1DCHEM - PP#6 (Chemical Properties) -...

2/8/2013

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SNC1DCHEMISTRY

ATOMS, ELEMENTS, & COMPOUNDS

L Chemical Properties

(P.152-155)

Chemical Properties

When we watch a fireworks displaywe are, in scientific terminology,seeing the chemical properties of thefireworks. A chemical property is aproperty of a substance that describesits ability to undergo changes to itscomposition to produce one or morenew substances.

February 8, 2013 1DCHEM - Chemical Properties 1

Chemical Properties

CHEMICAL PROPERTY

� describes the ability of asubstance to change and produceone or more new substances


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Observing Chemical Properties

For example, when a match burns, achemical change occurs because thematchstick is coated with a substancethat burns easily. This ability to burn,or its combustibility, is a chemicalproperty of the match. Chemicalproperties can be observed only whena chemical change occurs.


Observing Chemical Properties

PRACTICE

1. Classify each as a physical or chemical property:

(a) wood burns

(b) clay is brown

(c) steel wool rusts

(d) a paper clip is 3 cm long


chemical

physical

chemical

physical

Chemical Properties

The usefulness of many substances isdetermined by their chemicalproperties. Many substances, such aswood and coal, are useful becausethey burn easily. Other substances,such as liquid/powder fire retardantsused to make fire resistant materials,are useful because they do not burneasily.


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Chemical Properties

PRACTICE

2. (a) What chemical properties ofnail polish remover makes ituseful?

(b) What chemical propertymakes nail polish removerdangerous?

(a) removes nail polish

(b) flammable/poisonous


Chemical Properties

Metals are used to make jewellery, butonly some metals, such as stainlesssteel, titanium, and some types of goldare used for body piercings. This isbecause these metals have a chemicalproperty that make them useful forpiercings – these metals, unlike copperand silver, do not react easily withsubstances in the body.


Chemical Properties

PRACTICE

3. Surgeons sometimes use metalplates and screws to hold brokenbones together. What chemicalproperties do you think the metalshould have?

the metal should not react withsubstances in the body


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Chemical Changes

A change that results in the formation ofa new substance is called a chemicalchange. The original substances do notdisappear though. Instead, thecomponents of the original substancesare rearranged when the new substanceis formed.


Chemical Changes

CHEMICAL CHANGE

� change in which one or more newsubstances is formed

� components of original substance(s)(i.e. the atoms) are rearranged


Chemical Changes

For example, roasting a marshmallow ona campfire produces a brown, flakysubstance on the surface of themarshmallow. This new substance isclearly different from the gooey centre ofthe marshmallow. Many chemicalchanges are easy to observe and occurall around you.


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Chemical Changes

PRACTICE

4. Classify each as a physical or chemical change:

(a) folding a paper airplane

(b) water freezing on a pond

(c) a car rusting

(d) making a campfire

(e) melting a marshmallow

(f) dissolving sugar in coffee


P

P

C

C

P

P

Chemical Changes

Electrolysis is another example of a chemical change. Electrical energy isused to break water molecules apart into oxygen and hydrogen. But howdo we know when a chemical change has occurred?


Chemical Change Clues


PRACTICE

5. There are 6 distinctive clues (either alone or together) that indicate achemical change has occurred. What are they?

CHEMICAL CHANGE CLUES

Î a new colour appears

Ï a new odour appears

Ð heat/light is given off/absorbed

Ñ bubbles of gas are formed

Ò a solid material (precipitate) forms

Ó the change is difficult to reverse

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These “chemical change” clues can helpyou decide whether a chemical orphysical change has occurred. But it isimportant that you do not come to aconclusion too quickly. While all of theseclues suggest that a new substance hasbeen produced, any one of them couldalso accompany a physical change. Youmust consider several clues in order todetermine what type of change has takenplace.



PRACTICE

6. What evidence suggests that these changes are chemical changes?

(a) Bubbles form when baking soda is mixed with lemon juice.

(b) Cookies baking in the oven give off a delicious aroma.

(c) A match is struck and ignites.

(d) When two liquids are mixed a solid red substance appears.

(e) A banana tastes sweeter as it ripens.

(a) bubbles of gas are formed (& change is difficult to reverse)

(b) new odour appears (& change is difficult to reverse)

(c) heat/light is given off (& change is difficult to reverse)

(d) a solid precipitate forms (& change is difficult to reverse)

(e) the change is difficult to reverse


Physical or Chemical?

PRACTICE

7. When a frozen pizza is placed in the oven, the cheese begins to meltand then darken. The crust becomes brown on the edges. Are thesephysical or chemical changes? How do you know?

melts – physical (easy to reverse)

crust/cheese browns/darkens – chemical (change is difficult to reverse)


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PRACTICE

8. A candle burns for 15 minutes before it is extinguished. Some waxmelts, drips down the side, collects at the base of the candle, and thenhardens again. The candle becomes shorter.

(a) What changes were physical changes? Explain.

(b) Was there any evidence of a chemical change? Explain.

(a) wax melting/hardening and candle getting shorter – chemicalproperties did not change

(b) burns – heat/light is given off and the change is difficult to reverse



PRACTICE

9. Classify each of the following as a physical change or a chemicalchange. For each chemical change, explain how you can tell that anew substance has been formed.

(a) Water boils and turns into steam.

(b) Wood is sawed and made into a toy box.

(c) Firewood burns and ashes remain.

(d) Orange drink crystals are stirred into a pitcher of water.

(e) Sugar, eggs, and flour are mixed and baked into cookies.


P

P

C

P

C

Activity: Using Properties to … (B7/P.156)

INSTRUCTIONS

A. Read the activity “B7: Using Properties to Identify Pure Substances”.

B. Follow the instructions given (i.e. procedure 1 to 19).

C. Answer the questions given (i.e. analysis 15 to 19).

D. Submit a formal lab report.

NOTE!

• This is a formal lab report. Use your “practice” formal lab report as aguide.

• Make sure you do your “own” work!


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U Check Your Learning

TEXTBOOK

P.161 Q.4


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