Name: mole, mass, and avogadro’s number
Uploaded: 2020-09-03T13:38:25.000Z
Duration: 1 min 54 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.2.1

Molar Mass

Układ okresowy pierwiastków podaje średnią masę atomową każdego atomu. Jednak próbki makroskopowe zawierają niezwykle dużą liczbę atomów. Dlatego ważne jest, aby użyć jednostki liczącej zwanej liczbą Avogadro.

Liczba Avogadro, wyrażona symbolem NA, jest zwykle zaokrąglana do 6,022 × 1023. Jego wartość jest równa liczbie atomów w dokładnie 12 gramach czystego izotopu węgla-12.

Termin kret, w skrócie mol, jest używany do opisania liczby Avogadro, podobnie jak znany termin tuzin jest używany do opisania ilości 12.

Niemniej jednak kilkanaście różnych przedmiotów może ważyć inaczej, mimo że mają taką samą liczbę przedmiotów. Podobnie mole różnych pierwiastków mają różne masy, ale zawsze zawierają tę samą liczbę atomów. 

Masa w gramach jednego mola pierwiastka nazywana jest masą molową, wyrażoną w gramach na mol. Jego wartość jest liczbowo równa masie atomowej pierwiastka. Stąd definicja kreta pozwala nam liczyć cząstki poprzez ich ważenie. Masa molowa i liczba Avogadro mogą być używane jako współczynniki konwersji.

Można to wykorzystać do obliczenia liczby atomów w 5-gramowej sztabce złota. Średnia masa molowa złota wynosi 196.96 g/mol. Tak więc, aby przeliczyć masę na mole, podziel masę pręta przez średnią masę molową. Następnie pomnóż liczbę moli przez liczbę Avogadro, aby uzyskać całkowitą liczbę atomów w próbce. Tak więc ta sztabka złota zawiera 1,529 × 1022 atomów.

masa cząsteczkowa

Tożsamość substancji jest definiowana nie tylko przez rodzaj zawartych w niej atomów lub jonów, ale także przez ilość każdego rodzaju atomu lub jonu. Na przykład woda, H2O i nadtlenek wodoru, H2O2, są podobne pod tym względem, że ich cząsteczki składają się z atomów wodoru i tlenu. Jednakże, ponieważ cząsteczka nadtlenku wodoru zawiera dwa atomy tlenu, w przeciwieństwie do cząsteczki wody, która ma tylko jeden, te dwie substancje wykazują zróżnicowane właściwości.

Atomy i cząsteczki są niezwykle małe. Dlatego do pomiaru ich makroskopowych ilości potrzebna jest standardowa jednostka naukowa. Mol to jednostka ilości podobna do znanych jednostek, takich jak para, tuzin, brutto itp. Zapewnia konkretną miarę liczby atomów lub cząsteczek w próbce materii. Łacińska konotacja słowa „mol” to „duża masa” lub „luz”, co jest zgodne z jego użyciem jako nazwy tej jednostki. Mol zapewnia połączenie pomiędzy łatwą do zmierzenia właściwością makroskopową, masą nasypową i niezwykle ważną podstawową właściwością, jaką jest liczba atomów, cząsteczek i tak dalej.

Mol substancji to ilość, w której znajduje się 6,02214076 × 1023 odrębnych jednostek (atomów lub cząsteczek). Ta duża liczba, którą można wygodnie zaokrąglić do 6,022 × 1023, jest podstawową stałą, znaną jako liczba Avogadra (NA) lub stała Avogadra na cześć włoskiego naukowca Amedea Avogadr. Stała ta jest prawidłowo podawana z wyraźną jednostką „na mol”.

Zgodnie ze swą definicją jako jednostki ilości, 1 mol dowolnego pierwiastka zawiera taką samą liczbę atomów, jak 1 mol dowolnego innego pierwiastka. Masy 1 mola różnych pierwiastków są jednak różne, ponieważ masy poszczególnych atomów są drastycznie różne. Masa molowa pierwiastka (lub związku) to masa w gramach 1 mola tej substancji, właściwość wyrażona w gramach na mol (g/mol).

Masa molowa dowolnej substancji jest liczbowo równa jej masie atomowej lub masie wzorcowej w u. Zgodnie z definicją u pojedynczy atom węgla waży 12 u (jego masa atomowa wynosi 12 u). Mol węgla waży 12 g (12 g C = 1 mol atomów C = 6,022 × 1023 atomów C), a masa molowa węgla wynosi 12 g/mol. Zależność ta dotyczy wszystkich pierwiastków, ponieważ ich masy atomowe są mierzone w odniesieniu do substancji referencyjnej u, węgla-12. Rozszerzając tę zasadę, masa molowa związku w gramach jest również liczbowo równoważna jego masie wzoru w u. Na przykład hel ma masę atomową 4,002 u i masę molową 4,002 g/mol.

Chociaż masa atomowa i masa molowa są liczbowo równoważne, należy pamiętać, że znacznie różnią się one pod względem skali. Aby ukazać ogrom mola, rozważmy małą kroplę wody o masie około 0,03 g. Chociaż stanowi to zaledwie niewielki ułamek 1 mola wody (~18 g), zawiera więcej cząsteczek wody, niż można sobie wyobrazić. Gdyby cząsteczki były równomiernie rozmieszczone wśród około siedmiu miliardów ludzi na Ziemi, każdy człowiek otrzymałby ponad 100 miliardów cząsteczek wody.

Mol określa związek między masą a liczbą atomów. Pozwala to na obliczenie liczby atomów w oparciu o odpowiednie formy przelicznika: 1 mol atomowy = 6,022 × 1023 atomów. Aby przeliczyć masę pierwiastka (w gramach) na liczbę moli, jako współczynnik przeliczeniowy stosuje się masę molową pierwiastka (g/mol).

Masa cząsteczkowa

Tożsamość substancji jest określana nie tylko przez rodzaje zawartych w niej atomów lub jonów, ale także przez ilość każdego rodzaju atomu lub jonu. Na przykład...

Education

JoVE Core

Chemia

Jeden

Atoms and Elements

Atomy i pierwiastki

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

mole, mass, and avogadro’s number

The mole links mass and the number of particles in a substance. It gives chemists a standard way to count atoms and molecules in samples that are far too small to see. It also helps show why substances with the same kinds of atoms can still have very different properties, like water, H2O, and hydrogen peroxide, H2O2.

The mole is an amount unit, like a pair or a dozen. One mole contains 6.02214076 × 10^23 discrete entities, such as atoms or molecules. This number is usually rounded to 6.022 × 10^23 and is called Avogadro’s number, or the Avogadro constant, named for Amedeo Avogadro. The constant is written with the unit per mole.

One mole of any element contains the same number of atoms as one mole of any other element. The masses are different, though, because atoms have different individual masses. That is why one mole of one element does not weigh the same as one mole of another element.

Molar mass is the mass in grams of one mole of a substance. It is reported in grams per mole, or g/mol. The molar mass of an element or compound is numerically equal to its atomic mass or formula mass in amu. For example, carbon has an atomic mass of 12 amu, so 1 mole of carbon has a mass of 12 g and a molar mass of 12 g/mol.

This same relationship works for other elements and for compounds. Helium, for example, has an atomic mass of 4.002 amu and a molar mass of 4.002 g/mol. Although the numbers match, atomic mass and molar mass are very different in scale.

A tiny drop of water can still contain an enormous number of molecules. A drop that weighs about 0.03 g is only a small part of 1 mole of water, which is about 18 g. Even so, it holds more water molecules than can easily be imagined. If those molecules were shared equally among the roughly seven billion people on Earth, each person would still get more than 100 billion molecules of water.

The mole also lets scientists convert between mass and amount. Using the relationship 1 mole of atoms = 6.022 × 10^23 atoms, the number of atoms can be calculated from a sample. The molar mass of an element is also used as a conversion factor to move between grams and moles.

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molar mass

The mole links mass and the number of particles in a substance. It gives chemists a standard way to count atoms and molecules in samples that are far too small to see. It also helps show why substances with the same kinds of atoms can still have very different properties, like water, H2O, and hydrogen peroxide, H2O2. The mole is an amount unit, like a pair or a dozen. One mole contains 6.02214076 × 10^23 discrete entities, such as atoms or molecules. This number is usually rounded to 6.022 ×...

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Learn how the mole connects mass, atoms, and molecules through Avogadro’s number and molar mass, with clear examples for high school chemistry.

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ohios-learning-standards-and-model-curriculum

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Structure And Properties Of Matter

Quantifying matter

Interactions Of Matter

Stoichiometry

Virginia  Standards of Learning

HIgh School

CH.2

CH.2.a

CH.4

CH.4.a

Physical Science

PS.4

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Arizona Science Standards

High School

HS+C.P1

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Texas Essential Knowledge and Skills

CHEM.8

CHEM.8.A

CHEM.11

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Alabama Course of Study Science

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Florida Department of Education

SC.912.P.8

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IPC.7

IPC.7.A

Georgia Standards of Excellence

SC3.

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Mole, Mass, and Avogadro’s Number

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