chemistry Quiz: Standard Solutions and Titration

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• Standard Solution and Titration*
• A standard solution is a solution of known concentration, used to determine the concentration of another solution.
• Titration is a process of determining the concentration of a solution by reacting it with a standard solution.
• Types of titration:
  • Acid-base titration
  • Redox titration
  • Complexometric titration
• Normality, Molarity, Molality, and Mole Fraction*
• Normality (N): the number of gram equivalents of solute per liter of solution.
• Molarity (M): the number of moles of solute per liter of solution.
• Molality (m): the number of moles of solute per kilogram of solvent.
• Mole fraction (x): the number of moles of solute per total number of moles in the solution.
• Acid-Base Titration*
• The endpoint of acid-base titration is determined by a pH indicator, such as phenolphthalein or methyl orange.
• The pH at the endpoint of acid-base titration is 7.
• Strong Acid-Strong Base Titration*
• The reaction between a strong acid and a strong base is complete and irreversible.
• The pH at the endpoint of strong acid-strong base titration is 7.
• Indicator and pH Range*
• Indicators are substances that change color in response to a change in pH.
• pH range of indicators:
  • Methyl orange: 3.1-4.4
  • Phenolphthalein: 8.3-10.0
• Spectroscopy*
• Spectroscopy is the study of the interaction between electromagnetic radiation and matter.
• Types of spectroscopy:
  • Ultraviolet (UV) spectroscopy
  • Visible spectroscopy
  • Infrared (IR) spectroscopy
  • Nuclear Magnetic Resonance (NMR) spectroscopy
• Properties of electromagnetic radiation:
  • Wavelength (λ)
  • Frequency (ν)
  • Speed (c)
  • Energy (E)
• Beer-Lambert's Law*
• Beer-Lambert's law relates the absorption of radiation to the concentration of a solution.
• A = εbc, where A is the absorbance, ε is the molar absorptivity, b is the path length, and c is the concentration.

Let me know if you'd like me to add or clarify anything!### Beer's Law and Spectroscopy

Beer's Law

• Establishes a relationship between absorbance and concentration of a sample
• Derived assuming monochromatic radiation, which means if bandwidth increases, it will create deviation
• States that the intensity of light decreases with the concentration of the medium
• Represented as A = abc, where 'a' represents the absorption constant (absorptivity)

Lambert's Law

• States that the intensity of light decreases with respect to path length
• Represented by the equation A = abc, where 'b' represents distance

Absorption Spectroscopy

• Involves transmission, where some radiation is absorbed and the rest is transmitted
• Reflection and scattering are kept to a minimum
• Amount of absorption depends on the number of molecules in the material
• Intensity indication of concentration

Transmittance

• Given by TP/P, where P represents radiant power transmitted by the sample
• No unit for absorbance, as units of absorptivity, distance, and concentration cancel each other out

Molar Absorptivity (a)

• Unit is L/mol/cm
• Used to determine absorbance in Beer-Lambert's formula

Instrumentation

• Radiation source: tungsten lamp
• Detectors: photomultiplier tube, photovoltaic cell, photoemissive tubes
• Single beam instruments: do not use beam splitters
• Double beam instruments: use beam splitters to split the beam into two equal intensity beams

Applications

• Colorimetry: used for determining concentrations of solutions, not for colour measurement
• UV-Visible spectroscopy: used for determining concentrations of solutions
• IR spectroscopy: used for functional group identification and qualitative analysis

Infrared (IR) Spectroscopy

• Types of IR spectroscopy: near IR, mid IR, far IR
• Near IR: 0.8-2.5 mm
• Mid IR: 2.5-50 mm
• Far IR: 50-1000 mm
• Sources: Nernst glower, Globar rod
• Detectors: bolometer, thermistor

Fourier Transform Infrared (FTIR) Spectrophotometer

• A type of non-dispersive instrument
• Uses a beam splitter to split the beam into two
• Detector: pyroelectric transducer or pyroelectric crystals
• Drive mechanism: moves the mirror to obtain a satisfactory interferogram
• Advantages: high signal to noise ratio, information on all frequencies can be obtained, data retrieval is possible

Atomic Absorption Spectroscopy (AAS)

• Principle: radiation is absorbed by non-excited atoms in vapour state, exciting them to higher states

• Radiation source: hollow cathode lamp

• Function of chopper: breaks steady light into pulsating light

• Function of flame or emission system: reduces the sample into atomic state

• Detector: measures the absorbed radiation### Pressure Regulators and Flame Emission Photometers

• Pressure regulators maintain a steady, flicker-free flame.

• Pressure gauges indicate the pressure in a system.

Flame Emission Photometers

• Measure the colour and intensity of the flame when a sample is introduced.
• Used for qualitative and quantitative analysis.
• Qualitative analysis: determines the element present in the sample based on the colour of the flame.
• Quantitative analysis: determines the amount of the element present in the sample based on the intensity of the flame.

Laminar Flow Burners

• Also known as Premix burners.
• Sample, fuel, and oxidant are mixed thoroughly before reaching the burner.
• Advantages: noiseless, stable flame, efficient atomization of the sample, and steady movement of gas flow.
• Disadvantages: cannot be used for samples containing two or more solvents.

Monochromators

• Prism monochromators: dispersion is non-overlapping, but occurs in a non-linear manner.
• Grating monochromators: dispersion is linear, but overlapping.

Detectors

• Photovoltaic cells: less sensitive than phototubes.
• Phototubes: more sensitive than photovoltaic cells, used to measure low intensities.

Applications of Flame Emission Photometers

• Analysis of biological fluids, such as blood and urine.
• Determination of sodium and potassium in soil.
• Determination of metals such as manganese and copper.
• Analysis of plant materials and industrial cements.

Chromatography

• A physical method used to separate and analyze complex mixtures.
• Stationary phase: solid or liquid supported on a solid.
• Mobile phase: liquid or gas.
• Types of chromatography:
  • Column chromatography: stationary phase is solid, mobile phase is liquid.
  • Thin layer chromatography: stationary phase is solid, mobile phase is liquid.
  • Gas chromatography: stationary phase is liquid, mobile phase is gas.
  • Planar chromatography: stationary phase is solid, mobile phase is liquid.
  • Liquid chromatography: stationary phase is solid or liquid, mobile phase is liquid.

Chromatographic Processes

• Separation: different components of a mixture separate based on their affinity to the stationary phase.
• Elution: components elute from the column at different times based on their affinity to the stationary phase.
• Detection: a detector measures the concentration of the components as they elute from the column.

Chromatogram

• A graph obtained by plotting the concentration of the components against time.
• Used to identify the components of a mixture and their concentrations.
• The area under the peak is proportional to the concentration of the component.

Retention Time and Volume

• Retention time: the time taken by the analyte to reach the detector.
• Dead time: the time required for a molecule of the mobile phase to pass through the column.
• Adjusted retention time: the retention time minus the dead time.
• Retention volume: the volume of mobile phase required to make a solute band move from the point of injection to the detector.
• Adjusted retention volume: the retention volume minus the dead volume.

Distribution Constant and Retention Factor

• Distribution constant: the ratio of moles of solute in the stationary phase to the moles of solute in the mobile phase.
• Retention factor: the ratio of moles of solute in the stationary phase to the moles of solute in the mobile phase.

Total Porosity

• The ratio of interstitial volume of packing to the volume of its total mass.
• In capillary columns, total porosity is 1.