Chemistry Quantitative March 2018 Flashcards

1
Q

What is the equation of moles?

A

Moles = mass / Mr

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2
Q

What does ‘Mr’ stand for?

A

Relative formula mass

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3
Q

What is an excess substance?

A

A substance that there is more than we need

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4
Q

What is a limiting substance?

A

It dictates the mass of the product

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5
Q

What is the equation for % Yield?

A

actual mass obtained / calculated mass x 100

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6
Q

What are the definitions for Yield and % Yield?

A

Yield = The amount of product formed in a reaction.

% Yield = The amount of product gained in a reaction compared to the maximum theoretical mass.

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7
Q

What is the definition for atom economy?

A

A way of measuring what percentage of the mass of all atoms in the reactants ends up in the desired products.

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8
Q

What is the equation for atom economy? (%)

A

Mr of desired product / Σ Mr of all reactants x 100

Σ = sum of

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9
Q

If there is only 1 product what is the atom economy (%)?

A

100%

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10
Q

1 dm^3 = ?

A

1 L or 1000 ml

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11
Q

What is the equation for the moles of gas?

A

moles of gas = volume (dm^3) / 24

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12
Q

What is the definition of concentration?

A

A measure of how much solute (solid) is dissolved in a solvent (water)

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13
Q

If you have 90g of H2O, how many moles is there?

A
Mr = 2 x 1 + 16
moles = mass / Mr = 90 / 18 = 5 moles
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14
Q

If you have 102 tons of O2, how many moles do you have?

A

102 tons = 102,000,000g
Mr = 16 x 2 = 32
moles = mass / Mr = 102,000,000 / 32 = 3,190,000 moles or 3.19x10^6 moles.

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15
Q

If you have 4 moles or N2, how many grams do you have?

A
Mr = 2 x 14 = 28
moles = mass / Mr so mass = moles x Mr 
mass = moles x Mr = 4 x 28 = 112g
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16
Q

If you have 0.02 moles of K2O, how many grams do you have?

A
Mr = 2 x 39 + 16 = 94
mass = moles x Mr = 0.02 x 94 = 1.88g
17
Q

What 3 step process is used to find the mass of an unknown?

A

Step 1: Work out number of moles of mass given
Step 2: Use balanced equation ratio to find out moles of unknown
Step 3: Turn moles of unknown into mass of unknown

e.g. How much CO2 is made when 48g of CH4 is burnt
Mr of CH4 = 12 + 4 = 16
moles = mass / Mr =  48 / 16 = 3 moles
ratio = CH4 : CO2 = 1 : 1
moles of CO2 = 3 moles
Mr of CO2 = 14 + 16 x 2 = 44
mass = moles x Mr = 3 x 44 = 132g
18
Q

How do you find the simplest ratio by using mass?

A

Find the moles of all reactants and products by using moles = mass / Mr
then divide all moles by the smallest mole. With the numbers now put them into the equation to balance it

e.g. Equation = H2O2 –> H2O + O2
Mr = 34 18 32
Mass = 6.8g 3.6g 3.2g

Moles = 6.8 / 34 & 3.6 / 18 & 3.2 / 32
= 0.2 0.2 0.1

Ratio = 0.2 / 0.1 : 0.2 / 0.1 : 0.1 / 0.1
= 2 2 1
Balanced equation = 2H2O2 –> 2H2O + O2

19
Q

What is a mole?

A

A mole is a measurement of the amount of a substance

20
Q

What is the equation for concentration?

A

Concentration = moles / volume