Chemistry in the third year of junior high school Analysis

15:b Analysis: Dilute sulfuric acid is the same mass, so the mass of hydrogen produced after full reaction is the same. Therefore, a and d are excluded.

Because of the activity of the metal: mg zn fe, (when producing hydrogen of the same mass) mg must be reacted first, followed by zn and fe, so b is chosen.

16: C analysis: A, according to the image, it can be seen that the ordinate represents the mass of hydrogen, the abscissa represents the time, the slope represents the speed of the reaction, the slope of M is larger than N, so the speed of M is faster than N, so M is more active than N, so A is wrong;

B. According to the image, it can be seen that M produces more hydrogen and N produces less hydrogen, and the hydrogen produced by the two metals has different qualities, so the volume is different, so B is wrong;

C and M produce more hydrogen than N, and the metal with the same valence state reacts with a sufficient amount of acid, and the larger the relative atomic mass, the less hydrogen is produced, indicating that the relative atomic mass of N is larger, so C is correct;

d. If the two reactions consume the mass of hydrochloric acid, the mass of the displaced hydrogen is equal, and the mass of the hydrogen produced should be the same, and it can be seen from the image that the mass of the hydrogen produced is not equal, so D is wrong, so C is selected

17: No option (I don't know how to choose), but there must be extra iron powder in the correct answer, and the copper and silver that have been replaced!

Solution: In NF3 the nitrogen element is +3 valence, let the valency of the F element be x, according to the algebraic sum of the positive and negative valencies in the compound is 0, then.

3）+x×3=0

The solution is x=-1

Fluorine? Isn't it -1? Got the title wrong!

If it is n, it should be d

If it's not a competition question, choose D, the question stem is given the conditions, otherwise the valence is not 0.

Let the valency of element n be x, and the algebraic sum of positive and negative valencies in the compound is 0, then.

1）x3+×=0

The solution is x=+3

So choose D

Are you talking about nitrogen or fluorine? If it's fluorine, isn't it given, it's -1 valence, and if it's nitrogen, it's +3 valence, which is calculated according to the positive and negative sum of the valence of the compound.

Since the sum of the valencies of the compounds is 0.

Valency of nitrogen + valency of fluorine (-1 each, three in total, i.e. -3) = 0

So the valency of nitrogen is +3

n is +3 valence.

The valency of the n element can be set to x, then according to the algebraic sum of the valency of each element in the compound is zero, there is.

x+(-1) 3=0, find x=+3

d, let its valency be x, according to the principle that the algebraic sum of the valency of each element in the compound is zero: x+(-1*3)=0, x=+3 is calculated.

According to the algebraic sum of positive and negative valency is 0: (-1) 3+x =0, the valency of nitrogen is found to be +3 valence.

The valency of NF3 is 0

Then let the valency of nitrogen be x

x+3*-1=0x=3

+3 valence; I choose CFrom the positive and negative valency equal to 0, the valency of n can be obtained as 0.

+3 valence; Let the valency of nitrogen be x. x=-1*3

According to the algebraic sum of valency is zero, it should be +3 valence, so d is chosen

Nitrogen is +3 valent and fluorine is -1 valent.

D+3!

Because the valency of NF3 is 0, f is -1 and f3 is -3So the nitrogen element is +3

1.The molecules are constantly moving in random motion.

I'm not sure about this, you can tell me if you know it) Paint, synthetic alloy 3(1) Quicklime (because quicklime is dissolved in water and exothermic CaO+H2O=Ca(OH)2) (This our teacher said that it can be remembered: quicklime is dissolved in water and exothermic, so it is cooked and produces slaked lime) Salt (there can be no soda ash.)

Because soda ash is Na2CO3, there are carbonate ions, and carbonate ions will produce calcium carbonate to produce white precipitate when they encounter calcium ions).

2) agno3+nacl=agcl +nano3 I'm a junior high school student, maybe something is wrong, please advise! Hope you know the answer and tell me I'm doing it wrong, thanks!

1.Drip the ink into a glass of water, and the water will soon turn black, indicating that (the ink is diffusive) 2 iron is easy to rust in humid air, which is mainly because (2fe + o2 = 2feo) (expressed by chemical equations), the ways to prevent iron rust are (paint it) (write one) 3A white powder is available, which may be composed of one or more substances from table salt, soda ash or desiccant (the main ingredient of quicklime).

In order to study the composition of the white powder, the following experiments were carried out: (1).Put part of the powder into the beaker, add an appropriate amount of water and stir it fully to obtain a clear solution, the temperature of the solution increases, add phenolphthalein test solution dropwise, the solution turns red, and obtain:

The powder must contain (soda ash) and possibly (table salt). （2）.Add excessive dilute nitric acid dropwise to the clear solution in (1), and then add silver nitrate solution dropwise, and find that there is a white precipitate generated, please write the chemical equation of the reaction (NaCl+AgNO3=AGCL+Nano3).

1.Molecules are motile (diffusion).

2.4Fe + 3O2 + 2xH2O =, paint 3(1) It must contain quicklime, and may contain salt (2) Ca(OH)2+2Hno3=Ca(NO3)2+2H2O NaCl+Agno3=AGCL +Nano3

The first question is the diffusion principle.

The second question is 4Fe+3O2=2Fe2O3 and a layer of antioxidant metal can be plated outside.

The third question is that it must contain soda ash and may contain desiccant.

1. Molecules are constantly moving.

Fe+3O2=2Fe2O3 is painted or oiled to make alloy 3, (1) Ca(OH)2;nacl

2) agno3 + nacl = agcl (there is also a precipitation symbol after it) + nano3

Diffusion of molecules.

4 Fe +3O2=2Fe2O3 copper plating.

Desiccant, soda ash.

agno3+nacl==agcl+nano3

1. Diffusion.

Fe + 3O2 = 2Fe2O3 Brush paint, electroplating 3, (1) there must be quicklime, there may be table salt, must not contain soda ash (2) NaCl + Agno3 = Nano3 + AGCL

224ml* is the mass of oxygen.

According to the chemical equation, the corresponding proportions can be listed to find the mass of calcium peroxide.

It depends on what you're looking for, because after the equation is balanced, you only need to know two known quantities and then find the unknown quantities according to their atomic weights.

As inscribed: Fe2O3+3CO=== (high temperature)2Fe+3CO2160 .112

As long as you know the mass of one side of Fe or Fe2O3, you can find the mass of the other side. If the question requires the mass of CO or CO2, then their atomic weight is required.

Fe2O3+3CO=== (High temperature) 2Fe+3CO2160 84 112 132

a b c d

160 A==84 8==112 C==132 D, where ABCD represents the mass of 4 substances, the known quantity in the title is one, and the unknown quantity is another (set to X), CO and CO2 are not mentioned in the title, so there is no need to calculate them together.

Hello lz.

Isn't the answer that you have already written it in red?!

Oxygen is collected in and out because oxygen is much less dense than water (and insoluble), and the short feed retains oxygen in the upper part of the cylinder, while water is released from the long end of the duct due to oxygen pressure.

If it is reversed, the oxygen will enter from the long end, rise and accumulate at the top, and then escape from the short end in bulk concentrated sulfuric acid drying principle is similar, the purpose of this long in and short out is to ensure that the oxygen passes through the concentrated sulfuric acid in the gas collector cylinder If it is reversed, the concentrated sulfuric acid will be exported from the long port due to air pressure.

In short: long in and short out passing liquids; Short in and long out extruded liquid.