Topic: Density of substances and their mixtures in everyday life: density

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

I. Substances and their properties. Student:

10) carries out calculations using the terms: mass, density and volume.

General aim of education

The student carries out calculations using the term density

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to explain on the basis of the internal structure why the density of solids is greater than the density of gases;

• to carry out density calculations.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

Lesson plan overview

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on a traffic light technique. He presents the aims of the lesson in the student's language on a multimedia presentation and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determines the topic – based on the previously presented lesson aims – and then writes it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

3. Health and safety – before starting the experiments, students familiarise themselves with the safety data sheets of the substances that will be used during the lesson. The teacher points out the need to be careful when working with them.

Realization

1. The teacher, referring to various examples from the environment, emphasizes that daily we examine the density of the substance: sweetening tea, pouring salt into the soup, throwing potatoes, carrots, spices and other ingredients when cooking soup, etc. Some substances fall to the bottom of the dish, others swim liquid surface. Some everyday items, such as a styrofoam coffee cup or aluminum rims, are colloquially referred to as light, and others, such as steel rims or covering the patient with radiation apron containing lead as heavy. Although one kilogram of one substance has the same mass as one kilogram of another, these substances may have different volumes. They differ in density. Why is this happening? Does a higher density have a body which, for the same volume, has a larger mass or a body that occupies a larger volume with the same mass? The implementation of the content of this topic will allow you to answer these questions.

2. The teacher refers students to the abstract and asks for familiarization with the content under „What is density?” - there is a discussion regarding the command under the definition of density.

3. The teacher notes on the board the question: „How is the density calculated?” - then writes down the formula for the density of substances with the units given; explains the meaning of symbols and translators, explains what determines the density of a substance. Then he analyzes the comparison of the density of a substance with the density of water.

4. The teacher gives out job cards and then displays a movie on the multimedia board from the „Water rainbow” abstract. Before the screening, the students formulate and write them in the form in an abstract research question. During the screening they should observe the changes, then discuss them on the forum, set conclusions and also make a note about them. The teacher asks the students questions: „What happens if you use sugar instead of salt for the experiment? What happens if you dip the straw in solutions in a different order? „.

5. The teacher displays on the multimedia board a film from the abstract „Drink Density”. Students - as before - formulate a research question and hypotheses, write them in the form in an abstract. They observe changes in the experiment, draw conclusions and also write them in the form in an abstract.

6. The teacher asks students to do interactive exercises in the abstract.

Summary

1. The student indicated by the teacher sums up the lesson, telling what he has learned and what skills he/she has been practicing.

Homework

1. Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

2. Make at home a note from the lesson using the sketchnoting method.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Density of substances and their mixtures in everyday life: density

Density is the relation (ratio) between the given mass of substance and the volume it occupies - a physical characteristic of a given substance.

The bowling ball and the volleyball are the same size, but the first one has a higher mass, because it is made of plastic, which contains many tightly packed elementary particles. The volleyball is filled with air containing fewer elementary particles that are more apart. Typically, solids have the highest density, liquids – lower, and gases – the lowest.

The density of a given substance which has a solid state of matter is determined by modelling - making a cube with an edge of 1 m and then weighing it. The mass of such a cube expressed in kilograms is numerically equal to the density of the substance.

Density ($d$) is the ratio between mass ($m$) of the substance and the volume ($V$) that given mass occupies. It is expressed by the formula:

$\text{density=}\frac{\text{mass}\left[\text{kg}\right]}{\text{volume}\left[{\text{m}}^{\text{3}}\right]}d\text{=}\frac{\text{m}\left[\text{kg}\right]}{\text{V}\left[{\text{m}}^{\text{3}}\right]}$

The usual unit of the solids and liquids density is $\text{[}\frac{\text{g}}{{\text{cm}}^{\text{3}}}\text{]}$, and the usual unit of gases density is $\text{[}\frac{\text{g}}{{\text{dm}}^{\text{3}}}\text{]}$. Chemists usually mark density with a symbol $d$ (English density), and physicist mark it with Greek letter $\rho$ (ro).

The density of substance depends on:

• temperature – it usually decreases with increasing temperature;

• pressure – just for gases, because the impact of pressure on liquids and solids is so small that we omit it.

- classic coke drink,

• diet coke drink,

• aquarium or a tall vessel,

• water,

• sugar,

• scale.

You can calculate the density of the drink, if you know the mass and the volume. By placing beverage cans in a container filled with water, you can compare the cola density after considering the density of the cans themselves.

1. Weigh the cans of classic coke and diet coke. Remember to subtract the weight of an empty can from the weight of the canned drink. 2. Check the volume on the can or read it after pouring the content of the can to the measuring cylinder.
$V\text{= 350 ml = 350}{\text{cm}}^{\text{3}}$ 3. Calculate the density of the drink using the formula:
$\mathrm{density}=\frac{\mathrm{mass}\left[\text{g}\right]}{\mathrm{volume}\left[\text{c}{\text{m}}^{\text{3}}\right]}$ 4. Compare the contents of both drinks. Think about what can have the biggest impact on density differences. You can compare their density with the density of water. Density of water is 1 $\frac{\left[\text{g}\right]}{\left[\text{c}{\text{m}}^{\text{3}}\right]}$.

• One of the physical properties of the substance is density.

• Density is the size that characterizes a substance equal to the quotient of the mass and volume of a given substance.

• Experimentally determining the density of the object, we can determine from which substance it was made.

• The density of the substance depends on the temperature - it generally decreases with increasing temperature.