What are exercises on calculating molecular mass for grade 8 students in Vietnam (from basic to advanced)? What are evaluation formats of Natural Sciences subject for grade 8 in Vietnam?

What are exercises on calculating molecular mass for grade 8 students in Vietnam (from basic to advanced)?

Molecular mass or molecular weight is the total mass of all the atoms that make up a molecule.

In the grade 8 natural science subject, there are two main types of exercises on calculating molecular mass as follows:

Type 1: Identify the chemical element's name based on atomic mass

Given that element X has an atomic mass that is 3.5 times the atomic mass of oxygen. Identify the name and chemical symbol of element X.

Guidance:

Expressing X having an atomic mass that is 3.5 times the atomic mass of oxygen: X = 3.5.O

The atomic mass of O is known → find the atomic mass of X → refer to the table to determine the name of element X → chemical symbol

Solution:

X = 3.5 . O = 3.5 . 16 = 56

=> X is the element iron, chemical symbol Fe.

Type 2: Find the name of element X, chemical symbol when knowing the molecular weight

A compound consists of 1 atom of X bonded to 2 atoms of oxygen and is 22 times heavier than the hydrogen molecule.

a/ Calculate the molecular weight of the compound.

b/ Calculate the atomic mass of X, provide the name and chemical symbol

Guidance

The hydrogen molecule (2H) => Molecular weight = 2 . 1 = 2

The compound is 22 times heavier than the hydrogen molecule => Molecular weight of the compound: 2.22 = 44

1 atom of X is bonded to 2 atoms of oxygen => compound (1X; 2O) => Molecular weight = X + 2.16 = X + 32

=> X + 32 = 2 . 22 = 44

=> X = 44 – 32 = 12

Thus, X is the element carbon, chemical symbol is C.

Students can refer to following molecular mass calculation exercises.

Note: These exercises are for reference only!

What are exercises on calculating molecular mass for grade 8 students in Vietnam (from basic to advanced)? What are evaluation formats of Natural Sciences subject for grade 8 in Vietnam?​ (Image from the Internet)

What are evaluation formats of Natural Sciences subject for grade 8 in Vietnam?

According to clause 3 Article 5 of Circular 22/2021/TT-BGDDT:

Evaluation Method

...

3. Evaluation format for the subjects

a) Evaluating by comments for the subjects: Physical education, Arts, Music, Fine Arts, Local education content, Experiential activities, career orientation; study results by subjects are evaluated by comments at one of two levels: Achieved, Not achieved.

b) Evaluating by comments combined with scoring for the subjects in the general education program, except for the subjects specified at point a of this clause; study results by subjects are evaluated with scores on a scale of 10, if using a different scale, it must be converted to the scale of 10. Scores are whole numbers or decimal numbers rounded to the first decimal place.

Thus, the grade 8 natural science subject is evaluated by comments combined with scoring.

What are requirements for evaluating the study results of grade 8 Natural Science in Vietnam?

Based on Article 4 of Circular 22/2021/TT-BGDDT, the evaluation of grade 8 natural science must meet the following requirements:

- Evaluate based on the achievements required by the general education program.

- Ensure that the evaluation is accurate, comprehensive, fair, honest, and objective.

- Evaluate using various methods, formats, techniques, and tools; combine regular assessment and periodic assessment.

- Evaluate for the progress of students; emphasize encouragement and motivation of students' effort in practice and study; do not compare students with each other.