In the general review stage of chemistry for the high school entrance examination, we should review many knowledge sections and summarize and review them topically, among which, all the knowledge points of the "oxide" part of the knowledge topic are relatively basic and easy. However, when summarizing the topic of "oxides", we should not only understand the name of the substance and only write the chemical formula, but also "spread" more carefully for some commonly used oxides, after all, the chemistry test questions of the high school entrance examination in various places are comprehensive and comprehensive, that is, "in a small part of the test paper" may be tested about the knowledge points of "oxides".
Below, taking the two categories of "non-metal oxides" and "metal oxides" as clues, we will sort out some small and commonly tested knowledge points related to "oxides". Considering that there will be some "physics and chemistry comprehensive questions" in the science comprehensive test papers of the high school entrance examination in some regions, a part of the physics common test knowledge will also be appropriately inserted in the middle.
The common non-metallic oxides in the junior high school stage are generally "covalent compounds", that is, the molecules are connected by "covalent bonds", and the valency of element O is negative, and the valency of another element is positive.
Oxides of hydrogen
There are two main oxides of H: water and hydrogen peroxide. The chemical formula of both is as follows:
The product of the combustion of hydrogen in oxygen is water. Similarly, if water is electrolyzed, hydrogen and oxygen will be generated under "electrified" conditions.
Some beginners in chemistry will refer to "water" as "dihydrogen monoxide", so here you need to pay special attention to the difference in the chemical formulas of "water" and "hydrogen peroxide" (as shown in the figure above). Because of this, the valency of element O in the two compounds is different – for the water molecule, element O is -2 valence; For hydrogen peroxide, element O is -1 valence.
Water molecules will have different states of matter in different temperature ranges, and naturally will have different common names. At room temperature and pressure, the melting point of water molecules is 0 degrees Celsius and the boiling point is 100 degrees Celsius. The temperature of water molecules only at the "temperature between the melting point and the boiling point" is commonly known as "water" or "liquid water", the temperature below the melting point is commonly known as "ice", and the temperature above the boiling point is commonly known as "water vapor". Sometimes it is often "used to cool the drink with ice", and the principle is that "the process of melting the ice cube must absorb heat"; Water vapor at 100 degrees Celsius is more likely to burn people, and the reason is that "100 degrees water vapor needs to be liquefied and exothermic in the process of turning into 100 degrees liquid water".
Another oxide of H, "hydrogen peroxide", commonly known as "hydrogen peroxide", has oxidizing properties and has certain bactericidal and antiseptic effects.
c, n oxides
Among this type of oxides, the simplest chemical formula is carbon monoxide CO and nitric oxide NO, in these two compounds, the valency of O is -2 valence, and the valency of C and N is +2 valence. Both are colorless and odorless gases, and both are toxic gases. Among them, the toxicity of CO is reflected in the fact that it binds to hemoglobin in human blood 200 times more than "binding to oxygen". c Combustion under the condition of insufficient oxygen to generate CO; When oxygen is abundant, it is burned to produce carbon dioxide gas.
The chemical formulas of the other two compounds are shown below, and in both compounds, the valency of C and N is +4. Among them, carbon dioxide gas is a colorless gas, but it is also a greenhouse gas, and is often used to extinguish fires.
However, solid carbon dioxide, commonly known as "dry ice", is generally used to "spread in clouds for artificial rainfall", and its principle is also that "dry ice will absorb heat and refrigerate during the sublimation process".
Carbon dioxide can react with alkaline solutions to produce water and carbonates; CO monoxide is not able to react with alkaline solutions and is "not a salt oxide".
S oxide
As shown in the figure above, there are also two kinds of oxides of S, in sulfur dioxide, the valency of S is +4 valence, and sulfur dioxide has a pungent odor; In the chemical formula of sulfur trioxide, the valency of S is +6, and the substance can be combined with water to form sulfuric acid.
Miscellaneous
Si oxide silica, the main component of "glass". p oxide, which is "phosphorus pentoxide".
Unlike non-metallic oxides, metallic oxides are not "covalent compounds", but "ionic compounds".
oxide of Fe
For iron, there are three main oxides, of which the simplest chemical formula is ferrous oxide Feo, and the valency of Fe element in this substance is +2 valence.
Generally speaking, "iron oxide" refers to "ferric oxide", the valence of FE element in the substance is +3 valence, which is a red solid, commonly known as "rust", and is also the main raw material of "coke oven ironmaking" (in the ironmaking process, the commonly used reducing agent is CO, and the reaction condition is "high temperature"); Ferric oxide, commonly known as "magnetic iron oxide", is a product of the combustion of iron in pure oxygen. In this regard, we should also pay attention to the phenomena in the relevant experiments when reviewing.
Oxides of Cu
Among them, copper oxide is a black solid, and the valency of Cu element is +2 valence; The valency of the Cu element in cuprous oxide is +1 valence.
For the reduction of copper oxide CuO, "hydrogen" is generally used as the reducing agent, the reaction condition is "heating", and the reduction product is Cu and water.
Oxide of Mn
In junior high school chemistry experiments, the common oxide of MN is manganese dioxide, and the chemical formula is shown below.
Manganese dioxide is often used as a catalyst for "oxygen production" in junior high school chemistry experiments. For this, everyone should pay attention to these two points -
1. The role of manganese dioxide in the reaction is a "catalyst" with catalytic effect, not a reactant;
2. The reaction conditions for the decomposition of potassium chlorate include not only "manganese dioxide", but also "heating".
1. It is necessary to pay attention to distinguishing each group of "oxides with the same constituent elements", and distinguish the different chemical formulas, chemical properties and different effects of the two.
2. We should also record as many different groups of "substances with the same constituent elements" as much as possible, which are often used in chemical substance inference problems.
3. You should also pay attention to the chemical reactions that occur between "substances with the same constituent elements" (such as the combination of carbon dioxide and carbon at high temperatures to form CO), which is also beneficial for answering inference questions.
4. For each kind of oxide, we should also pay attention to reviewing the chemical reactions related to it, as well as the experimental phenomena of chemical experiments.