5 Indicators of a Chemical Change

From this lesson you will be able to determine if a

chemical change has taken place

What is a Chemical Change?• It is a change that occurs when a

substance changes composition by forming one or more new substances.

• The new substances/products that are formed have a different chemical formula from the original substances/reactants at the beginning.

5 Indicators of a Chemical Change

• Take a look at the video of Hydrochloric Acid (HCl) reacting with Magnesium (Mg) strips. What do you observe that indicates a chemical change is taking place.

Hydrochloric Acid + Magnesium

http://www.youtube.com/watch?v=cpy_Zh-8sKA

Hydrogen from Hydrochloric acid and Magnesium ribbon BANG…

http://youtu.be/afxwDTz_JTk

What did you observe?Bubbles

Mg + 2HCl MgCl2 + H2

Production of Gas is an indicator of a Chemical

Change.

This reaction is very similar to the reactions that take place in the digestive track when Hydrochloric Acid (HCl) in your stomach aids in the digestive process. Digestion is a chemical change.

5 Indicators of a Chemical Change

• Take a look at the video of a Magnesium (Mg) strip reacting with Oxygen (O2) while burning. What do you observe that indicates a chemical change is taking place?

Burning Magnesiumhttp://youtu.be/84v8yRPwo5A

What did you observe?Light

2Mg + O2 2MgO

Formation of Light is an indicator of a Chemical

Change.This is the same reaction that is used to make fireworks and sparklers.

5 Indicators of a Chemical Change

• Take a look at the video of two clear liquids, Lead II Nitrate Pb(NO3)2 reacting with Potassium Iodide (KI). What do you observe that indicates a chemical change is taking place?

Reaction of LEAD NITRATE & POTASSIUM IODIDE solutions

http://www.youtube.com/watch?v=DITY2rXYU-I

Double Displacement Lead Nitrate and Potassium Iodide

http://www.youtube.com/watch?v=X2mB-q2NQXY

What did you observe?Yellow Color Change and aPrecipitate (insoluble solid)

Pb(NO3)2 + 2KI PbI2 + 2KNO3

Permanent Color Change and Formation of a Precipitate are two indicators of a Chemical Change.

Reactions like these are used in water treatment plants to form precipitates that help remove calcium, magnesium, iron, and manganese ions from the water.

5 Indicators of a Chemical Change

• Take a look at the video of two solids, Barium Hydroxide Octahydrate reacting with Ammonium Thiocyanate. What do you observe that indicates a chemical change is taking place?

http://youtu.be/MyAzjSdc3Fc

What did you observe?A Temperature Change

Ba(OH)2.8H2O + 2 NH4SCN --> Ba(SCN)2 + 10 H2O + 2 NH3

Temperature Change is an indicator of a Chemical Change.

Endothermic Reactions = absorb heat and feel cold

Exothermic Reactions = release heat and feel hot

Let’s ReviewThe 5 Indicators of a Chemical Change are…

1. Production of Gas

2. Production of Light

3. Permanent Color Change

4. Formation of a Precipitate

5. Temperature Change

Test Your Knowledge

• Go to the Live Chem website below:• http://www.chem.ox.ac.uk/vrchemistry/LiveChem/transitionmetals_content.html

• While in the Virtual Chemistry Lab, perform the following 5 experiments and record whether they demonstrate a chemical change. Then choose 5 other experimental mixes of your own and record whether they demonstrate a chemical change. Use the 5 Indicators of a Chemical Change to support your findings for all 10 experiments conducted.

• Click on the next slide for the Lab Write-up.

5 Indicators of a Chemical Change LabPurpose: The purpose of this lab experiment is to determine whether a chemical change has taken place using the 5 indicators of a chemical change.

Safety Equipment Necessary: If you were performing these experiments in the laboratory, what safety measures would you need to take to ensure your safety and the safety of others around you?

Data Table:Salt from the Top + Reagent from the Bottom Is there a chemical change? Evidence to support your findings:

Cu +2 + Na2SO3

Fe +3 + Mg Turnings

Cu +2 + Zinc Granules

Ti +3 + AgNO3

Cu +2 + KI