Observe the acid-base neutralization reaction

Observe the acid-base neutralization reaction

Science - Grade 6-8

Objectives

In this chapter, we will use the BOSON to check whether the pH is approximately 7 and represents an aqueous solution neutral. 

Except for the pH sensor used in the previous chapter , a waterproof temperature sensor is also used device to further learn about the temperature change of the aqueous solution in this chapter.

Standards

NGSS - NEXT GENERATION SCIENCE STANDARDS - MIDDLE SCHOOL (MS)

From Molecules to Organisms: Structures and Processes - MS-LS1-5

Ecosystems: Interactions, Energy and Dynamics - MS-LS2-5  

Earth and Human Activity - MS-ESS3-3, MS-ESS3-4, MS-ESS3-5 

Engineering Design - MS-ETS1-1, MS-ETS1-3

Materials

Activity

We can use BOSON pH sensor to detect the pH of a liquid, so what happens if we mix liquids of different pH?

● Pour four different liquids into four containers

● Use pH sensor and display modulen to detect the pH of these liquids

● Record the detected values in a table

● Discuss the acidity and alkalinity of these liquids

● Discuss what happens when you mix acidic and alkaline liquids?

Explore

In this activity, your group needs to mix acidic and alkaline liquids together and use BOSON waterproof temperature sensor to detect temperature changes as they are mixed.

Activity Procedure:

Experiment

1. The amount of baking soda added should be the same each time.

2. Clear pH sensor and waterproof temperature sensor are required before each test.

3. Each test needs to stand for 30 seconds before recording data.

Data Record

Copy the Data Table below into your notebook.

Explain

Making Sense of the Data:

Create a Multi-Colored Line Graph according to the directions below:

1. Use graph paper and draw the results for each color. For each line, use a different color that matches the color of the worksheet. The operating variable is the number of times the liquid is added, and the response variable is temperature.

2. The manipulated variable is plotted along the X axis, and the response variable is plotted along the Y axis.

3. Use variables to name the graph.

4.Add a legend to the diagram.

Create a Bar Graph according to the directions below:

1. Use graph paper and draw the results for each color. For each row, use a different color that matches the worksheet color. The operating variable is the number of times the liquid is added, and the response variable is the pH value.

2. Manipulated variables are plotted along the X axis, and response variables are plotted along the Y axis.

3. Use variables to name the graphics.

4.Add a legend to the diagram.

Data Analysis:

In your groups discuss the following questions:

1.Examine the the various lines on the Multi-Colored Line Graph.

a.What are the trends in temperature and pH values?.

2.If I add more baking soda to white vinegar at one time (for example, 2 drops to 4 drops), will the temperature change speed be different? Please write down what you observed.

Elaborate

Vocabulary:

● Meaning of neutralization

● Acid-base neutralization

● Neutralization heat

Science Background: In the context of a chemical reaction the term neutralization is used for a reaction between an acid and a base or alkali. Historically, this reaction was represented as

acid + base (alkali) → salt + water

For example:

HCl + NaOH → NaCl + H2O

The statement is still valid as long as it is understood that in an aqueous solution the substances involved are subject to dissociation, which changes the substances ionization state. The arrow sign, →, is used because the reaction is complete, that is, neutralization is a quantitative reaction. A more general definition is based on Brønsted–Lowry acid–base theory.

AH + B → A + BH

Electrical charges are omitted from generic expressions such as this, as each species A, AH, B, or BH may or may not carry an electrical charge. Neutralization of sulphuric acid provides a specific example. Two partial neutralization reactions are possible in this instance.

H2SO4 + OH− → HSO4−+ H2O

HSO4− + OH− → SO42−+ H2O

Overall: H2SO4 + 2OH− → SO42−+ 2H2O

After an acid AH has been neutralized there are no molecules of the acid (or hydrogen ions produced by dissociation of the molecule) left in solution.

When an acid is neutralized the amount of base added to it must be equal the amount of acid present initially. This amount of base is said to be the equivalent amount. In a titration of an acid with a base, the point of neutralization can also be called the equivalence point. The quantitative nature of the neutralization reaction is most conveniently expressed in terms of the concentrations of acid and alkali. At the equivalence point:

volume (acid) × concentration (H+ ions from dissociation) = volume (base) × concentration (OH− ions)

In general, for an acid AHn at concentration c1 reacting with a base B(OH)m at concentration c2 the volumes are related by:

n v1 c1 = m v2 c2

An example of a base being neutralized by an acid is as follows.

Ba(OH)2 + 2H+ → Ba2+ + 2H2O

The same equation relating the concentrations of acid and base applies. The concept of neutralization is not limited to reactions in solution. For example, the reaction of limestone with acid such as sulfuric acid is also a neutralization reaction.

[Ca,Mg]CO3(s) + H2SO4(aq) → (Ca2+, Mg2+)(aq) + SO42−(aq) + CO2(g) + H2O

Such reactions are important in soil chemistry.

The heat of reaction in which the acid and base are neutralized in a dilute solution to produce 1 mol of water. The heat of neutralization between a strong monobasic acid and a strong base is about 57kJ, regardless of the type of acid and base, because this is actually the heat of reaction when 1molH + reacts with 1molOH- to form 1molH2O. The heat of neutralization of weak acids, weak bases, and polybasic acids is not a constant value due to the influence of ionization heat.

Evaluate

Consider the following questions:

1.After reading the above material, please explain why pouring soda water into white vinegar will increase the pH value. 2.Why does the temperature rise after I add baking soda?