"Seven Traps" in the Application of Avogadro's Constant (NA) "Important elements in seawater—sodium and chlorine PPT

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"Seven Traps" in the Application of Avogadro's Constant (NA) "Important elements in seawater—sodium and chlorine PPT

Part One: Knowledge and Ability

Trap 1: Applicable conditions for gas molar volume

22.4 L·mol-1 refers to the molar volume of gas under standard conditions (0 ℃, 1.01×105 Pa). In many questions, the volume of gas under normal temperature and pressure (non-standard conditions) is often set. Students tend to treat it as under standard conditions and make calculations based on n=Vgas 22.4 L·mol-1, and fall into the trap by mistake.

Trap 2: Aggregation state of matter

22.4 L·mol-1 is applicable to gases (either a single gas or a mixed gas). Many questions often include liquid or solid substances that are easily overlooked, such as water, ethanol, salt, etc. Students can easily mistake them for gases and fall into a trap.

For example, under standard conditions, the number of molecules contained in 22.4 L H2O is NA(×).

Trap 3: Quantity (or quality) and condition of matter

The amount (or quality) of a substance has nothing to do with external conditions such as temperature and pressure. Many questions often give the amount (or mass) of a gas substance at normal temperature and pressure, which interferes with students' correct judgment. Some students mistakenly believe that it is impossible to find the number of particles contained in a substance.

For example, at normal temperature and pressure, the number of oxygen atoms contained in 8 g O2 is 0.5NA(√).

Trap 4: The composition of simple substances

In addition to common diatomic molecules, gas elements also include monatomic molecules (such as rare gases), triatomic molecules (such as O3), etc. Students tend to ignore this and fall into traps.

For example, under standard conditions, the number of oxygen atoms contained in 11.2 L of ozone is NA(×).

Trap 5: Volume of solution

When determining the amount of solute contained in a solution, calculations must be made based on "n=cV". Many questions often only give the quantity and concentration of substances, and students can easily fall into the trap of calculating based on 1 L of solution.

For example, the number of Na+ contained in 0.5 mol·L-1 Na2CO3 solution is NA(×).

Trap 6: Solvent composition

When determining the number of oxygen or hydrogen atoms contained in an aqueous solution of a substance, the composition of the solvent water must be considered. Many questions often provide the amount, concentration, and volume of the substance in the solution. Students tend to ignore the composition of the solvent water and fall into the trap.

For example, the number of oxygen atoms contained in 1 L of 0.5 mol·L-1 Na2SO4 solution is 2NA(×).

Trap 7 Number of particles

Particle types generally include molecules, atoms, ions, protons, neutrons, electrons, etc. The number of specified particles in 1 mol is Avogadro's constant, from which the number of molecules, atoms, ions, protons, neutrons, electrons and other particles can be calculated. In many questions, traps are often set up through the conversion of NA and the number of particles (N).

For example, at normal temperature and pressure, the number of molecules contained in 1 mol NaCl and 1 mol HCl is both NA(×).

Seven traps in the application of Avogadro's constant (NA) PPT, Part 2: Navigation of typical examples

[Typical example] NA represents the value of Avogadro's constant. The following statement is correct ()

A. At normal temperature and pressure, 22.4 L CO2 contains NA CO2 molecules

B． The number of electrons contained in 1.7 g H2O2 is 0.9NA

C. 2.24 L H2O contains the number of molecules equal to 0.1NA

D． The volume of CO and C2H4 mixed gas with molecular number NA is approximately 22.4 L and the mass is 28 g.

B - Item A, under normal temperature and pressure, the gas molar volume is greater than 22.4 L·mol-1, then the amount of substance in 22.4 L CO2 is less than 1 mol, which is wrong; Item B, one H2O2 molecule has 18 electrons, H2O2 The molar mass of the substance is 34 g·mol-1, and the amount of 1.7 g H2O2 is 0.05 mol. Then the amount of the substance containing electrons is 0.9 mol, and the number is 0.9NA, which is correct; item C, water is not gaseous under standard conditions. , cannot be calculated using the gas molar volume 22.4 L·mol-1 under standard conditions, which is wrong; item D, the mass of 1 mol CO, C2H4 mixed gas is 28 g, but because the state of the mixed gas (temperature and pressure ), so it cannot be judged whether its volume is 22.4 L, which is wrong. ]

Seven traps in the application of Avogadro's constant (NA) PPT, part three: experience training

1. Assuming NA represents Avogadro's constant, which of the following statements is correct ()

A. The number of electrons transferred when 5.6 g of iron reacts with sufficient hydrochloric acid is 0.3NA

B. At normal temperature and pressure, the number of hydrogen atoms contained in 11.2 L of methane is 2NA

C. Under standard conditions, the number of atoms contained in 22.4 L helium and 22.4 L fluorine is both 2NA.

D. At room temperature, when 2.7 g aluminum reacts with sufficient hydrochloric acid, the number of electrons lost is 0.3NA

2. Use NA to represent Avogadro's constant. Which of the following statements is wrong ()

A. The number of sodium ions contained in 1 L 1 mol·L－1 NaCl solution is NA

B. Under standard conditions, the volume occupied by NA water molecules is approximately 22.4 L

C. The number of anions contained in 7.8 g Na2O2 is 0.1NA

D. When 0.1 mol Cl2 reacts with a sufficient amount of sodium hydroxide solution, the number of transferred electrons is 0.1NA

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Update Time: 2024-11-02

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