What happens when acid meets base? | DFRobot Science Lab EP04

Ashg Apr 16.2020

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Welcome back to the DFRobot Science Lab!

In this brand new series, we will work together to graph the data from the experiments with Boson Science Kit, and develop a set of guidelines which will explore the magic of our daily-life science.

EP02 Neutralization Reaction

When a mosquito bites you, we will put some soapy water to ease the itchiness. Why? Is there any magic substance in the soapy water?

Check this video out from the perspective of chemistry.

Key points for today:

● Neutralization reaction: when acid solution and alkaline solution are mixed, the pH value will approach 7.

When mosquitoes bite you, they produce acidic substance. The soapy water you put on is alkaline substance.Those two substance have a neutralizing reaction,where it gives you relief on the mosquito bite.

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Play and Learn with Boson Science Kit: https://www.dfrobot.com/product-1743.html.

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

In the previous chapter, we used a pH sensor to measure the acidity or alkalinity of a common solution in life.So, what happens if you add acidic solution and alkaline solution together? This process is called "acid-base neutralization" or "neutralization reaction", which refers to a reaction when acids and bases exchange with each other to generate salt and water. In this process, heat is released as an exothermic reaction. Forexample, after the neutralization between hydrochloric acid and sodium hydroxide, sodium chloride (the main component of salt) and water will be produced. Acid-base neutralization is widely used in our daily life, such as sewage treatment, edible medicines, fertilizers, and even summer must-have mosquito repellents which also use the principle of acid-base neutralization to neutralize the itch and pain after being bitten by mosquitoes.

● 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.Take two containers, pour white vinegar and baking soda into the containers respectively, and stir well. The capacity is based on the height that the pH sensor can measure.

2.Connect the pH sensor,MainBoard, and display module. This means that we want to display the value of the pH sensor on the display module

3.Remove the front cover of the pH sensor and clean the front glass beads with pure water.

4.Put the pH sensor in the solution for about 30 seconds to measure the pH of white vinegar. From the figure, you can see that the pH value of white vinegar is 1.4, which is a strong acid.

5.To measure the temperature, remove the pH sensor, replace it with a waterproof temperature sensor, and switch the display module switch to i19 to display the temperature.

6.Put the metal tip of the waterproof temperature sensor in white vinegar and let it stand for 30 seconds.Obtain a stable value and record it in a table. The figure shows that the temperature of white vinegar is 25.8 degrees Celsius.

7.Next, use baking soda to neutralize the white vinegar. Take an appropriate amount of baking soda with a dropper, drip it into the white vinegar solution, and leave it for 30 seconds before recording the new temperature. Then replace the waterproof temperature sensor with a pH sensor, and after leaving it for 30 seconds, observe the pH value on the display module again. Is there any change? Please record the changed values in the table. Repeat this step to complete the form below.

8.Try the other two solutions using the same steps.The table is in the appendix after the course.

PS：

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

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.

1. Neutralization reaction occurs when acid solution and alkali solution are mixed together

2.Vinegar and baking soda will heat up when mixed

3. After the neutralization reaction, the pH of the solution will be closer to the pH of the liquid after adding the liquid