Q1) How many resonances are expected in the 13C NMR spectrum of propan-1-ol?
Q2) A student measures the EMF of the following electrochemical cell at 31oC in a solution that is 0.22 molL-1 in Hg2+ against a Saturated Calomel Electrode as the reference. The reduction potential of the Saturated Calomel Electrode is +0.244 V.
Hg2+ + 2e- �¨ Hg
The measured value is 0.556 V with the mercury as the cathode. What is the standard reduction electrode potential for mercury (in V) calculated from this measurement?
Q3) A student performs the reduction of a sample of 1.90 mL of acetone with 0.21 g NaBH4 and obtains 1.1 g propan-2-ol. The density of acetone is 0.79 gmL-1.The percentage yield of propan-2-ol based on the limiting reagent is ___ %
Q1) To determine the number of resonances in the 13C NMR spectrum of propan-1-ol, you need to consider the different carbon environments in the molecule. Propan-1-ol has three carbon atoms, labeled as C1, C2, and C3.
In this case, each carbon atom can have a unique chemical environment, which can result in different chemical shifts in the 13C NMR spectrum. The chemical shifts are affected by factors such as neighboring atoms and functional groups.
To determine the number of resonances, you need to identify any different chemical environments for the carbon atoms. In propan-1-ol, all three carbon atoms are different from each other due to their connectivity and the presence of the hydroxyl group. Hence, you would expect three different resonances in the 13C NMR spectrum of propan-1-ol.
Q2) To calculate the standard reduction electrode potential for mercury (Hg), we need to use the Nernst equation. The Nernst equation relates the standard reduction potential (E°) to the measured potential (E) and the concentrations of reactants and products.
The Nernst equation is given by:
E = E° - (RT/nF) * ln(Q)
Where:
E is the measured potential,
E° is the standard reduction potential,
R is the gas constant (8.314 J/molK),
T is the temperature in Kelvin,
n is the number of electrons transferred in the reaction,
F is the Faraday constant (96,485 C/mol),
ln is the natural logarithm function, and
Q is the reaction quotient, which is the product of the concentrations (in this case, activity) of the species on the right side divided by the product of the concentrations of the species on the left side of the reaction.
In this case, the reaction is:
Hg2+ + 2e- → Hg
Given:
E = 0.556 V (measured potential),
E° (standard reduction potential of Saturated Calomel Electrode) = +0.244 V,
T = 31 °C = 31 + 273 = 304 K,
Concentration of Hg2+ is 0.22 mol/L.
Since the reaction involves two electrons (n = 2), we can plug in the values into the Nernst equation and solve for E°:
0.556 = E° - (8.314 * 304 / (2 * 96485)) * ln(0.22)
Solving this equation will give you the value for E°, which is the standard reduction electrode potential for mercury.
Q3) To calculate the percentage yield of propan-2-ol based on the limiting reagent, you need to first determine the limiting reagent in the reaction.
Given:
Volume of acetone = 1.90 mL = 1.90 g (since the density is 0.79 g/mL)
Mass of NaBH4 = 0.21 g
Mass of propan-2-ol obtained = 1.1 g
To determine the limiting reagent, you need to calculate the number of moles of each reactant.
First, calculate the number of moles of acetone:
Moles of acetone = Volume of acetone (in liters) * Concentration of acetone (in mol/L)
Concentration of acetone = Mass of acetone / (Density of acetone * Volume of acetone)
Substituting the given values:
Concentration of acetone = 1.90 g / (0.79 g/mL * 1.90 mL) = 3.81 mol/L
Moles of acetone = 1.90 mL * (1 L/1000 mL) * 3.81 mol/L = 0.00724 mol
Next, calculate the number of moles of NaBH4:
Moles of NaBH4 = Mass of NaBH4 / Molar mass of NaBH4
The molar mass of NaBH4 is 37.83 g/mol.
Moles of NaBH4 = 0.21 g / 37.83 g/mol = 0.00555 mol
The limiting reagent is the reactant that produces the fewer moles of product. In this case, NaBH4 produces fewer moles of the product, propan-2-ol.
To calculate the theoretical yield of propan-2-ol based on the limiting reagent, you can use the stoichiometry of the balanced chemical equation. The balanced chemical equation for the reduction of acetone (CH3COCH3) by NaBH4 is:
CH3COCH3 + 2H → CH3CHOHCH3
According to the equation, 1 mole of acetone reacts with 0.5 moles of NaBH4 to produce 1 mole of propan-2-ol.
Moles of propan-2-ol expected = Moles of NaBH4 used
Therefore, the theoretical yield of propan-2-ol = Moles of propan-2-ol expected * Molar mass of propan-2-ol
Substituting the values:
Theoretical yield of propan-2-ol = 0.00555 mol * 60.1 g/mol = 0.333 g
The percentage yield can be calculated using the formula:
Percentage Yield = (Actual Yield / Theoretical Yield) * 100%
Substituting the values:
Percentage Yield = (1.1 g / 0.333 g) * 100% = 330%
Therefore, the percentage yield of propan-2-ol based on the limiting reagent is 330%.