In junior high school, chemistry kids won t help

1 15 grams are all copper, so the mass fraction of copper is 15 20 = 75%2 Let the unknown metal be x, because these three metals react with sulfuric acid are all 2-valent, so the following equation can be listed.

x+h2so4=xso4+h2x 98

x=56 so change the metal to iron.

3 The third reaction is complete, the solute is FeSO4, the mass of the solution is the mass of sulfuric acid plus the mass of iron, minus the mass of hydrogen, and the mass of FeSO4 can be known to be multiplied by 3= according to the previous question

The mass of the solution is 75+ times 3=

So the mass fraction of feso4 is.

15 grams is the copper in the mixture.

The valency of the metal is all plus two.

Write the chemical equation and let the relative atomic mass of the metal be x

Using the first set of data, the reaction mass of sulfuric acid is calculated as 25 times the mass of the metal as the column equation 98 :x==25 times :

The mass fraction of the third solution is the same as that of the first and second times, so the mass of the salt produced and the mass of hydrogen produced are directly calculated by the first time, and the mass of salt is divided by (hydrogen mass).

Mass fraction of copper: 5 15 100% = 75%; A metal is iron, (;

Option 2 can prove it. HCl+NaHCO3=NaCl+H2O+CO2 (gas).

2HCl+Na2CO3=2NaCl+H2O+CO2 (gas).

Because 30 ml of solute mass fraction is equal to hydrochloric acid. Illustrates that the amount of hydrochloric acid is certain and is an equal amount. The ratio of carbon dioxide produced by the reaction of NaHCO3 and Na2CO3 to hydrochloric acid is 2:

1 So it can be judged by the size of the balloon's expansion... Hope you understand ...

The second one is okay, but it has no connection with the comparative trial.

If the leavening agent is sodium bicarbonate, the resulting carbon dioxide will not be "resoluble" in solution;

In the case of sodium carbonate, the resulting carbon dioxide will be dissolved in the solution "again" to deflate the balloon.

If you are comparing sodium bicarbonate, you can compare the size of the two balloons.

However, carbon dioxide and sodium carbonate react very quickly, and carbon dioxide reacts with sodium carbonate at the same time, so it may not be possible to distinguish the size of the two balloons with the naked eye at first. And as the reaction progresses, it will continue to dissolve, become smaller, and it will be more difficult to distinguish in the later stage.

Option 2 is OK, because the reaction between sodium carbonate and hydrochloric acid must be carried out step by step, that is, after the carbonate is completely converted into bicarbonate, the hydrochloric acid added will react with the bicarbonate to form carbon dioxide. Thus, the balloon in the device containing sodium carbonate will bulge first, and the balloon in the device containing sodium bicarbonate will bulge later. ps:

This question generally appears in the first year of high school chemistry.

Yes, just look at the size of the two balloons.

Judging from your title, your title may be written incorrectly, and the first question is estimated to contain barium chloride, not silver chloride.

Let the mass containing BaCl2 be X

BACl2 + Na2CO3 = = BaCO3 + 2NaClx = grams.

Contains 2 grams of BACL.

The mass scramble fraction is.

2.Contains chlorine free rent residual sodium in grams.

The mass fraction is greater than that meets the requirements of industrial salts.

I don't understand hi me.

Solution: 2kClO3=mNO2= ===2kCl+3O2 245 149 96

y(1) According to the law of conservation of mass, the mass of oxygen produced is .

The volume of 32go2 is.

Let the volume be x

m=v, get v=m....Yes density ==

2) Let the mass of KCL be y

= ——y=y

The mass of mnO2 in the mixed solid is.

3) The mass fraction of kclo3 in the original mixture is ——100 = 86%Answer: (1).

2kcio3 = 2kci + 3O2 (the condition of the reaction is heated by the action of mno2), then the mass of the residue is subtracted from the mass of the mixture, because only oxygen is produced as a gas, the mass obtained is the mass of oxygen, and then the mass of KCL can be calculated by using the equation, and then the mass of KCL is subtracted from the mass of the residue to obtain the mass of manganese dioxide. At the same time, the mass of kclo3 can be calculated by equation, and the mass fraction is obtained by dividing the mass of kclo3 by the mass of the mixture.

Because manganese dioxide is a catalyst, the mass remains unchanged before and after the reaction.

First, write the equation 2kclo3==(mno2)2kcl+3o232

m(g) calculates m and then substitutes oxygen volume m =

2kclo3==（mno2）2kcl+3o232

x m calculates x, and then the manganese dioxide mass.

2kclo3==(mno2)2kcl+3o232

y m writes the relation and then substitutes it to find the quality score.

Solution: q put=q*v=

According to the title. Q suck 50%*Q put 50%*

According to Q absorbs C water *m* (t-t0).

m=q water absorption c*(t-t0)=degrees Celsius)] (100 degrees Celsius 25 degrees Celsius) 5kg

Let the child take a look at it first, and if there are any questions, please follow up.

I hope it will be helpful for children.

Such a basic question.

Use w=vq to find the first question.

Find t and w actually.

Then m=w is actually divided by t divided by the specific heat capacity.

The work done is w = m*g*h = 300 * 10 * 14 = 42000 joules = 42kj

3. The maximum power is 70 watts p = f*v so v = p f = 70 (30*10) = meters per second.

This time it took 14 seconds.

A total of 10 transports will be shared in 600 seconds.

It's so hard to type, give it some points.

Total = GH = MGH = 42000J

2 As can be seen from the figure, the power is the largest when each handling of 30kg, and the mass of each box is m1 = m total 30 = 10kg, so each time 30 10 = 3 boxes.

Total p=42000 70s

Can you type out the problem, I can't see it clearly.

1) The figure is not drawn, the rope starts on the movable pulley, and there are 3 sections of rope around the pulley.

2) Because it is the distance that is moved in the direction of gravity w useful = gh = 2 to the power of 4 10 2m = 4 to the power of 10 j

3) W total = w useful 80% = 5 10 to the 4th power j 'f pull = w total s = w total 3h = 5 10 4 power j 3 2m The tensile force of each section of rope is f pull 3

In the third year of the lower junior high school. If I do something wrong, I'll keep thinking about it.

Forehead. The reaction is over.

The answer is 150g

caco3---co2

x 66gx=150g

Responses have been completed. CaCO3 + 2HCl = CaCl2 + H2O + CO2, according to the ratio of CaCO3 to CO2 in this column: 100 x = 44 66, x = 150

Responses have been completed. The formula amount of calcium carbonate is 100

caco3 + 2hcl --cacl2 + h2o + co2 ^x mol mol

x = g = x 100 = 165g

Mass fraction=(165g divided by 200g) x 100%=