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CSEC CHEMISTRY > C2: The Mole Concept > Flashcards

C2: The Mole Concept Flashcards

1
Q

definition of relative atomic mass

A

the average mass of one atom of an element compared to one-twelfth the mass of an atom of carbon-12

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2
Q

why is relative atomic mass used instead of actual masses when measuring atoms

A

because atoms are too small to be measured directly.

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3
Q

what isotope of carbon is used as the standard for determining relative atomic mass (Ar)?

A

Carbon-12

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4
Q

what is the unit of Ar ?

A

relative atomic mass has no units

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5
Q

why relative atomic mass has no units

A

relative atomic mass is a comparison of masses with that of carbon-12

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6
Q

what is the unit mass of each atom of carbon-12?

A

12 amu (atomic mass units)

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7
Q

Since one carbon atom has a mass of 12 amu, then the mass of 1/12th the mass of carbon 12 is ______

A

1 amu

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8
Q

the masses of ionic and covalent compounds are compared to cabon 12 atoms also and give rise to the term (1)______________

and (2)______________

A
  1. relative formula mass
  2. relative molecular mass
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9
Q

definition of relative molecular mass

A

the average mass of one molecule of an element or compound compared to 1/12th the mass of an atom of carbon 12.

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10
Q

relative molecular mass and relative formula mass are calculated by ________________

A

adding together all the relative atomic masses of all the elements present in the compound

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11
Q

definition of relative formula mass

A

the average mass of one molecule of an ionic compound compared to 1/12th the mass of an atom of carbon 12.

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12
Q

which numbers represent the relative atomic mass

A

1, 2, 3 ,6 , 7, 8

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13
Q

definition of a mole

A

the amount of a substance that contains 6x1023 particles of the same substance

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14
Q

what is Avogadros constant?

A

6 x 1023

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15
Q

hwo to calculate relative molecular and relative formula mass

A

add all the Ar of all the elements in the compound

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16
Q

how would you define 1 mole of any gas

A

the volume of gas that contains 6x1023 molecules of the gas

17
Q

(1)The ___________________ of a substance is the mass of 1 mol of the substance and is equal to the (2)________________, (3)_________________, or (4)_______________ expressed in grams

A
  1. molar mass
  2. relative atomic mass,
  3. relative molecular mass,
  4. formula mass
18
Q

the molar mass of an element or compound is simply its (1) ______________, (2)______________ or its (3)_______________ expressed in grams

A
  1. relative atomic mas
  2. relative molecular mass
  3. relative formula mass
19
Q

when performing mole calculations involving mass of a substance apply this formula triangle

20
Q

when performing mole calculations involving number of particles apply this formula triangle

21
Q

when performing calculations involving volume of gases apply this formula triangle

22
Q

molar volume is defined as (1)_________________ and 1 mol of a gas containes (2)__________ molecules,

therefore (3)____________ of a gas contains 6x1023 molecules. The molar volume of any gas is (4)__________ at stp and (5) ___________ at rtp.

A
  1. the volume occupied by 1 mole of a gas
  2. 6x 1023
  3. 1 mole
  4. 22.4dm3
  5. 24.0dm3
23
Q

the molar volume of any gas contains this amount of molecules

24
Q

THE MOLE AS THE ‘MIDDLE MAN’

what is common with all these triangle formluas and what does this mean:

NA - Avogadros constant

N - number of particles

Mr - Relative molecular or relative formula mass

Vm - Molar volume

V - volume

C- concentration

n - number of moles

m - mass

A

All the formulas n - (number of moles). This means that the number of moles will either be given or needs to be calculated in order to complete the triangle calulations

25
Q

what do chemical formulas represent?

A

how many of moles of each element are combined to form 1 mole of a compound

26
Q

what do you understand from the following formulae:

  1. CO2
  2. NH4
  3. CaCO3
  4. H2SO4
A
  1. 1 mol of carbon combines with 2 mol oxygen to form 1 mol carbon dioxide
  2. 1 mol of nitrogen combines with 4 mol hygrogen to form 1 mol of ammonia
  3. I mol calcium combines with 1 mol carbon and 3 moles oxygen to form 1 mole calcium carbonate
  4. 2 moles hydrogen combines with 1 mol sulphur and 4 moles oxygen to form 1 mol sulphuric acid
27
Q

this give the simplest mole ratio between atoms or ions present in a compound

A

empirical formula

28
Q

this gives the actual number of moles of atoms of each element in one mole of a compound

A

molecular formula

29
Q

Ionic compounds are represented by (1)___________, while covalent compounds are represented by (2)________________

A
  1. empirical formula
  2. molecular formula
30
Q

what is the ratio of the atoms in the following compounds

  1. CO2
  2. NH4
  3. CaCO3
  4. H2SO4
A
  1. 1:2
  2. 1:4
  3. 1:1:3
  4. 2:1:4
31
Q

definition of empirical formla

A

the simples mole ratio of each atom or ion present in a compound

32
Q

molecular formula definition

A

the actual number of moles of atoms of each element present in 1mol of a compound

33
Q

difference between relative formula mass and relative molecular mass

A

relative formula mass is used when refering to ionic compounds while relative molecular mass refers to covalently bonded elements or compounds

34
Q

can one determine the molecular formula of a salt?

A

no. salts are ionic compounds and so are always represented by empirical formulas

35
Q

How to determine the empirical formula of an ionic compound in which the ratios of its elements are expressed in percentages

Hint: draw a table

A
  1. write down the relative atomic mass of each of the elements in the compund
  2. give a percentage value to all of the elements in the compound. The sum of all the elements represents 100%, so missing percentages are calculated using simple algebra
  3. let 100% = 100g and convert each percentage value to grams by simply changing their units form % to grams.
  4. convert each given mass to moles
  5. divide each result by the smallest mole amount. This will give the simplest mole ratio which is the empirical formula.
36
Q

How to determine the molecular formula of a compound with known relative molecular mass and in which the ratios of its elements are expressed in percentages.

Hint: draw a table

A
  1. write down the relative atomic mass of each of the elements in the compound
  2. give a percentage value to all of the elements in the compound. The sum of all the percentages is 100%, so missing percentages are calculated using simple algebra
  3. convert each percentage value to grams by simply changing their units form % to grams.
  4. convert each given mass to moles
  5. divide each result by the smallest mole amount. This will give the simplest mole ratio of the elements, which is the empirical formula.
  6. determine the relative molecular mass of the emiprical formula. we now have 2 relative molecular masses - one for the actual compound and one for the empirical formula.
  7. Determine the ratio between the 2 relative molecular masses. This must be a whole number equal to or greater than one.
  8. multiply the empirical formula by this value to obtain the molecular formula of the compound.
37
Q

How to determine the molecular formula of a compound with known relative molecular mass, in which the masses of its elements are known

Hint: draw a table

A
  1. write down the relative atomic mass of each of the elements in the compound and determine the molar mass of each element
  2. convert each given mass to number of moles
  3. divide each result by the smallest mole amount. This will give the simplest mole ratio of the elements, which is the empirical formula.
  4. determine the relative molecular mass of the emiprical formula. we now have 2 relative molecular masses - one for the actual compound and one for the empirical formula.
  5. Determine the ratio between the 2 relative molecular masses. This must be a whole number equal to or greater than one.
  6. multiply the empirical formula by this value to obtain the molecular formula of the compound.
38
Q

How to determine the empirical formula of an ionic compound in which the masses of its elements are known

Hint: draw a table

A
  1. write down the relative atomic mass of each element in the compound and determine its molar mass
  2. convert each given mass to moles
  3. divide each result by the smallest mole amount. This will give the simplest mole ratio which is the empirical formula.
39
Q

important points to consider when given problems to determine the empirical and molecular formulas of compounds.

A
  • only ionic compounds are represented by empirical formula
  • molecular compounds are represened by molecular formulas
  • The actual Mr of the compound is divided by the Mr of the empirical formula to give a whole number ratio
  • if the problem gives the percentages of each element, convert each percentage to grams by simply replacing the % with g. Then convert to number of moles

CSEC CHEMISTRY (17 decks)

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