Introduction To Acids And Bases Worksheet Answer Key

[Rodney Liuzzo]

Beforeviewing an episode, download and print the note-taking guides, worksheets, and lab data sheets for that episode, keeping the printed sheets in order by page number. During the lesson, watch and listen for instructions to take notes, pause the video, complete an assignment, and record lab data. See your classroom teacher for specific instructions.

This semester begins with the introduction of the mole. This important concept will be used during the remainder of the year as the basis for many calculations involving chemical reactions, solutions, and gases. In the units on thermochemistry and chemical kinetics, you will learn how energy is absorbed and given off during chemical reactions and how energy, and factors affect the rates of reactions. The study of reaction rates will lead you into the study of chemical equilibrium. In this semester, you will also study electrochemistry, from batteries to electroplating. And you will learn about acids, bases and salts. Unit 15 is a brief study of the atomic nucleus, which your teacher may introduce at any time during the year.

The first scientist to create a definition for acids and bases.

The name for the definition for acids and bases which describes bases as a chemical which can accept a proton.

The definition for acids and bases which depends only on the movement of electron pairs.

What acids generally taste like.

This type of gas will be produced when an acid is mixed with a metal

The color which Litmus or pH paper will turn when dipped in an acid.

The type of acid in vinegar

A common use for a base

A strong acid or strong base will completely do this in water

An example of a common strong base

What does pH measure the concentration of?

concentration when measured in mol per liter is known as this

pH of 7

Generally the highest value pH can reach

A type of paper which indicates pH

The pH value of a very acidic solution

A scale used to measure the acidity of a solution

A chemical which produced hydroxide ions

The second acid/base definition says a hydrogen ion is also called this

This type of rain is damaging to the environment

If an acid does not completely break into its ions it is called this.

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Note: This video is designed to help the teacher better understand the lesson and is NOT intended to be shown to students. It includes observations and conclusions that students are meant to make on their own.

Students will be able to explain, on the molecular level, that pH is a measure of the concentration of the H3O+ ions in water and that adding an acid or a base to water affects the concentration of these ions.

Be sure you and the students wear properly fitting goggles during the activity and wash hands afterwards. Sodium carbonate may irritate skin. Citric acid is an eye irritant. Universal indicator is alcohol-based and flammable. Read and follow all safety warnings on the label. At the end of the lesson, have students pour their used solutions in a waste container. Dispose of this waste down the drain or according to local regulations. The leftover citric acid and sodium carbonate powders can be disposed of with the classroom trash.

Because of their chemical properties, reactions involving acids and bases are different from the chemical reactions students have seen so far in Chapter 6. In the previous lessons, it was always the electrons that were being shared or transferred when atoms interacted. In the next three lessons about acids and bases, things are a little different. With acids and bases, it is a proton from a hydrogen atom that is transferred from one substance to another.

The main aspect of acids and bases that students will explore in the next three lessons deals with the influence of acids and bases on water. The reactions of acids and bases with water are measured using the pH scale. Understanding pH on the molecular level will give students a better appreciation for some of the environmental issues involving acids and bases. The meaning of pH and the way it is affected by acids and bases can be a little tricky, but by using animations, drawings, and some simplifications, students should be able to understand the main ideas.

Note: Your local tap water is likely fine for the demonstration and activities in this lesson. If the indicator solution you make is not green, this means that your water is either acidic or basic. If this happens, use distilled water, which is available in supermarkets and pharmacies.

Note: In the activity, students will fill 12 wells with universal indicator solution. Check to make sure that 25 mL of solution is enough. You will need about 50 mL of indicator solution for your demonstration. If 250 mL of solution is not enough, make more using the same proportions.

Tell students that when you poured universal indicator solution into the cups, the acid and base each reacted with the indicator and changed its color. Usually, when two substances are mixed and a color change results, that is a clue that a chemical reaction has taken place. The cause of this color change will be discussed later in this lesson when students do their own activity.

Tell students that they will use an acid, a base, and universal indicator solution to learn about how acids and bases affect water. They will also learn how to measure the effect with colors and numbers on the pH scale.

Distribute one Universal Indicator pH Color Chart to each group. The charts can be found right before the student activity sheets. Explain that the chart shows the range of color changes for universal indicator when acidic or basic solutions are added to the indicator.

Point out that each color has a number associated with it and that students will learn more about these numbers later in the lesson. As the solution becomes more acidic, the color changes from green toward red. As the solution becomes more basic, the color changes from green toward purple.

Explain that before class, you placed a small amount of citric acid in the cup that turned red and a small amount of sodium carbonate in the cup that turned purple. So citric acid is an acid and sodium carbonate is a base.

Students will record their observations and answer questions about the activity on the activity sheet. The Explain It with Atoms & Molecules and Take It Further sections of the activity sheet will either be completed as a class, in groups, or individually depending on your instructions. Look at the teacher version of the activity sheet to find the questions and answers.

Explain to students that in this activity they will fill the wells in each spot plate with universal indicator solution. Then in the first spot plate, they will test how different concentrations of citric acid affect the color of universal indicator solution. In the other spot plate, they will test how different concentrations of sodium carbonate affect the color of universal indicator solution.

The color of the indicator should turn yellow-green or yellow. If there is no obvious color change after adding a toothpick of citric acid, have students add a little more citric acid to the solution. Tell them to be sure to pick up as much citric acid as they can on the end of a toothpick.

Help students fill out the chart on their activity sheet. Students may say that the color of the solution in well 2 is yellow or yellow-green. Then have students assign a number for pH. Tell students that if the color in the well seems to be between two colors on the chart, they should assign a pH value between the two.

Tell students that in the next part of the activity they will add a little more citric acid to the citric acid solution. This will make the citric acid solution more concentrated. Just as they did before, they will add one drop of citric acid solution, but this time the citric acid solution will be more concentrated.

As the citric acid solution becomes more concentrated, the color should change to variations of yellow-green, yellow, yellow-orange, orange, orange-red, and red. The colors obtained will vary from group to group because of the different amounts of citric acid students can pick up on the end of a toothpick. Students may be able to get 4 or 5 different colors. The answers and colors included in the chart below will vary.

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