Carminic acid is a naturally occuring red pigment and contains only carbon, hydrogen, and oxygen. It is 53.66% C and 4.0p% H by mass. A titration required 18.02 mL of 0.0406 M NaOH to neutralize 0.3602 g of carminic acid. Assuming that there is only one acidic hydrogen per molecule, what is the molecular formula of carminic acid?
Take a 100 gram sample.
That gives you
53.66 g C =
4.0p (or whatever that p is supposed to be) grams.
100-4.0p-53.66 = g oxygen.
Now convert to moles.'
53.66/molar mass C
4.0p/1 = moles H
g oxygen/16 = mols O
Now find the ratio of these three elements to each other, in small whole numbers, with the lowest number being no less than 1.00. The easy way to do that is to divide the smallest number by itself (thus 1.000 for that element), then divide the other two numbers by the same small number. Round to whole numbers but don't round too much; i.e., no more than about 0.1 or so.
Post your work if you get stuck. I've looked at the numbers and they don't look that good. Check to make sure you didn't make a typo in the numbers.
To determine the molecular formula of carminic acid, we need to follow several steps:
Step 1: Calculate the number of moles of carminic acid used in the titration.
First, divide the given mass of carminic acid (0.3602 g) by its molar mass.
The molar mass of carminic acid can be calculated by summing the molar masses of carbon, hydrogen, and oxygen in the compound.
The molar mass of carbon (C) is 12.01 g/mol.
The molar mass of hydrogen (H) is 1.01 g/mol.
The molar mass of oxygen (O) is 16.00 g/mol.
Calculating the molar mass of carminic acid:
Molar mass of carminic acid = (12.01 g/mol × %C) + (1.01 g/mol × %H) + (16.00 g/mol × %O)
Given that carminic acid is 53.66% carbon and 4.0% hydrogen:
Molar mass of carminic acid = (12.01 g/mol × 53.66%) + (1.01 g/mol × 4.0%) + (16.00 g/mol × %O)
Step 2: Calculate the number of moles of NaOH used in the titration.
Given the volume of NaOH used (18.02 mL) and the molarity of NaOH (0.0406 M), we can use the formula:
Number of moles of NaOH = Volume of NaOH (in liters) × Molarity of NaOH
Convert the volume of NaOH from milliliters to liters:
Volume of NaOH (in liters) = 18.02 mL ÷ 1000 mL/L
Step 3: Use stoichiometry to find the ratio of moles between carminic acid and NaOH.
Since carminic acid has one acidic hydrogen per molecule and NaOH is a strong base, the neutralization reaction between carminic acid and NaOH can be written as follows:
Carminic acid + NaOH → Sodium salt of carminic acid + H2O
The balanced equation tells us that one mole of carminic acid reacts with one mole of NaOH.
Step 4: Use the number of moles from step 1 and the ratio from step 3 to determine the molecular formula of carminic acid.
To find the molecular formula of carminic acid, divide the number of moles of carminic acid by the number of moles of carminic acid per formula unit.
Now, you can perform the calculations to find the molecular formula of carminic acid.