Junior High School Chemistry Solving Troublesome Speed Points Finding Process Finding the Easiest Wa

I guess it's a quality score! The mixture of NaOH and Na2O2, no matter what ratio it is mixed in, in which Na and O appear as a 1:1 number of atoms, so the elemental mass ratio of Na and O is 23:

16 is constant, so when the mass fraction of the H element is 1%, then the Na and O elements account for 99%, where the mass fraction of the Na element is 23 (23+16)*99%=.

It's probably the mass fraction, and I don't tell you the total mass, but how to calculate the quality.

Let the total mass be m

Then the mass of h is.

By the ratio of h to NaOH is the mass fraction, the mass of NaOH is calculated as the mass of NaOH then the mass of NaOH in NaOH is .

Then the Na2O2 mass is.

Then the mass of the Na element in Na202 is fractional.

na%=( (can be calculated with the previous fraction can be more precise but does not affect here).

There's h in Naoh! So the mass fraction of NaOH is 1 (23 16 1) 40

Na2O2 is 60

Let's say there are 100 grams in total! Then the mass of sodium is 100 (23 to 40) to 78) to 13

Solution: Let the mass of water produced by the reaction of 4g of hydrogen with a sufficient amount of oxygen be x.

2H2+O2==Ignition==2H2O

4 364g x4 36

4g xx = 32×4g÷4=36g

A: The mass of water produced by the reaction of 4g of hydrogen with sufficient oxygen is 36g.

Four grams of hydrogen is two moles of hydrogen, and two moles of hydrogen will be combined with one mole of oxygen to produce one mole of water, because the relative molecular mass of water is 18, so two moles is 36. It's very simple.

2H2+O2=2H2O This is the equation The relative atomic masses are h(4)o(32)2h2o(36) Let the mass of water be x, so 4 4 grams = 36 x get x = 36 The mass of water is 36 grams.

1.After mixing, the total mass of the solution is 150g, and it is calculated that it contains H2SO4 = (50g + 100g ) * 12% = 18g

So that, the mass of H2SO4 in 50g of dilute sulfuric acid:

The mass of H2SO4 in the mixture minus 16% of the mass of H2SO4 in sulfuric acid is 18g-100g*16%=2g, so the mass fraction is 4%.

2.Calcium hydroxide is slightly soluble, and the solubility is usually in the following, so"Calcium hydroxide potato brother letter"is sodium hydroxide, then.

After dust bonding, there is a total of NaOH = 250g * 60% + 150g * 20% = 180g, mass fraction = 180g 400g = 45%.

3.After cooling, the crystals are precipitated, and the quality of the solution decreases, which is 100g-10g=90g, so the mass of a in the precipitated solution is calculated to be 18g, plus the precipitated 10g, a total of 28g. Because there is crystal precipitation, the solution is saturated at this time.

So the mass fraction of the solution is equal to the solubility. Therefore, at 20, the solubility of A is 20g, and before precipitation, the mass fraction is (18g+10g) 100g=28%.

1. Inertia is related to mass, not speed.

2. I have done my job. 3-6 have not been studied.

1. Inertia is only related to mass and does not change with speed.

2. The force is divided into horizontal and vertical directions, and the displacement occurs in the direction of the force, so the work is done.

1.Wrong. Inertia is only related to mass.

2.Count as work. You can orthogonally decompose the force above the diagonal angle.

3.There is no necessary connection between them, because the density of an object depends not only on the gap between the molecules, but also on the mass of the molecule.

It can only be said that for the same substance, if the gap between the molecules is larger, the density is smaller; The smaller the gap, the greater the density.

4.OK. Yes.

5.OK. 6.Insoluble bases ionize hydroxide ions in the molten state.

1 Inertia is only related to mass.

2 does not count as no displacement in the direction of the force . Junior high school seems to be decomposed without academic ability.

3 There is a relationship This is the root cause of the difference in density.

4 can not affect each other.

5 NOT solutes will not be reduced.

6 Insoluble alkali can also be weakly soluble in water, but the solubility in water is very small, and they all have the general properties of alkali.

1 Inertia is not related to velocity, kinetic energy is related to velocity.

2. Calculation: As long as the moving distance is not perpendicular to the direction of force, it is considered work.

1. 200 grams of potassium nitrate solution at t, after evaporating 20 grams of water, 8 grams of crystals are precipitated, indicating that the remaining solution at this time is saturated solution, on this basis, 12 grams of water are precipitated after evaporating 20 grams of water, where 12 grams of solute is the maximum mass dissolved in 20 grams of water in saturated solution at t, and solubility is the maximum mass dissolved in 100 grams of water at t, that is: 20g 12g = 100g s

s = 60 g2, saturated solution: m (solution) = p v

At 20, mg ( p v ) g = s (100 + s) s = 100 m (pv-m).

3. If the guess is correct, the solution should be a solid mixture composed of sodium chloride and sodium nitrate: let the mass of sodium chloride in the reactant be x, and the mass of sodium nitrate generated is yagno3 + NaCl = AGCL + nano385

x y x/ x =

y = reaction mixture mass is, so m (sodium nitrate) =

So after the reaction, m (sodium nitrate) =

Post-reaction solution: m(solution) =

100g 40g = 15g m m = 6g so: 10 hours (40g —

s=80g

In the first question, after evaporating 20 grams of water to precipitate 8 grams of crystals, a saturated solution is obtained, and after evaporating 20 grams of water, 12 grams are precipitated, then the solubility at t = 12 20 * 100 = 60 grams 100 grams of water.

The second question is 20, not 200. The mass of the saturated solution = v* and the mass of water = v* -m, so the solubility = m (v* -m)*100.

The third question is to talk about it when you have time.

1.It is saturated when it evaporates again, so there are 12 grams of potassium nitrate in 20 grams of water Formula s 100 = m (quality) m (agent).

Gives s = 60 grams.

2.Solubility is different at different temperatures, so only the solubility of 20 degrees can be calculated, at this time the mass of the solution is m (liquid) = v*, the previous formula changes s (100 + s) = m (quality) m (liquid), and the solubility is obtained as s = 100m (v*p-m) grams.

3.How do I feel about being less conditional??? No, please be smart!

From the law of conservation of mass, m(caCO3)=10g, it can be seen that the amount of carbonate is available m(Na2CO3)=. Then the mass fraction of the original solution can be known as.

In this problem, first find the mass of the precipitate according to the law of conservation of mass, 14 + 96-100 = 10 grams, and then find the mass of the sodium carbonate solute according to the mass of calcium carbonate, and then divide the solute mass by 96 grams.