Chemistry problems in junior high school, chemistry problems in junior high school

1. Except for ace, it is all chemical changes. 2d3ab

1. Physical changes; a b

chemical changes; c d e

1) Physical A chemical BCD (C seems to be a biochemical reaction).

2) D is all black powder, a I don't know how to distinguish it, it seems to be hardness.

3) A only has a description of solubility.

1 Physical: A (activated carbon has adsorption) E (calcium hydroxide solubility becomes smaller) Chemical BCD 2D (all black solids) 3A

1. Physical change: a Others are chemical changes.

2. Choose D, because they are all black powder solids.

3. Choose C, because the former is the use, and the latter is the phenomenon.

1 Physical change a c Physical change is that the structure of matter does not change, but simply a change in state or a combination of matter.

Chemical change b d e The structure of the substance changes in chemical change 2 a a looks the same b can be distinguished by taste c the former is black and the latter is reddish-brown by color d the former is red and the latter is black powder both are distinguished by physical properties

3 A b The general properties of acids include chemical properties (acid-base neutralization reactions, etc.) c Hydrogen reduces iron is a chemical change, using the reducing property of hydrogen, the iron wire uses the oxidation of oxygen, d quicklime absorbs water in the air, and a chemical reaction occurs to generate calcium hydroxide.

1 A is the adsorption of activated carbon, which is a change in physical force B is a chemical reaction, and the molecular formula of copper sulfate in crystal water and copper sulfate without crystalline water is different, so it is a chemical reaction c chemical reaction, oxygen is transported through hemoglobin through the chemical reaction and hemoglobin molecule combination, transported to the manifold and then decomposed process. The combination of CO and hemoglobin is the same as the chemical reaction of phenolphthalein when it encounters alkali, but it actually turns red when it encounters hydroxide ions, and a red substance is formed.

2 A Iron and aluminum are not the same appearance color, iron is gray, aluminum is white, iron is hard, aluminum is soft, iron is heavy, aluminum is light, these are all physical properties, it is easy to distinguish by physical properties.

bSmell can be easily distinguished, smell is a physical nature.

c Ferric oxide is insoluble in water and will not make water reddish-brown, while iron oxide slightly melted in water can discolor water.

d Copper oxide and manganese dioxide are both black, and there is no taste, only the density of physical properties is different, and the external ** can not come out, I think the answer is d.

3 A volatilization is a change in physical resources, and iodine wine is rubbed with alcohol is the principle of using iodine to dissolve in alcohol, which is a change in physical resources, and the answer is a

b It has the general property of acid, which means that it also has H ions and is chemical. The concentrated sulfuric acid sucks the water in the air openly, and the solid mass increases, which is a change in physical resources.

Both are typical chemical changes.

d The taste of sulfur dioxide belongs to the physical properties of bulk lime is mainly calcium oxide, which is placed in the air for a long time, first absorbing water in the air into calcium hydroxide, and then absorbing carbon dioxide in the air into calcium carbonate, and after a long time, it becomes calcium carbonate powder, which is a chemical change.

Over, I'm so tired

I suggest you watch a little more book

And do a little more practice.

Not much to say about the other questions, the upstairs is very clear. Let's talk about question 1: change in the molecular formula of water loss. c. The two combine to form a new molecule, D complexation reaction, E to generate calcium carbonate.

1 a e belongs to physical changes and the others are chemical changes.

2 d3 a

1. Physical change: b, d

Chemical changes: a, c, e

2、d3、b

The first question, a b e is a physical change, a is because of the adsorption of activated carbon, adsorbed the pigment in magenta, b is the decomposition of copper sulfate, lost the crystal water, but did not generate new substances, heating lime water will lead to a decrease in the solubility of calcium hydroxide, so turbidity. C, D are chemical changes due to the generation of new substances.

For the second question, D should be chosen, because both of these are black and not easy to distinguish.

The third question, choose A, because A is similar and soluble, B is water absorption, C is redox reaction, D is quicklime reaction with water vapor.

The conversion between the following substances, whether it can be derived, write the chemical formula.

Fe(OH)3 – Feci3 is added to HCl

CO2 CaCO3 passes into Ca(OH)2

KNO3 KCI cannot be converted.

CACAcI2 was added to HCL

Can Fe(OH)3+HCl=FeCl3+3H2OCan CO2+Ca(OH)2=CaCO3 +H2O can not be 1 step.

But I can take a few steps.

Can cao+2HCl=caCl2+h2O