Empirical Formula Practice

Question

Lactic acid, employed in pharmaceutical technology to produce water-soluble lactates, has the following elemental composition: , 40.00 ; , 6.71 ; , 53.29 .

Calculate the empirical formula of lactic acid.    

Express your answer as a chemical formula.

Answer 1

Hello, Katrina,

Some information seems to missing from your question. I see percentages, but not element ID's.

I'll assume the percentages are for C, H, and O, respectively.

Take each percentage and divide by that elements atomic mass (amu) to yield a weighted value. Since we need whole numbers for each element, we need to normalize each by a factor that gives all whole numbers. Looking at carbon, we can take the 0.0333 weighted value and create a conversion factor that, when multiplied by the weighted value, will result in 1 carbon. That value is (1/0.333), or 30. Multiply all three weighted averages by 30, and round to the nearest whole number. That results in an empirical formula of C₁H₂O₁.

The actual formula for lactic acid is C₃H₆O₃. This is exactly three times the number of each element. The empirical formula is the "simplest whole-number ratio of atoms in a compound," so C₁H₂O₁ is correct.

I hope this helps,

Bob