2.1- RELATIVE ATOMIC AND MOLECUALR MASSES, THE AVOGADRO CONSTANT, AND THE MOLE Flashcards

1
Q

What does comparing masses of atoms give?

A

relative masses

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2
Q

Why are relative masses used instead of actual masses in grams?

A

actual mass in grams of atoms/ molecules too tiny to find by weighing

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3
Q

How was finding relative masses done in the past?

A

by defining the relative atomic mass of hydrogen, lightest element as 1

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4
Q

Using the old method of relative mass, what would oxygen’s mass be like?

A

average mass of atom of oxygen is 16 times heavier, to nearest whole number, so oxygen has relative atomic mass of 16

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5
Q

What do scientists now use for relative masses?

A

use isotope carbon-12 as baseline for relative atomic masses

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6
Q

Why do scientists now use carbon-12 as the baseline for relative atomic masses? (mass spectrometer)

A

as mass spectrometer has allowed us to measure masses of individual isotopes extremely accurately

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7
Q

What is the value of one twelfth of the relative atomic mass of carbon-12?

A

gives value of exactly 1

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8
Q

What is the definition of relative atomic mass?

A

weighted average mass of an atom of an element, taking into account its naturally occurring isotopes, relative to 1/12 the relative atomic mass of an atom of carbon-12

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9
Q

What is the formula for relative atomic mass?

A

1/12 mass of one atom 12C

mass of one atom of 12C

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10
Q

What is the definition of relative molecular mass?

A

mass of that molecule compared to 1/12 the relative atomic mass of an atom of carbon-12

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11
Q

What is the formula for relative molecular mass?

A

1/12 mass of 1 atom of 12C

mass of 1 atom of 12C

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12
Q

How do you find the relative atomic mass?

A

add up relative atomic masses of all the atoms present in molecule

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13
Q

What is the term relative formula mass used for?

A

ionic compounds

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14
Q

Why is the term relative formula mass used for ionic compounds?

A

they don’t exist as molecules

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15
Q

What is the value of Avogadro’s constant?

A

6.022* 10^23

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16
Q

What is the definition of Avogadro’s constant?

A

number of atoms in 12g of carbon-12

17
Q

What is a mole?

A

amount of substance that contains 6.022* 10^23 particles

18
Q

What does the relative atomic mass of an element in grams contain? (moles?)

A

contains one mole of atoms

19
Q

What does the relative molecular mass of a substance in grams contain? (mole?)

A

contains mole of entities

20
Q

What else can you have a mole of? (2)

A

ions or electrons

21
Q

What is the formula for the number of moles?

A

moles = mass
———-
Mr