Topic: Precipitation of sediment pt 2

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

VII. Salts. Pupil:

5) explains the course of the precipitation reaction; designs and conducts experiments that allow obtaining sparingly soluble substances (salts and hydroxides) in precipitation reactions, writes the appropriate equations of reaction in molecular and ionic form; based on the solubility table of salts and hydroxides, the result of the precipitation reaction.

General aim of education

The student works with the salt solubility table and plans chemical reactions that will result in the formation of sediments.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to predict whether or not a sparingly soluble compound will form as a result of mixing solutions of substances being dissociated;

• to explain what the precipitation reaction is;

• to depict the precipitation equation equations using molecular, ionic and abbreviated ion.

Methods/techniques

• expository

  • talk.

• activating

  • discussion.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• 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. Students read the fragment „Predicting the course of the precipitation reaction”. Then, working in pairs, they analyze the solubility table of salts and hydroxides in water. The indicated couples discuss their conclusions on the class forum. The teacher complements or straightens the statements of the students.

2. The teacher recalls the class participants to the abstract and asks you to read the experiment's instructions (Experiment 1: „Obtaining calcium phosphate”). Divides students into groups and distributes the appropriate equipment, glass and reagents to perform the experiment. Students - with the teacher's help - formulate a research question and a hypothesis and write them on the form in an abstract, then follow the instructions, write the observations in the form, the teacher asks questions in relation to the observations made, initiates the discussion, the conclusions of which students write in the form.

3. Students will get acquainted with the fragment „Can the precipitation of a sparingly soluble compound be planned?” Working in pairs, they discuss the solubility tables of substances listed in the abstract and analyze examples of two possible reactions of obtaining calcium phosphate(V). The teacher monitors the work of the students.

4. Students perform an interactive exercise. The teacher together with them discusses the right solution.

5. The teacher plays the abstract recording for all students. Participants listen carefully and give feedback on the difficulty of the text being heard using the traffic light method. Students are provided with green, yellow and red cards. While listening to the recording, they display the appropriate color for self‑assessment and to inform the teacher: green - I'm fine, I understand everything; yellow - I have some doubts; red - I do not understand anything, please help. The teacher responds depending on the needs of the students, deciding to repeat the recording, listen to the recording while following the text or translate the text.

Summary

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

2. The teacher asks the students questions:

   • What did you find important and interesting in class?

   • What was easy and what was difficult?

   • How can you use the knowledge and skills you have gained today?

   Willing/selected students summarize the lesson.

Homework

1. Create an infographic showing the issues learned during the lesson.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Precipitation of sediment pt 2

When we mix solutions of substances which occur in the form of ions, it may happen that a cation of one substance will create a sparingly soluble compound with an anion of the other substance. We then observe precipitation.

To anticipate whether the precipitation will occur after mixing two ionic substances, we can use the solubility table. On its basis we can assess whether the ions present in the formed mixture will create a sparingly soluble compound.

If we want to carry out a precipitation reaction, we have to mix together two solutions of soluble substances, the ions of which will form a sparingly soluble compound.

In order to obtain, for example, calcium phosphate that is sparingly soluble in water, we have to mix together two solutions, one of which should contain calcium cations, and another one – phosphate anions. Then it will be possible to precipitate the required salt from the solution.

Calcium phosphate can be formed as a result of mixing together the solutions of appropriate salts. Below there are examples of two possible reactions of obtaining calcium phosphate:

1. The reaction of potassium phosphate with calcium chloride

• molecular equation: 2KIndeks dolny 3₃POIndeks dolny 4₄ + 3CaClIndeks dolny 2₂ → CaIndeks dolny 3₃(POIndeks dolny 4₄)Indeks dolny 2₂↓ + 6KCl

• complete ionic equation: 6KIndeks górny +⁺ + 2POIndeks dolny 4₄Indeks górny 3-^3- + 3CaIndeks górny 2+²⁺ + 6ClIndeks górny -^- → CaIndeks dolny 3₃(POIndeks dolny 4₄)Indeks dolny 2₂ + 6KIndeks górny +⁺ + 6ClIndeks górny -^-

• net Ionic equation: 2POIndeks dolny 4₄Indeks górny 3-^3- + 3CaIndeks górny 2+²⁺ → CaIndeks dolny 3₃(POIndeks dolny 4₄)Indeks dolny 2₂

2. The reaction of sodium phosphate with calcium nitrate

• molecular equation: 2NaIndeks dolny 3₃POIndeks dolny 4₄ + 3Ca(NOIndeks dolny 3₃)Indeks dolny 2₂ → CaIndeks dolny 3₃(POIndeks dolny 4₄)Indeks dolny 2₂↓ + 6NaNOIndeks dolny 3₃

• complete ionic equation: 6NaIndeks górny +⁺ + 2POIndeks dolny 4₄Indeks górny 3-^3- + 3CaIndeks górny 2+²⁺ + 6NOIndeks dolny 3₃Indeks górny -^- → CaIndeks dolny 3₃(POIndeks dolny 4₄)Indeks dolny 2₂ + 6NaIndeks górny +⁺ + 6NOIndeks dolny 3₃Indeks górny -^-

• net Ionic equation: 2POIndeks dolny 4₄Indeks górny 3-^3- + 3CaIndeks górny 2+²⁺ → CaIndeks dolny 3₃(POIndeks dolny 4₄)Indeks dolny 2₂

Precipitation reactions occurring in water between salts as well as salts and hydroxides are the examples of an exchange reaction:

$\text{salt 1 + salt 2 → salt 3↓ + salt 4}$
$\text{salt 1 + hydroxide 2 → hydroxide 1↓ + salt 2}$

• Reactions occurring in an aqueous solution between ions from two different substances, which together form a sparingly soluble compound, are called precipitation reactions.

• Precipitation reactions can be predicted on the basis of the solubility table by checking whether the ions that are found in the solution after mixing of two soluble substances will combine into a compound that is sparingly soluble in water.

• Reaction between salts as well as between salts and hydroxides are examples of an exchange reaction.