Questions about junior high school chemistry Urgent junior high school chemistry questions

What is the meaning of fecl2? Is there such a thing as 2-valent iron?

This is a ferric 2 ion, also called an iron ion (different from a ferric ion), and two chlorine atoms each get a valence electron of iron. The element iron includes elemental iron, as well as various forms of iron in chemical compounds. So it's okay to say divalent iron, but it is customary not to say divalent iron element, but divalent iron ion.

Acids are compounds, not mixtures The teacher seems to say that dilute sulfuric acid is not an acid, is that true?

Dilute sulfuric acid can completely ionize hydrogen ions and is a typical acid, and you must have heard it wrong.

Acids are not necessarily compounds, such as hydrochloric acid and hydrofluoric acid, which are aqueous solutions of HCL and HF, respectively, which are mixtures. There are some acids that must be present in solution or even not to make a concentrated solution, such as hypochlorous acid (HCLO).

Q: Add Agno3 to the final filtrate, and answer Yes: There is H2O

Question addendum: Why don't you use dilute nitric acid with metal only H2?

Water is generally not used, because since it is in solution, everyone knows that there must be water molecules, and solvents generally do not make answer requirements.

Due to its strong oxidizing properties, nitric acid tends to undergo redox reactions with metals to produce hydrogen gas.

There are +2 valence iron ions, acid is of course a compound, and finally there are Zn ions, NO3 ions, because the activity of Zn ions is the strongest, so it can replace Ag, Cu, Fe, speaking of water, since it is AgNO3 solution, how can there be no water.

The valency of iron in ferric chloride is positive bivalent. No.

Wrong, such as: aqua regia.

No. No, because there is no element H in the reactants.

ferrous chloride; Elements refer to a class of substances, there is no such statement.

Acid is not a mixture, dilute sulfuric acid is the product of ionization of sulfuric acid after dissolving in water, it is a mixture.

No, people ask about solutes, solvents don't have to.

Reacting with metal with dilute nitric acid, hydrogen is not released, but nitrogen dioxide is released.

Question 1: It is enough to calculate according to the conservation of atomic mass. Before and after the reaction, the number of atoms of the same kind is the same.

m+4hno3=pbo2+2pb(no3)2+2h2o, so m is pb3o4. If you wrote the equation correctly, it's pb3o4

Question 2: The method is the same as that of Question 1.

4c3h5(ono2)3=wn2+xco2+yh20+zo2

From this equation we know that w=6; x=12,y=10,z=1

So x, y, and are 22

Question 3: From the meaning of the question, A+B+C D, "If you increase 10Ga, A and C just react completely", we can see that 25Ga and 15GC just react completely, A:C=25G:15G=5:3;

Then after the 15Ga reaction, C 9G is required, and according to the law of conservation of mass, the mass of B participating in the reaction is: 30G-15G-9G=6G, B:C=6G:9G=2:3

Question 4: The relative atomic mass of Zn is 65, and the relative atomic mass of Fe is 56, the amount of Zn and Fe of the same mass, Zn is less than the amount of Fe, in the case of the same amount of H2SO4 matter, it is possible that the amount of H2SO4 is just completely reacting with Fe and the amount of Reacting with Zn is insufficient. So choose d, zn can't be left.

Question 5: a, add the same mass of aluminum, zinc and complete solution, that is, they are completely reacted, and the mass of H2 generated is not the same, so it will not be balanced.

b, add iron, magnesium, will react, and there is a surplus, it is possible to balance, not necessarily balanced.

c, add iron, copper, all remaining can not be balanced, because iron reacts with sulfuric acid, and copper does not react with dilute sulfuric acid, so it is impossible to balance.

d, according to the conservation of mass on the line. The added mass of the solution is not the same. So unbalanced.

Study hard, make progress every day, I hope it can help you.

1.Using the law of conservation of mass, the types and numbers of atoms remain unchanged.

2.Ditto. 3.

If 10 GA is added, A and C happen to react completely, indicating that 25 GA and 15 g C happen to react completely, that is, in the first reaction, 15 g A and 9 g C happen to react completely, then the mass of B participating in the first time is 6 g, so 6 g: 9 g, 2:3

4.When dilute sulfuric acid with equal mass and equal mass fraction reacts with zinc powder and iron powder of equal mass, there are two situations, (1).If there is an excess of sulfuric acid, then iron produces more hydrogen, and the c option is correct, (2

If the sulfuric acid is insufficient, the amount of hydrogen produced is equal, and the balance is finally balanced, but under the same conditions, zinc is more active than iron, and the rate of hydrogen production is faster, and the decrease is faster, a option is correct; When producing the same mass of hydrogen, less iron is required than zinc, so b is correct, so d is chosen

5.Beaker of the same mass, the same kind of dilute sulfuric acid, add the same mass of iron, magnesium, after the reaction of the two metals are left, indicating that the amount of sulfuric acid is insufficient, then the amount of hydrogen produced is equal, then the balance is finally balanced, so choose B

1. The chemical equation is balanced, the number of atoms is counted, the number of atoms on both sides is removed, and the remaining combination is it. 2. From the breakthrough of hydrogen atoms, you can know by counting; 3. Conservation of mass, 4. Breakthrough in active size, atomic weight, zinc atomic weight-iron atomic weight, 2. Hydrogen atomic weight, atomic weight and atomic weight; 5. The amount of hydrogen released is the same.

1.Because the total number of atoms before and after the reaction is unchanged. There are 14 oxygen in the back and 12 in the front, so there are two oxygen in the unknown chemical formula. And you made a mistake in writing dilute sulfuric acid.

2.Similarly. 3.3 to 2

4.Because zinc has a higher metallic activity than iron, it is not possible for iron to react completely under the condition of the problem, and zinc has not yet reacted.

5.If there is a surplus of metal, it means that the dilute sulfuric acid has been completely recycled, and the hydrogen is all from the dilute sulfuric acid, and the mass of the hydrogen that escapes out is equal, so the balance will be flat.

It is inferred from the conservation of mass, that is, the type and number of atoms of the element before and after the reaction are equal

1. The left side lacks pb and o elements, and the ratio of atoms is 1:2, so...

2. According to the conservation of c, it can be known that there are 12 C, so x=12, according to the conservation of h, it can be known that there are 20 h, so it is 10h2o, that is, y=10, so...

Others are not easy to express, sorry.

1, according to the atomic balance m=pb3o4 (your answer is a bit of a problem) 2 according to the atomic balance can be obtained x=12,y=10, so the relative molecular mass of x+y=224zn is 65, fe is 56, in the case of equal mass, the amount of zn is less than the amount of fe substance, and because the mass fraction of sulfuric acid, and the mass is equal, when the fe reaction is complete, zn will never be left. At the same time, if there is a surplus of zn, there must be a surplus of fe. By the way, 1molZn reacts with H2SO4 in the same way as Fe, transferring 2mol of electrons.

5. The metal residue proves that the acid reaction is completed, and the acid is the same, so the same amount of H2 is released, so the same amount is reduced, so it is flat.

1. According to the law of conservation of atoms, the number of elements on both sides of the equation should be equal.

Left: 4 Hs, 4 NO3s

Right: 3 pb, 4 h, 4 no3, 4 0, so m is pb3o42, the law of conservation of atoms:

Left: 3x4=12 C, right 2x C, then x=6, left: 4x5=20 h, right 2yh, y=10, left:

3x4=12 n, 2*w n on the right, then w=6, left: 3*3*4=36 o, 2x+y+2z o's on the right, then z=7

One. Mass reduction.

1, HCl and Na2CO3

2 na2CO3 and ca(oh)2 (I don't know if it was taught in junior high school, +naco3caco3 +naoh).

It is to test the complex decomposition reaction, and the conditions for the formation of precipitation, gas, and water can be met.

The quality is constant.

Acid-base neutralization reaction.

2hcl＋ca(oh)2=cacl2＋2h2ohcl＋naoh＝h2o＋nacl

Two. hcl＋naoh＝h2o＋nacl

40*20%*Let me help you explain, 40g sodium hydroxide solution *20% = 8g sodium hydroxide solute, 40*20%* hydrochloric acid solute)

HCL photodecomposition.

The mass minus 1 is: Na2CO3 and HCl. It is a metathesis reaction HCl + NaOH ==NaCl+H2O 2HCl+Ca(OH)2=CaCl2+2H2O

Obviously, to reduce the mass, only gas needs to be generated or precipitate can be generated, and (1) HCl and Na2CO3 are obtained(2) Na2CO3 and Ca(OH)2·

Second, HCl+NaOH=NaCl+H2O

1, HCl and Na2CO3(2) Na2CO3 and Ca(OH)2·

Second, HCl+NaOH=NaCl+H2O is the decomposition of the examination.

1) HCl and Na2CO3 are formed as gas, and Na2CO3 and Ca(OH)2 are precipitated.

II. HCl and NaOH, HCl and Ca(OH)2

Sodium hydroxide may have deteriorated, and sodium carbonate is present, so more hydrochloric acid is consumed.

(1) The reason for the deterioration of lime water may be that the reagent bottle is not tightly sealed, and the chemical equation of the reaction during the deterioration process is = Ca(OH)2+CO2=CaCO3+H2O

2) Whether the lime water used in the experiment is deteriorated, draw a small amount into the test tube, and add phenolphthalein reagent dropwise, and the solution turns red. Description: Conjecture The solution turns red, indicating that it contains calcium hydroxide and is alkaline.

3) Whether the obtained gas contains HCL gas, it is passed into a mixture of dilute nitric acid and nitric acid, and a white precipitate is found. The chemical formula of the reaction is AGNo3+HCl=AGCL+HNO3

Conclusion] The gas does contain HCl, and the best way to remedy it is to ———

When the concentration of hydrochloric acid is ———, it should be diluted.

(3) In the question, you should have made a few mistakes: "dilute nitric acid and nitric acid mixture" should be "dilute nitric acid and silver nitrate mixture", and "chemical formula of reaction" should be "chemical equation of reaction".

The chemical equation for this reaction is HCl + AGnO3 === AGCl +HNO3

Conclusion] The gas does contain HCl, and the best way to remedy it is to ———

Saturated sodium carbonate solution is used to filter out HCl gas, reason: HCl can react with Na2CO3, NaHCO3 is generated when HCl is small, and CO2 is generated when HCl is excessive (generally there is no excess, so there is no need to worry about the influence of the generated CO2 on the experimental results); In addition, saturated sodium carbonate solution (the action of (CO3)2- ions) can inhibit the dissolution of CO2 in solution, and the solubility of HCl in water is large.

When the concentration of hydrochloric acid is ———, it should be diluted.

I don't know what it means, which problem is this aimed at?

Remedy: Pass the gas into three bottles, the first.

One is filled with distilled water, the second is desiccant, and the third is a collection bottle (because HCl is very soluble in water, CO2 is less soluble in water. ）

30%；Density of water: ;

Remedy: The gas is filtered into pure water, and HCl is very soluble in water.

Then count it yourself.

The upstairs method is so bad that it should be passed into a saturated sodium bicarbonate solution.