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chemistry module 2 foundations in chemistry > Chapter 3 Amount Of Substance > Flashcards

Chapter 3 Amount Of Substance Flashcards

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1
Q

What do moles refer to?

A

The amount of a substance

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2
Q

What is the unit for moles?

A

Mole/ moles/ mol

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3
Q

What is the definition of Relative Molecular Mass?

A

The weighted mean mass of a molecule when compared to 1/12th mass of carbon-12

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4
Q

What is the definition of Relative Formula Mass?

A

The weighted mean mass of a compound when compared to 1/12th mass of carbon-12

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5
Q

What is Molar Mass?

A

Mass of 1 mole of a substance

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6
Q

What is the unit of Molar Mass?

A

gmol^-1

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7
Q

What is the equation for the number of moles?

A

Number of moles= Mass (g)
————
Molar Mass (Mr)

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8
Q

How do you find the number of particles?

A

Number of particles= number of moles x Avogrado’s constant

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9
Q

Find the Molar Mass of Calcium Carbonate

A

CaCO3=
40.1+12.0+ (16.0 x 3)= 100.1gmol^-1
Mr= 100.1gmol^-1

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10
Q

What is the molecular formula?

A

Shows the number and type of each atom of an element present in a compound, eg C4H10

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11
Q

What is the empirical formula?

A

The simplest whole number ratio of each atom of an element present in a compound
eg C2H5

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12
Q

A compound is found to contain 72.4% Fe and 27.6% O. Calculate its empirical formula.

A

Fe
Mass/ %= 72.4%
Ar=55.8

O
%= 27.6%
Ar=16.0

Moles= Mass/Mr

Moles Fe
72.4/55.8=1.30 mol

Moles O
27.6/16.0=1.73 mol
Always divide by the smallest

Fe- 1.30/1.30=1
O- 1.73/1.30=1.333…
Multiply by 3

Ratio Fe=3 O=3.99.. or 4.00

Therefore= Fe3O4

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13
Q

How do you convert from cm cubed to dm cubed?

A

Divide by 1000

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14
Q

How do you convert from dm cubed to cm cubed?

A

X1000

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15
Q

How do you convert from cm cubed to m cubed?

A

Divide by 1,000,000

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16
Q

How do you convert from m cubed into cm cubed?

A

X1,000,000

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17
Q

What is the equation for concentration?

A

Concentration (mol/dm^3)= Moles/ volume (dm^3)
OR
Concentration (gmol^-3) = Mass (g)/ volume (dm^3)

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18
Q

What is Molar Volume?

A

Vm is the volume of 1 mole of gas

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19
Q

What is the average room temperature and pressure?

A

RT-20 degrees
Pressure- 101kPa

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20
Q

What does 1 mole of any gas occupy at normal RTP (room temperature and pressure)?

A

24.0dm^3

21
Q

How do you calculate the volume of gas?

A

Volume= number of moles x 24.0
(Dm^3)

22
Q

What is the ideal gas equation?

A

pV=nRT

P= Pressure- Pa
V=Volume -m^3
n= Number of moles
R= gas constant
T= temperature- kelvin (k)

All need to be in Si units

23
Q

How do you convert from Degrees Celsius into kelvin?

A

+273

24
Q

How many Pa equals 1kPa?

A

1000

25
Q

How do you rearrange the ideal gas equation to find pressure?

A

Move the volume diagonally (v)

P=nRT
——
V

26
Q

How do you rearrange the ideal gas equation to find Volume?

A

Move pressure (p) diagonally

V=nRT
——
P

27
Q

How do you rearrange the ideal gas equation to find number of moles?

A

Move Pressure and volume across

n= PV
——
RT

28
Q

How do you rearrange the ideal gas equation to find temperature (T)?

A

Move Pressure and Volume across

T= PV
——
nR

29
Q

What volume of carbon dioxide gas, measured at 800 K and 100 kPa, is formed when 1 kg of propane is burned in a good supply of oxygen?
C3H8 + 5 O2 —> 3 CO2 + 4 H2O

A

Propane C3H8= (12.0 x 3) + 8.0= 44.0
Moles= mass / Mr
1Kg= 1000g
1000/ 44.0= 22.727272…mol

Multiply by 3 to get the number of moles of CO2
22.72 x 3 = 68.18181818…

100kPa= 100,000Pa

Equation = V= nRT
———-
P

(68.18 x 8.31 x 800)
—————————- = 4.5327272727…
100,000

= 4.5 m^3

30
Q

Calculate the mass of oxygen needed to react 10.0g of calcium to form calcium oxide
2Ca + O2 —-> 2CaO

A

Ca= 40.1- dont count the moles number in front of the number when calculating Mr
Moles= mass/Mr

10/40.1= 0.2493765586
Divide by 2 as there is a 2:1 ratio between Ca and O
=0.1246882793
O2= (16.0 x 2) = 32.0

0.1246882793 x 32.0 = 3.990024938g

31
Q

What does hydrated mean?

A

A crystalline compound containing water molecules

32
Q

What does anhydrous mean?

A

Containing no water molecules

33
Q

What does water of crystallisation mean?

A

Water molecules that are bonded into a crystalline structure of a compound.

34
Q

How is percentage yield calculated?

A

Percentage yield= actual yield X100
———————
Theoretical yield

35
Q

Why are the reactants not completely converted into the desired product?

A

The reaction may not have gone to completion
Other reactions (side reactions) may have taken place alongside the main reaction
If the process of the reaction occurs in stages, some product may be lost on extraction between stages
The reaction may be reversible

36
Q

How is atom economy calculated?

A

Atom economy
= sum of molar masses of desired product. X100%
————————————————————
Sum of molar masses of all products

37
Q

1.15g of sodium reacts with an excess of chlorine, forming 1.872g of sodium chloride. What is the percentage yield of sodium chloride?
2Na + Cl2 —> 2NaCl

A

Calculate the number of moles
Moles= mass/ Mr
1.15/ 23.0= 0.0500 moles
Use the equation to find the theoretical yield of NaCl
2 mole of Na = 0.0500 mole
=0.0500 mole NaCl
Calculate the actual yield
NaCl= 58.5
1.872/ 58.5= 0.0320 mole
Calculate the percentage yield
0.0320/ 0.0500 x100= 64.0%

38
Q

Hydrogen is an important raw material and is produced from the reaction of carbon with steam.
What is the atom economy of this reaction?

A

1- Write the equation and the molar masses of the products
REMEMBER: Always use the large number to calculate also
C + 2H2O —> 2H2 + CO2
—-> 2 x 2.0 12.0+ (16.0 x 2) = 44.0
2- Calculate the atom economy
2 x 2.0
———- X100 = 8.3%
(2 x 2.0)+ 44.0

39
Q

A student carried out an experiment to calculate the water of crystallisation of two hydrated salts. For the first salt, the student did not remove all the water of crystallisation. For the second salt, the student removed all the water of crystallisation, but the salt decomposed further.

For each salt, explain whether the students calculated value of x, the number of water molecules in the formula unit, would be greater or smaller than the actual value of x in data books.

A

The first salt would not lose all H2O so x would appear to be smaller than it should be.
The second salt loses more mass than just water so x would appear to be greater than it should be.

40
Q

What is atom economy?

A

The measure of the efficiency of a reaction in terms of the atoms involved

41
Q

What does atom economy not account for?

A

The efficiency of a reaction in relation to a process (eg, the reaction not going to completion, being reversible, or loss of material)

42
Q

What is the atom economy of addition reactions?

A

Addition reactions are always 100% because only one product is made

43
Q

What is the atom economy of substitution and elimination reactions?

A

Less than 100% because more than one product is made

44
Q

What is the purpose of having magnesium inside the test tube within the conical flask?

A

When the flask is shaken, the Magnesium and Hydrochloric acid will mix and the reaction will start so all the gas will be collected within the syringe.
Therefore, preventing any gas from escaping.

45
Q

When magnesium reacts with acid the reaction is exothermic, it gives out heat. Magnesium reacts with hydrochloric acid according to the following reaction:
Mg + 2HCl —> MgCl2 +H2
The student recorded the actual volume of gas produced and it was slightly higher than expected. Suggest a reason for this other than experimental error.

A

As temperature increased, because the reaction is exothermic, the volume of gas produced increases as well.
NOTE: REMEMBER DONT MENTION FACTORS RELATED TO THE CONDUCTED EXPERIMENT THAT IS KNOWN AS EXPERIMENTAL ERROR

46
Q

Hydrated pink chloride crystals were heated in a crucible until all the water of crystallisation was removed.
Suggest an extra step that could be added, that would allow you to know when all the water of crystallisation has been removed.

A

Continue heating until the crystals are a constant mass.

47
Q

A student followed the original method but noticed that when strongly heating their crystals some of them spat out of the crucible. Will this make their calculation of X too high or too low? Explain.

A

Too high because some of the hydrated salt is lost and therefore the water value will not account for what has been lost- there will be too fewer moles.

48
Q

Dilute cobalt chloride solution can be used as invisible ink. The solution is a very pale pink and so appears virtually colourless when written on paper. The ink is made visible by holding the paper over a hot lightbulb.
Suggest the chemistry that makes this ink visible again.

A

The lightbulb releases heat, so the pink hydrated salt will start to evaporate its water forming blue anhydrous crystals which are visible.

49
Q

Suggest how a chemical process could have a high percentage yield, but a low atom economy

A

High percentage yield as there is a high conversion rate of the desired product, however there are waste products that are also made.

chemistry module 2 foundations in chemistry (5 decks)

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