50 minutes!! To solve a high school chemistry problem, you need to solve the process and ideas of th

Solution: 5

Let the mass of Nabr be X, and the mass of CaCl2 be Y2Nabr Cl2 br2 2NaCl MX

x＝cacl2＋na2co3＝caco3↓＋2nacly

Y then the quality of NaCl 5

Therefore, in the original mixture, the mass of Nabr, the mass of CaCl2, and the mass of NaCl are 5

The remaining ones are NaCl and CaCl2, and the reduced mass is the difference between the mass of Br and Cl.

nabr---br - cl

xx =cacl2 --caco3yy=

So in the original mixture Nabr= CaCl2= NaCl= This is not detailed. How did you learn chemistry in high school Difference calculation method does not need equations.

The remaining after evaporation is NaCl and CaCl2, and the precipitate obtained after adding sodium carbonate solution is calcium carbonate.

cacl2 +na2co3 ====caco3 + 2naclx=

2Nabr + Cl2 ===2NaCl + br2 The Nabr NaCl mass in the original mixture was y and z, respectively

yy+z+ z=synchronously solve y= z=

Or use the difference method upstairs.

The correct answer is A

A: The valency of C in C2H5OH is 2X+6+(-2)=0, X=-2 valence.

The valency of C in CH3CHO is 2X+4+(-2)=0, X=-1 valence, and the valency of C is increased and oxidized in the reaction.

B: The CR valency in CR3 is +6 valence, and the CR valency in CR2(SO4)3 is +3 valence, and the valency reduction in the reaction is reduced, which occurs.

Reduction reaction. C: The oxidation of the oxidant in the redox reaction is stronger than that of the oxidation product, CH3CHO is the oxidation product, and CRO3 is the oxidant.

D: C2H5OH is converted into CH3CHO, and for every 1mol of ethanol reaction, there is 2*[(1)-(2)]mol electron transfer.

The valency of organic matter is generally difficult to determine, so it is better to determine it by other substances, here.

CR changes from +6 to +3 valence, and the valency decreases, so CRO3 is used as an oxidant, and C2H5OH is used as a reducing agent here, which is oxidized. A correct.

CRO3 in b acts as an oxidant and a reduction reaction should occur.

C. CRO3 is used as an oxidant, C2H5OH is used as a reducing agent, and CH3CHO is an oxidation product, so oxidation: CRO3>CH3CHo

D. From the reaction equation, N(C2H5OH):N(CRO3)=3:2 and N(C2H5OH)=1 mol

i.e.: 1:n(CRO3)=3:2 N(CRO3)=2 3 mol

Cr changes from +6 to +3 valence, and the transferred electrons = (6-3) 2 3 = 2 mol

Let me tell you a useful concept - in organic matter, h is +1 valence, and o is -2 valence.

C is -2 valence, and C is -1 valence in CH3CH, that is, it is oxidized. A correct.

Medium CR is +6 valence, and Cr2(SO4)3 is +3 valence, that is, it is reduced. b error.

Oxidized by CRO3, i.e., CRO3 is more oxidizing than error.

d.From A, it can be seen that 1 mol of C2H5OH transfers 2 mol of electrons (there are 2 Cs); Or if it can be seen from b that 1 mol of CRO3 transfers 3 mol of electrons, then 1 mol of C2H5OH transfer 3 (2 3) = error.

Personal analysis, hope to be useful.

A is correct, B should be a reduction reaction, C is an oxidation product in acetaldehyde, the oxidation of the oxidation product is lower than the oxidation of the oxidant, C is wrong.

d should be 1 mole of ethanol reaction, there will be 2 moles of electron transfer.

2.The element to be reduced in the reaction is Au, and the reducing agent is Na2S2O3.

The sulfur elements in Na2S2O3 are +6 and -2

The sulfur element in Na2S4O6 is +4, +4, +4, -2 from the reaction formula, 2S2O3 S4O6, so the valency of sulfur in the reactant is 2 +6, and the valency of sulfur in 2 -2 products is 3 +4, 1 -2

i.e., +6, +6, -2, -2 before the reaction

+4, +4, +4, -2 after reaction

In this way, +6 +4, each price drop by 2, a total of 4 price drops -2 +4, up 6 price, and the other -2 price does not change the price, which is equivalent to a price increase of 2 in general.

S in Na2S2O3 transfers 4E- to Au.

This problem is easier to solve with the average price state:

Naoh, Au2O3, Na2S4O6 (S average price is average price 2), Au2O, H2O

1.Please fill in the following fields for reactants and products other than AU2O3.

2.The element being reduced in the reaction is the au reducing agent that makes s

3.Fill in the following blanks with oxidant and reducing agent, and mark the direction and number of electron transfers.

Au2O3 4Na2S2O3 is a single-wire bridge electron, pointing from S to gold, which is 4 moelectrons.

I can solve this problem and wait for me to explain it slowly, and the typing is slow, no wonder.

You are mistaken about the valency of sulfur, the valency of sulfur in sodium tetrasulfate is +. Hua Daolong.

The one that can be split into ions in the ion reaction equation cannot be insoluble, and BaCO3 is insoluble.

The ionic equation for c should be BaCO3+2H+ +SO42-=BaSO4 +CO2 +H20

CBACO3 is insoluble, and when writing the ion equation, it should continue to be written as BACO3, and cannot be disassembled into ionic form.

Of course I choose C-pull. Because the product water in C is a weak electrolyte, and carbon dioxide is a non-electrolyte, neither can be rescheduled.

(1) △h0 = 0

There is no chemical reaction here, and there is no change in matter and state.

Its thermochemical equation can be written:

cnh2n+2(l) +3n+1)/2o2(g) -3n+1)/2o2(g)=cnh2n+2(l) △h0

The shifts are: CNH2N+2(L) +3N+1) 2O2(G) = CNH2N+2(L) +3N+1) 2O2(G) H0

So h0=0

2) H is the alkane combustion, H2 and H3 are C (S) and H2 (G) combustion, respectively, which is an exothermic process, and its enthalpy change is less than 0

Yes: h, h2, h3 are all less than 0

3) Take CNH2N+2(L) +3N+1) 2O2(G) in the lower left corner as the starting point and the lower right corner as the end point. If there are two paths, then there are two paths.

The enthalpy is equal in disguise. h = h1 + h2 + h3 and only h1 is greater than 0, the rest are less than 0

The substitution values are (all units omitted): = -

Yes + = +

n=8 The molecular formula is: C8H18

c8h18(l) +25/2 o2(g) →8co2(g) +9h2o(l) △h=

(1) h0 = 0, reason: no chemical reaction has taken place, and the state of the alkane has not changed, i.e., there is no change in heat before and after the reaction.

2) Less than 0 is h, h2,, h3

In this type of question, you have to learn to write about the conservation of electrons and the conservation of atoms, and through the subtraction of these two conservation relations, you will get a formula, so that the basic questions will be based on these formulas. Let me give you an example:

CH3COOH - CH3COO- +H+ : Conservation of electrons means that the positive charge in the solution is equal to the number of negative charges In the acetic acid solution, there is also this electrolysis H2O——H+ +OH- so the conservation of electrons* (charge) is H+ =CH3COO- +OH-

The conservation of atoms is the conservation of atoms c, which is the direction of the electrolysis of the solution solute :ch3cooh = ch3coo- In this way, if you subtract the two formulas, you will get a formula: H+ =CH3CoOH +OH - It seems that this has nothing to do with this problem, but you must practice this method well when you go back, find a topic to practice by yourself or ask the teacher to explain it to the system, I am very good at chemistry, but it has been a year and a half, and I only remember some essences The specific steps or something still need you to work your own This is basic Because when we took the college entrance examination, the teacher wrote these conservation relationships on the blackboard every day, as long as you grasp the weak acid, weak alkali, strong acid, weak alkali, and weak alkali and weak salt, and weak alkali and weak acid (the so-called double solution) Come on, I hope you can extend the idea I said and learn chemistry well!!

2 is double hydrolysis to promote water ionization.

4 It should be sodium carbonate with -2 valence ionization, easy to combine with water, promote water ionization1 acetic acid, is weakly acidic, inhibits water point separation.

3. Sodium bicarbonate is weakly alkaline, but stronger than sodium acetate 5, and strong alkali inhibition.

5 The weakest, strong alkali inhibits the ionization of water.

2 is the strongest, is the double hydrolysis that promotes water ionization.

4 and 3 are the same.

1 Acetic acid is weakly acidic and inhibits water ionization.

3 Sodium bicarbonate is hydrolyzed into a weakly alkaline HCO3 ion that promotes water ionization.

The ionization of water is affected by the concentration of external hydrogen ions and hydroxides, and if the concentration of hydroxides and hydrogen ions is greater, the ionization degree of water is weaker.

Analysis: a The starting temperature observed from the diagram is the ambient temperature during the experiment;

b Analyze the temperature change of the measured solution according to the figure;

c Calculated according to C acid V acid = C alkali V alkali;

d. This conclusion cannot be drawn based on a reaction Answer: Solution:

A from the diagram to observe the starting temperature is the first blind of the ambient temperature at the time of the experiment, so the temperature at the beginning of the experiment is 20, so A is wrong;

b From the diagram, it can be seen that the reaction process emits heat, indicating that the chemical energy may be converted into heat energy, so b is correct;

c When the volume of hydrochloric acid participating in the reaction is 30ml, the volume of the base is 20ml, c(NaOH)=(, so c is wrong;

d is only exothermic of the reaction, and other reactions with water generation are not necessarily, so d is wrong;

Therefore, choose B

Select B, according to the diagram, the neutralization reaction occurs per 5 ml of HCl, and the temperature rises: (28-22) 5=degrees, so the temperature of the environmental slag jujube is dismantled as degrees, and A is wrong.

As the amount of HCl in the neutralization reaction increases, the temperature increases, proving that the chemical energy in the reaction can be converted into heat energy. b right.

30 ml HCl and 20 ml NaOH emit the most heat, proving that the reaction is the most complete. So the amount of beam nuclei of the substances HCl and NaOH in 30 ml HCl and 20 ml NaOH solution is equal. When the amount of a substance is equal, the volume of the solution is inversely proportional to the concentration of the quantity.

So the concentration of the NaOH solution is wrong.

This reaction is an exothermic reaction, which does not mean that the reaction to produce water is an exothermic reaction. D false.