Acid-base Theories and Conjugate Acid-base Pairs

Introduction

In this  lesson we will look at the different ACID-BASE theories as well as CONJUGATE ACID- BASE PAIRS.

All around you there are chemical reactions taking place. Green plants are photosynthesizing, car engines are relying on the reaction between petrol and air and your body is performing many complex reactions.                                                        

 

 

                                                                  What are ACID -BASE reactions?

 

 

The Bronsted-Lowry model defines acids and bases in terms of their ability to donate or accept protons.

 

 

  • A Bronsted-Lowry acid is a substance that gives away protons (hydrogen cations H+), and is therefore called a proton donor.

 

  • A Bronsted-Lowry base is a substance that takes up protons (hydrogen cations H+), and is therefore called a proton acceptor.

 

 

Consider the following reaction:

 

 

                                               HCl (aq)+NH3(aq)NH+4(aq)+Cl(aq)

 

We highlight the chlorine and the nitrogen so that we can follow what happens to these two elements as they react. We do not highlight the hydrogen atoms as we are interested in how these change. This colour coding is simply to help you identify the parts of the reaction and does not represent any specific property of these elements.

                                           HCl (aq)+NH3(aq)NH+4(aq)+Cl(aq)

 

In order to decide which substance is a proton donor and which is a proton acceptor, we need to look at what happens to each reactant. The reaction can be broken down as follows:

                                            HCl (aq)Cl(aq)

and

                                             NH3(aq)NH+4(aq)

 

From these reactions, it is clear that HCl is a proton donor and is therefore an acid, and that NH3 is a proton acceptor and is therefore a base.

 

 

 

 

 

 

Conjugate Acid-Base Pair

 

 

 

 

NOTE:Use the links below to gain a better understanding of today's lesson.

https://intl.siyavula.com/read/science/grade-11/types-of-reactions/13-types-of-reactions-01

https://phet.colorado.edu/sims/html/ph-scale/latest/ph-scale_en.html

 

 

Task

Task 2:

Date: 5 September 2021

Due Date: 15 September 2021

Marks: 25

 

Instructions: This is an individual assessment.

                       Read the questions carefully and answer the following questions.

                       Use the links provided to assist you in answering the questions below.

                      

 

 

 

 

Question 1

How do acids and bases differ in:

1.1 How they feel?                                                                                                       (2)

 

1.2 How they taste?                                                                                                      (2)

Question 2

Give the definition of an acid and a base according to:

2.1 Arrhenius’ theory                                                                                                     (3)

 

2.2 The Brønsted - Lowry theory                                                                                   (3)

 

Question 3

Identify the conjugate acid-base pairs in the following reactions:

3.1 CH3COO- + H2O CH3COOH + OH-                                                                  (2)

 

3.2 NH4+ + H2O NH3 + H3O+                                                                                 (2)

 

3.3 H2SO4 + H2O HSO4- + H3O+                                                                          (2)

 

3.4 H2SO4 + Cl- HSO4- + HCl                                                                                (2)

 

Question 4

 

When hydrogen fluoride reacts with water, it ionizes as shown in the balanced equation below:

                                        HF(ℓ)+H2O(ℓ) H3O+ (aq)+ F−(aq)

 

4.1 What is a Brønsted-Lowry acid?                                                                             (2)

 

 

 

        A - a substance that produces H3O+ ions when it dissolves in water.

 

        B - an H+ ion acceptor.

 

        C - a proton donor.

 

        D - a substance that produces hydroxide ions when it dissolves in water.

 

                                                     

                                                                                                                                                  Total: 25

Process

Step 1

Thoroughly read through the introduction content on the "Introduction" Page to understand the ACID -BASE reaction concept.

Make use of the links provided in the introduction page  by clicking on each link and watching attentively.

 

Step 2

Go to "Task" page and read the instructions carefully.Read through the questions before answering.

 

Step 3

Go to "Evaluation" page and see how your task will be evaluated.

 

Step 4

Answer all task questions.Once you have completed your task,submit it to thanzi90@gmail.com

NB:Task is due on the 12th October 2021.No late tasks will be accepted!!!

 

Step 5

Go to  "Conclusion" page.Read the content provided and click on the link provided which concludes the concept of Acid -Base reactions.

 

 

 

Evaluation

                                                                                  Acid -Base Evaluation

 

 

 

NB: You will be assessed according to the mark allocations in the task per question.

        Extra ( 5)  marks can be obtained by learners who are able to do the following from the Task.

 

Score Poor

1 -2

Fair

3 -4

Good

5

Identifying Acids - Bases
 

 

Poor

Students can't identify Acid -Base.

Fair

Students stated the acids, bases & salts but can't give the examples.

Good

Students were well stated the acids,bases &salts with so many examples.

Defining Acids -Base theories
 

 

Poor

Students can't define acid- base theories concept.

Fair

Students explain the concepts but not clearly.

Good

Students easily explain the concept of acids,bases &salts.

Reaction involving Conjugate acids & bases
 

 

Poor

 

Student is unable to identify the Conjugate Acid -Base pairs.

Fair

 

Student partially identified the Conjugate Acid -Base pairs.

Good

Student easily identified the Conjugate Acid - Base Pair.

Conclusion

WELL DONE !!!

 

In this lesson we have learned the following about of Acid - Base reactions:

 

The Bronsted - Lowry model defines acids and bases in terms of their ability to donate or accept protons.

 

  • A Bronsted-Lowry acid is a substance that gives away protons (hydrogen cations H+), and is therefore called a proton donor.

 

  • A Bronsted-Lowry base is a substance that takes up protons (hydrogen cations H+), and is therefore called a proton acceptor.

 

  • A conjugate acid-base pair refers to two compounds in a reaction (one reactant and one product) that transform or change into the other through the loss or gain of a proton.

 

 

 

Our next class will focus on Amphiprotic Substances. Use the link below in preparation for our next class.

 

 

 

Credits

I would like to Thank Mr Moyo,who inspired me to make this lesson.

I acknowledge all the websites I have used in creating this lesson.

All the attached links have helped me to make this lesson a success.

 

 

https://www.expii.com/t/conjugate-acid-base-pairs-overview-examples-8458

https://www.expii.com/t/bronsted-lowry-acids-and-bases-definition-examples-11125

https://intl.siyavula.com/read/science/grade-11/types-of-reactions/13-types-of-reactions-04

https://phet.colorado.edu/en/simulations/acid-base-solutions

 

 

 

 

 

 

 

 

 

 

Teacher Page

For any queries,

 

Mrs Luvalo

+2778 123 4567

luvalo@gmail.com