"The Composition of Water" Water in Nature PPT Courseware 2

"The Composition of Water" Water in Nature PPT Courseware 2

Task 1: Explore the combustion of hydrogen

What are the physical properties of hydrogen?

How to collect hydrogen?

Why does hydrogen need to be tested for purity? How to verify purity?

Observe the phenomenon of hydrogen combustion and write a literal expression for hydrogen combustion.

1. Properties of hydrogen gas

1. Physical properties: colorless, odorless, difficult to dissolve in water, and less dense than air.

Collection method

a. Drainage method

b.Downward exhaust air method

2. Chemical properties: flammability

(Purity must be verified before lighting or heating)

(2) Chemical properties of hydrogen - flammability

Burns in air to produce a light blue flame

Conclusion: Hydrogen burns in oxygen to form water, proving that water contains hydrogen and oxygen elements

(3) Purpose

1. Since it is less dense than air, it can fill balloons

2. Because it is flammable, it can be used as a high-energy fuel

practice

1. As shown in the picture, a student ignited pure hydrogen and placed a cold and dry small beaker over the flame. ______ appeared on the inner wall of the beaker. Based on this, you can find that the property of hydrogen is ______; the literal expression of this reaction is ______; using this property, hydrogen can be used as fuel, and its outstanding advantage is ______

2. Colorful hydrogen balloons are often used as decorations in festivals and celebrations, and are also favorite toys for children.

(1) The explosion of a hydrogen balloon when it encounters an open flame shows that hydrogen has ______ properties. At the same time, we are warned that we must ______ before igniting hydrogen; when igniting hydrogen, a sharp popping sound indicates that the gas is ______, and ______ indicates that the gas is pure.

(2) In view of the above situation, people are now using other gases, such as helium and neon, to replace hydrogen to fill balloons. (According to the information, it can be seen that the density of helium and neon is smaller than that of air) Do you think it is feasible?

______, the reason is ____________________

Task 2: Explore the experiment of electrolyzing water

Watch the video of electrolyzed water and think about the following questions:

1. What gas is produced at the positive and negative poles?

2. Write a literal expression for this reaction.

3. What elements are hydrogen and oxygen composed of? From this, what elements does water consist of?

2. Determine the composition of water by electrolyzing water

1. Experimental device:

2. Experimental phenomenon: Bubbles are generated on the electrodes. After a period of time, the volume ratio of the gas collected by the positive and negative electrodes is about 1:2.

Positive oxygen and negative hydrogen; oxygen one hydrogen two

3. Check the gas: Use a wooden stick with sparks to check the gas in the positive tube. If the wooden stick re-ignites, it means it is oxygen. When the gas in the negative tube is close to the flame, the gas can burn and the flame will turn light blue, which means it is hydrogen.

1. The experiment of electrolyzing water proved that water is made of ( )

A. Composition of hydrogen and oxygen

B. Composition of hydrogen and oxygen elements

C. Composed of hydrogen atoms and oxygen atoms

D. Composed of two hydrogen atoms and one oxygen atom

2. The picture below is a schematic diagram of a microscopic model of electrolyzed water. The incorrect information obtained from it is ( )

A. The ratio of the number of molecules of the two products is 2: 1

B. This is a chemical reaction

C. There is no change in the type and number of atoms before and after the reaction

D. In chemical reactions, molecules are divided into atoms, and atoms cannot be divided further.

3. When electrolyzing water, a small amount of dilute sulfuric acid or sodium hydroxide solution is generally added. The reason is ( )

A. It can decompose water

B. Can increase the conductivity of water

C. Can generate more hydrogen and oxygen abnormalities

D. It can be used to remove harmful substances in water

4. Which of the following statements about hydrogen is incorrect ( )

A. Hydrogen burns in oxygen to produce a light blue flame

B.Be sure to check the purity of hydrogen before igniting it

C. Ignition of hydrogen will definitely cause an explosion

D. Hydrogen is poorly soluble in water and can be collected by drainage and gas collection.

3. Elements and compounds

1. Compounds: Pure substances composed of different elements are called compounds

Examples: water (H2O), carbon dioxide (CO2), potassium permanganate (KMnO4)

Oxide: A compound composed of two elements, one of which is oxygen

Examples: water (H2O), carbon dioxide (CO2), phosphorus pentoxide (P2O5)

2. Elemental substance: A pure substance composed of the same element is called an elemental substance.

Examples: Hydrogen (H2), Nitrogen (N2), Oxygen (O2), Iron (Fe)

1. Water is a kind of ( )

①Element; ②Mixture; ③Compound; ④Pure substance; ⑤Oxide

A.①②③ B.③④⑤ C.①③⑤ D.②③④⑤

2. Which of the following substances is pure ( )

A. River water B. sea ​​water c. Distilled water d. mineral water

3. Water is decomposed into hydrogen and oxygen under the action of direct current. Description ( )

A. Water is composed of hydrogen and oxygen

B． Water is composed of hydrogen and oxygen elements

C. There is hydrogen and oxygen in water

D． Just mix hydrogen and oxygen thoroughly to get water

4. Electrolysis of a certain amount of water. When 5 ml of gas is produced on one electrode, the volume of gas produced by the other electrode may be ( )

A.2.5 ml or 5 ml B.5 ml or 10 ml

C.10 ml or 15 ml D.10 ml or 2.5 ml

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