Ayo Belajar "Massa Atom Relatif dan Massa Molekul Relatif"

Summary

This educational video provides a clear explanation of relative atomic mass (Ar) and relative molecular mass (Mr), two essential concepts in chemistry. The video defines both terms, explains their formulas, and provides practical examples, such as calculating the relative atomic mass of chlorine (Cl) and the relative molecular mass of compounds like Fe2SO4 3 and CaOH2. The lesson emphasizes the importance of these calculations in understanding the mass relationships in atoms and molecules. The video is aimed at students learning the foundational concepts of atomic and molecular masses.

Takeaways

• 😀 The relative atomic mass (Ar) compares the average mass of an atom of an element to 1/12 of the mass of a C12 atom.
• 😀 Ar = (average mass of an element's atom) / (1/12 of the mass of a C12 atom).
• 😀 The atomic mass of elements often includes isotopes, so Ar is based on the average mass from a mixture of isotopes.
• 😀 For example, chlorine (Cl) has isotopes Cl35 and Cl37 in a 75% to 25% ratio, with the average ArCl = 35.5.
• 😀 Relative molecular mass (Mr) compares the average mass of a molecule to 1/12 of the mass of a C12 atom.
• 😀 Mr = (average mass of a molecule) / (1/12 of the mass of a C12 atom).
• 😀 Mr is used to calculate the mass of molecules and applies only to substances made of molecules.
• 😀 To calculate atomic mass, Ar should be used, while for molecular mass, Mr is the appropriate term.
• 😀 Example 1: The Mr of Fe2SO4 3 is calculated as 400 by using ArFe = 56, ArS = 32, and ArO = 16.
• 😀 Example 2: The Mr of Ca(OH)2 is calculated as 74 by using ArCa = 40, ArO = 16, and ArH = 1.
• 😀 Example 3: The Mr of H2SO4 is calculated as 98 by using ArH = 1, ArS = 32, and ArO = 16.
• 😀 The video concludes with a reminder to use the proper methods for calculating atomic and molecular masses for various elements and compounds.

Q & A

What is the definition of relative atomic mass (Ar)?

Relative atomic mass (Ar) is the comparison of the average mass of an atom of an element to 1/12 of the mass of a carbon-12 (C12) isotope.

How is the relative atomic mass (Ar) of an element calculated?

It is calculated by dividing the average mass of an atom of the element by 1/12 of the mass of a carbon-12 atom.

Why is the mass of a carbon-12 isotope used as a reference in relative atomic mass calculations?

The carbon-12 isotope is used because its mass is defined as exactly 12 atomic mass units, providing a standard reference for measuring the masses of other atoms.

What is an example of calculating the relative atomic mass (Ar) of chlorine?

Chlorine has two isotopes: Cl-35 (75%) and Cl-37 (25%). The relative atomic mass is calculated as (0.75 × 35) + (0.25 × 37), which equals 35.5.

What is the formula for relative molecular mass (Mr)?

Relative molecular mass (Mr) is the comparison of the average mass of a molecule to 1/12 of the mass of a carbon-12 atom. The formula is Mr = (sum of Ar of all atoms in the molecule).

How is relative molecular mass (Mr) different from relative atomic mass (Ar)?

Relative molecular mass (Mr) is used to calculate the mass of a molecule, while relative atomic mass (Ar) is used to calculate the mass of individual atoms. Mr applies to molecules, whereas Ar applies to atoms.

What does the term 'relative molecular mass' apply to?

Relative molecular mass applies only to substances made of molecules, such as molecular compounds.

How is the relative molecular mass (Mr) of Fe2SO4(3) calculated?

The relative molecular mass of Fe2SO4(3) is calculated by adding the contributions of all elements: (2 × 56) + (3 × 32) + (12 × 16) = 400.

What is the relative molecular mass of calcium hydroxide (CaOH2)?

The relative molecular mass of calcium hydroxide (CaOH2) is calculated as 40 (Ca) + 2 × 16 (O) + 2 × 1 (H), which equals 74.

How is the relative molecular mass (Mr) of H2SO4 calculated?

The relative molecular mass of H2SO4 is calculated as (2 × 1) + (1 × 32) + (4 × 16), which equals 98.