I need help on this question. I can't seem to understand it.
Find the molecular formula of a compound with a gram molecular mass of 30 g and an empirical formula of CH3.
Please show your work! and briefly explain how you got it!
The empirical formula mass is 15; i.e., 12 for C + 3*1 for H = 15.
The molecular formula mass is 30 g so the question is asking how many units of CH3 make up the molecule.
That's 30/15 = 2 or the molecular formula is(CH3)2 = C2H6. You can check it this way.
2*12 + 6*1 = 30
Wow thank you for putting the time to answer that! I appreciate it. That's a simpler understanding. My teacher explained it horribly and much more complex! Thank you again.
To start, we need to understand the concepts of empirical formula and molecular formula.
The empirical formula represents the simplest whole-number ratio of atoms in a compound. It can be determined from the percentages of the elements present or from the given molecular formula.
The molecular formula represents the actual number of atoms of each element in a compound.
Given:
Gram molecular mass = 30 g
Empirical formula = CH3
Step 1: Find the empirical formula mass
The empirical formula mass can be calculated by summing the atomic masses of the elements in the empirical formula.
Empirical formula mass = (C atomic mass) + (H atomic mass * number of H atoms)
Empirical formula mass = (12.01 g/mol) + (1.01 g/mol * 3)
Empirical formula mass = 12.01 g/mol + 3.03 g/mol
Empirical formula mass = 15.04 g/mol
Step 2: Calculate the empirical formula molar mass
The empirical formula molar mass is the mass of one mole of the compound, which is equal to the given gram molecular mass.
Empirical formula molar mass = 30 g
Step 3: Determine the ratio between the empirical and molar masses
To find the molecular formula, we need to determine the ratio between the empirical formula mass and the empirical formula molar mass.
Ratio = Empirical formula molar mass / Empirical formula mass
Ratio = 30 g / 15.04 g/mol
Ratio ≈ 1.996213 g/mol
Step 4: Determine the subscripts for the molecular formula
The ratio calculated in step 3 represents the number of empirical formula units (CH3) present in one mole of the compound. To convert this ratio to the simplest whole-number ratio, we can round it to the nearest whole number.
Since the ratio is close to 2, we can assume that there are two empirical formula units (CH3) in the molecular formula.
Therefore, the molecular formula would be (CH3)2, which simplifies to C2H6.
So, the molecular formula of the compound with a gram molecular mass of 30 g and an empirical formula of CH3 is C2H6.
By following these steps, we found the molecular formula C2H6 based on the given information and using the concept of empirical formula and molar mass.