Topic: Precipitation of sediment pt 1

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 explains the mechanism of the precipitation reaction

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 (precipitation) is;

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

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

• exposing

  • exposition.

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.

Realization

1. The teacher gives students work cards. He informs them that in a moment they will watch the film from the experiment described in the abstract „Comparison of the course of reaction of sodium chloride with potassium nitrate and silver nitrate”. Before this happens, they should formulate a research question and hypothesis and write them down in the work sheets. After the film's release, the teacher and the students summarize the observations - the students write them in the work sheets. The lecturer writes the equations of reactions on the board in the form of molecular, ionic and shortened ion, and at the same time explains the mechanism of this reaction. Students rewrite equations to work cards. For the consolidation of the message, the teacher displays on the multimedia table the full and abbreviated form of the equation. He asks for the conclusion of the application resulting from this experience, which also students write in the work sheets. Note: the pupils can also follow the instructions in the abstract. The film can then be treated as a summary and comparison of the results of the experiment.

2. The teacher divides the students into groups. He gives instructions to Experiment 2 in abstract - „Can other substances than salts” take part in the precipitation reactions - and glass, equipment and reagents. Teams carry out the experience, write notes in the work sheets and talk about them on the class forum. The lecturer asks eager students to write equations of chemical reactions on the board - the others record them in the work sheets. Based on the record of reaction equations, the teacher asks students about the conclusions from this experience, which after being determined are also recorded in the work sheets.

3. In order to consolidate the message, the teacher asks students (working in pairs) to do interactive exercises in the abstract.

Summary

1. 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

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

Precipitation of sediment pt 1

A reaction in which a sparingly soluble compound is formed after mixing together the solutions of two soluble substances is called a precipitation reaction. Its essential element is the reaction between some ions formed from dissociation of the substances mixed together.

We can present a precipitation reaction in various ways. It will be discussed using the example of the reaction taking place in experiment 1. As you remember, as a result of the reaction of silver nitrate with sodium chloride, silver(I) chloride was precipitated in the form of sediment. This transformation can be described with a chemical equation in molecular form, i.e. containing molecular formulas of compounds:

${\text{AgNO}}_{\text{3}}\text{ + NaCl → }\text{AgCl}\text{↓ + }{\text{NaNO}}_{\text{3}}$
$\text{silver(I) nitrate + sodium chloride → silver(I) chloride + sodium nitrate}$

You remember that the above reaction takes place in an aqueous solution, and the substrates used for the experiment are soluble in water and occur in it in the form of ions. Two of them joined together to form a chemical compound that is sparingly soluble in water. In the equation, we can include the form in which substances occur during the reaction:

${\text{Ag}}^{\text{+}}\text{+ }{\text{NO}}_{\text{3}}^{-}\text{ + }{\text{Na}}^{\text{+}}\text{+ }{\text{Cl}}^{-}\text{ → AgCl + }{\text{NO}}_{\text{3}}^{-}\text{ + }{\text{Na}}^{\text{+}}$

You already know that this way of expressing a chemical equation, which includes the formulas of all ions present in the reaction mixture, is called a complete ionic equation. In a chemical equation presented in this way, we do not use arrows that symbolize the formation of sediment, because the method of writing (molecular formula for salt) already informs about the formation of a product that is sparingly soluble (no free ions).

Note that there are identical ions on the sides of both substrates and products, and that the presented reaction happens only between two types of ions: silver cation and chloride anion. In the complete ionic equation, we can cross out recurring ions on both sides of it:

We can therefore write down an equation that contains only symbols of ions that react with each other:

${\text{Ag}}^{\text{+}}\text{ + }{\text{Cl}}^{-}\text{ → AgCl}$

This is a net ionic equation.

After mixing the two solutions, copper(II) cations and hydroxide anions formed the sparingly water‑soluble copper(II) hydroxide:

${\text{CuSO}}_{\text{4}}\text{ + 2NaOH →}{\text{ Cu(OH)}}_{\text{2}}\text{↓ + }{\text{Na}}_{\text{2}}{\text{SO}}_{\text{4}}$
$\text{copper(II) sulfate + sodium hydroxide → copper(II) hydroxide + sodium sulfate}$

The above reaction takes place between ions, so it can be described with the following complete ionic equation:

${\text{Cu}}^{\text{2+}}\text{+ }{\text{SO}}_{\text{4}}^{2-}\text{ + }{\text{2Na}}^{\text{+}}\text{+ }{\text{2OH}}^{-}\text{ → }\text{Cu}\text{(}{\text{OH)}}_{\text{2}}\text{ + }{\text{SO}}_{\text{4}}^{2-}\text{ + }{\text{2Na}}^{\text{+}}$

The net ionic equation for this reaction is as follows:

${\text{Cu}}^{\text{2+}}\text{ + }{\text{2OH}}^{-}\text{ → }\text{Cu}\text{(}{\text{OH)}}_{\text{2}}$

• Salts can react with other salts and hydroxides in an aqueous solution, provided that this reaction produces sparingly soluble products.

• If there is a reaction between two salts, the sparingly soluble product is also a salt.