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Chemistry > Amount of substances > Flashcards

Amount of substances Flashcards

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1
Q

what is relative atomic mass

A

Therelative atomic mass(Ar) of an element is the weighted average mass of all its naturally occurring isotopes

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2
Q

what is relative formula mass

A

The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of all the atoms in the compound’s formula unit

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3
Q

how do u calculate the relative atomic mass ar

A

Multiply each isotope’s relative isotopic mass by its isotopic abundance.

Sum these quantities.

Divide by the sum of the isotopic abundances.

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4
Q

what does the y and x axis show in the mass spectrum

A

the y axis shows the percentage abundance and the x axis shows the mass/charge

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5
Q

how do you calculate the relative formula mass

A

Step 1: Write down the molecular formula

H2O

Step 2: Multipy each element’s atom count by its Ar

H: 1.0 × 2 = 2.0

O: 16.0 × 1 = 16.0

Step 3: Calculate Mr

Relative molecular mass = 2.0 + 16.0 = 18.0

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6
Q

what is a mole

A

Themoleis a convenient unit that allows us to count extremely large numbers of atoms and molecules.

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7
Q

what is the avogadros connstant ( and the number )

A

Avogadro’s constanthas a value of6.02 x 1023. This very large number represents how many particles are contained in one mole.

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8
Q

what is the triangle that links avogadros constant no.of particles and number of moles

A

no.of moles = no.of particles / avogadro cons.

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9
Q

what is the molar mass

A

Themolar mass(M) represents the mass in grams of 1 mole of a given substance.

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10
Q

what is the triangle that links mass in g molar mass and no. of moles

A

no.moles=mass in g / molar mass

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11
Q

what is the unit for molar mass

A

g/mol^-1

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12
Q

what is the concentration of a solution measured in

A

g/dm^-3 or mol/dm^-3

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13
Q

what is the equation linking mass,volume and concentration

A

concentration= mass/ volume

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14
Q

what is the equation linking moles,volume and concentration

A

concentration= moles/ volume

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15
Q

how do you convert cm3 to dm3

A

divide by 1000

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16
Q

how do convert dm3 to cm3

A

multiply by 1000

17
Q

how do you convert g/dm^-3 to mol/dm^-3

A

Divide the concentration in g dm-3by the Mrof the solute

For example, a 58.5 g dm-3solution of NaCl (Mr= 58.5)= 1.00 mol dm-3

18
Q

how do u convert mol dm-3to g dm-3

A

Multiply the concentration in mol dm-3by the Mrof the solute

For example, a 2.00 mol dm-3solution of NaCl (Mr= 58.5)= 117 g dm-3

19
Q

what are the assumptions that the ideal gas equation obeys

A

Gas particles move rapidly and randomly.

The volume of the actual gas particles is negligible compared to empty space between them.

There are no intermolecular attractions or repulsions.

Collisions between particles are elastic - no energy is lost.

The average kinetic energy of particles depends only on their temperature.

20
Q

why does the real gas deviate from these assumptions

A

because they have weak intermolecular attractions and non negligible volumes

21
Q

what are the names of the two gases that come close to the ideal gas

A

noble gases like helium and neon because their intermolecular forces are minimal

22
Q

what is the formula for ideal gas

A

pressure (pa) X volume(m3) = moles of gas X the gas constant X temperature (K)

23
Q

what is teh value for the gas constant

A

8.31

24
Q

how do u convert kPa to Pa

A

multiply by 1000

25
Q

how do u convert degree celcius to kelcius

A

add 273 to the original number

26
Q

how do u convert cm3 to m3

A

divide 1,000,000

27
Q

what is the empirical formula

A

The empirical formula gives the simplest whole number ratio of atoms of each element present in a compound.

28
Q

what is the molecular formula

A

The molecular formula gives the actual number and type of atoms of each element in a molecule.

29
Q

give an example of both empiral and molecular formular

A

An empirical formula of CH2O as this gives the simplest ratio.

A molecular formula of C6H12O6as this shows the actual numbers of atoms in a glucose molecule.

30
Q

what are the two ways to find the empirical formula

A

percentage composition
combustion data

31
Q

explain how to find the empiraical forrmula from the percentage composition

A
  1. assume that all the percentages are in g
  2. then find the number of moles in each molecule
  3. find the ratio btw them by dividing everything by the smallest no of moles
32
Q

explain the way from a combustion data

A

A hydrocarbon sample weighing 2.20 g was completely combusted in oxygen, producing 3.30 g of CO2and 1.35 g of H2O.

Determine the empirical formula of the hydrocarbon.

Step 1: Calculate moles of CO2produced

moles of CO2​ =Mr ​mass​=44.03.30​=0.075 mol

Step 2: Calculate moles of carbon in the sample

Each molecule of CO2contains 1 atom of carbon.

Moles of C atoms = Moles of CO2= 0.075 mol

Step 3: Calculate moles of H2O produced

moles of H2​O =Mr ​mass​=18.01.35​=0.075 mol

Step 4: Calculate moles of hydrogen in the sample

Each molecule of H2Ocontains 2 atoms of hydrogen.

Moles of H atoms = 2 x moles of H2O= 2 x 0.075 = 0.150 mol

Step 5: Determine the simplest C : H mole ratio

C : H = 0.075 : 0.150 = 1 : 2

Step 6: Write the empirical formula

The empirical formula is CH2.

33
Q

what are the ways to calculate the molecular formulae

A

from the empiral formula
and from a hydrated ionic salt

34
Q

how to u calculate the molecular mass fro the empiral formula

A
  1. finding the empiral formula form the question ( calculate the Mr )
  2. then divide the molecular mass by the empiral formula mass
  3. the number u get is the number present in the equation basically
35
Q

how do u calculate the molecular formula from the hydrated ionic salt

A

calculate the mass of water lost
them moles of the anydrous thingy lost my dividing mass / Mr
then do the same for hydrated ( water)
then find the ratio

36
Q

what is the formula to calculate the number of atoms

A

no.of atoms = amount of substance / moles X avogadro’s constant

Chemistry (3 decks)

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