The compete oxidation of 2g of an aldehyde A by acidified potassium chromate produces 2.1g of carboxylic acid B which is dissolved in 50 ml of distilled water .
The obtained solution reacts with exactly 1.05 g of solid lime to form salt C
a) Write the equation of the reaction B with the lime.
b) Calculate the molar mass of acid B. Deduce its molecular formula
A + [O] ==> B + Ca(OH)2 ==> C
2g.........2.1....1.05.........
Ca(OH)2 + 2XCOOH ==> Ca(XCOO)2 + 2H2O
mols Ca(OH)2 = grams/molar mass = approx 0.014 but you need to do that more accurately.
mols XCOOH must be twice that or about 0.028.
mols = grams/molar mass or
molar mass = grams/mols = approx 2.1/about 0.028 = 74.
If the molar mass is 74, the COOH part of that must be 45 which leaves for the X part of it 74-45 = 29. That's probably CH3CH2 so I would think B is CH3CH2COOH or propanoic acid.
To solve this problem, let's break it down step by step:
Step 1: Calculate the number of moles of carboxylic acid B.
We can use the equation:
moles = mass / molar mass
Given that the mass of carboxylic acid B is 2.1g and the volume of the solution is 50 mL (which is equivalent to 50 cm³), we need to convert the volume to the corresponding mass of water.
Density of water = 1g/cm³
Mass of water = Volume of water × Density of water
Mass of water = 50 cm³ × 1 g/cm³ = 50 g
Now, the total mass of the solution is:
Total mass = Mass of acid B + Mass of water
Total mass = 2.1 g + 50 g = 52.1 g
Using the formula above, we can find the number of moles of acid B:
moles of B = 2.1 g / molar mass of B
Step 2: Determine the equation of the reaction between carboxylic acid B and solid lime (calcium hydroxide, Ca(OH)₂).
The reaction between the acid B and lime will yield the corresponding salt C, which is calcium carboxylate.
The balanced equation for the reaction is:
2 B + Ca(OH)₂ → Ca(B)₂ + 2 H₂O
Step 3: Calculate the molar mass and molecular formula of acid B.
To calculate the molar mass of acid B, we need to know the number of moles. Since we calculated the number of moles in Step 1, we can rearrange the formula above to solve for the molar mass:
molar mass of B = 2.1 g / moles of B
Once we have the molar mass, we can use the periodic table to find the elements present in the compound and deduce its molecular formula.
Please provide the molar mass of acid B to proceed with the calculation of its molecular formula.