Junior High School Chemistry Learning Network Junior High School Chemistry Learning Network?

No, if you can't find it yourself, it's gone.

b c Let you take your time

Because iron and magnesium can replace hydrogen, copper cannot. According to the dropwise addition of dilute hydrochloric acid to the filtered solid, no bubbles are generated. Judgment.

b.The filtered solids must contain copper and must be free of iron and magnesium.

In addition, since the copper is replaced, there must be magnesium chloride in the filtrate, because mg and CuCl2 may react just right, and there is no CuCl2 left. If the iron is not replaced, there must be ferrous chloride in the filtrate.

Second, there is no magnesium without bubbles.

Choose B and C

This is because iron and copper (and possibly excess magnesium) are displaced, but hydrochloric acid is added to the solids without bubbles.

Explain that it contains only copper, does not contain magnesium and iron, so the filtrate may only have magnesium chloride and ferrous chloride, and there may be copper chloride.

Select BC to add hydrochloric acid to the filtered solid, no bubbles, indicating no iron and magnesium, while copper chloride is uncertain.

There is nothing in junior high school chemistry, the most important thing is interest, understand the principle, everything is easily solved, mainly valence, several reaction principles, some chemical elements, the properties of elemental compounds, etc., there is absolutely no problem in remembering what the teacher has talked about in class.

The molecular weight of water is 18 hydrogen 2 and the utilization rate of the atom is 100%, 4 * 18 2 = 36kg

25 + 10-5 = 30 mass ratio.

So the d mass is 10 5*6=12

(1) 2H2O === (electrolytic) 2H2 + O236 4x 4kgx=36kg

Two. Conservation according to mass.

25+10=5+xx=30

Deriving a is more than b than c than d equals.

5 to 2 to 1 to 6

So 10 (a) to y (d) = 5 to 6

Launch y=12

(1) 2 h2+ o2 = 2 h204 36

m(h2o)= 9 m(h2)=36 kg(2) according to the law of conservation of mass: 25g a reacts with 10g b to produce 5g c and 30g d. Therefore 10 g a full reaction should.

Generate 12g d.

Copper does not react with dilute sulfuric acid, so the equation of Cu+H2SO4 cannot be used to solve Zn+H2SO4=ZNSO4+H2

65 2x65/x=2/

x = mass fraction of copper in this brass sample (

Because the metal activity of Cu is after H, it does not react with dilute sulfuric acid.

Let the mass of zn be x.

zn+h2so4=znso4+h2↑

65 2x65/x=2/

The mass of x=cu is.

Mass fraction of copper =

Copper plus sulfuric acid does not react at room temperature. Do the rest yourself. It's simple.

Cu and H2SO4 don't react at room temperature, and you'll have to learn it in high school.

The reaction of Cu+H2SO4 is only reacted in concentrated H2SO4.

Cu does not react with dilute sulfuric acid, and H2 is produced by Zn.

Therefore Cu+H2SO4 cannot be used

It may be easier to understand that the mass of 1 mole of carbon atom is numerically equal to the relative atomic mass of carbon, that is, 12 grams, and the mass of carbon is divided by 1 mole of carbon to obtain the mass, that is, the amount of carbon is obtained, and the ratio of the amount of each atomic substance is equal to the ratio of its number, so the calculation formula is obtained.

In junior high school, it can be understood in this way: "12" is the relative atomic mass of carbon, that is, the ratio of the mass of a carbon to the "1 12 mass of carbon-12", and "1" and "16" are also the ratios calculated from hydrogen and oxygen respectively, divide the mass by the relative atomic mass and then compare the three atoms to simplify, that is, reduce the "1 12 of the mass of carbon-12" to get the atomic mass divided by one of the atomic masses and then compare, that is, the ratio of the number of atoms.

Divide the mass by the relative molecular weight. This quantity is the amount that represents the amount of matter. For example, 1mol H2O is about 18g.

Elemental mass ratio = the ratio of the relative atoms of the element to the product of the number of atoms.

Therefore, the ratio of the number of primitive subs = the ratio of the relative atomic mass of each atom.

The answer is as follows: a d c a

If you don't understand, you can continue to ask questions.

Chemical changes are caused by the formation of new substances, color, odor, density, solubility, these are all physical properties, and melting, solidification, gasification, liquefaction, sublimation, and condensation are all physical changes.

aObviously studied in physics.

d. In the process of food decay, a series of chemical reactions occurred in Brother Yin.

c is only a change in shape, and does not give birth to a new substance.

4.aFlammability is a type of chemical property.

With so much oxygen, you still have to outwit idle eggs.