Physics
Chem
Substance density. Solving problems using the density formula
Author
Lina Kankeviciene
Target Group
11-13 years old students
Brief Description
Learn to solve experimental problems of various complexity using the density formula.

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## 1 - Getting started

### Integrated lesson of Physics and Chemistry

Type of the lesson: Problem solving.

Subject of the lesson: Substance density.

Goal: Learn to solve experimental problems of various complexity using the density formula.

Objectives of the lesson: In pairs and small groups, using the tables of substance density, formulae, substances and materials, you will do the following:

1. Solve experimental problems of complexity
2. Check the results and assess yourselves.

#### Methods of the lesson

• Group work: pupils are divided into groups considering the number of pupils in the class
• Practical experiment : a group of pupils perform an experiment described in the task sheet
• Discussing specific situations, generalization and submission of the conclusions: in groups, pupils fill in the task sheets)
• Presentation of the work to the class: one or two pupils from the group present the work to the class
• Self-assessment: pupils assess the knowledge gained according to the number of correct answers

#### Procedure or the lesson

• At the beginning of the lesson, the subject and objectives of the lesson are announced. Pupils make groups for work (they may be divided into groups by the teacher) (5-7 min.)
• At the beginning of the lesson a few qualitative (1-4) and quantitative (5, 6) problems are provided in slides.
• Pupils work in groups according to the tasks given. (Teachers of Physics and Chemistry monitor the pupils’ work, advise them when needed on how to proceed with the work (12-15 min.).
• Pupils groups present the tasks performed to the whole class (The screen shows the task or task answers if possible). Pupils of the class correct the mistakes noticed, evaluate and discuss). (12-15 min.).
• Pupils perform tasks 11 and 12 of the workbook (handouts  may be given). Correct answers of the task are provided. (Pupils assess themselves according to the number of correct answers) (5-7 min.).
• Generalization of the lesson. Teachers assess pupils work (5 min.)

## 2 - Problems to solve

### Qualitative, quantitative and practical problems

#### #1 Qualitative problem

We have three cubes of the same size which we immerse into water. Which cube has the lowest density?

Choose the correct answer: A, B or C.

#### #2 Qualitative problem

Three beakers of the same size are filled with 100 g of different liquids. Which liquid has the lowest density?

Choose the correct answer: Petrol, Olive oil or Water.

#### #3 Qualitative problem

Two equally the same buckets are filled with 5 litres of water each: one with drinking water, the other one – with sea water. Is the mass of the buckets with water the same?

• The mass of the bucket with drinking water is bigger because it does not contain melted salt.
• The mass is the same because each bucket is filled with 5 litres of water.
• The mass of the bucket with sea water is bigger because the density of salty water is higher.

#### #4 Qualitative problem

Density of a heated metal ball decrease?

• The number of particles in the unit of the ball volume decreases.
• The distance between the particles comprising the ball increases.
• The mass comprising the ball decreases.
• Water evaporates from the ball when heating.

#### #5 Quantitative problem

The mass of the nut-screw in the Picture is 135 g. Calculate the density of the substance that the nut-screw is made of...?

• 0,370 g/cm3
• 6750 kg/m3
• 0,675 g/cm3
• 2700 kg/m3

#### #6 Quantitative problem

A cake recipe indicates that you need 200 g of sugar to make a cake. A girl did not have the scale, so she measured the amount of sugar with a glass. She poured a full glass of sugar of 200 ml into the dough. How many grammes of sugar did the girl pour into the dough if the density of sugar is p=1600 kg/ m3?

• 320 g.
• 200 g.
• 320.000 g.
• 125 g.

#### #7 Practical problem

GROUP 1 - Identify and demonstrate by calculations what substance this body is made of.

#### #8 Practical problem

GROUP 2 - Calculate the mass of a copper cube.

#### #9 Practical problem

GROUP 3 - Identify the density of water and demonstrate it by calculations.

#### #10 Practical problem

GROUP 4 - Identify the density of oil and demonstrate it by calculations.

#### #11 Self-assesment

Pupils wrote statements about substance density on the board but some of them are false. Which statements are true and which ones are false?
• Density shows the mass of substance in 1 m3.
• Distances between molecules in gases are big.
• The desnsity of a heated substance does not change.
• The density of ice is higher than that of water because ice is a solid body.
• Substance density depends on atom mass and their arrangement.
• The density of the same body on the Moon is lower because a body is lighter on the Moon than on the Earth.