FORMULA WRITING
What is the formula for strontium chloride?
SrCl2
How many molecules are in 1 mole of CO₂?
6.022 × 10²³ molecules CO2
What is the percent composition of hydrogen in H₂O?
11.2%
A compound is 75% carbon and 25% hydrogen. Find the empirical formula.
CH₄
Why do ionic compounds use prefixes while molecular compounds do not?
Ionic compounds have charges!
What is the molecular formula for diphosphorus pentachloride?
P2Cl5
How many moles are in 88 g of CO₂?
2.00 moles CO2
A compound contains 12 g of C, 4 g of H, and 16 g of O. What is the percent composition of each element?
C = 37.5%, H = 12.5%, O = 50.0%
A compound contains 8.0 g of carbon, 2.0 g of hydrogen, and 10.7 g of oxygen. Find the empirical formula.
CH₂O
How does Avogadro’s number help convert between atoms and moles?
It provides a bridge between microscopic and macroscopic quantities.
What is the formula for iron(III) oxide?
Fe₂O₃
How many grams are in 4.2 × 10²³ molecules of NH₃?
11.9 g NH3
Find the percent composition of sodium in Na₂CO₃.
43.4%
The empirical formula of a compound is C₂H₅, and its molar mass is 58 g/mol. What is the molecular formula?
C₄H₁₀
If a molecular formula is C₆H₆, what could its empirical formula be?
CH
What is the formula for ammonium sulfate?
(NH₄)₂SO₄
Convert 3.5 moles of O₂ gas to liters at STP
78.4 L O2
A compound has a molar mass of 180 g/mol and an empirical formula of CH₂O. Find its molecular formula.
C₆H₁₂O₆
A compound is 40% sulfur and 60% oxygen by mass. Determine its empirical formula.
SO₃
What is the difference between an empirical and a molecular formula?
Empirical = simplest ratio; molecular = actual number of atoms.
A compound consists of magnesium, nitrogen, and oxygen. If it contains magnesium nitrate, what is the correct formula?
Mg(NO₃)₂
A sample of NaCl contains 2.5 × 10²³ formula units. How many grams is this?
24.3 g NaCl
Why is percent composition useful in identifying unknown compounds?
It allows scientists to compare experimental mass data to known values.
In what real-world applications do empirical and molecular formulas play an important role? THINK HARD.
Drug development, material science, forensic chemistry, etc.
If an empirical formula is CH3O, what could its molecular formula be?
Answers vary!