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A-Level Chemistry > Amount of Substance > Flashcards

Amount of Substance Flashcards

1
Q

Define a mole

A

the amount of a substance that contains as many particles of that substance as there are atoms in exactly 12.00 g of carbon 12

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2
Q

How many particles does one mole have

A

The Avogadro number of particles

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3
Q

What is Avogadro number of particles

A

6.02 x 10 to the 23

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4
Q

How many oxygen atoms and hydrogen atoms are there in 5 water molecules

A

5 oxygen atoms

10 hydrogen atoms

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5
Q

How many oxygen atoms and hydrogen atoms are there in 1 mole of water

A 
1 x (NA) oxygen atoms 
2 x (NA) hydrogen atoms
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6
Q

How many oxygen atoms and hydrogen atoms are there in 5 moles of water

A 
5 x (NA) oxygen atoms 
10 x (NA) hydrogen atoms
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7
Q

Give the equation for the number of moles

A

n = Mass / Mr

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8
Q

Give the equation for mass

A

mass = n x Mr

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9
Q

Give the equation for Mr

A

Mr =mass / n

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10
Q

Calculate the number of moles in 2.30 g of sodium

A

2.3 / 23 = 0.1

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11
Q

Calculate the number of moles in 50.0 g of calcium carbonate CaCO3

A

50 / 40.1 + 12 + ( 3 x 16 ) = 0.50

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12
Q

Calculate the mass of 4.00 moles of calcium

A

4 x 40.1 = 160.4 g

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13
Q

Calculate the mass of 5 moles of (NH4)2SO4

A

5 x 132.1 = 660.5 g

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14
Q

Calculate the Mr of a substance if 0.600 moles has a mass of 35.1 g

A

35.1 / 0.6 = 58.5

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15
Q

Calculate the Mr of a substance if 5.25 moles has a mass of 556.5 g

A

556.5 / 5.25 = 106

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16
Q

HARD QUESTION

0.300 moles of hydrated salt COCl2.xH2O has a mass of 71.37g

Find the value of x …

A

Mr = mass / n
71.39 / 0.3 = 237.9

Mr of COCL2 = 58.9 + (35.5 x 2) = 129.9

Mr of H2O = 237.9 - 129.9 = 108

Moles of H2O = 108/18 = 6

X = 6 , SO THE FULL FORMULA IS COCl2.6H2O

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17
Q

Define empirical formula

A

This is the simplest whole number ratio of atoms in a compound

18
Q

If Benzene has the formula C6H6 , what is its empirical formula

A

CH

19
Q

a compound contains 72 percent magnesium and 28 percent nitrogen , what is its empirical formula

A

Mg N

mass = 72g 28g

Mr = 24.3 14

n = 2.96 2.00

ratio= 3 2

SO THE EMPIRICAL FORMULA IS Mg3N2

20
Q

Define molecular formula

A

the actual number of atoms of an element in a compound

21
Q

What are the steps you have to take to calculate the molecular formula

A
  • First calculate the ratio which is , molecular mass / empirical mass
  • Then Molecular formula = Ratio x empirical formula
22
Q

Find the molecular formula of NH2 when its Mr is 32

A

ratio = 32 (molecular mass) / 16 (empirical mass) RATIO = 2

2 x NH2 = N2H4

23
Q

EXPANDED QUESTION

Find the value of x in MgSO4.XH2O

When your hydrated mass is 4.312 g and the anhydrous mass is 2.107 g

A

Find mass of water of crystallisation by taking the anhydrous mass away from the hydrated mass = 2.025g

Then find the number of moles in each :
0.018 MgSO4 and 0.113 of H2O

Then find the ratio which is 1:7

Answer is MgSO4.7H2O

24
Q

What is an uncertainty measurement

A

this is an interval that indicates a range within which we are reasonably confident that the true value lies

25
Q

What is the uncertainty value of a mass balance

A

0.01

26
Q

Give the equation for finding the percentage uncertainty

A

Uncertainty value
————————————– x 100 = ‘ ‘ percent
Measured quantity

27
Q

How many sulfur atoms are there in in two moles of sulfur S8

A

2 x 8 = 16

16 x NA

28
Q

How many chlorine atoms are there in 5 moles of chlorine

A

5 x 2 x NA

times by 2 because Cl is diatomic

29
Q

One mole of gas occupies approximately ? at RTP

A

24 dm3

0r

24,000 cm3

30
Q

Number of moles of gas =

A 
   24

or ..

volume cm3 --------------------------
   24,000
31
Q

Volume of gas in dm3 =

A

number of moles X 24

32
Q

Volume of gas in cm3 =

A

number of moles X 24 000

33
Q

Give the ideal gas law equation

What does each letter mean ?

A

PV = nRT

p= pressure in Pa

v= volume in m3

n = number of moles

R = ideal gas constant (8.314)

T = temperature in K

34
Q

Give the conversions between Pa and KPa

A

Pa —> KPa. you divide by 1000

KPa —> Pa you times by 1000

35
Q

Give the conversions between cm3, dm3 and m3

A

cm3 —> dm3 you divide by 1000
dm3 —> m3n you divide by 1000

m3. —> dm3 you times by 1000
dm3 —> cm3 you times by 1000

36
Q

Give the conversions between degreed Celsius and K

A

C —–> K you add 273

37
Q

define a solution

A

a solute dissolved in a solvent

38
Q

define concentration

A

tells you how many moles of solute are dissolved in 1 dm3

39
Q

Give the Concentration equation

A

C = number of moles
—————————
volume (dm3)

C = number of moles
—————————
volume (cm3) / 1000

40
Q

Give the equation for number of moles in terms of concentration

A

n = C x V (dm3)

n = C X V( cm3)
————————
1000

41
Q

what is 1 dm3 in cm3

A

1 dm3 = 1000 cm3

A-Level Chemistry (4 decks)

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