Empirical and Molecular Formula

Chemists use different formulas to describe compounds. The formula that shows the simplest whole-number ratio of atoms is called the:

• Empirical formula

• Expanded formula

• Molecular formula

• Structural formula

A student sees the chemical formula H₂O, which shows the actual number of atoms present in water. What kind of formula is this?

• Chemical symbol

• Empirical formula

• Isotope notation

• Molecular formula

Subscripts in a chemical formula are very important. What do they tell us?

• The molar mass of the compound

• The state of matter of the compound

• The number of bonds between atoms

• The number of atoms of each element

Vinegar is used in cooking and cleaning. Its molecular formula is C₂H₄O₂. What is its empirical formula?

• CHO

• CH₂O

• C₂H₄O₂

• C₄H₈O₄

Bleach is used as a disinfectant. If its chemical formula is Nalo, what does the subscript in ClO mean?

• The total molar mass

• The number of bonds

• The number of isotopes

• The number of atoms of each element

Salt (NaCl) is widely used for cooking. What is the relation between its empirical and molecular formula?

• They are the same

• They are always different

• Salt has no molecular formula

• The empirical formula does not apply to ionic compounds

A sample contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen. What is the empirical formula?

• CH₂O

• C₂H₄O₂

• C₆H₁₂O₆

• C₂H₂O

Sometimes, the molecular formula is a multiple of the empirical formula. Why does this happen?

• Because atoms cannot combine in fractions

• Because molecular formulas ignore atom ratios

• Because empirical formulas always reduce to single atoms

• Because molecules may contain more atoms than the simplest ratio

Learners are asked to compare empirical and molecular formulas. Which statement is correct?

• Empirical formulas give more structural information

• Empirical formulas always equal molecular formulas

• Molecular formulas only show ratios, not actual counts

• Molecular formulas can be a multiple of empirical formulas

Methane gas is used for cooking in many households. Its molecular formula is CH₄. What is its empirical formula?

• CH₂

• CH₄

• C₂H₂

• C₃H₆