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Chemical Formula in Chemistry Questions with Solutions, Cheat Sheet of Chemistry

Philippine Women's University (PWU)Chemistry

A comprehensive overview of chemical formulas, including the definition of a chemical formula, the difference between a chemical formula and a molecular formula, examples of molecules with one, two, and three different types of atoms, and the calculation of formula unit mass. It also includes several practice questions with solutions on topics such as the simplest formula of a substance, the formula of a compound with a given mole ratio, the amount of oxygen in a mole of calcium carbonate, the formula of copper sulfate pentahydrate, the formula weight of a compound, and the identification of the chemical formula of hyposulfurous acid. Fundamental concepts in chemistry related to chemical formulas and their representation, making it a valuable resource for students studying chemistry at the university level.

Typology: Cheat Sheet

2022/2023

Uploaded on 02/25/2023

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Chemical Formula in Chemistry Questions with Solutions
Q1. The simplest formula of a substance shows-
a) The actual number of atoms of each element in one molecule of a
substance.
b) The elements that make up one molecule of the substance and the
simplest whole-number ratio between the atoms.
c) The number of molecules in a sample of the substance.
d) The molecular mass of the substance.
Correct Answer.(b) The elements that make up one molecule of the
substance and the simplest whole-number ratio between the atoms.
Q2. A substance of phosphorus (P) and oxygen (O) is found to have a
mole ratio of 0.4 moles of P for every mole of O. The simplest formula
for this substance is:
a) PO2
b) P0.4O
c) P5O2
d) P2O5
Correct Answer.'(d) P2O5
Q3. How many grams of oxygen are in one mole of calcium carbonate,
CaCO3?
The atomic mass of O = 16 amu.
a) 3 grams
b) 16 grams
c) 32 grams
d) 48 grams
Correct Answer.(d) 48 grams
Q4. Copper sulphate crystals are actually pentahydrate crystals of
copper sulphate. Copper sulphate pentahydrate has the following
molecular formula:
a) CuSO4.5H2O
b) CuSO4+ H2O
c) CuSO4
d) CuSO4+ 5H2O
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Chemical Formula in Chemistry Questions with Solutions Q1. The simplest formula of a substance shows- a) The actual number of atoms of each element in one molecule of a substance. b) The elements that make up one molecule of the substance and the simplest whole-number ratio between the atoms. c) The number of molecules in a sample of the substance. d) The molecular mass of the substance. Correct Answer. (b) The elements that make up one molecule of the substance and the simplest whole-number ratio between the atoms. Q2. A substance of phosphorus (P) and oxygen (O) is found to have a mole ratio of 0.4 moles of P for every mole of O. The simplest formula for this substance is: a) PO 2 b) P0.4O c) P 5 O 2 d) P 2 O 5 Correct Answer. (d) P 2 O 5 Q3. How many grams of oxygen are in one mole of calcium carbonate, CaCO 3? The atomic mass of O = 16 amu. a) 3 grams b) 16 grams c) 32 grams d) 48 grams Correct Answer. (d) 48 grams Q4. Copper sulphate crystals are actually pentahydrate crystals of copper sulphate. Copper sulphate pentahydrate has the following molecular formula: a) CuSO 4 .5H 2 O b) CuSO 4 + H 2 O c) CuSO 4 d) CuSO 4 + 5H 2 O

Correct Answer. (a) Q5. A compound with molecular formula Fe 2 (SO 4 ) 3 would be called: a) ferrous sulfate b) iron(II) sulfate c) iron(III) sulfite d) iron(III) sulfate Correct Answer. iron(III) sulfate Q6. What will the formula weight of the compound Al 2 (SO 4 ) 3 .18H 2 O? Answer. The formula weight of the compound Al 2 (SO 4 ) 3 .18H 2 O can be calculated as- 2 × 27 + [32 + (16 ×4)] × 3 + 18 × 18 = 54 + 288 + 324 = 666 Therefore, the weight of the compound is 666 g. Q7. State True or False. The chemical formula is the same as a chemical structure or molecular formula. Answer. False. The formula unit mass is the same as the molecular mass, which is equal to the sum of the masses of the atoms in the formula unit. Q8. What is the chemical formula of Hyposulfurous acid? Answer. The chemical formula of Hyposulfurous acid is H 2 SO 2. Q9. What is meant by the term chemical formula? Answer. A compound’s chemical formula is a symbolic representation of its composition and the actual number of atoms in one molecule of a pure substance, which could be an atom or a compound. Q10. Write down the formula of- (i) Sodium oxide (ii) Aluminium chloride (iii) Sodium sulphide (iv) Magnesium hydroxide Answer. (i) Sodium oxide – Na 2 O (ii) Aluminium chloride – AlCl 3 (iii) Sodium sulphide – Na 2 S

Q14. An unknown compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen with a molecular mass of 60.0 g/mol. What is the molecular formula of the unknown compound? Answer. In 100 g of the unknown compound, the ratio of C : H : O = 3.33 : 6.665 : 3. When we divide each elemental ratio by the lowest number, we get an empirical formula of CH 2 O. i.e, near enough to whole numbers. The molecular formula is always a multiple of the empirical formula- (EF)n = MF. So 60.0 g mol

  • = n × (12.011 + 2 × 1.00794 + 16gmol - ). Clearly n=2, and the molecular formula is 2×(CH 2 O) = C 2 H 4 O 2. Therefore, the molecular formula of the given compound is C 2 H 4 O 2. Q15. Find the molecular and empirical formula- When vapour density = 83 Carbon=57.8% Oxygen=38.6% Hydrogen=3.6% Answer. Element R.N of atoms Simple ratio C 57.8/12 = 4.8 4.8/2.4 = 2 O 38.6/16 = 2.41 2.4/2.4 = 1 H 3.60/1 = 3.6 3.6/2.4 = 3/ C:O:H = 2:1:3/2 = 4:2: Simple ratio of whole numbers = 4:2: Empirical formula is C 4 O 2 H 3 Empirical formula weight = 4 × 12 + 2 × 16 + 3× 1 = 83 Vapour Density = 83 Molecular formula weight = 2 × V.D = 2 × 83 = 166 n= Molecular formula weight / Empirical formula weight = 166/83 = 2 ∴ Molecular formula = n × EF Molecular Formula = 2 × [C 2 H 4 O 2 ] = C 8 H 6 O 4 Practise Questions on Chemical Formula

Q1. An oxide of lead contains 90.65% Pb, by weight. The empirical formula is: a) Pb b) PbO c) Pb 3 O 4 d) Pb 2 O 3