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Questions and Answers
The Evans balance measures the ______ force exerted by the sample on a suspended permanent magnet.
The Evans balance measures the ______ force exerted by the sample on a suspended permanent magnet.
opposite
The Evans balance determines the force by measuring the change in ______ required to maintain the balance of suspended magnets.
The Evans balance determines the force by measuring the change in ______ required to maintain the balance of suspended magnets.
current
The change in position of the balance beam is detected by a pair of ______ positioned on either side of its equilibrium position.
The change in position of the balance beam is detected by a pair of ______ positioned on either side of its equilibrium position.
photodiodes
The signals from the photodiodes are sent to an ______ that provides a current to a coil.
The signals from the photodiodes are sent to an ______ that provides a current to a coil.
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Equation (4) gives the ______ magnetic susceptibility in the cgs-units of erg∙G–2∙cm–3 (where G is Gauss).
Equation (4) gives the ______ magnetic susceptibility in the cgs-units of erg∙G–2∙cm–3 (where G is Gauss).
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A digital voltmeter measures the current directly by being connected across a precision ______ in series with the coil.
A digital voltmeter measures the current directly by being connected across a precision ______ in series with the coil.
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The sample's ______ susceptibility per gram is referred to as the mass magnetic susceptibility, χg.
The sample's ______ susceptibility per gram is referred to as the mass magnetic susceptibility, χg.
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The calibration standards usually employed in magnetic susceptibility measurements are Hg[Co(SCN)4] (χg =1.644 10–5) or [Ni(en)3]S2O3 (χg = 1.104 10–5 erg∙G‒2cm–3), which are ______ compounds.
The calibration standards usually employed in magnetic susceptibility measurements are Hg[Co(SCN)4] (χg =1.644 10–5) or [Ni(en)3]S2O3 (χg = 1.104 10–5 erg∙G‒2cm–3), which are ______ compounds.
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The molar magnetic susceptibility, χM, is obtained from the ______ magnetic susceptibility by multiplying by the molecular weight of the sample in units of g/mol; i.e., M = M g (5)
The molar magnetic susceptibility, χM, is obtained from the ______ magnetic susceptibility by multiplying by the molecular weight of the sample in units of g/mol; i.e., M = M g (5)
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The general expression for the mass magnetic susceptibility in the Evans balance includes terms like sample ______, sample mass, balance calibration constant, and volume susceptibility of air.
The general expression for the mass magnetic susceptibility in the Evans balance includes terms like sample ______, sample mass, balance calibration constant, and volume susceptibility of air.
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The ______ susceptibility of air is usually disregarded when working with solid samples.
The ______ susceptibility of air is usually disregarded when working with solid samples.
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The units of χM are erg∙G–2. This experimentally obtained value of χM includes both ______ and diamagnetic contributions, which we may identify as χA and χα, respectively.
The units of χM are erg∙G–2. This experimentally obtained value of χM includes both ______ and diamagnetic contributions, which we may identify as χA and χα, respectively.
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All sources of paired electrons (e.g., ligands, counter ions, core electrons on the paramagnetic species) contribute to the ______ portion of the overall susceptibility.
All sources of paired electrons (e.g., ligands, counter ions, core electrons on the paramagnetic species) contribute to the ______ portion of the overall susceptibility.
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In 1910, Pascal observed that these contributions were approximately additive and consistent from sample to sample. Consequently, the diamagnetic contribution to the observed molar susceptibility can be estimated as the sum of constants (called Pascal's constants) for each ______ species in the sample.
In 1910, Pascal observed that these contributions were approximately additive and consistent from sample to sample. Consequently, the diamagnetic contribution to the observed molar susceptibility can be estimated as the sum of constants (called Pascal's constants) for each ______ species in the sample.
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We are interested in the paramagnetic molar susceptibility, which can be obtained by removing the ______ contributions from χM. Thus we may write A = M − (6)
We are interested in the paramagnetic molar susceptibility, which can be obtained by removing the ______ contributions from χM. Thus we may write A = M − (6)
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Values of χA (sometimes called the corrected magnetic susceptibility, M corr) are inherently positive, while those of χα are inherently ______.
Values of χA (sometimes called the corrected magnetic susceptibility, M corr) are inherently positive, while those of χα are inherently ______.
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The formula for the spin-only magnetic moment is µs = g S ( S + ______)
The formula for the spin-only magnetic moment is µs = g S ( S + ______)
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The gyromagnetic ratio, g, is approximately equal to ______.
The gyromagnetic ratio, g, is approximately equal to ______.
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In the expression for spin-only moment, µs = n ( n + ______), n corresponds to the number of unpaired electrons.
In the expression for spin-only moment, µs = n ( n + ______), n corresponds to the number of unpaired electrons.
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The units of the magnetic moment are ______ magnetons (BM).
The units of the magnetic moment are ______ magnetons (BM).
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Actual magnetic moments are often larger than the spin-only values due to incomplete quenching of the ______ contribution.
Actual magnetic moments are often larger than the spin-only values due to incomplete quenching of the ______ contribution.
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The magnetic field inside a substance can be represented as B = H0 + ΔH = H0 + ______ I.
The magnetic field inside a substance can be represented as B = H0 + ΔH = H0 + ______ I.
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The effective magnetic moment, µeff, helps determine the number of unpaired ______ in a complex.
The effective magnetic moment, µeff, helps determine the number of unpaired ______ in a complex.
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Paramagnetism adds to the applied magnetic field, while ______ subtracts from it.
Paramagnetism adds to the applied magnetic field, while ______ subtracts from it.
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The value of the effective magnetic moment, µeff, can be determined from χA by the ______ Law equation.
The value of the effective magnetic moment, µeff, can be determined from χA by the ______ Law equation.
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In equation (7), µeff becomes 2.828 χA ______.
In equation (7), µeff becomes 2.828 χA ______.
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To obtain a value of C, the instrument constant, the first measurement will be made with the calibration standard ______.
To obtain a value of C, the instrument constant, the first measurement will be made with the calibration standard ______.
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The adjustments for the balance should be made in the middle of the range of ______ turns.
The adjustments for the balance should be made in the middle of the range of ______ turns.
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When using the balance, zero should be readjusted if the ______ is changed.
When using the balance, zero should be readjusted if the ______ is changed.
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Place a clean, dry, empty sample tube of known weight into the tube ______.
Place a clean, dry, empty sample tube of known weight into the tube ______.
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The digital display should fluctuate by no more than ±______ on the x 1 scale.
The digital display should fluctuate by no more than ±______ on the x 1 scale.
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The instrument signal can drift over short periods of time and should be ______ before each measurement.
The instrument signal can drift over short periods of time and should be ______ before each measurement.
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The ratio of the intensity of magnetism induced in a substance to the magnetizing force is known as the magnetic ______.
The ratio of the intensity of magnetism induced in a substance to the magnetizing force is known as the magnetic ______.
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For paramagnetic materials, the susceptibility, κ, is ______ values.
For paramagnetic materials, the susceptibility, κ, is ______ values.
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The specific susceptibility is defined by the formula χg = κ/______.
The specific susceptibility is defined by the formula χg = κ/______.
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The Evans balance, developed by D.F. Evans, employs the ______ method.
The Evans balance, developed by D.F. Evans, employs the ______ method.
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The Gouy method measures the apparent change in ______ of the sample due to diamagnetic and paramagnetic effects.
The Gouy method measures the apparent change in ______ of the sample due to diamagnetic and paramagnetic effects.
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Only the Faraday and ______ methods are suitable for microscale samples of 50 mg or less.
Only the Faraday and ______ methods are suitable for microscale samples of 50 mg or less.
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The relationship B/H0 = 1 + 4π(κ) describes the behavior of materials in an applied ______.
The relationship B/H0 = 1 + 4π(κ) describes the behavior of materials in an applied ______.
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Diamagnetic materials show repulsion, implying that their susceptibility κ is ______ values.
Diamagnetic materials show repulsion, implying that their susceptibility κ is ______ values.
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The chemical equation shows that NiBr2 reacts with 2 N(C2H5)4Br to produce [NEt4]2[NiBr4], indicating that nickel(II) bromide acts as a ______.
The chemical equation shows that NiBr2 reacts with 2 N(C2H5)4Br to produce [NEt4]2[NiBr4], indicating that nickel(II) bromide acts as a ______.
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The solid tetraethylammonium bromide is dissolved in ______ to facilitate the reaction.
The solid tetraethylammonium bromide is dissolved in ______ to facilitate the reaction.
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To achieve the final crystals, the solution is boiled until the beaker is covered about ______ with crystals.
To achieve the final crystals, the solution is boiled until the beaker is covered about ______ with crystals.
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Electrons can align with or against an applied magnetic field, and for paired electrons, the overall spin quantum number, ______, is zero.
Electrons can align with or against an applied magnetic field, and for paired electrons, the overall spin quantum number, ______, is zero.
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When a diamagnetic material is placed between strong magnet poles, it experiences a ______ for the applied magnetic field.
When a diamagnetic material is placed between strong magnet poles, it experiences a ______ for the applied magnetic field.
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In the experiment, 1.75 g of finely ground ______ is added to the solution for the preparation of bis(tetraethylammonium) tetrabromonicklate(II).
In the experiment, 1.75 g of finely ground ______ is added to the solution for the preparation of bis(tetraethylammonium) tetrabromonicklate(II).
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The final product obtained from the evaporation process is [NEt4]2[NiBr4], which contains tetraethylammonium ions and ______.
The final product obtained from the evaporation process is [NEt4]2[NiBr4], which contains tetraethylammonium ions and ______.
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The process of filtering the hot solution is essential to remove any ______ or undissolved reagents.
The process of filtering the hot solution is essential to remove any ______ or undissolved reagents.
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Study Notes
Experiment 7: Preparation of Bis(tetraethylammonium) Tetrabromonicklate (II)
- Chemical Equation: NiBr₂ + 2 N(C₂H₅)₄Br → [N(C₂H₅)₄]₂[NiBr₄]
- Materials Required: tetraethylammonium bromide, ethanol, nickel(II) bromide
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Procedure:
- Place 3.5 g tetraethylammonium bromide in a 100 mL beaker on a stirrer hotplate in a fume hood.
- Add ethanol slowly until the solid nearly dissolves (13-18 mL).
- Gently warm the solution until the residue dissolves.
- Add 1.75 g finely ground nickel(II) bromide with rapid stirring.
- Heat the solution to boiling and filter the hot solution to remove impurities or undissolved reagents.
- Evaporate the filtrate until dry.
Experiment 7 - 3: Crystal Field Splitting Diagrams
- Crystal field splitting diagrams: Illustrate the splitting of d-orbitals in transition metal complexes when subjected to ligands.
- Octahedral field: shows splitting of d orbitals in an octahedral structure.
- Tetrahedral field: shows splitting of d orbitals in a tetrahedral structure.
- Square-planar field: shows splitting of d orbitals in a square planar structure.
Experiment 7 - 4: Magnetic Moments of Substances
- Paramagnetism: Substances with unpaired electrons experience attraction in a magnetic field (S > 0).
- Diamagnetism: Substances with all paired electrons experience repulsion in a magnetic field (S = 0).
- Magnetic moment: Repulsion and attraction caused by circulation of electrons when applied magnetic fields. This can be measured using a Gouy balance.
- The sample is weighed in a magnetic field, and it will weigh less. If removed from the field, it will weigh its normal weight.
Experiment 7 - 6: Calculating Magnetic Moments
- Paramagnetic species: Have unpaired electrons (S > 0) and are attracted to a magnetic field.
- Diamagnetic species: Have all paired electrons (S = 0) and are repelled by a magnetic field.
- Spin-only magnetic moment: Estimated magnetic moment considering only spin contributions of unpaired electrons. Formula: μs = n√(n² + 2), where n = Number of unpaired electrons.
- Effective magnetic moment: Experimentally measured magnetic moment, often larger than spin-only because of incomplete orbital contributions.
Experiment 7 - 7: Spin-Only Magnetic Moments
- **Spin-only magnetic moments (μs):**Used to estimate the magnetic moment when orbital contributions are insignificant.
- Formula: μs = √n(n+2), where n is the number of unpaired electrons.
- Units: Bohr magnetons (BM)
Experiment 7 - 9: Experimental Determination of Magnetic Moments
- Magnetic moment determination: Calculated from experimentally measured magnetic susceptibility to estimate magnetic moments indirectly.
- Techniques: Gouy method, Faraday method, NMR method.
Experiment 7 - 10: Magnetic Susceptibility Measurement Methods
- Techniques: The Gouy method, Faraday method, and NMR method are common techniques used to determine magnetic susceptibilities and thus magnetic moments of transition metal complexes.
- Microscale samples(50 mg or less) are better measured with Faraday method and NMR
- Evans balance: Suitable for semimicroscale samples as it is compact, lightweight, and self-contained, and does not require separate magnets or power supplies.
Experiment 7 - 11: Operation of the Evans Balance
- Principle: Measures the force by the equal and opposite force the sample exerts on a suspended permanent magnet.
- Measurement: A digital voltmeter connected across a precision resistor shows the current displayed as a digital readout.
- Formula: Xg = CL(R-Ro)/(10^9) m
- Instruments: Digital voltmeter, digital display, coil
Experiment 7 - 13: Calculation of Magnetic Moments
- Molar magnetic susceptibility (ΧM): Calculated from experimental data, considering mass susceptibility.
- XM = M x Xg where M is the molecular weight of the sample, and Xg is the mass susceptibility (Units: erg-G2-cm3, or units of cgs)
Experiment 7 - 14: Diamagnetic Corrections
- Diamagnetic corrections: Subtractions from the experimentally obtained molar magnetic susceptibility to estimate the actual paramagnetic contribution to account for electron pairing.
- Pascal's constants: Used to estimate the diamagnetic susceptibility contributions for various atoms or ions in the sample.
Experiment 7 - 15: Operation of the balance; Calibration Standards
- Calibration standard: A standard with a known magnetic susceptibility is needed to find a relationship between magnetic susceptibility and the instrument reading before using the instrument to measure the unknown sample.
- The first measurement is made using the calibration standard [Ni(en)₃]S₂O₃ to obtain the instrument constant (C) in the formula.
- The procedure is repeated with the unknown compounds, using the experimentally determined value of C.
Experiment 7 - 16-18: Preparation and Measurement of Samples in the Evans Balance
- Sample preparation: Samples are packed into glass tubes (1.5-3.5 cm).
- Sample placement: The prepared tube is placed into the sample guide of the balance.
- Reading measurement: Reading from the instrument must be taken by visually averaging the fluctuations observed.
- Calibration calculations are necessary to obtain the appropriate instrument constant.
- Temperature is measured using a thermometer placed near the instrument.
Experiment 7 - 19-20: Sample Removal and Additional Calculations
- Sample removal: After measurement, the sample is safely removed by careful inversion to avoid breakage.
- Cleaning: The sample tubes are rinsed with a suitable solvent.
- Calculations: Additional steps for calculating the instrument constant and the molar magnetic susceptibility are provided.
Experiment 7 - 21-23: Additional Calculations, and Examples of Data Analysis
- Diamagnetic Corrections: Calculations for subtracting the influence of diamagnetism from molar susceptibility and obtaining the paramagnetic contribution.
- Pascal's Constants: Tables of diamagnetic factors (Pascal's constants) for various substances (atoms, ions, and ligands) are used to estimate diamagnetic contributions to the total magnetic susceptibility.
- Illustrative example: calculation of paramagnetic molar susceptibility (XM) and effective magnetic moment (μeff) for Fe(NH₄)₂(SO₄)₂∙6H₂O.
Experiment 7 - 24: Summary of Calculations
- μeff: calculation: Example of calculation and use of formula to find the magnetic moment using the diamagnetic correction and the molar magnetic susceptibility (XM) values.
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Description
This quiz explores the principles and components involved in measuring magnetic susceptibility using the Evans balance. It covers the forces exerted by samples, the apparatus used for detection, and the significance of calibration standards in the measurements. Test your understanding of these concepts in magnetic studies!
