Excess fluorine, F2(g), reacts at 150°C with bromine, Br2(g), to give a compound BrFn. If 423 mL Br2(g) at 150°C and 748 mmHg produced 4.20 g BrFn, what is n? Predict the shape of this molecule using the VSEPR model.
To determine the value of n, we need to use the stoichiometry of the reaction and the given information.
1. Convert the volume of Br2(g) to moles:
We use the ideal gas law equation to convert the volume to moles.
PV = nRT
P = 748 mmHg (convert to atm by dividing by 760 mmHg/atm)
V = 423 mL (convert to L by dividing by 1000 mL/L)
R = 0.08206 L.atm/(mol.K) (gas constant)
T = 150°C = 273 + 150 = 423 K
n = PV / RT
n = (748/760) * (423/1000) / 0.08206 / 423
n = 0.0193 moles Br2
2. Determine the number of moles of BrFn produced:
The balanced equation tells us that the stoichiometric ratio between Br2 and BrFn is 1:1.
Therefore, the number of moles of Br2 is equal to the number of moles of BrFn.
3. Calculate the molar mass of BrFn:
We assume that this compound consists of 1 mole bromine and n moles of fluorine.
The molar mass of BrFn is therefore:
molar mass of BrFn = molar mass of Br + n * molar mass of F
molar mass of Br = 79.904 g/mol (molar mass of bromine)
molar mass of F = 18.9984 g/mol (molar mass of fluorine)
4. Calculate the mass of BrFn:
Given: 4.20 g BrFn
5. Determine the value of n:
mass of BrFn = (molar mass of Br + n * molar mass of F) * moles of BrFn
4.20 = (79.904 + n * 18.9984) * 0.0193
Solve the equation for n:
4.20 = 79.904 * 0.0193 + n * 18.9984 * 0.0193
4.20 = 1.54198 + 0.368064n
3.35 = 0.368064n
n ≈ 9.10
Therefore, the value of n is approximately 9.
To predict the shape of the BrFn molecule using the VSEPR model, we need to know the number of bonding pairs and lone pairs around the central atom, bromine.
Since there are no charges on the molecule mentioned, bromine will not have any lone pairs of electrons and only be connected with fluorine (Fn).
The general formula for a molecule with n bonding pairs is AXn. In this case, bromine is the central atom (A) and there are 9 fluorine atoms (Fn).
According to the VSEPR theory, the molecule BrFn will have a linear shape since it has only one bond angle, which is 180 degrees.
To find the value of n, we need to use the given information about the reactants and products of the reaction. Let's break down the steps to find the value of n:
Step 1: Convert the volume of Br2(g) to mols of Br2.
Given:
Volume of Br2(g) = 423 mL
Temperature (T) = 150°C
First, we need to convert the volume of Br2(g) from milliliters to liters, as the standard unit for molar calculations is liters.
1 L = 1000 mL
Therefore, the volume of Br2(g) in liters is:
423 mL * (1 L / 1000 mL) = 0.423 L
Next, we need to apply the Ideal Gas Law to find the number of moles of Br2(g).
PV = nRT
Where:
P = Pressure = 748 mmHg
V = Volume = 0.423 L
n = number of moles
R = Ideal Gas Constant = 0.0821 L.atm/(mol.K)
T = Temperature in Kelvin
To convert the temperature from Celsius to Kelvin:
T(K) = T(C) + 273.15
T(K) = 150 + 273.15 = 423.15 K
Now, let's calculate the number of moles of Br2(g):
(748 mmHg) * (0.423 L) = n * (0.0821 L.atm/mol.K) * (423.15 K)
318.204 = 35.042 n
n = 318.204 / 35.042 ≈ 9.08 mol
Step 2: Convert the mass of BrFn to moles of BrFn.
Given:
Mass of BrFn = 4.20 g
To convert the mass of BrFn to moles, we need to know the molar mass of BrFn. Unfortunately, the molar mass is not provided in the question, so we cannot proceed further without this information.
Use PV = nRT to calculate n for Br2 and convert to grams. Subtract from 4.20 to find grams fluorine.
Then convert g bromine to moles. moles = g/molar mass.
convert g fluorine to moles same way.
Now find the ratio of the elements to each other with the lowest number being 1.00. The easy way to do that is to divide the smaller number by itself (thereby getting 1.000000 for that one) then divide the other number by the same small number. Round to whole numbers to find the empirical formula.
After determining the formula, write a Lewis electron dot structure to deduce the VSEPR shape. Post your work if you get stuck.