Chemistry in the third year of junior high school within 2 hours

The mixture is not unclean, it is just impure, in fact, there are many reagents that are mixtures, such as aqua regia.

1, Mix 2, Pure 3, Pure 4, Pure 5, Mix.

Dissolution filtration. Because usually chemical reactions use pure substances.

There are many ways to do this.

Dissolution filtration separates soluble and insoluble.

Fractionation separates two reagents with different boiling points.

Centrifugation is usually the separation of components in the blood.

And many more ...

1. A mixture is one that contains more than one compound or element, and it is not necessarily unclean, for example, iodine is a mixture, because it contains alcohol and iodine.

2 mixtures have 1 2

3. Add water Salt will dissolve.

4. Filtration: It is suitable for solid-liquid separation.

Heating is suitable for substances containing gases that can be completely evaporated or reflect all of the gases generated.

1. A mixture is a synthesis of a variety of pure substances, not necessarily unclean substances, such as sugar water mixed with sugar.

2 (1) Mix 2 Pure 3 Pure 4 Pure 5 Mix.

3 Tolerant of water, salt can tolerate iron, but not iron.

4 That's too much

1.A substance consisting of two or more substances: not necessarily, sugar water.

2.Mix, pure, pure, mix, pure, 3magnet, put in the water.

I only know this, I don't know if it's right or not, it's okay to refer to it.

1) The basis for confirming that the precipitate has been washed is that it is washed and filtered again, and the phenolphthalein reagent added to the filtrate will not turn red, that is, the filtrate does not contain sodium hydroxide, indicating that the previous step has been washed.

2) Both barium chloride solution and calcium chloride solution can react with the sample solution to form a precipitate, but the results obtained with barium chloride solution are more accurate than those obtained by calcium chloride Wakaba because:

The use of barium chloride solution is certainly a little excessive, and will produce a barium carbonate precipitate, and it will not react with sodium hydroxide.

The use of calcium chloride solution is definitely a little excessive, which will form a barium carbonate precipitate, and at the same time will produce a slightly soluble calcium hydroxide with sodium hydroxide, which will affect the quality of the precipitate, so the use of barium chloride solution has a higher accuracy.

Because barium chloride reacts with sodium carbonate to form sodium chloride and barium carbonate precipitates. Therefore, there will be sodium chloride on the barium carbonate, so to check whether the barium carbonate is clean, as long as the presence of chloride ions in the last washing solution is checked.

1) Answer: Add silver nitrate to the last washing solution, and no precipitation is generated, which means that it has been washed.

In addition, the mass fraction of sodium hydroxide is determined by the mass of the precipitate in the question. Therefore, the selected substance must try to precipitate the carbonate ions completely, so that the calculation is more accurate. From the title, it can be seen that barium chloride is better than calcium chloride, so barium chloride can precipitate carbonate ions more completely, that is, the solubility of barium carbonate is smaller than that of calcium carbonate.

2) Answer: Barium carbonate is more difficult to dissolve in water than calcium carbonate.

1) Drop a few drops of phenolphthalein solution into the filtrate and observe the color of the solution. If the solution turns red, the precipitate has not been washed clean.

2) The calcium hydroxide produced by the reaction of calcium chloride and sodium hydroxide is slightly soluble, which will affect the observation of precipitation.

1 (phenolphthalein added to the filtrate does not change color) 2The calcium hydroxide produced when calcium chloride is used is a microscopic substance and partially dissolved.

At the beginning of the experiment, piston B is turned off, and the gas mixture is allowed to enter through the catheter orifice, and the resulting pure gas escapes from tube C (assuming the reaction is fully carried out), at which point the escaping gas is CO

After the gas mixture is passed, piston A is closed and piston B is opened, so that the dilute hydrochloric acid in the separating funnel enters the jar, and the escaping gas is CO2

3. Write the chemical equation of the above reaction - CO2 + Ca(OH)2 = CaCO3 + H2O; 2hcl+caco3=cacl2+co2+h2o

It's CO that's starting to come out.

CO2 + Ca(OH)2 = CaCO3 + H2O The other time it comes out is CO2.

caco3+2hcl=cacl2+h2o+co2↑

20.There is a mixture of CO2 and CO, and in order to separate them, some students designed an experimental apparatus as shown in the figure. In the picture, the flask contains a calcium hydroxide solution, and the separating funnel contains dilute hydrochloric acid.

At the beginning of the experiment, piston B is turned off, and the gas mixture is allowed to enter through the catheter orifice, and the resulting pure gas escapes from tube C (assuming the reaction is fully carried out), at which point the escaping gas is CO

Explanation: If the carbon dioxide reacts completely with the clarified lime water, the carbon dioxide in the mixed gas of carbon dioxide and carbon monoxide is reflected, and only the carbon monoxide is left without reacting with the clarified lime water, and only carbon monoxide escapes).

After the gas mixture is passed, piston A is closed and piston B is opened, so that the dilute hydrochloric acid in the separating funnel enters the jar, and the escaping gas is CO2

Explanation: After the reaction is completed, calcium carbonate is left and reacts with dilute sulfuric acid to form carbon dioxide).

3. Write the chemical equation of the above reaction: CO2 + Ca(OH)2=CaCO3 + H2O (question), CaCO3+2HCl=H2O+CO2 +H2CO3 (question).

Precipitate barium carbonate, according to the equation, the mass of sodium chloride and sodium carbonate are generated, the mass of primary sodium chloride is 100+, and the solute mass fraction in the solution after the reaction is (

Barium chloride and sodium carbonate produce barium carbonate precipitates. This, the relative molecular mass of barium carbonate is 197, then precipitated into a molar mixture of sodium carbonate, that is, gram of original sodium chloride gram of newly generated gram solute cogram. The quality of the solution is.

The precipitate is barium carbonate, the relative molecular weight is 197, the precipitate mol, the sodium carbonate gram in the original mixture, and the sodium carbonate of the original sodium chloride gram reacts into sodium chloride gram. The mass of the solute total gram solution is 100+, and the solute mass fraction is (

The precipitate is barium carbonate, and the relative molecular weight of barium carbonate is 197, then the precipitate is mol, that is, the carbonate is mol, and in the original mixture, sodium carbonate mol, that is, grams, then the original sodium chloride grams. Later, moles of sodium carbonate reacted into sodium chloride, i.e., grams. The solute totaled 20 grams.

In c is oxygen. A is a hydrogen peroxide solution, B is water, D is hydrogen, E is calcium hydroxide, and F is carbon dioxide.

2) (3) H2O=== Water Electrolysis) H2+O2 2It's a bit complicated, hydrogen needs to react with water first, and then (OH)2 + CO2 = CaCO3 (precipitation symbol) + H2O

I wrote it myself, it must be right.

A is hydrogen peroxide H2O2, B is water H2O, C is oxygen O2, D is hydrogen H2, E is calcium hydroxide Ca(OH)2, and F is carbon dioxide CO2

A is hydrogen peroxide, B is water, C is oxygen, D is hydrogen, E is calcium hydroxide Ca(OH)2, and F is carbon dioxide (CO2).

a. Hydrogen peroxide, b. Water, c. Oxygen, d. Calcium hydroxide, e. Carbon dioxide, f. Carbon monoxide.

1. Calculated according to chemical equations;

2. Calculated according to the chemical formula:

mg ~ mgo

x column formula to find x

3. Use the mass fraction of an element in the compound to find:

Disagree with the views upstairs.

This question depends on whether the container is pure oxygen or air; I can't count the air, so let's assume it's pure oxygen.

According to the reaction formula: 2mg+o2=2mgo, it is easy to see that a magnesium atom absorbs an oxygen atom, considering the atomic weight mg is 24 o is 16, so the mass of oxygen absorbed by these magnesium is converted, and the mass of oxygen absorbed by weight is increased); The total weight of magnesium oxide produced is 8g;

If the landlord still doesn't understand, please follow up

（1）mg：o2=2:1

Oxygen is required for complete combustion of mg, which is the added weight, so the weight of solid powder is increased by (2) mg:mgo = 1:1

The amount of the substance of mg is also for the mass of MGO is 8g, and the weight gain of solids (3) is analyzed in MGO: O = 1:1

Therefore, the amount of matter of o is increased, for, and gained.

2mg + o2 --2mgo：m(mg):80 = :48；m(mgo)=8g

MG: 24 40;m(mgo)=

It is necessary to lose electrons and get 04mol electrons; m(mgo)=

The formula after trimming: 2mg + O2 = ignition = 2mgo

So get solid.

Depressed, the culture of answering is too high, first look at the chemistry textbook of the third year of junior high school and then answer, okay? What mol, which version of the textbook has this?

Let me talk about it: First, review the topic.

The surface is polished, that is to say, this is pure magnesium, and it is completely burned in a closed container with a sufficient amount of oxygen, which means that there is only one reaction that occurs, that is, 2mg+O2=2mgo

Second, the method of problem solving.

Method 1, equation calculation.

Solution: Let the mass of magnesium oxide produced by the reaction be x

2mg+o2=2mgo

x48/x=8g

Method 2, Conservation of Mass.

The increased mass is the mass of the oxygen element, and the method is similar to the equation method 3, using the mass ratio.

Find the mass of oxygen in the MGO, where magnesium is accounted for.

1.When pure oxygen.

2mg+o2=2mgo

mg=24 , mgo=40

So gain weight. 2.If there is CO2.

2mg+o2+2co2=2mgco3

1) CO2 is sufficient, and the weight gain at this time is 12g

2) Gain weight when CO2 is insufficient.

Method.

1. According to the principle of mass conservation of the reaction equation, the difference between the mass of the generated magnesium oxide and the mass of the magnesium strip is calculated.

Method. 2. Calculate how much magnesium there is in grams, and the ratio of oxygen to magnesium in magnesium oxide is one to one, and then multiply the oxygen number by 16

The third I can think of is not suitable for your grade, so I can only ask a master to come out.

From the analysis of mass conservation, 1. Since this reaction is a chemical reaction, the weight gain of the solid powder is the mass of oxygen consumed by the complete reaction of the magnesium strip. 2. The mass fraction of oxygen in magnesium oxide is used to calculate. 3. The mass ratio of oxygen and magnesium in the chemical formula of magnesium oxide is used to calculate.

There are three kinds of chemical calculation problems, can I use one of them? The essence of any method is the conservation of mass.

Equation: 2mg+o2==2mgo

1.The mass of the weight gain is equal to the mass of oxygen involved in the reaction = * 1 2 (reaction ratio of mg and O2) * 32 =

2.The mass of the weight gain is equal to the mass of the MGO minus the mass of MG = *3The mass of the weight gain is equal to the mass of the o of the MGO = * 32 80 =