A compound is found to be 51.39% carbon, 8.64% hydrogen, and 39.97% nitrogen. It has a molecular molar mass of 140.22 g/mol. (This question requires one to find the empirical formula to end up with the final answer in molecular formula)
A. C10H14N2
B. C7H9N
C. C6H12N4
(The numbers are supposed to be subscripts)
I tried this problem by converting the percentages to grams, then dividing each element by its atomic mass, and lastly dividing each one by the lowest quotient. However, for the empirical formula I got C2H3N, which is wrong when you want to calculate the molecular formula using the empirical formula. Please help!
your technique should work
... not sure about the last "lowest quotient" step
C ... 140.22 * .5139 / 12.011 = 5.999
H ... 140.22 * .0864 / 1.0079 = 12.02
N ... 140.22 * .3997 / 14.007 = 4.001
looks like C.
thank you!
Well, it seems like you're in quite a "compound" situation here. Let's see if I can help you out with a little chemical humor!
To find the empirical formula, you're on the right track. You need to convert the percentages to grams, divide by the atomic masses, and then divide by the lowest quotient. So, let's crunch some numbers!
Assuming we have 100 grams of the compound, we would have:
- 51.39 grams of carbon
- 8.64 grams of hydrogen
- 39.97 grams of nitrogen
Now let's divide these amounts by their respective atomic masses:
- Carbon (C): 51.39 g / 12.01 g/mol = 4.284 mol
- Hydrogen (H): 8.64 g / 1.01 g/mol = 8.564 mol
- Nitrogen (N): 39.97 g / 14.01 g/mol = 2.852 mol
Now, let's find the lowest ratio by dividing each of the above values by the smallest value, which is 2.852 mol (rounding to three significant figures):
- Carbon: 4.284 mol / 2.852 mol = 1.501 ≈ 1.5
- Hydrogen: 8.564 mol / 2.852 mol = 3 ≈ 3
- Nitrogen: 2.852 mol / 2.852 mol = 1
Since we want the formula in whole numbers, we can multiply all the subscripts by 2, resulting in the empirical formula: C3H6N2.
Finally, to determine the molecular formula, we need to know the molar mass of the compound. Given that it is 140.22 g/mol, we need to compare it to the empirical formula's molar mass.
The molar mass of the empirical formula C3H6N2 can be calculated as follows:
- Carbon (C): 3 atoms x 12.01 g/mol = 36.03 g/mol
- Hydrogen (H): 6 atoms x 1.01 g/mol = 6.06 g/mol
- Nitrogen (N): 2 atoms x 14.01 g/mol= 28.02 g/mol
Adding them up, we get a molar mass of 70.11 g/mol.
Now, to find the ratio between the molar mass of the compound and the empirical formula, we divide them:
- Molecular mass / Empirical formula mass: 140.22 g/mol / 70.11 g/mol = 2
This means that the molecular formula is twice the empirical formula. Thus, taking into account the 2x multiplier, we get the molecular formula: C6H12N4.
So, after all that number crunching, the correct answer is C) C6H12N4.
Got to love chemistry! It's like telling a joke. Sometimes you need to go through a lot of steps to get to the punchline. Keep up the good work!
To find the empirical formula, we need to determine the ratio of the atoms present in the compound. We can do this by assuming we have 100g of the compound, which will allow us to directly convert the percentages to grams.
Given:
Carbon (C) = 51.39g
Hydrogen (H) = 8.64g
Nitrogen (N) = 39.97g
Next, we need to convert the grams of each element into moles by dividing the grams by their respective atomic masses.
The atomic masses are:
C: 12.01 g/mol
H: 1.01 g/mol
N: 14.01 g/mol
Moles of carbon (C) = 51.39 g / 12.01 g/mol ≈ 4.28 mol
Moles of hydrogen (H) = 8.64 g / 1.01 g/mol ≈ 8.56 mol
Moles of nitrogen (N) = 39.97 g / 14.01 g/mol ≈ 2.85 mol
Now, we need to find the simplest whole number ratio of moles by dividing each value by the smallest value, which is 2.85 mol.
Ratio of C: 4.28 mol / 2.85 mol ≈ 1.5
Ratio of H: 8.56 mol / 2.85 mol ≈ 3
Ratio of N: 2.85 mol / 2.85 mol = 1
The empirical formula is C1.5H3N.
To convert the empirical formula to the molecular formula, we need to multiply the empirical formula by a whole number to get the molecular molar mass (140.22 g/mol).
The molecular molar mass of C1.5H3N = 1.5(12.01) + 3(1.01) + 14.01 = 18.015 + 3.03 + 14.01 ≈ 35.06 g/mol
Now, we can calculate the whole number multiple by dividing the molecular molar mass by the empirical molar mass.
Whole number multiple = 140.22 g/mol / 35.06 g/mol ≈ 4
Finally, we multiply the empirical formula by the whole number multiple to obtain the molecular formula.
Molecular formula = (C1.5H3N) x 4 = C6H12N4
Therefore, the correct answer is C6H12N4.
To find the empirical formula, you need to determine the ratio of the different elements present in the compound. Here's how you can solve this problem step by step:
Step 1: Convert the percentages to grams.
Assume you have 100 grams of the compound. Therefore, you have 51.39 grams of carbon, 8.64 grams of hydrogen, and 39.97 grams of nitrogen.
Step 2: Calculate the moles of each element.
To find the moles of each element, divide the mass of each element by its atomic mass. The atomic mass of carbon is 12.01 g/mol, the atomic mass of hydrogen is 1.008 g/mol, and the atomic mass of nitrogen is 14.01 g/mol.
Moles of Carbon = 51.39 g / 12.01 g/mol ≈ 4.28 mol
Moles of Hydrogen = 8.64 g / 1.008 g/mol ≈ 8.57 mol
Moles of Nitrogen = 39.97 g / 14.01 g/mol ≈ 2.85 mol
Step 3: Divide each mole value by the smallest mole value.
In this case, the lowest mole value is 2.85 mol (from nitrogen). Divide each mole value by 2.85 mol to obtain the simplest, whole-number ratio.
Moles of Carbon = 4.28 mol / 2.85 mol ≈ 1.5
Moles of Hydrogen = 8.57 mol / 2.85 mol ≈ 3
Moles of Nitrogen = 2.85 mol / 2.85 mol = 1
This gives you the empirical formula: C1.5H3N.
Step 4: Adjust the subscripts to obtain whole numbers.
Multiply each subscript by 2 to obtain whole-number subscripts.
Empirical formula: C1.5H3N
Adjusted empirical formula: C3H6N2
Step 5: Calculate the molecular formula.
To find the molecular formula, you need to know the molecular molar mass, which is given as 140.22 g/mol. Divide the molecular molar mass by the empirical formula molar mass to determine the ratio between the molecular formula and empirical formula.
Molecular formula molar mass = 140.22 g/mol
Empirical formula molar mass = (12.01 g/mol * 3) + (1.008 g/mol * 6) + (14.01 g/mol * 2)
= 114.21 g/mol
Molecular formula ratio = Molecular molar mass / Empirical formula molar mass
= 140.22 g/mol / 114.21 g/mol
≈ 1.23
When rounding to the nearest whole number, the ratio is approximately 1:1. Therefore, the molecular formula is also C3H6N2.
So, the correct answer is C. C6H12N4, which matches the empirical formula C3H6N2 when multiplied by a ratio of 2.