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CHEMISTRY > Chemical calculations > Flashcards

Chemical calculations Flashcards

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1
Q

How do you find the atomic mass of an element

A

Larger number on periodic table (protons + neutrons)

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2
Q

What is the equation relating Moles, Mr and Mass?

A

of Moles = Mass (g)/Mr

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3
Q

How many moles are there in 48g of Magnesium

A

48/24

= 2 moles

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4
Q

Calculate the mass of 4 moles of NaCl

A

4 x (23 + 35.5)

=234g

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5
Q

What is a mole of a substance

A

6.02 x 10^23 atoms/particles of any substance

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6
Q

How many moles of atoms are there in H20 ?

A

3 Moles

H2 = 2 moles
O = 1  mole

2+1 = 3 moles of atoms

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7
Q

Calculate the number of atoms in 56g of Calcium Oxide

Ar Ca =40 ArO =16

A

56/56
= 1 mole of CaO
=6.02 x 10^23 atoms

2 moles of atoms in CaO

multiply by 2
2 x (6.02 X 10^23)

=1.204 x 10^24

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8
Q

Does the Mr include subscripts (delete this card is doesnt make the sensde

A

No :(

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9
Q

What is a limiting reactant?

A

A reactant that is fully used up

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10
Q

What is an excess reactant

A

A reactant that isn’t used up and is left in excess

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11
Q

How many moles of Zinc Iodide would be produced if we used 0.5 moles of Zinc and 1 mole of Iodine?

Ar Zn = 65 Ar I2 =254

Zn + I2 ===> ZnI2

A

a) 0.5 moles, as Zinc is the limiting reactant
b) Rearrange mole equation for mass:

  Mass = Moles x Mr

 Mass (ZnI2) = 0.5 ( 65 + { 127 x 2})

=159.5g
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12
Q

What is the equation relating Concentration, Mass and Volume?

A

Concentration (g/dm^3) = Mass (g) / Volume (dm^3)

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13
Q

What is the equation relating Concentration, Moles and Volume?

A

Concentration (Mol/dm^3) = # of moles / Volume (dm^3)

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14
Q

What is a solute

A

A substance dissolved in a solvent

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15
Q

If a solution’s mass increases, while maintaining the same volume, what happens to its concentration>

A

It increases

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16
Q

If a solution’s volume increases, while maintaining its mass, what happens to its concentration?

A

It decreases

17
Q

Calculate the mass of a chemical needed to dissolve in a volume of 0.4 dm^3 to give a final concentration of 600g/dm^3

A

Rearrange for mass:
Mass = Concentration x Volume

Mass = 0.4 x 600
=240g

18
Q

How do you get from cm^3 to dm^3 ?

A

divide by 1000

19
Q

What is the yield of an experiment?

A

The mass obtained from a reaction

20
Q

Why is it difficult to achieve an 100% yield?

A
  • Some of the product may be lost when being separated
    from the mixture
  • Reversible reactions may not react to completion
21
Q

Why can’t a yield over 100% be achieved?

A
  • It would mean that we’ve created atoms, which is impossible
22
Q

What is the formula for percentage yield?

A
  • Yield = ( Mass of actual product made / Maximum theoretical mass of product ) x 100
23
Q

What is the atom economy?

A
  • A measure of starting materials that end up as useful products
24
Q

How do you calculate the Atom economy of a reaction?

A
  • RFM of the desired product (from the reaction) / Sum of

the RFM’s of all the reactants x 100

25
Q

What are the benefits of atom economy?

A
  • Minimises the production of unwanted elements,

saves money and increases sustabinability

26
Q

Why can’t the atom economy be over 100%?

A
  • It would mean we’re creating atoms, which is

impossible

27
Q

Calculate the atom economy:

C6H12O6 —– 2C2H5OH + 2CO2
(glucose) (ethanol) (carbon dioxide)

Desired product : Ethanol

Ar O = 16 Ar C = 12 Ar H = 1

A

RFM of desired product (ethanol) =

(2 x (12x2)) + ( 1 x 5) + 16 + 1 )
= 92

RFM of all reactants =

( 12 x 6 ) + 12 + (16 x 6)
= 180

100 (92/180)

= 51.1%

28
Q

Are large numbers used in atom economy?

A
  • YES
29
Q

What is Avogrado’s law relating gas volumes, moles and room temperature?

A
  • One mole of any gas occupies a volume of 24dm^3 at
    room temperature and pressure

Room temp: 20 degrees celsius
Room pressure : 1 atmosphere

30
Q

What is the equation relating the volume of a gas, and moles?

A

Volume (dm^3) = # of moles x 24

31
Q

Calculate the volume of 51g of ammonia gas ( NH3)
Assume that the gas is at room temp and pressure
[ Mr NH3 = 17 ]

A
  • # Moles NH3 = 51/17= 3 Moles

3 x 24 = 72

=72dm^3

32
Q

Calculate the volume of of Hydrogen gas produced from 325g of Zinc. Assume that the gas is at room temperature and pressure. [Ar Zinc = 65 ]

Zn + 2HCL —— ZnCl2 + H2

A
  • # Moles Zn = 325/65= 5 molesVolume H2 = 5 x 24
    = 120dm^3

CHEMISTRY (18 decks)

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