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Find empirical and molecular formulae

12th grade (Year 13 in England) · 11 questions · Common Core: NGSS.HS-PS1-7 · England: GCSE Chemistry: Quantitative chemistry, A level Chemistry: Amount of substance

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Date

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1
Question 1
Find the empirical formula: 11.2 g of iron combines with 4.8 g of oxygen (Ar: Fe = 56, O = 16).
- A. Fe₂O₃
- B. FeO₃
- C. FeO
- D. Fe₃O₄
Question 2
A compound has the empirical formula CH (mass of one unit = 13) and Mr = 78. How many empirical units are in one molecule?
Answer
3
Question 3
Find the empirical formula: a compound is 30.4 % nitrogen and 69.6 % oxygen (Ar: N = 14, O = 16).
- A. N₂O₄
- B. NO₂
- C. NO
- D. N₂O
Question 4
A compound has the empirical formula CH₂O (mass of one unit = 30) and Mr = 180. How many empirical units are in one molecule?
Answer
5
Question 5
Find the empirical formula: 11.2 g of iron combines with 4.8 g of oxygen (Ar: Fe = 56, O = 16).
- A. FeO₃
- B. FeO
- C. Fe₃O₄
- D. Fe₂O₃
Question 6
A compound has the empirical formula CH (mass of one unit = 13) and Mr = 78. How many empirical units are in one molecule?
Answer
7
Question 7
Find the empirical formula: a compound is 40 % carbon, 6.7 % hydrogen and 53.3 % oxygen (Ar: C = 12, H = 1, O = 16).
- A. CHO
- B. CH₂O
- C. C₆H₁₂O₆
- D. C₂H₄O
Question 8
A compound has the empirical formula NO₂ (mass of one unit = 46) and Mr = 92. How many empirical units are in one molecule?
Answer
9
Question 9
Find the empirical formula: a compound is 30.4 % nitrogen and 69.6 % oxygen (Ar: N = 14, O = 16).
- A. NO₂
- B. N₂O
- C. NO
- D. N₂O₄
Question 10
A compound has the empirical formula CH₂O (mass of one unit = 30) and Mr = 180. How many empirical units are in one molecule?
Answer
11
Question 11
Find the empirical formula: 2.4 g of magnesium combines with 1.6 g of oxygen (Ar: Mg = 24, O = 16).
- A. Mg₂O
- B. Mg₃O₂
- C. MgO
- D. MgO₂

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