Subject: 8th grade science
OBJECTIVES: TEKS 112.24 (b) (9)
(b)(9) Students know that substances have chemical and physical properties
(A) substances may react chemically to form new substances
(B) interpret information on the periodic table to understand that physical properties are used to group elements ( discussed in Atomic Structure Lecture)
(C) recognize the importance of formulas and equations to express what happens in a chemical reaction;
(D) physical and chemical properties influence the development and application of everyday materials such as cooking surfaces, insulation, adhesives, and plastics
LESSON GOALS:
-To understand the difference between a chemical change/reaction and a physical change/reaction
Background context and Purpose
To understand how matter is classified we must understand its chemical constitution (how it is put together or what it is made of) its structure. A physical change is a change in the form of matter but not in its chemical identity. Matter exists in three states (s, l, and g). In addition, we could have a physical change by disolving one material into another. (EX: One could dissolve NaCl sodium chloride (Halite, which is the mineral form of table salt) in water). This mixture can be separated by distilation. A mixture can be separated by physical means into two or more substances. Chemical change or reactions occur when one or more kinds of matter are transformed into a new kind of matter or several kinds of matter. The identity is changed and electrons are rearranged. (EX: Rust is a chemical change, Fe + O = Fe (n)O(n) or iron oxide). A chemical property of iron is its ability to react with oxygen to produce rust. A substancne cannot be separated into other kinds of matter by any physical process. (Ex: Na metal reacts with water giving off hydrogen gas and sodium hydroxide, which can change the substance phenolphthalein from clear to pink). Pure water is a substance, it exists in s, l, and g, which can change physical properties NOT chemical (unless you react it with electricity and acid). We use different elements and chemicals together to aid our daily lives. One example would be Teflon C8 is used for none stick surfaces in pans.
MATERIALS:
Dry ice CO2 (s) to CO2 (g) by sublimation
Ice, water, and steam (still water)
Bunsen burner
50 ml beaker
Na (metal)
Phenolphthalein
