Without knowing a lot of information about the structure of molecules, it can be difficult to determine if a chemical formula is empirical or molecular

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Without knowing a lot of information about the structure of molecules, it can be difficult to determine if a chemical formula is empirical or molecular. For example, the molecular formula for water is H
O; this is also the empirical formula since the 2:1 ratio cannot be simplified. Assume that each of the following chemical formulas is molecular. For each compound, fill in the blank with the proper subscripts for the empirical formula. You will have to show a value for each subscript, even if the value is 1. C
H
Empirical formula is C H H
O
Empirical formula is H O[1] C
H
O
Empricial formula is C O[2] K
Cr
O
Empirical formula is K[2]Cr[2]O C
H
Empirical formula is C[5]H H

The Correct Answer and Explanation is:

To determine the empirical formula of a compound, we must simplify the molecular formula to its simplest whole-number ratio of atoms. The molecular formula represents the actual number of atoms in a molecule, while the empirical formula shows the simplest ratio.

Let’s work through each one:

  1. CH:
    • The empirical formula for CH is CH. This is already in the simplest form since there is only one carbon (C) and one hydrogen (H) atom.
  2. H₂O:
    • The molecular formula for water is H₂O, which indicates there are two hydrogen atoms for every oxygen atom. This is already the empirical formula, as the ratio (2:1) cannot be simplified further. Therefore, the empirical formula for H₂O is H₂O.
  3. CH₂O:
    • The formula for CH₂O represents one carbon atom, two hydrogen atoms, and one oxygen atom. This ratio (1:2:1) is already in its simplest form. Therefore, the empirical formula for CH₂O is CH₂O.
  4. K₂Cr₂O₇:
    • The formula for potassium dichromate, K₂Cr₂O₇, can be simplified by dividing each subscript by 2. This gives a ratio of K:Cr:O as 1:1:3. Therefore, the empirical formula for K₂Cr₂O₇ is KCrO₃.
  5. C₆H₁₂O₆:
    • The formula for glucose is C₆H₁₂O₆. The ratio of carbon to hydrogen to oxygen is 6:12:6. Dividing each subscript by 6 simplifies the ratio to C₁H₂O₁ (or CH₂O). Therefore, the empirical formula for C₆H₁₂O₆ is CH₂O.
  6. C₈H₁₀N₄O₂:
    • This molecular formula represents caffeine. The ratio of carbon to hydrogen to nitrogen to oxygen is 8:10:4:2. Dividing each subscript by 2 simplifies the ratio to C₄H₅N₂O. Therefore, the empirical formula for C₈H₁₀N₄O₂ is C₄H₅N₂O.

To summarize:

  • CH → CH
  • H₂O → H₂O
  • CH₂O → CH₂O
  • K₂Cr₂O₇ → KCrO₃
  • C₆H₁₂O₆ → CH₂O
  • C₈H₁₀N₄O₂ → C₄H₅N₂O

This process of simplifying to the empirical formula is important because it helps in understanding the ratio of elements in a compound without needing to know its complex structure.

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