"Law of Conservation of Mass" Chemical Equations PPT Courseware 4

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"Law of Conservation of Mass" Chemical Equations PPT Courseware 4

scientific inquiry

1.Ask a question

Will the sum of the masses of each substance change before and after a chemical reaction?

2. Conjectures and Assumptions

(1) The sum of the masses of the substances participating in the reaction is greater than the sum of the masses of the substances produced.

(2) The sum of the masses of the substances participating in the reaction is equal to the sum of the masses of the substances produced.

(3) The sum of the masses of the substances participating in the reaction is less than the sum of the masses of the substances produced.

Solution 1: Mass determination of white phosphorus before and after combustion

Ignite white phosphorus in a closed container

Note 1. The combustion of white phosphorus consumes oxygen in the air, so the experiment must be carried out in a closed container.

2. White phosphorus has a low ignition point and is prone to spontaneous combustion and should be stored in water.

3. White phosphorus is toxic

Option 2: Determination of mass before and after the reaction of iron and copper sulfate solution

material:

1. There is an oxide film on the surface of the iron nail

2. Copper sulfate solution generally does not deteriorate in the air; however, it is toxic. Do not touch the solution with your hands when using it.

1. Law of conservation of mass

The sum of the masses of each substance participating in a chemical reaction is equal to the sum of the masses of each substance produced after the reaction.

Question: Why is the mass of the solid after the reaction lighter than before the reaction in some experiments?

reason:

1. A portion of magnesium oxide remains on the crucible tongs;

2. Some magnesium oxide diffuses into the air with the white smoke.

Key points of the concept of the law of conservation of mass:

The sum of the masses of each substance participating in a chemical reaction is equal to the sum of the masses of each substance produced after the reaction.

1. "Sum" means counting the reactants and products in various states. Gases such as precipitation and invisible to the naked eye should also be considered.

2. The sum of the masses of each substance participating in a chemical reaction is not the sum of the arbitrary masses of each substance, and the mass of substances not participating in the reaction cannot be calculated.

3. The "conservation" of the law of conservation of mass refers to the conservation of mass, not the conservation of volume or the number of molecules of reactants.

Exercise: 1. What may change before and after the chemical change ( )

①The total number of molecules ②The total number of atoms ③The total number of protons in the nucleus

④The number of electrons outside the nucleus of a certain element

A ②③ B ③① C ②④ D ①④

2. What has definitely not changed before and after the chemical reaction is ( )

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

Application of the law of conservation of mass:

1. Explain the mass change of substances before and after the reaction and use the mass difference to determine the mass of a reactant or product.

(1) In the reaction of A+B=2C, after a sufficient amount of B reacts with W grams of A completely to produce 12 grams of C, then the mass of B participating in the reaction is ____________ grams

(2) In the reaction A+B=C+D, 5 grams of A react completely with a certain amount of B to produce 3 grams of C and 10 grams of D. Then the mass of B is _____ grams.

(3). If a gram of phosphorus reacts completely with b grams of oxygen, the mass of phosphorus pentoxide produced after the reaction is _____ grams

(4). When a gram of potassium permanganate is heated until it no longer decomposes, the masses of potassium manganate and manganese dioxide produced are b grams and c grams respectively, then the mass of oxygen is __________

(5). Heating 10 grams of a mixture of potassium chlorate and manganese dioxide, the total mass of the residue after the reaction is 9.52 grams, then the mass of oxygen generated is _____.

Application 1: Infer the constituent elements of reactants or products

1) Substance A is decomposed by heat to produce ammonia, water and carbon dioxide. The elements that make up substance A are ( )

2) If a combustible material burns in oxygen to produce carbon dioxide and water, the combustible material must contain ( ) elements and may contain ( ) elements;

3) If a combustible material burns in oxygen to produce carbon monoxide, carbon dioxide and sulfur dioxide, the combustible material must contain ( ) elements and may contain ( ) elements;

4) If a combustible material burns in oxygen to generate sulfur dioxide and water, the combustible material must contain ( ) elements and may contain ( ) elements;

Application 2: Find chemical formula

1.CaCO3+2R=CaCl2+H2O+CO2↑, then the chemical formula of R is ( )

2.2C2H5SH + 9O2 = 4CO2+6H2O+2X, then the chemical formula of X is ( )

3.SO2 + I2 +2X = H2SO4 + 2HI, then the chemical formula of X is ( )

4. According to the law of conservation of mass, in X2+3Y2=2Z, the chemical formula of Z expressed by X and Y should be ( )

Exercise: Write the chemical equation for the combustion of phosphorus in oxygen, calculate the mass ratio of each substance, and state the meaning of the chemical equation.

4P + 5O2= 2P2O5

① Phosphorus and oxygen generate phosphorus pentoxide under ignition conditions

② Every 124 parts by mass of phosphorus reacts completely with 160 parts by mass of oxygen to produce 284 parts by mass of phosphorus pentoxide

③Every four phosphorus atoms react with five oxygen molecules to form two phosphorus pentoxide molecules

Exercise question: It is known that 48g magnesium reacts completely with 32g oxygen to produce 80g magnesium oxide, then the following statement is correct ( )

A. 5g magnesium and 5g oxygen produce 10g magnesium oxide

B. 6g magnesium and 4g oxygen produce 10g magnesium oxide

C. 3g magnesium and 7g oxygen produce 10g magnesium oxide

D. 4g magnesium and 6g oxygen produce 10g magnesium oxide

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