Monosodium glutamate (MSG), a food-flavor enhancer, has been blamed for “Chinese Restaurant Syndrome,” the symptoms of which are headaches & chest pains. MSG has the following composition by mass: 35.51 percent C, 4.77 percent H, 37.85 percent O, 8.29 percent N, & 13.60 percent Na. What is its molecular formula if its molar mass is about 169 g?

I don't know how to start this problem, please help!!

start by figuring out what 35.51 percent of 169 grams is. It is around 60 grams (60.0119g to be exact) this is the percentage of carbon in MSG. Now look at the bottom number on the periodic table for carbon 12.01, meaning one Mol is 12.01g, therefore 5 carbons will be needed for 60 grams... 60/12 = 5. So you have your first part of the formula C5. (169 * 0.3551 gives you the 60.0119)

I disagree with the way Kyle has worked the problem. I've posted by answer at your first query. Kyle's solution will give you the correct answer but it is based on his assumption (Kyle may not have assumed that in his mind but his solution does that automatically) that the simplest empirical formula and the molecular formula are the same. It turns at that is correct but if that were not so his method would not work.

To determine the molecular formula of MSG, you will need to follow these steps:

1. Start by assuming you have 100 grams of MSG. This way, the percentages given can be directly converted into grams.

2. Calculate the number of moles of each element using their respective molar masses. The molar mass of carbon (C) is 12 g/mol, hydrogen (H) is 1 g/mol, oxygen (O) is 16 g/mol, nitrogen (N) is 14 g/mol, and sodium (Na) is 23 g/mol.

Mass of C = 35.51% * 100 g = 35.51 g
Mass of H = 4.77% * 100 g = 4.77 g
Mass of O = 37.85% * 100 g = 37.85 g
Mass of N = 8.29% * 100 g = 8.29 g
Mass of Na = 13.60% * 100 g = 13.60 g

Moles of C = 35.51 g / 12 g/mol ≈ 2.96 mol
Moles of H = 4.77 g / 1 g/mol ≈ 4.77 mol
Moles of O = 37.85 g / 16 g/mol ≈ 2.37 mol
Moles of N = 8.29 g / 14 g/mol ≈ 0.59 mol
Moles of Na = 13.60 g / 23 g/mol ≈ 0.59 mol

3. Find the simplest whole number ratio of moles for each element by dividing the number of moles by the lowest number, which is 0.59 in this case.

Simplest ratio of C: 2.96 mol / 0.59 mol ≈ 5
Simplest ratio of H: 4.77 mol / 0.59 mol ≈ 8
Simplest ratio of O: 2.37 mol / 0.59 mol ≈ 4
Simplest ratio of N: 0.59 mol / 0.59 mol = 1
Simplest ratio of Na: 0.59 mol / 0.59 mol = 1

4. Write the molecular formula using the simplest whole number ratio. In this case, the molecular formula is C5H8O4N2Na2.

Therefore, the molecular formula of MSG is C5H8O4N2Na2.

To determine the molecular formula of monosodium glutamate (MSG), we need to find the empirical formula first. The empirical formula represents the simplest ratio of atoms in a compound.

Step 1: Calculate the number of moles of each element in the compound.
To do this, we need to convert the percentages given into grams. Assume we have 100g of MSG, which means 35.51g is carbon (C), 4.77g is hydrogen (H), 37.85g is oxygen (O), 8.29g is nitrogen (N), and 13.60g is sodium (Na).

Step 2: Convert the grams into moles.
To convert the grams of each element into moles, divide the mass of each element by its molar mass.

The molar mass of carbon (C) is 12.01 g/mol, hydrogen (H) is 1.01 g/mol, oxygen (O) is 16.00 g/mol, nitrogen (N) is 14.01 g/mol, and sodium (Na) is 22.99 g/mol.

For carbon (C): 35.51g / 12.01 g/mol ≈ 2.96 mol
For hydrogen (H): 4.77 g / 1.01 g/mol ≈ 4.72 mol
For oxygen (O): 37.85 g / 16.00 g/mol ≈ 2.36 mol
For nitrogen (N): 8.29 g / 14.01 g/mol ≈ 0.59 mol
For sodium (Na): 13.60 g / 22.99 g/mol ≈ 0.59 mol

Step 3: Divide the number of moles by the smallest number of moles.
This step will give us the simplest ratio of atoms in the compound.

In this case, the smallest number of moles is 0.59 mol. Dividing each of the other values by 0.59, we get:
Carbon (C) ≈ 2.96 mol / 0.59 mol ≈ 5
Hydrogen (H) ≈ 4.72 mol / 0.59 mol ≈ 8
Oxygen (O) ≈ 2.36 mol / 0.59 mol ≈ 4
Nitrogen (N) ≈ 0.59 mol / 0.59 mol ≈ 1
Sodium (Na) ≈ 0.59 mol / 0.59 mol ≈ 1

Step 4: Write the empirical formula.
Based on the previous calculations, the empirical formula is C5H8O4NNa. This represents the simplest ratio of atoms in MSG.

To find the molecular formula, which represents the actual number of atoms in a molecule, we need to know the molar mass of MSG. In this case, the molar mass is given as 169 g/mol.

Step 5: Calculate the empirical formula mass.
To do this, we sum up the atomic masses of all the atoms in the empirical formula.

The atomic mass of carbon (C) is 12.01 g/mol, hydrogen (H) is 1.01 g/mol, oxygen (O) is 16.00 g/mol, nitrogen (N) is 14.01 g/mol, and sodium (Na) is 22.99 g/mol.

For the empirical formula, C5H8O4NNa:
Empirical formula mass = (5 × 12.01 g/mol) + (8 × 1.01 g/mol) + (4 × 16.00 g/mol) + (1 × 14.01 g/mol) + (1 × 22.99 g/mol) ≈ 147.15 g/mol

Step 6: Determine the molecular formula.
To find the molecular formula, divide the molar mass by the empirical formula mass.

Molar mass: 169 g/mol
Empirical formula mass: 147.15 g/mol

169 g/mol ÷ 147.15 g/mol ≈ 1.15

Since the result is approximately 1.15, we need to multiply all the subscripts in the empirical formula by 1.15 to find the molecular formula.

The molecular formula for monosodium glutamate (MSG) is C5.75H9.2O4.6N1.15Na1.15.

Note that we rounded the subscripts to the nearest whole number to get a whole number composition, as subscripts represent the ratio of atoms in a molecule.