Redox reactions
(Cr2O7)2- + 2Al + 14H+ <—> 2Cr3+ + 2Al3++ 7H2O
1) how many ml of solution 1.50 M e (Cr2O7)2- are needed to act without residue with 0.8 grams of Al?
2) what is the concentration of the solution (Cr2O7)2-
I don't know what 1.5 M e (Cr2O7)2- means.
To answer both questions, we need to use the balanced redox equation and perform stoichiometry calculations. Let's go step by step:
Step 1: Write the balanced redox equation.
The balanced redox equation is:
(Cr2O7)2- + 2Al + 14H+ <—> 2Cr3+ + 2Al3++ 7H2O
Step 2: Determine the mole ratio between (Cr2O7)2- and Al.
From the balanced equation, we see that 1 mole of (Cr2O7)2- reacts with 2 moles of Al.
Step 3: Calculate the moles of Al.
Given that you have 0.8 grams of Al, you can calculate the moles of Al by dividing the mass by its molar mass. The molar mass of Al is 26.98 g/mol.
0.8 g Al × (1 mol Al / 26.98 g Al) ≈ 0.0296 mol Al
Step 4: Calculate the moles of (Cr2O7)2- needed.
Since the mole ratio between (Cr2O7)2- and Al is 1:2, you need twice the moles of Al.
Moles of (Cr2O7)2- needed = 2 × 0.0296 mol Al
Moles of (Cr2O7)2- needed = 0.0592 mol (Cr2O7)2-
Step 5: Calculate the volume of the 1.50 M (Cr2O7)2- solution needed.
Use the equation:
Moles = Concentration × Volume
0.0592 mol = (1.50 mol/L) × Volume
Volume = 0.0592 mol / 1.50 mol/L
Volume ≈ 0.0394 L
Since 1 L = 1000 mL, the volume is 0.0394 L × 1000 mL/L ≈ 39.4 mL
Answer to question 1:
You would need approximately 39.4 mL of the 1.50 M e (Cr2O7)2- solution to react without residue with 0.8 grams of Al.
Now, let's move on to question 2:
Step 6: Calculate the concentration of (Cr2O7)2-.
From the equation, we see that the mole ratio between (Cr2O7)2- and (Cr3+) is 1:2.
If "x" represents the concentration of (Cr2O7)2-, then the concentration of (Cr3+) is 2x (according to the mole ratio).
Step 7: Use the equation to establish an equation for Cr:
(Cr2O7)2- + 14H+ + 6e- → 2Cr3+ + 7H2O
From the equation, we see that 1 mole of (Cr2O7)2- reacts with 6 moles of electrons (e-).
Step 8: Calculate the concentration of (Cr2O7)2-.
Use the equation:
Moles = Concentration × Volume
From the equation, 1 mole of (Cr2O7)2- reacts with 6 moles of electrons (e-). So, 6 times the moles of (Cr2O7)2- will be equal to the moles of electrons (e-) generated by the reaction.
Step 9: Calculate the concentration of (Cr2O7)2-.
Given that you need 0.0592 moles of (Cr2O7)2- (as calculated in question 1), we can calculate the moles of electrons (e-) as follows:
Moles of electrons (e-) = 6 × 0.0592 mol (Cr2O7)2-
Finally, divide the moles of electrons (e-) by the volume to calculate the concentration of (Cr2O7)2-.
Answer to question 2:
The concentration of the (Cr2O7)2- solution is calculated by dividing the moles of (Cr2O7)2- by the volume.
To solve these questions related to the redox reaction, we will go step by step.
1) To determine the volume of the solution required, we need to use the stoichiometry of the balanced equation and convert grams of Al to moles of (Cr2O7)2-, then use the molarity of the (Cr2O7)2- solution to calculate the volume.
a) Calculate the number of moles of Al:
Given: Mass of Al = 0.8 grams
To calculate the moles, we need to divide the given mass by the molar mass of Al (26.98 g/mol):
Moles of Al = 0.8 g / 26.98 g/mol
b) Use the stoichiometry of the balanced equation to find the moles of (Cr2O7)2-:
From the balanced equation, we can see that the stoichiometric ratio between Al and (Cr2O7)2- is 2:1. This means that for every 2 moles of Al, we need 1 mole of (Cr2O7)2-.
Moles of (Cr2O7)2- = (Moles of Al) / (2 moles of Al : 1 mole of (Cr2O7)2-)
c) Calculate the volume of the (Cr2O7)2- solution:
The given molarity of the (Cr2O7)2- solution is 1.50 M (moles per liter).
To convert moles of (Cr2O7)2- to volume, use the equation:
Volume of (Cr2O7)2- solution (in liters) = Moles of (Cr2O7)2- / Molarity
2) To determine the concentration of the (Cr2O7)2- solution, we need to use the stoichiometry of the balanced equation and the known volume and mass of reactants.
a) Calculate the moles of Al:
Given: Mass of Al = 0.8 grams
To calculate the moles, we need to divide the given mass by the molar mass of Al (26.98 g/mol):
Moles of Al = 0.8 g / 26.98 g/mol
b) Use the stoichiometry of the balanced equation to find the moles of (Cr2O7)2-:
From the balanced equation, we can see that the stoichiometric ratio between Al and (Cr2O7)2- is 2:1. This means that for every 2 moles of Al, we need 1 mole of (Cr2O7)2-.
Moles of (Cr2O7)2- = (Moles of Al) / (2 moles of Al : 1 mole of (Cr2O7)2-)
c) Calculate the volume of the (Cr2O7)2- solution:
The volume of the (Cr2O7)2- solution is not given in the question. You will need the volume of the (Cr2O7)2- solution to find its concentration.
To calculate the concentration, you need to know the volume and moles of (Cr2O7)2- in the solution, as well as the equation's balanced stoichiometry. If the volume is known, you can divide the number of moles by the volume in liters to calculate the concentration in moles per liter (M).