Some 9th grade chemistry questions, 9th grade chemistry questions

2 80 * 20% = 16g 80-16 = 64g requires 16g of potassium nitrate and 64g of water.

2. The mass of potassium nitrate = 80 * 20% = 16g, the mass of water = 80-16 = 64g g of 10% sodium chloride solution in the mass of sodium chloride = 200 * 10% = 20g, plus 10g of solute, then the solute mass fraction of the solution = 20 + 10 200 + 10 =

The mass of sodium chloride in 10% sodium chloride solution = 200 * 10% = 20g, plus 10g of solvent, then the mass fraction = 20 (200 + 10) =

5. The mass fraction of the two parts of the solution is the same, and the mass fraction after mixing is also the same = 10%. It can also be calculated, first calculate the solute and then add it and divide it by the mass of the solution. That is, (200*10%+100*10%)200+300=10%.

2.Requires potassium nitrate 80g* Requires water 80-16=64g3The solute mass fraction of 200g* sodium chloride solution is 30g 210g = 5

200* sodium chloride solute mass fraction of solution 30 300 = the topic is not rigorous, and the temperature should be emphasized.

1 Mass fraction of solute in solution 5 25 = 20%2 Mass of potassium nitrate 80 20% = 16g Mass of water 80 - 16 = 64g

3 NaCl mass in the original solution 200 10% = 20g after dissolving 10 g of sodium chloride.

Mass fraction of solute in solution (20+10) (200+10)=4 Mass of NaCl in the original solution 200 10% = 20g Add 10 grams of water.

The solute mass fraction in the solution is 20 (200+10) = 5, because the concentration of the two is the same, the concentration is still unchanged, and it is still 10%, and the solute mass fraction (20+10) (200+100) = 10% can also be calculated

When n = 1, B is a common acid with a relative molecular mass of 98 and C has a relative molecular mass of 120. Then the chemical formula of B is H2SO4, the relative molecular mass of A is 40, and the chemical formula of A is speculated to be Mgo.

B: H2SO4 sulfuric acid.

The relative molecular mass of A is 40 (MGOs), and the chemical formula of A is MGO

Water is generated, so it is not elemental magnesium that reacts with sulfuric acid.

A: The relative molecular mass is 40, the chemical formula MGO (magnesium oxide), B: H2SO4 (sulfuric acid).

C: MgSO4 (magnesium sulfate).

Lengthen the catheter and pass it through a sink of ice-water mixture, then try to ignite it at the tail.

If it is Beibei's statement, then there will be no cured wax on the inner wall of the catheter, and it will be ignited If it is Fang Fang's statement, then there is cured wax, but it will not be ignited If it is Tingting's statement, then even if there is cured wax, it will also be ignited.

If it is CO, the flame will be light blue, and if it is wax vapor, it should be yellow.

Properties of salt: 1: The chemical equation for salt to react with a certain metal:

FC+CUSO4====CU+FESO4 Corresponding use: it is hydrometallurgy, which is used to make metallic copper! 2：

Properties of salt: can react with the base to reflect the chemical equation that occurs: Na2CO3 + Ca(OH)2=CaCO3 +2NaOH Corresponding use:

It is used industrially to make alkali NaOH

1. The salt reacts with the acid to form another salt and another acid. For example: Na2CO3+2HCl=2NaCl+H2O+CO2

2. The salt reacts with the alkali to form another salt and another base. For example: Na2CO3 + Ca(OH)2=CaCO3 +2NaOH

3. Salt reacts with salt to form two other salts. For example: BaCl2 + Na2CO3 = BaCO3 + 2NaCl

The reactants are required to be accommodating).

After graduating from college, I suddenly found that such a simple problem had to be thought about for a long time, and I really didn't know what I used to do with a bunch of chemistry and a bunch of experiments I did now.

Summary of chemical equations and phenomena in the third year of junior high school.

(Relative atomic mass: ca-40 c-12 h-1 o-16) solution: Let the mass of calcium tablets that need to be eaten every day be x.

C6H11O7)2Ca, the mass fraction of calcium is:

x A: You need to take calcium tablets every day.

..The whole process.

(1)120s

2) Omitted. 3) The mass fraction of calcium carbonate in the scale is x

caco3---co2

200x66100:44=200x:66

Solution x = 75%.

The mass fraction of calcium carbonate is 75%.

Some of them are not, you wrote in the question: chemical changes are generally manifested in color changes, gas releases, precipitation, etc., which generally exist, and some are physical changes, and chemical changes are the generation of substances that were not originally there.

Not necessarily, the most fundamental thing in a chemical reaction is that there is something new"substance"generated, the physical change is simply a change in the state of matter.

Some physical changes are also color changes, such as oxygen becoming liquid oxygen, which is pale blue.

1. Concentrated sulfuric acid.

It can react with zinc, and conditions (heating) are required at this time, and concentrated sulfuric acid is not only expressed.

Dilute sulfuric acid is acidic, and strong.

oxidizing, and the product is not the same as dilute sulfuric acid.

zn+h2s

o4=znso4

h2zn+2

H2SO4 concentrate) = ZNSO4+

SO2+2H2O (there is a heating symbol in this reaction).

2. Most of the qualitative pH values such as litmus, phenolphthalein originated from colored flowers, and acid and alkali can be estimated according to their reaction after encountering acid and alkali. And litmus is exactly like this, because litmus turns red when it encounters acid, and turns blue when it encounters alkali, it can be used.

Red litmus test paper.

to verify whether a solution is alkaline, if so, the test strip will turn blue; Similarly, you can use a blue litmus test strip to verify that a solution is acidic, and if so, the test strip turns red. (a method: Yes.)

The glass rod takes up a small amount of the solution and drops it on the test strip) of course, the litmus solution itself is purple.

3. Sulfurous acid.

H2S03) sulfuric acid (H2SO4) first of all, the valence state of sulfur in the two substances is different, +4 in sulfurous acid, and +6 in sulfuric acid;Sulfurous acid is less acidic than dilute sulfuric acid; Sulfurous acid is unstable and easily decomposes into water and.

Sulfur dioxide. Sulfuric acid, on the other hand, is very stable; Sulfurous acid will react with O2 when left in the air for a long time and become dilute sulfuric acid.

4. React with flame color.

5. Clarify lime water.

Calcium hydroxide. The aqueous solution, when it encounters a small amount of carbon dioxide, will form calcium carbonate precipitates; In the event of an excess of carbon dioxide, the resulting calcium carbonate precipitate reacts with the excess carbon dioxide to form a mixture.

Calcium bicarbonate. Calcium bicarbonate is soluble in water.

Equation: Ca(OH)2+CO2=

caco3h2o

caco3+co2+h2o=ca(hco3)2

I know some of these things about ninth-grade chemistry, and I don't need to fully understand them, of course, my advocacy is like this, you still have to take the high school entrance examination, so I won't give you too much to say about this.

Concentrated sulfuric acid and zinc flakes can only react on the surface, forming a mysterious oxide protective film that prevents the reaction from proceeding;

Physics includes light, heat, sound, electricity, and electricity, and the one you are referring to is the category of light, and there can be physical changes that are not pure in chemical changes, but there are never chemical changes that are impure in physical changes, remember.

;For the weight gain (which is the weight of sulfate, then there is hydrogen 2, then find hydrogen as.

People in 9th grade, what molar quality are you talking about. I don't think they can understand what they are talking about in the 9th grade, and I am also in the third year of junior high school, so I will tell you the idea, the amount of hydrogen produced is only related to the amount of dilute hydrochloric acid, you can directly write any equation and use it to calculate the quality of hydrogen.

Upstairs bai, the answer is not comprehensive. Sulphur dioxide can also make the clarified lime water turbid. The gas body should be collected first, and the whole plate should be passed.

If there is no change in the solution of potassium permanganate, it means that there is no sulfur dioxide. Then use clarified lime water. 2. Put a gas collector cylinder in the playground, and cover it with glass after a while. 3. That's because the outer flame is in direct contact with oxygen, the oxidation is violent, and the temperature is high.

this topic.

It's very simple, don't use the mass bai fraction of iron at all, the question itself is a mystery and a void, hehe, assuming that the mass of fes is m, then the mass of daofebr2 is also m; Then the mass fraction of BR is 2m=, which is the correct answer.

A is methane, B is water, C is carbon dioxide, D is carbon monoxide, E is hydrogen, F is copper oxide, G is elemental copper, and H is iron oxide.

i is iron. The equation will not be written.

The main thing to know here is that the products produced by the incomplete combustion of methane include carbon dioxide, carbon monoxide, and water. Hope it helps.

Copper sulphate is blue and the first one can be seen.

Sodium sulfate, sulfuric acid, and sodium hydroxide are dropped into copper sulfate respectively, and the precipitation is produced by sodium hydroxide, and the sulfuric acid test tube is heated.

The rest is sodium sulfate.

The first question, A can be counted right, steelmaking should be filled with air (so it can also be miscalculated, look at it) B is right, don't explain it... c False, oxygen itself does not burn, is not flammable, and is combustible.

d Wrong, a little bigger, specific high school will learn.

The second question A is also right or wrong, the sufficient amount of oxygen is carbon dioxide, and the insufficient amount is carbon monoxide B to C is not to explain D wrong, the air is changed to oxygen, and iron is only oxidized but not burned in the air.

1b, the physical properties of oxygen. a, oxygen is flammable, c, the same as left, d, gases with a relative atomic mass of less than 29 are less dense than air (the most golden thing).

2b, c, d are all correct. A, this is a conclusion, not a phenomenon.

Question 1, b Explanation: aAt high temperatures, oxygen reacts with copper to form copper oxide cOxygen is a combustible, not a combustible dThe density of oxygen is 32 at room temperature and pressure, and the density of air is 25

1. The ionization formula of acid: hx====h+ +x-2, the ionization formula of alkali: moh====m+ +oh-3, the total number of positive ion charges carried by cations in alkali solution is equal to the total number of negative ion charges carried by anions, so the alkali solution is not electrically external.

4. The alkaline substance can be added to increase the alkalinity of the solution; The addition of acidic substances can increase the acidity of the solution.

Although the score is very tempting, the question is very simple, but it is too troublesome to type...

Also, I seem to be talking about high school ......Sorry, but it's always good to learn more......