Chemistry questions for the first semester, one chemistry question for the third year of junior high

Because hydrogen is pure, there will be no popping sound if you have ordered hydrogen should.

You know, I clicked, and I removed my thumb from the mouth of the test tube, and there was no explosion when I lit it. Sound.

Only oxygen can be identified with sparks, and burning sticks of wood will burn when they enter the oxygen.

If it burns more violently, it will go out in CO2 and will continue to burn in the air.

1) False. CH4+O2==CO2+2H2O(conditional ignition)2) False. CO2 + 2MG = = 2MGO + C (Conditioned Ignition) 3) Wrong. For example, a mixture of ozone and oxygen.

4) Metals and non-metals refer to elemental substances, but compounds such as caCO3 are not.

Belong. 5) Right.

6) Wrong, the main components of petroleum liquefied gas are propane and butane, if leaking, one.

When it encounters an open flame, it will**.

B, no, I'm sure.

a, unchanged in the air, extinguished in carbon dioxide, and re-ignited in oxygen.

1) False. ch4+2o2=co2+2h2o

2. False. CaCO3+2HCl=CaCl2+CO2+H2O3, false. Red phosphorus and white phosphorus.

4. False. Oxide.

5, Yes. 6. Wrong, open flames are strictly prohibited.

Question 1 should choose B, Question 2 should choose B (after all, the change in the brightness of the flame is much more obvious than the change of Mars), Question 2, 2 (if there is oxygen in the reactant, it is also possible to form oxides), 3 (substances composed of the same element such as sulfur, which have S2, S4, S8; There are mixtures of O2 and O3 in oxygen), four (substances that are not metals may be semiconductors composed of transition elements, etc.), "iodine" in the iodine content refers to potassium iodate), six (soapy water should be used to check whether there are no bubbles, and it is easy to cause it with an open flame).

Then try it one by one, the mass ratio of carbon to oxygen in option A is uncertain, but there is a range, only the CO time ratio is 3:4, only oxygen is 0, so the range is 0. And in this range, so the option is compliant.

The ratio in option b is definite, is, not true. 3:8 in option c is not in line with the topic.

The ratio in d is also a range, it is 3:8 when there is only CO2, and 0 when there is only oxygen, so it is 0, not in it, it does not match.

To sum up, option A is the correct answer.

C:O=3:4 in CO, C:O=3:8 in CO2, so BC is excluded, and C:O<3 8 in D phase A

Shangjingyou Internet café children's paper is very useful.

Select B.

This question examines the chemical properties of iron and aluminum.

Iron and aluminum are chemically reacted with hydrochloric acid to form water-soluble salts FeCl2 and AlCl3;

When the caustic soda solution is added to it, Fe(OH)2 and Al(OH)3 are formed, and the properties of these two substances are investigated here, ferrous hydroxide is white, but it is generally difficult to see, and it is often seen light green.

Because there is oxygen dissolved in the solution and the reaction system (open system) and the outside world there is a material exchange and energy exchange, and the oxygen in the air is constantly dissolved into the solution, and the newly formed ferrous hydroxide is quickly oxidized to iron hydroxide, so it is difficult to observe the formation of white ferrous hydroxide precipitation during the experiment, and only the mixture of oxidized ferrous hydroxide and newly formed ferrous hydroxide can be seen: some gray-green flocculent precipitates. When all are oxidized, a dark brown flocculent precipitate is generated

4fe(oh)2 + o2 + 2h2o = 4fe(oh)3

When heated, it gradually decomposes into iron oxide:

2Fe(OH)3 ==Fe2O3+ 3H2O(heating).

Aluminium hydroxide Al(OH)3, is the hydroxide of aluminum. It is a kind of alkali, because it has a certain acidity, so it can also be called aluminic acid (H3alo3), but when it reacts with the base, metaaluminate is formed, so it is usually regarded as metaaluminic acid monohydrate (halo2·H2O). Soluble in inorganic acids and alkaline aqueous solutions, insoluble in water and ethanol.

The alkaline solution in this question has no aluminum hydroxide precipitation).

From the above analysis, it can be seen that in the end, only Fe2O3 remains, because the mass before and after does not change, and the iron does not change, and there is aluminum and iron in the original alloy, and now it has become only ferric oxide, so the content of aluminum should be the same as the oxygen content in ferric oxide. From the fact that the mass in the question is still 2g, it can be seen that the content of o is equal to the mass fraction of aluminum in the primary alloy, that is:

30% from Fe-Al to Fe2O3; Fe quality does not change, Al quality is O quality; So the AL is: 48 160.

Hehe, in fact, you want to be complicated! The reddish-brown precipitate is Fe2O3 after cauterization, according to the relative atomic mass of 70 of the iron of two grams So according to the conservation of mass, iron also accounts for 70% of the alloy, so aluminum accounts for 30%, choose b Related chemical formula: Fe + 2HCl = H2 (gas) + FeCl2 2Al + 6HCl = 2AlCl3 + 3H2 (gas) FeCl2 + 2NaOH = Fe (Oh) 2 (white precipitate) + 2NaCl

AlCl3+3NaOH=Al(OH)3 (white precipitate)+3NaCl 4Fe(OH)2+2H2O+O2=4Fe(OH)3 (reddish-brown precipitate) 2Fe(OH)3=Fe2O3+3H2O Actually, these chemical formulas are useless, but if you want it, I'll give it! There will be a lot of false information in science questions, and you have to learn to distinguish them in order to get them right! I wish you the next level of achievement!

Let's pick it!

Solution: (1) The mass of CAC2O4 generated by 10ml of blood conversion is X.

cac2o4+h2so4=caso4+h2c2o4x

Punch this round 128 x=90

x=2).

Mass of ca per liter of blood sample = (1000 10).

88mg＜100mg＜108mg

The blood sample has normal calcium levels

Answer: The mass of CAC2O4 generated by the transformation of 10ml of blood is 100mg per liter of the blood sample, and the calcium content of the blood sample is normal

This is the question of the third year of junior high school. Nima, for Mao, we learned it in the second year of junior high school... Chemical poisoning is quite deep.

Mass fraction = mass of solute (mass of solute + mass of water) 80g in 15% sodium nitrate solution. Mass of solute = 80 * 15% = 12 The first type: mass fraction = 12 (80 + 20) = 12% The second type:

Mass fraction = (12 + 20) (80 + 20) = 32%.

(!Add 20 grams of water 80*15% (80+20)=12%.

2) Add 20 grams of sodium nitrate (80*15%+20) (80+20)=32%.