Menentukan Mr ( massa molekul relatif )

Summary

This educational video explains the concepts of relative atomic mass (Ar) and relative molecular mass (Mr) in chemistry. It demonstrates how to find Ar values using the periodic table and how to calculate Mr by adding the Ar values of atoms in a molecule. Practical examples include the molecular masses of H2O, HNO3, H2SO4, and glucose (C6H12O6). Viewers are encouraged to practice these calculations to enhance their understanding of chemical mass concepts. The video aims to simplify these foundational concepts for better learning in chemistry.

Takeaways

• 😀 The video introduces the concept of relative atomic mass (Ar) and molecular mass (Mr).
• 😀 Relative atomic mass (Ar) refers to the weighted average mass of atoms of an element, taking into account the isotopes present.
• 😀 To find the relative atomic mass (Ar), refer to the periodic table where it is usually indicated as a number below the element symbol.
• 😀 The periodic table also includes other information, such as the atomic number, which is displayed above the element symbol.
• 😀 For elements like Carbon, Hydrogen, and Oxygen, their relative atomic masses are provided: Carbon (12), Hydrogen (1), and Oxygen (16).
• 😀 The molecular mass (Mr) is the sum of the relative atomic masses of all atoms in a molecule.
• 😀 To calculate the molecular mass (Mr) of a compound, multiply the relative atomic mass (Ar) of each element by the number of atoms of that element in the molecule.
• 😀 Example: For H2O, the molecular mass is calculated by (2 x 1 for H) + (1 x 16 for O), resulting in a molecular mass of 18.
• 😀 In the case of HNO3, the molecular mass is calculated as (1 x 1 for H) + (1 x 14 for N) + (3 x 16 for O), resulting in a molecular mass of 63.
• 😀 For more complex compounds like H2SO4 and glucose (C6H12O6), similar calculations are done using their respective atomic masses, resulting in molecular masses of 98 and 180, respectively.

Q & A

What is the relative atomic mass (Ar)?

The relative atomic mass (Ar) is the mass of an atom compared to the mass of a carbon-12 atom. It is typically found on the periodic table of elements.

How can you find the relative atomic mass of an element from the periodic table?

You can find the relative atomic mass by looking at the larger number in the element's box in the periodic table. This number represents the atomic mass (Ar) of the element.

What does the symbol 'Ar' stand for in chemistry?

'Ar' stands for the relative atomic mass of an element.

What is the relative atomic mass (Ar) of carbon (C)?

The relative atomic mass of carbon (C) is 12, which is found on the periodic table.

In the periodic table, what does the number below the element symbol represent?

The number below the element symbol represents the atomic mass (Ar), which is usually a larger number and indicates the mass of the atom.

How do you calculate the molecular mass (Mr) of a compound?

To calculate the molecular mass (Mr), sum the relative atomic masses (Ar) of all the atoms in the compound, each multiplied by the number of times that atom appears in the formula.

What is the molecular mass (Mr) of H2O (water)?

The molecular mass (Mr) of H2O is 18. This is calculated as (2 × 1 for hydrogen) + (1 × 16 for oxygen) = 18.

How do you determine the molecular mass (Mr) of HNO3 (nitric acid)?

To calculate the Mr of HNO3, use the formula: (1 × 1 for hydrogen) + (1 × 14 for nitrogen) + (3 × 16 for oxygen) = 63.

What is the molecular mass (Mr) of H2SO4 (sulfuric acid)?

The molecular mass (Mr) of H2SO4 is 98. This is calculated as (2 × 1 for hydrogen) + (1 × 32 for sulfur) + (4 × 16 for oxygen) = 98.

How do you calculate the molecular mass (Mr) of glucose (C6H12O6)?

To calculate the molecular mass of glucose (C6H12O6), use the formula: (6 × 12 for carbon) + (12 × 1 for hydrogen) + (6 × 16 for oxygen) = 180.

Why is it important to understand relative atomic mass and molecular mass in chemistry?

Understanding relative atomic mass and molecular mass is essential for performing calculations involving moles, stoichiometry, and understanding the composition of substances in chemical reactions.

What is the significance of the number 12 in the context of relative atomic mass?

The number 12 is significant because it represents the mass of the carbon-12 isotope, which is used as a standard for defining relative atomic mass (Ar).