Chemistry Molar Mass and Laws Quiz

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Questions and Answers

What is the molar mass of carbon-12?

44 g

12 g (correct)

24 g

6.022 g

Which option correctly identifies the elementary entity of sodium (Na)?

Molecule

Formula unit

Ion

Atom (correct)

What type of elementary entity is represented by the molecular formula H2O?

Molecule (correct)

Atom

Ion

Formula unit

What is the elementary entity for the ionic compound NaCl?

Formula unit Signup and view all the answers

If a substance is classified as a molecular compound, what would its elementary entity be?

Molecule Signup and view all the answers

What was the main conclusion reached by Lavoisier regarding mass in chemical reactions?

The total mass of reactants equals the total mass of products. Signup and view all the answers

Which compound did Lavoisier decompose in his experiment?

Mercury (II) oxide Signup and view all the answers

What principle did Joseph Proust establish in relation to compounds?

The law of definite proportions Signup and view all the answers

In pure water, what is the mass ratio of hydrogen to oxygen?

1:8 Signup and view all the answers

What happens when 3.0 g of hydrogen is mixed with 8.0 g of oxygen?

9.0 g of water is produced, with hydrogen remaining. Signup and view all the answers

Which of the following represents the law of conservation of mass?

Mass remains constant throughout a chemical reaction. Signup and view all the answers

Which statement about water decomposition is true?

Decomposing 9.0 g of water always results in 1.0 g of hydrogen and 8.0 g of oxygen. Signup and view all the answers

What color indicates mercury (II) oxide before decomposition?

Red Signup and view all the answers

What is the significance of the number of atoms or molecules in a chemical reaction compared to their masses?

Number of atoms or molecules is more significant for reactions. Signup and view all the answers

Which mass ratio of iron to sulfur results in some sulfur being left unreacted?

1:1 ratio by mass Signup and view all the answers

What is the molar mass of K2SO4?

174.3 g mol–1 Signup and view all the answers

How many atoms of iron react with how many atoms of sulfur to form iron (II) sulfide?

1 iron atom and 1 sulfur atom Signup and view all the answers

How is the molar mass of Ba3(PO4)2 calculated?

By multiplying the molar mass of Ba by 3 and adding twice the molar mass of PO4 Signup and view all the answers

What is the chemical equation representing the reaction between iron and sulfur?

Fe + S → FeS Signup and view all the answers

What do we commonly use to express the number of atoms or molecules in chemistry?

Dozen Signup and view all the answers

What is the molar mass of Aluminium Oxide (Al2O3)?

102.0 g Signup and view all the answers

What is the first step in calculating the molar mass of a compound?

Find the molar mass of each individual element Signup and view all the answers

What is the definition of a mole in chemistry?

The amount of substance containing as many entities as atoms in 12g of carbon-12. Signup and view all the answers

What is the percentage composition of Aluminium in Aluminium Oxide (Al2O3)?

52.9% Signup and view all the answers

What would be the mass of carbon-12 that contains 1.0 × 10^19 atoms?

0.5 g Signup and view all the answers

If the molar mass of O is 16.0 g mol–1, what is the contribution of oxygen in K2SO4?

64.0 g mol–1 Signup and view all the answers

Why is the term 'mole' derived from the Latin word 'moles'?

It represents a large collection of entities. Signup and view all the answers

How many moles of Oxygen are contained in one mole of Butanoic Acid (C4H8O2)?

2 mol Signup and view all the answers

What is true regarding the number of entities in one mole of any substance?

It is always the same no matter what the substance is. Signup and view all the answers

What is the correct method to calculate the percentage of an element in a compound?

Mass of element in one mole of compound / Total mass of compound × 100 Signup and view all the answers

What is the molar mass of phosphorus used in the calculation of Ba3(PO4)2?

31.0 g mol–1 Signup and view all the answers

What is the total mass of oxygen in one mole of Aluminium Oxide (Al2O3)?

48.0 g Signup and view all the answers

In determining molar mass, what does 'g mol–1' represent?

Grams of the substance per mole Signup and view all the answers

What is the total number of moles of Carbon, Hydrogen, and Oxygen in one mole of Butanoic Acid (C4H8O2)?

10 Signup and view all the answers

What contribution does the sulfur atom have to the molar mass of K2SO4?

32.1 g mol–1 Signup and view all the answers

Which of the following best describes the term 'percentage composition'?

The mass of each element in one mole of a compound as a percentage of the total mass Signup and view all the answers

If the molar mass of Butanoic Acid (C4H8O2) is calculated, what would it yield?

86.0 g Signup and view all the answers

Study Notes

Molar Mass Calculation

Molar mass of K₂SO₄: (2 * molar mass of K) + (molar mass of S + 4 * molar mass of O) = (2 * 39.1) + (32.1 + 4 * 16) = 174.3 g/mol
Molar mass of Ba₃(PO₄)₂: (3 * molar mass of Ba) + 2 * (molar mass of P + 4 * molar mass of O) = (3 * 137.3) + 2 * (31.0 + 4 * 16.0) = 601.9 g/mol

Law of Conservation of Mass

Lavoisier's experiments showed that the total mass of reactants equals the total mass of products in a chemical reaction.
This is known as the law of conservation of mass.

Law of Definite Proportions

Proust's work established the law of definite or constant proportions.
This law states that the mass ratio of elements in a compound is fixed, regardless of its source or preparation.
Example: Water always contains hydrogen and oxygen in a 1:8 mass ratio (11.11% hydrogen and 88.89% oxygen).

Atomic and Molecular Ratios in Reactions

Substances react in simple ratios of atoms or molecules, not just by mass.
Example: Iron and sulfur react to form iron(II) sulfide (FeS) in a 1:1 atom ratio.

The Mole Concept

The mole (mol) is a unit representing 6.022 x 10²³ entities (atoms, molecules, ions, etc.).
It's based on the number of atoms in 12 grams of carbon-12.
One mole of any substance has the same number of entities.
Molar mass is the mass (in grams) of one mole of a substance.

Elementary Entities per Substance Type

Elements (atomic form, e.g., Na, K): Atom
Elements (molecular form, e.g., O₂, N₂, H₂): Molecule
Molecular compounds (e.g., NH₃, H₂O): Molecule
Ions (e.g., Na⁺, Cl⁻): Ion
Ionic compounds (e.g., NaCl, K₂SO₄): Formula unit

Percentage Composition

Percentage mass of an element in a compound = (mass of element / molar mass of compound) * 100
Example: In Al₂O₃, the percentage of aluminum is calculated as (54.0 g Al / 102.0 g Al₂O₃) * 100 = 52.9%

Elemental Analysis Example

Butanoic acid (C₄H₈O₂) elemental analysis:
- 4 moles of carbon atoms per mole of butanoic acid
- 8 moles of hydrogen atoms per mole of butanoic acid
- 2 moles of oxygen atoms per mole of butanoic acid

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Description

Test your knowledge on molar mass calculations and the fundamental laws of chemistry such as the law of conservation of mass and the law of definite proportions. This quiz covers essential concepts that are pivotal to understanding chemical reactions and their principles. Perfect for students studying general chemistry.