High School Chemistry Competition Questions, Senior One Chemistry Competition Questions

b,d difference method m=<255-120> <>=300g from 40 to 70 degrees, if it has been dissolved, it should be reduced by 225g, so 20g is insoluble impurities, a total of kno3 255-20+300*, dissolved at about 55 degrees, the multiple-choice question should be easy and quick to answer.

Let the mass of the water be m grams, then there is the following relationship: (65-20) 100 = (250-120) m

m = 290 g (.)

The mass of dissolved kno3 at 10 degrees is: 20 * 290 100 = 58 g The total mass of the sample is: 58 + 250 = 308 g c correctly 290 g of water at 70 degrees The mass of dissolved kno3 is:

140*290 100 = 406 grams 308 grams Therefore, 20 grams of undissolved substances at 70 degrees are insoluble impurities. A is wrong, B is correct when the mass of KNO3 in the sample is: 308-20 = 288 grams at 55 degrees, the mass of dissolved KNO3 in 290 grams of water is:

100*290 100 = 290 grams 288 grams.

Therefore, at 55 degrees Celsius, all KNO3 dissolves. d correct.

Temperature 10 40 55 70

Solubility: 20g, 65g, 100g, 140g, solid weight: 255g, 120g---20g

From 10 to 40 more soluble solutes 250-120 = 135 g set the mass of the solvent is x grams.

At 40, 100 (65-20) = x 135x = 300 grams.

When 300 grams of water is from 40 to 70, it is necessary to dissolve y grams of solute to be saturated.

100/(140-65)=300/y

y = 225 grams.

Actual from 40 to 70 more dissolved solute 120-20 = 100 grams, 100 less than 225, the solution is not saturated. The remaining 20 grams are insoluble.

Answer B: The sample is mixed with impurities that are insoluble in water.

1.Choose d3 hydrogen nuclei H3 with 3 positive charges, plus 2 electrons, there are still three hydrogen, and only one positive charge remains, written as H3+ (i.e. H2 + H+, H+ is the hydrogen nucleus).

2.If the molecular formula of a gaseous hydride is RHM, the valency of R is -M, that is to say, the outer shell of R can obtain m electrons to achieve the stable structure of the octaposome, that is, its outermost shell has 8-M electrons, so when it loses electrons, it can lose up to 8-M electrons, that is, its highest valency is +(8-m). Let the molecular formula of the most ** oxygenated acid of r be Hxrob, then H shows +1 valence, R shows +(8-m) valence, O shows -2 valence, according to the total valency of the compound is zero, (+1)X+(8-M)-2B=0, X=2B-8+M.

Did you learn so much chemistry in your first year of high school?

The first one: should be d

A allotrope is relative to organic matter, and the molecular formula of both is the same.

b isotopes are relative to elements, with the same number of protons, different neutron numbers (or different masses) of different nuclides of the same element are isotopes to each other.

C particles are not indicated to be molecules, so they cannot be simply expressed by molecular formulas.

The DH2 molecule has two nuclei, while the text says that there are three hydrogen nuclei, so there is one more.

Second: First of all, the negative valence of the r element is known from RHM as -m, so there is the highest positive valence = 8-m, which is known from the sum of the valence 0.

Number of hydrogens*1+8-m=2b

The number of hydrogens = 2b + m-8

The answer is a

1.Pick D. Allotropes are elemental substances composed of the same elements and in different forms. For example, carbon elements include allotropic forms such as diamond, graphite, and amorphous carbon. That is, its object is elemental, not elemental. So a mistake.

An isotope is a group of nuclides that have the same atomic number (i.e., the same number of protons but different masses, i.e., different numbers of neutrons). It is aimed at the elements. The number of h3+ protons is three, and the number of h-protons is one, so b is wrong.

C false. d right.

2.Choose. The molecular formula of the gaseous hydride of a non-metallic element R is rhm, which means that the valency of R is -m, according to the absolute value of the highest positive price + lowest negative price of the non-metallic element = 8 (e.g., the highest positive price of sulfur +6, the lowest negative price -2, 6+2=8).

Therefore, the highest positive valence of r is 8-m, in acid, h is +1, r is 8-m, o is -2, and there are b oxygen atoms in the molecule of the hydrate corresponding to its most ** oxide. So.

Question 1; d If you think about it, nothing else is true. Question 2: a.

In hydride, r is negative, so the most ** r is 8—m, and the valency of the hydrate is unchanged. There is a positive and negative valence algebraic sum of zero to obtain the number of hydrogen atoms + (8-m) = 2b so the number of hydrogen atoms is 2b-8 + m, so choose a