Topic: Plaster mortar and application of gypsum rock

Target group

High school / technical school student

Core curriculum

New core curriculum:

High school and technical high school. Chemistry – basic level:

XI. Applications of selected inorganic compounds. Pupil:

5) writes formulas of hydrates and anhydrous salts (CaSO Indeks dolny 4₄, (CaSO Indeks dolny 4₄) Indeks dolny 2₂ · H Indeks dolny 2₂ O and CaSO Indeks dolny 4₄ · 2H Indeks dolny 2₂ O); gives their mineralogical names; describes the differences in the properties of hydrates and anhydrous substances; predicts hydrate behavior during heating and verifies its predictions experimentally; lists the applications of gypsum rocks; explains the hardening process of gypsum mortar; writes the appropriate equation of reaction.

High school and technical high school. Chemistry – extended level:

XI. Applications of selected inorganic compounds. Pupil:

5) writes formulas of hydrates and anhydrous salts (CaSO Indeks dolny 4₄, (CaSO Indeks dolny 4₄) Indeks dolny 2₂ · H Indeks dolny 2₂ O and CaSO Indeks dolny 4₄ · 2H Indeks dolny 2₂ O); gives their mineralogical names; describes the differences in the properties of hydrates and anhydrous substances; predicts hydrate behavior during heating and verifies its predictions experimentally; lists the applications of gypsum rocks; explains the hardening process of gypsum mortar; writes the appropriate equation of reaction.

Old core curriculum:

High school and technical high school. Chemistry – basic level:

XI. Applications of selected inorganic compounds. Pupil:

1) writes formulas of hydrates and anhydrous salts (CaSOIndeks dolny 4₄, (CaSOIndeks dolny 4₄)Indeks dolny 2₂ · HIndeks dolny 2₂O and CaSOIndeks dolny 4₄ · 2HIndeks dolny 2₂O); gives their mineralogical names; describes the differences in the properties of hydrates and anhydrous substances; predicts the behavior of hydrates during heating and verifies its predictions experimentally; mentions the use of gypsum rock; explains the hardening process of gypsum mortar; he writes the appropriate equation of reaction.

General aim of education

The students describe the hardening process of gypsum mortar and discuss the use of gypsum rock.

Key competences

• communication in the mother tongue;

• communication in foreign languages;

• digital competence;

• learning to learn;

• mathematical competence and basic competences in science and technology.

Criteria for success
The student will learn:

• describe the hardening process of gypsum mortar and record the appropriate reaction equation;

• discuss the use of gypsum rock;

• justify why burned gypsum is used in medicine.

Methods/techniques

• expository

  • talk.

• activating

  • discussion.

• 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 asks the class participants to read the experiment's instructions in the abstract (Experiment 1: “Preparation of gypsum mortar and testing the rate of its hardening”). The teacher divides students into groups and distributes appropriate equipment, glass and reagents to perform the experiment. Students - with the help of the teacher - formulate a hypothesis and a research question and write them on the form in the abstract. Then they follow the instructions. They record the observations in the form. The teacher asks questions in relation to the observations noted. He initiates a discussion, the conclusions of which students write on the form.

2. The teacher asks a willing student to write on the board the equation of reaction that took place during the experiment. If the lack of volunteers, displays on the interactive whiteboard its equation, placed in the absurd (if there are no volunteers, he plays the equation on the interactive whiteboard), and then explains its mechanism.

3. The teacher asks the pupils: „How can can we distinguish gypsum rocks from calcareous rock?”. Students write the answer in the abstract. Volunteers read them, the teacher corrects any mistakes.

4. Students get acquainted with the content of the fragment titled „Application of gypsum rock” and analyze the interactive illustration. Then the participants, working in pairs, ask each other about the knowledge of the fragment and they answer the question why calcined gypsum is used for immobilizing limbs instead of calcined lime. They write the answer in the form in the abstract.

5. Students read the fragment titled „Gypsum karst”. Then, still working in pairs, look for information about the Skorocicka Cave in the vicinity of Busko‑Zdrój and the Crystal Cave in Naica, also known as the Crystal Sistine Chapel. They answer the question: „Why nature was the most perfect creator in terms of exhibits obtained from gypsum?”. They write the answer in the form in the abstract.

6. Volunteers read the answers noted in the forms. The teacher complements or straightens them. He asks the proteges to do an interactive exercise and then discusses the correct solution with them.

Summary

1. The students consolidate the acquired information, discussing it with their nearest neighbors („tell your neighbor” method.

2. The teacher asks the students to finish the following sentences:

   • Today I learned ...

   • I understood that …

   • It surprised me …

   • I found out ...

   The teacher can use the interactive whiteboard in the abstract or instruct students to work with it

Methodological commentary:

Teacher demonstration “Preparation of phosphoric acid” – problem‑verification experiment

List of required materials/teaching aids

Laboratory equipment and glassware: gas burner, beaker, conical flask, matches/lighter, lab spoon, aluminium foil, dropping funnel

Reagents: water, red phosphorus, methyl orange

Performing the experiment

1. Pour approx. 5 cmIndeks górny 3³ of water into the flask, add 2‑3 drops of methyl orange.

2. Place a small amount of red phosphorus on the lab spoon and place it in the flame of the gas burner until the phosphorus ignites, then transfer the spoon to the flask with water and keep it above the water until phosphorus combusts, cover the outfall of the flask with aluminium foil, so that gas does not escape.

3. After combustion of the phosphorus, remove the spoon from the flask, stir the contents of the flask until the gas disappears.

4. Observe the changes.

Homework

1. Imagine that you have the opportunity to interview an academic - a specialist in the field of today's lesson. What questions would you like to ask him? Write them down.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Plaster mortar and application of gypsum rock

Due to the time of hardening of the mixture of calcined gypsum and water, there are several types of gypsum mortars that have different composition, which is why they are widely used in construction industry.

The building mortar hardens the quickest, after about 10 minutes of mixing it with water. Filler needs approx. 30 minutes. On the other hand, plaster mortar needs long‑time of water binding (including plaster), and hardening depends on the thickness of the layer and can take one to several hours.

Applications of gypsum are very diverse, especially in construction, where it is used to the formation of gypsum mortar, prefabricates, self‑levelling floors, for the production of cement and plasterboards, so‑called gypsum boards, sheets consisting of gypsum protected by cardboard. Gypsum is an ecological material, friendly to humans. Easily absorbs excess dampness from the atmosphere, and when the air in the room is dry, it gives off excessive dampness.

Gypsum is also used in the ceramic industry for the production of moulds. It is also used for the production of paints and varnishes. In agriculture it is used as a fertilizer and soil fertilizer, and in the food industry – for clarification of wines. A special application of gypsum is in medicine, where purified gypsum varieties are used, so‑called surgical and dental plaster.

Fracture fixation is known since ancient times. Wooden boards and ribbons of material impregnated with starch, resin, wax, egg whites and even lime were used for this purpose. Gypsum dressings arrived from Arabia to Europe in the eighth century. These did not have too many followers. This method was commonly used at the beginning of the ninth century when the powdered and calcined gypsum was used to immobilize the limbs.

Significant quantities of gypsum are used to create artistic products (modelling gypsum), such as gypsum figurines, masks, stucco, castings. In sculpting, alabaster is a particularly valuable material. It is used to manufacture, among others vases, cups, trays, candlesticks, ashtrays, lamp shades, stuccos and sculptures.

The karst processes and forms of gypsum karst are rare phenomena. This is caused by relatively small deposits of gypsum in the Earth's crust, as opposed to the amount of limestone. The karst processes of gypsum depend on dissolving by water, which, unlike limestone, does not have to contain carbon dioxide. This is possible because gypsum and anhydrite are moisture absorbent and moderately soluble in water. It also means that forms of gypsum karst are very unstable and relatively young compared to the limestone karst. These can be found in various parts of the world, also in Poland. In our country, these mainly occur in Ponidzie. Skorocicka Cave next to the Busko‑Zdrój is the largest Polish gypsum cave in the country. However, the most unusual gypsum cave is the Cave of the Crystals in the Mexican state of Chihuahua.

Cave of the Crystals, so‑called Sistine Chapel of Crystals, was discovered accidentally in 2000 by tunnelling miners.

This cave is famous due to the largest gypsum specimens discovered so far (many of them are huge, up to 15 meters in length, and weight up to 55 tons). The crystals in this cave are also one of the largest minerals in the world. The grotto has extreme climatic conditions, i.e. the temperature is up to 65.5°C, and the air humidity is almost 100%. For this reason, its exploration is possible only in special protective suits, equipped with masks connected to oxygen tanks. Otherwise, people should not stay in the cave for longer than 10 minutes.

• Gypsum rock contains calcium sulphate in its composition.

• As a result of roasting a crystalline gypsum at about 120°C, gypsum is formed and anhydrous calcium sulphate is formed above 180°C.

• Crystal gypsum and calcined gypsum are examples of hydrated salts (hydrates). Anhydrite is an example of anhydrous salt.

• Hydrates are unstable and, during heating, go into anhydrous or lower hydration salts.

• Plaster mortar is an example of hydraulic mortar.

• Gypsum rock is used in construction, medicine, agriculture, in the industry: ceramic, food, chemical. They are also a valuable material in the hands of artists.