Lala!!! A junior high school chemistry problem

Test Center: Calculation according to the chemical reaction equation; Simple Calculations of Solute Mass Fraction Special Topic: Calculation of Chemical Equations

Analysis: According to the chemical equation of the reaction between sodium hydroxide and sulfuric acid and the mass of sodium hydroxide, the mass of H2SO4 in the wastewater can be calculated, and then the quality of the wastewater can be calculated according to the "mass of the solution after the reaction - the mass of sodium hydroxide = the mass of the wastewater taken from", and then calculated according to the mass fraction formula

Answer: Solution: Let the mass of H2SO4 in the wastewater be X, 2NaOH + H2SO4 = Na2SO4 + 2H2O80 9840g 1% x 8098 = 40g 1%x

The solution obtains: x =, the quality of the wastewater taken: 138g-40g=98g, the mass fraction of sulfuric acid in the wastewater = A: The mass fraction of sulfuric acid in the wastewater discharged from the chemical plant is.

Comments: This question mainly tests students' ability to use chemical equations to make calculations

Solution: Let the mass of sulfuric acid be x, the mass of the generated H2O is y, and NaSO4 is zh2SO4+NaOH=NaSO4+H2O

x 4 z y

The solution yields x= , y= , z= The mass of water in sodium hydroxide is the total mass of water, and according to the conservation of mass, it is obtained: 103 + 18 = 40 + H2SO4 solution.

The H2SO4 mass is 81g

So the sulfuric acid mass fraction is about.

It's a bit of a trouble, there may be another way, you can take a look!

fe+h2so4==>feso4+h2↑

So the mass ratio of iron to hydrogen is 56:2

Grams should correspond to grams of hydrogen.

Now there is only a fraction of the ratio, so there is a substance greater than the value of 56:2 that participates in the reaction.

Na is an alkali metal, the reaction is complex, and it is not discussed in junior high school, and it is excluded.

mg is 24:2

al is 18:2

ZN is 65:2

Years of not doing it, I hope I remember the molecular weight correctly ==

So choose D

The mass of CO2 produced is: grams.

caco3+2hcl=cacl2+h2o+co2↑100 73 111 44

x y z column ratio, solved.

x= 20g y= z= calcium carbonate mass fraction in limestone: 20

Mass fraction of solutes in dilute hydrochloric acid:

Mass fraction of solute in the solution obtained after the reaction: Here the mass of 20 grams of calcium carbonate is used instead of the mass of the sample, because there are no reactive impurities that are insoluble in water and cannot be added for calculation.

Solution:1Let the mass of calcium carbonate be X, and the mass of solute in dilute hydrochloric acid is the mass of YCO2: g+146g -

CAC03 + 2HCl = CACl2 + CO2 (rise) + H2O100 73 111 44x y z100 x = 44 73 y = 44 111 z = 44

x=20g y= z=

Mass fraction of calcium carbonate in limestone: 20g * 100% = 90% (the mass of calcium carbonate in the reaction divided by the mass of limestone).

Mass fraction of solute in dilute hydrochloric acid: 146 *100 % = 10% (mass of HCl in reactant divided by mass of dilute hydrochloric acid).

The mass of the solution obtained after the reaction: +146g - z = + 146g - =

According to the conservation of mass, the mass of the reactant is subtracted from the gas).

The mass fraction of the solute in the solution obtained after the reaction: z (the solute in the solution obtained after the reaction is calcium chloride, and the mass of the solution obtained after the reaction is divided by calcium chloride).

CaCO3+2HCl (dilute) = CaCl2+H2O+CO2 reacts like this, right? I haven't been involved in science for a long time, and if the formula is wrong, the following will be ignored directly.

Then, when limestone (i.e. CaCO3 with impurities) is mixed with a dilute HCl solution, only the mass of the escaped CO2 is lost, i.e., the mass of CO2.

Hey, I knew I was going to be answered. Forget it, the skills are not as good as people, let's continue to return to my empty and muddy life......One final word: science is wonderful, uh, alas, alas......

Chemical element PB (lead) People who eat fish containing lead (like in the early days of Japan) will have lead poisoning, which is advantageous for printing fonts, newspapers, and can also make shot put for exercise.

Fluorine, fluorine, fluorine.

1. Barium can be used to make barium swallow for medical treatment, but soluble barium salt is highly toxic.

2. Mercury can be used to catalyze many reactions, but it is highly toxic.

All three parentheses are: fluorine.

Example 1: The water in our natural environment is generally hard water, which contains heavy metal ions that encounter the precipitate of surfactants, so that when we wash clothes, the concentration of surfactants in the laundry detergent will drop to the bottom, and the resulting precipitation will also slip off traces on the clothes. In order to reduce the hardness of the bottom water, that is, to reduce the concentration of heavy metal ions in the bottom water and improve the washing efficiency, it is necessary to add substances that can soften the water to the washing powder.

Sodium polyphosphate is a kind of reagent that can generate complex feeds with heavy metal ions, added to laundry detergent, in the water can be combined with heavy metal ions in water to form water-soluble substances, increase the effective concentration of surfactants, reduce precipitation, so everyone uses polyphosphate as a water softener. But now, because phosphorus causes eutrophication in water bodies, new ones are being studied to soften water bodies. Other softeners that do not cause harm to the environment.

This is what we now call phosphorus-free laundry detergent.

Example 2: The hardness of pure iron is relatively low, which cannot meet the needs of people's daily life, and the addition of C element to pure iron can significantly improve the hardness and mechanical strength of iron, but when too much carbon is added, iron will become brittle and cannot meet the needs of life.

2hg+o2=2hgo 2hgo=2hg+o2 This is a reversible process, if it corresponds to this problem, the first equation is fine;

Because of such a large-scale event, the safety awareness is very strong, although hydrogen is light, but there is a high risk, such a grand gathering, it is not allowed to have potential safety hazards, so the choice of helium, the same is very light, but his advantage is that it is extremely inert, very safe, the only drawback is that the rare gas can be imagined, ** expensive.

Strengthening heat = 2hgo;

2.Hydrogen helium is also much less dense than air, but because hydrogen is flammable, it is easy to be dangerous after mixing with impure air, while helium is chemically stable, non-toxic and non-dangerous. It is filled with helium instead of hydrogen.

2hg+o2=2hgo

Because hydrogen is flammable and explosive, helium is safer.

1) 2 hg+o2=2hgo

2) A: Because the density of helium is also very small, each balloon is buoyant more than gravity and therefore "flies" upwards.