Chemical Reactions Lesson for Lab

Atomic Origins

Observing Chemical Reactions Lab

2020-08-10

www.njctl.org

Thoughts on the Nature of Matter

Earth

Air

Fire

Water

According to this theory, every unique substance would be made up of different combinations of the 4 elements.

Since ancient times, humans have pondered the nature of matter.

Thousands of years ago, some humans speculated all matter was made up of some combination of four "elements"

The Idea of the Atom

In ancient Greece (460 BC to 370 BC) a
philosopher named Democritus formulated
what is thought to be the first atomic theory.
Democritus reasoned that matter must be
made up of tiny, indivisible spheres he
called "atomos" (Greek for indivisible)
moving through empty space.

He was right, atoms are small! If you made a tiny dot with the tip of a sharp graphite pencil, guess how many atoms of carbon would be in that dot?

Answer

Alchemy

It would be almost 2000 years from the time of Democritus for humans to prove atoms are the building blocks of matter. In the meantime, the study of alchemy was a major precursor to modern chemistry.
Alchemists tried to transform matter to
convert base metals into gold or create powerful potions.

Isaac Newton famously practiced alchemy, attempting to turn substances into gold.

As we now know, elements like gold can only be formed in the
intense heat and pressure of exploding stars.

Chemistry

Through controlled experiments and observation, alchemy evolved into the branch of science we know as chemistry.

By the 1800's a couple of major principles had been established:

Law of Conservation of Mass

For any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant or be conserved over time. The law implies that mass can neither be created nor destroyed but it can change forms.

Atomic Theory

Matter is composed of atoms

In a chemical reaction, atoms are not created or destroyed, but are rearranged.

Open Ended

In a sentence, please explain what is meant by "matter cannot be created or destroyed".

John Dalton

1.

All matter consists of indivisible particles called
atoms.

2.

Atoms of the same element are similar in shape and mass, but differ from the atoms of other elements.

3.

Atoms cannot be created or destroyed.

4.

Atoms of different elements may combine with each other in a fixed, simple, whole number ratios to form compound atoms.

5.

Atoms of same element can combine in more
than one ratio to form two or more compounds.

6.

The atom is the smallest unit of matter that can take part in a chemical reaction.

In 1808 John Dalton published his atomic theory. It
contained 6 postulates:

John Dalton

Many of Dalton’s findings are consistent with modern
scientific theory, but some of his postulates have been disproved.

For example, it turns out atoms are divisible! What are
the parts of an atom called?

Multiple Choice

What are the three parts of an atom?

• protons, neutrons, electrons

• proteins, carbs, fats

• Protons, nucleons, elections

• protons, neutrons, elections

Chemical Changes

Dalton arrived at his theory by gathering data from chemical reactions.
During a chemical reaction a substance or substances can be
transformed into chemically different substances. Common indications include of a chemical reaction include:
·A change in temperature such as wood burning or fireworks
exploding
·A change in color such as metal rusting
·The production of an odor such as an egg rotting
·The formation a precipitate (a solid formed when two liquids are
combined)
·The formation of bubbles (gas) such as the carbon dioxide that
makes bread rise

Multiple Choice

True or False: A chemical change can be indicated by gas formation (bubbling)

• False

• True

Multiple Choice

What is a precipitate?

• A solid that forms when two liquids are mixed

• It is a part of the water cycle

• It is a liquid that forms from a solid

• It is a type of chemical used in lab

Multiple Choice

True or False: A color change can indicate a chemical reaction

• True

• False

Physical Changes

In some cases the properties of a substance may change, although
the substance remains the same. These changes are called physical
changes. For example, water can be turned from a free flowing liquid into a hard cube (ice). Its properties have changed but it’s still water!

Examples of physical changes include:
·Changes in texture such as sanding wood
·Changes in shape such as pulling metal into wires
·Changes in state (freezing, melting, boiling, condensing)

Multiple Choice

Ice melting is an example of what kind of change?

• chemical

• physical

• anatomical

• astronomical

Objectives

The goals of this lab are to:

·Observe a number chemical reactions.

·Outline the indications that a chemical reaction has occurred while observing the chemical reactions in this lab.

·Outline those changes in properties or changes in energy that result from the chemical reactions you observe.

·Differentiate between a physical and a chemical change.

Acetate sheet, reaction grid, goggles and aprons

The following solutions with their designations

A. 1 M hydrochloric acid

B. 0.1 M copper (II) sulfate

C. 0.1 M potassium iodide

D. 0.1 M lead (II) nitrate

E. Mossy zinc metal or zinc chips

Materials

Guided Lab - Procedure and Examples

Safety Warning:

·Always wear your goggles and aprons while completing this
lab.

·Also wear your goggles and aprons when you're near
someone working with chemicals.

·Familiarize yourself with the location of the eyewash and the
emergency shower in the room. If you get any chemicals in
your eye, use the eyewash.

·If any of the chemicals come in contact with your skin rinse
them off immediately with lots of water and let the instructor
know what you spilled --- on your way to rinsing them off.

·Never mix chemicals that you haven't been told to mix.

·Tell the instructor of any accidents immediately.

·Keep food and drinks out of the laboratory work area.

·Identify the two chemicals to be mixed for a given trial.

·Mix the two chemicals for a given trial on the actetate sheet which has been clipped to a reaction grid, make observations and note these observations on your lab sheet.

Procedure

Data Collection

·After you mixed each set of chemicals note your observations.

·After you have mixed your last set of chemicals, review all the reactions that you completed to see if there are any new changes. Some chemical reactions are slow and you may be surprised by what you will see after
some time has passed.

Open Ended

Why should you take your initial (beginning) observations and then take observations a little later?