Gizmos Student Exploration| Chemical Changes Answer Key| Grade A+| SCIENCE 101 verified answers-2023 100% Complete Solutions.

Student Exploration: Chemical Changes

Vocabulary: acid, base, catalyst, chemical change, coefficient, conservation of matter, decomposition,

dissolve, double replacement, endothermic, exothermic, indicator, ion, physicalchange, product, reactant,

single replacement, subscript, synthesis

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

1. A student mixes baking soda and vinegar in a glass. The resultsare

shown at left. Do you think any new substances are being created in

this mixture? If so, how do you know?

Yes, because, as shown in the image, there are bubbles,therefore

gas is being released, which are characteristics of a chemical

change.

2. Suppose this was done on top of a balance. Do you think themass

would change as the reaction proceeded? yes

3. What do you think would happen to the mass if the reaction took place inside a sealed plastic bag?

Then, the mass would not change, because the gases being released in

the reaction are being collected

Gizmo Warm-up

A chemical change, (or chemical reaction) occurs when oneor

more substances, called reactants, are transformed into different

substances, or products. In the Chemical Changes Gizmo, you

will look for evidence of chemical changes by looking at changes

you can see, touch, or smell.

To begin, check that Reactant 1 is Sodium and Reactant 2

is Water. Sodium is a metal so soft you can cut it with a knife.

1. Click Play ( ). What do you observe?

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When the Sodium is put inside the water container, there is a chemical reaction, because gas is

created, there is a fizzing sound. Also the sodium dissolves in the water, but there is not a change of

color.

2.Do you think a chemical reaction has taken place? Explain.

I think there is a chemical reaction, because there was a change of temperature, evolution ofgas and

there was a fizzy sound coming from the reaction. In addition, the PH of the water changed, which

means hydrogen ions were released.

Activity A:

Observing chemical

changes

Get the Gizmo ready:

• Click Reset ( ). Check that the reactants are still

Sodium and Water.

• Turn on the Label reactants checkbox.

Introduction: It is important to distinguish chemical changes, in which new substances are formed, from

physical changes, which do not create new substances. In this activity, you will look at many kinds of

evidence that chemists use to see if a chemical change has taken place.

Question: What kinds of evidence indicate a chemical change has taken place?

1. Observe: Some chemical reactions release heat, and others absorb heat. In an exothermicreaction,

heat is released and the temperature of the system rises. In an endothermic reaction, heat is

absorbed and the temperature of the system decreases.

In the Gizmo, drag the Thermometer into the flask of water.

A. What is the starting temperature? 21

B. Click Play, and wait for the reaction to end. What is the final temperature? 59

C. Was this reaction exothermic or endothermic? exothermic

2. Observe: Two families of chemicals are acids and bases. Acids and bases can be detectedby an

indicator, which is a substance that changes color in the presence of an acid or a base. Phenol red is

an indicator that is yellow in an acid, orange in a neutral solution, and pink in a base.

A. Click Reset. Drag the Phenol red next to the flask of water. What does the indicatorshow?

It shows that water is neutral

B. Click Play, and wait for the reaction to end. What does the indicator show now?

The indicator shows that the substance is a base, after the reaction

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3. Observe: Click Reset. Select the Gas collection setup. Chemists use this apparatus to collect any

gases produced in the reaction. From the reaction flask, gases travel through along tube and into a

cylinder of water. As gases bubble into the cylinder, the water is displaced (removed) until the

cylinder is filled with gas.

Click Play and observe the cylinder. Was any gas produced in the reaction? yes

How do you know? Because the water in the cylinder was pushed down by the gas

created, as two things cannot occupy the same space. In addition, there was a formation ofbubbles

when the sodium was put in the water, which means some type of gas was released.

(Activity A continued on next page)

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Activity A (continued from previous page)

4. Analyze: One way to test what kind of gas is in the cylinder is to use a glowing splint. A glowing

splint is a wooden stick that has been lit on fire and then blown out, resulting in a glowing, red-hot

tip. The table shows how a glowing splint reacts to some common gases:

Gas: Carbon dioxide (CO2)

or ammonia (NH3)

Oxygen (O2) Hydrogen (H2)

Splint reaction: Goes out Burns brightly Small explosion and

“pop” sound

A. Drag the glowing splint next to the cylinder, and observe. What do you see?

There was a small explosion and a pop sound created.

B. Based on the table above, what gas do you think was produced in this reaction?

Hydrogen

5. Interpret: Turn on Show chemical equation. A chemical equation is a shorthand way to describe a

chemical reaction. Symbols represent the elements: H for hydrogen, O for oxygen, and Na for

sodium. The reactants are to the left of the arrow, and the products areto the right. For example, the

equation H2 + O2 → H2O shows that the reactants hydrogen and oxygen combine to form the

product H2O, or water.

A. Look at the reaction shown in the Gizmo. What are the reactants in this reaction?

The reactants are sodium (Na) and water (H2O)

B. What are the products in this reaction?The products are sodium hydroxide (NaOH)and

hydrogen (H2)

These symbols represent sodium hydroxide and hydrogen gas. Sodium hydroxide isa strong

base. (Chemicals that contain the hydroxide ion (OH–

) are bases.)

C. How do the products of the reaction relate to the phenol red test and the splint test?

When a substance is a base, that means it has a lot of hydrogen ions in its

composition. As the water was neutral before the chemical reaction, that means there was

not a lot of hydrogen ions. However, when the sodium was added, compounds with a lot of

hydrogen ions were formed in the chemical reaction, such as hydrogen and sodium

hydroxide, causing the substance to be a base, as shownin the phenol red test.