"Law of Conservation of Mass" Source of Life - Water PPT Courseware 3

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"Law of Conservation of Mass" Source of Life - Water PPT Courseware 3

my question?

In a chemical change process, after the new substance is generated, does the total mass of the substance change compared with before the reaction? Ask students to make bold guesses...

Explore: Explore the relationship between the sum of the masses of the reactants before the reaction and the sum of the masses of the products after the reaction.

How to use a pallet balance

1. Calibration: Calibrate the balance before weighing, that is, check whether the balance is balanced. The method is to put clean paper on the weighing plate first, place the scale at the zero mark of the scale, and see whether the number of grids the pointer swings on the left and right sides of the dividing plate is close to the same, or whether the pointer stops in the center. If it is not balanced, adjust the balance nut to bring the balance into balance.

2. Weighing: Place the object to be weighed on the left pan, and the weight on the right pan. (The object on the left is on the right.) Use tweezers to add or subtract weights. Increase the weight first, then the smaller one. You can move the weight below 1g until the balance is balanced. The sum of the masses shown by the weight and the weight is equal to the mass of the object being weighed.

After weighing, put the weight back into the box and move the weight back to zero.

Question: What conclusions can students draw through experimental exploration?

In a chemical reaction, the sum of the masses of the substances participating in the chemical reaction is equal to the sum of the masses of the substances produced after the reaction. --Conservation of mass

Analysis and discussion: How many key words does this law contain?

Warm tips

1. Applicable to "all chemical reactions", not applicable to physical changes.

2. It only refers to the conservation of "mass", not other physical quantities.

3. Refers to the "various substances" that are reacted or generated, including solids, liquids, and gases.

4. Refers to the substances that "participate" in the reaction. Substances that have not completed the reaction are not included.

think about it

Why is the sum of the masses of each substance before and after a chemical reaction equal?

Analysis and discussion:

①Did the types of molecules change before and after the chemical reaction?

②Have the types of atoms changed before and after the chemical reaction?

③What is the essence of the chemical reaction process?

Knowledge summary:

Reasons for conservation of mass:

Macro:

The types of elements remain unchanged before and after the reaction.

The mass of the element remains unchanged before and after the reaction.

Micro:

The types of atoms have not changed.

The number of atoms does not increase or decrease.

Atomic mass does not change.

formative assessment

1. Xiao Ming said that the mass of a candle becomes smaller after burning. This fact does not comply with the law of conservation of mass. Do you think it is correct? Why?

wrong. The CO2 and H2O generated after the candle burns run away, so the mass of the candle becomes smaller after burning, which still complies with the law of conservation of mass.

2. A certain master said that he could use his power to chemically change aluminum (Al) into gold (Au). Is there any scientific basis for his statement?

No. Before and after a chemical reaction, the types of atoms and elements remain unchanged.

Give it a try:

1. In the reaction of A+B - C+D, 5 grams of A and a certain amount of B react completely, producing 3 grams of C and 10 grams of D, then the mass of B is ( )

A. 18 grams B. 7 grams

C. 8 grams D. 6 grams

2. After the candle burns in oxygen, it only produces CO2 and H2O. Try to infer that the candle must contain ( )

A. Carbon B. Hydrogen

C. Three elements: carbon, hydrogen and oxygen. D. Carbon and hydrogen elements

3. Among the following items, before and after the chemical reaction, the one that will definitely remain unchanged is ______, the one that will definitely change is _____, and the one that may change is ___.

①Number of atoms ②Type of substance ③Type of atom ④Total mass of substance ⑤Number of molecules ⑥Type of element ⑦Type of molecule

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Update Time: 2024-10-02

This template belongs to Chemistry courseware Cantonese Education Edition Ninth Grade Chemistry Volume 1 industry PPT template

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