2. Amount of Substance Flashcards

0
Q

Define a mole

A

The amount of substance that contains 6.022 x 10^23 particles

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1
Q

See questions in mixed batch containing:

A

Definitions of relative atomic mass, relative molecular mass and the Avogadro constant.

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2
Q

Compare the number of entities in 18g of water and 1g of hydrogen. (Mr of water = 18)

A

18g of water contains the same number of molecules as there are atoms in 1g of hydrogen

NB: Even if elements are usually found diatomically, you count the number of atoms e.g. In H2

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3
Q

What is the ideal gas equation?

A

PV=nRT

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4
Q

What does P represent in the ideal gas equation?

A

Pressure measured in Pa (Nm^-2)

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5
Q

What does V represent in the ideal gas equation?

A

Volume, measured in m^3

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6
Q

What does T represent in the ideal gas equation?

A

Temperature measured in K

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7
Q

What unit is R (in the ideal gas equation) measured in?

A

J K^-1 mol^-1

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8
Q

Do all gases obey the ideal gas equation?

A

No gases obey it exactly, but at room temperature and pressure it holds quite well for many gases.

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9
Q

Define ‘empirical formula’

A

The simplest whole number ratio in which the atoms in a compound combine together.

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10
Q

What does a solution consist of?

A

A solvent with a solute dissolved in it

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11
Q

What does the concentration of a solution tell us?

A

How much solute is present in a known volume of solution.

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12
Q

What is concentration measured in?

A

mol dm^-3

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13
Q

Give the two triangle formulas used in calculations in ‘Amount of Substance’.

A

/moles\ /mass\

/volume x conc\ /moles x Mr\

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14
Q

You must be able to:
Balance equations
Find ionic equations

A

Tips for balancing:
- It often takes more than one step to balance an equation, but too many steps suggest that you have an incorrect formula.

  • When dealing with ionic equations the total of the charges on each side must be the same.
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15
Q

In a world of scarce resources it is not a good idea to waste unwanted products of a reaction. What is one technique that chemists use to assess a given process?

A

They determine the percentage atom economy.

16
Q

Is atom economy theoretical or practical?

A

Theoretical

17
Q

Give the equation for % Atom economy.

A

Mass of desired product
%Atom economy = _____________________ x 100
Total mass of reactants

18
Q

Is percentage yield practical or theoretical?

A

Practical

19
Q

Give the equation for % Yield.

A

Number of moles or grams of a product
% yield = ______________________________x 100
Theoretical number of moles/grams of a product

20
Q

What problems can arise when trying to calculate ether percentage yield?

A
  • Droplets get left in the apparatus
  • Precipitate gets left in filter paper
  • A reaction is reversible and a complete reaction does not take place (Haber process)
21
Q

Ibuprofen production was improved because…

A

A new company were able to increase the percentage atom economy from 40% to 77%