Chemistry questions in the second year of junior high school Is there chemistry in the second year o

1.Yes, e.g., carbon, carbon is a substance c

H2 represents hydrogen, which is a substance, and can also represent a molecule such as hydrogen.

2.Element is a macroscopic concept, element refers to more than 100 basic metal and non-metal substances in nature, they are only composed of a few kinds of atoms with common characteristics, each nucleon in its atom has the same number of protons, with ordinary chemical methods can not make it simpler, and alone or in combination constitute all matter. is an abbreviation for a chemical element.

Hydrogen, on the other hand, is a substance.

Element symbols generally denote an element, and can also represent an atom of that element, and most solid elements are also commonly represented by element symbols.

3.Strictly speaking, matter is made up of atoms, molecules, ions, and elements are constituent substances.

4.Probably not.

5.See 26OK.

7.Belongs to the group of compounds, which are substances that are made up of atoms of two or more elements. It refers to a pure substance (as distinct from an elemental substance) produced from a chemical reaction. 』

There are a lot of mistakes you ask, so I won't leave you alone:

Elemental matter is composed of a single atom and is directly represented by elemental symbols: such as metals, noble gases, and most non-metals.

Only H2, N2, O2, O3, F2, Cl, and I2 are diatomic or polyatomic elemental substances, and of course P4 (white phosphorus), which can also be written as p.

CH4 can represent methane, which is a substance, which belongs to the chemical compound.

Oh, you're not right, how can I tell you.

No! Only a single symbol on the periodic table does!

H2 denotes one molecule of hydrogen. It is a microscopic concept, and h represents the element of hydrogen, which is hydrogen, which is the substance of hydrogen, which is a macroscopic concept.

Is 1 nitric acid or ammonium nitrate? Yes nitric acid, the answer is that the mass fraction of nitrogen is multiplied by 902) 400x35%.

2 Let the valency of r be xWhen x is an odd number. The chemical formulas are R2(SO4)X and R(OH)X

2r+96x=m

r+17x=n.

The solution yields r=+m-2n 62

Instead of molar mass, the difference method is used. The evaporated solid is a mixture of magnesium sulfate and zinc sulfate, and the solid before the reaction is magnesium and zinc, so n-m is the mass of sulfate, and then divided by the molar mass of sulfate 96, the amount of sulfate can be obtained, that is, the amount of sulfuric acid is the amount of sulfuric acid, that is, the amount of hydrogen. Then n-m 96 is multiplied by the molecular weight of hydrogen 2 to get option a.

mg+h2so4=mgso4+h2

zn+h2so4=znso4+h2

Two-formula merge. mg+zn

2h2so4=

znso4+mgso4+2h2m

mnxn-m

x=n-m/48

Hope my answer helps you!

The answer is that process a is: m (representing any metal) + h2so4 = h2 + mso4n-m is the mass of mso4.

The mass of SO4 is calculated from this time.

According to the ratio of H2 and SO4, the answer A can be obtained.

There is no chemistry in the second year of junior high school, and chemistry is a subject offered in the third year of junior high school. The main subjects in the second year of junior high school are: Chinese, Mathematics, English, Geography, History, Politics, Biology and Physics.

The curriculum that runs through the three years of junior high school includes: Chinese, Mathematics, English, Ethics and the Rule of Law. Physics will be taught in the eighth grade, and Chemistry will be taught in the ninth grade.

Chemistry

Chemistry is a kind of natural science, mainly at the molecular and atomic levels, studying the composition, properties, structure and change laws of matter, and creating new substances (essentially molecules that do not exist in nature).

The world is made up of matter, and there are two main forms of change: chemical and physical changes (and nuclear reactions).

Different from particle physics and nuclear physics, which study the smaller scale, the material structure of atoms, molecules, ions (groups), chemical bonds, intermolecular forces and other interactions are studied in chemistry, and the scale in which they are located is the closest to the macroscopic in the microscopic world, so their natural laws are also most closely related to the physical and chemical properties of matter and materials in the macrocosm of human existence. As an important bridge between the microscopic and macroscopic material worlds, chemistry is one of the main methods and means for human beings to understand and transform the material world.

1) Calculations show that the substance is composed of C, H, and O.

Because CO2 and H2O are generated

2) Water divided by the relative molecular mass of water18

Therefore, the oxygen content in water (H2O) is 16*; Therefore, the mass of the hydrogen element is carbon dioxide divided by the relative molecular weight of carbon dioxide44

Therefore, the oxygen content in carbon dioxide (CO2) is 32*; Therefore, the mass of the carbon element is the reaction of organic matter with oxygen, then the mass of oxygen can be determined according to the law of conservation of mass: the mass of oxygen is:

Oxygen divided by the relative molecular mass of oxygen32

Therefore, the oxygen content in oxygen (O2) is 32*; Therefore, the mass of the oxygen element is, so the ratio of the number of atoms of the three elements is:::16:6 3:8:3, so the simplest formula of the substance is C3H8O3

So 2 C3H8O3 + 7 oxygen, 6 carbon dioxide + 8 water.

You just need to calculate according to the law of conservation of mass, and the calculation of this kind of problem mainly depends on the law of conservation of mass.

It is not certain that the coefficient of this organic matter in the chemical equation is 1

The molecular formula of the substance is still uncertain, C3H4O3 is just the simplest formula, its molecular formula may be C3H4O3, or C6H8O6, etc., the combustion chemical equation written with C3H4O3 is before C3H4O3 is 2, and the chemical equation written with C6H8O6 is before C6H8O6 is 1

1) There must be H, C, and possibly O (combustion in oxygen).

2) It would be much better to remove the oxygen part.

1) Carbon, hydrogen, oxygen (TBD, probably in the air).

2) The organic matter contains element C, element H, and oxygen elements, so the ratio of the number of atoms of the three elements is:::4:3, so the simplest formula of the substance is C3H4O3. You're right.

"Sarin" molecular formula: C4H10O2PF

p%= p/c4h10o2pf= 31/(12*4+ 1*10+16*2+ 31*1+ 19*1)=22％

So choose B

As long as you remember the molar mass of each atom, you are not afraid of this kind of problem.