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Fundamentals Of Chemistry > Calculations > Flashcards

Calculations Flashcards

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1
Q

How to work out empirical formula?

A

Divide masses by relative atomic mass (to find moles)
Divide each number by the smallest one
These numbers show the ratio required

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2
Q

What is a mole?

A

The amount of substance that contains 6.022x10(23) particles

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3
Q

What is Avogadro’s number?

A

6.022x10(23) (the same as the number of particles in each mole of carbon 12)

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4
Q

One mole of any substance is equal to?

A

It’s relative atomic mass turned into grams

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5
Q

What are moles measured in?

A

g/mol

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6
Q

How to work out number of moles?

A

Mass divide by formula mass

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7
Q

How to work out mass?

A

Moles multiplied by formula mass

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8
Q

How to work out formula mass?

A

Mass divided by moles

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9
Q

What is percentage composition?

A

The percentage by mass of each element present in a compound

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10
Q

How to work out percentage composition?

A

Multiple relative atomic mass by number of atoms
Divide by molecular mass of compound
Multiple by 100

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11
Q

What is molecular formula?

A

The actual number of atoms of each element in a molecule.

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12
Q

What is empirical formula?

A

The simplest whole number ratio of atoms or ions of each element in a compound

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13
Q

How to work out molecular formula?

A

Find empirical formula
Divide actual mass by empirical formula mass

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14
Q

What is a solution?

A

A mixture of solute and solvent particles

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15
Q

Concentration definition?

A

Amount of solute in a given amount of solution

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16
Q

Molarity meaning?

A

An expression of concentration 1M = 1 mole of substance in 1dm(3) of its solution

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17
Q

How to work out concentration?

A

Number of moles divided by volume

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18
Q

Molar gas volume definition?

A

The volume per mole of gas molecules at a stated temperature and pressure

19
Q

What is the volume of one mole of any gas at room temperature and pressure?

A

24dm(3)

20
Q

How to convert cm(3) to dm(3)?

A

Divide by 1000

21
Q

How to calculate the volume of gas (dm3)?

A

Number of moles of gas x 24

22
Q

How to calculate the number of moles of a gas?

A

Volume of gas (dm3)
——————————
24

23
Q

Percentage yield definition?

A

Shows how much product is obtained compared to the maximum possible mass

24
Q

Atom economy definition?

A

The percentage of atoms in reactants that form the desired product

25
Q

Theoretical yield meaning?

A

The maximum amount of product that could be formed

26
Q

Why is it difficult to achieve theoretical yield?

A

Reaction may not have gone to completion
Other side reactions may have taken place
Purification of the product may result in some loss of product
Some product may be left behind in apparatus
Raw materials may not be pure

27
Q

How to calculate percentage yield?

A

1) find moles of product
2) find ratio of moles of product to reactant
Actual yield
—————— x 100
Theoretical yield

28
Q

Limiting reagent meaning?

A

Any reactant that is not in excess. Meaning the reacting will stop as soon as this is used up.

29
Q

How to work out the limiting reagent?

A

Used the balanced equation to see which reactant is used up quicker

30
Q

How to work out atom economy?

A

The mass of useful product
————————————x 100
Total mass of all products

31
Q

Why is it useful to maximise percentage yield and atom economy?

A

Reduce energy use
Reduce costs
Conserve raw materials
Reduce waste
Reduce pollution

32
Q

What is a titration used for?

A

To calculate the concentration of an unknown

33
Q

How to work out concentration from a titration?

A

1) calculate the volume, concentration and moles of the known substance
2) use the balance equation to work out mole ratio
3) use the mole ratio to work out the moles of the unknown
4) use the moles and volume of the unknown to finally workout the concentration

34
Q

What is volumetic analysis?

A

Finding the concentration of a solution by measuring the volume of a solution that will react with a known volume of standard solution

35
Q

What is the equation to work out a dilution?

A

Initial conc. x initial vol. = new conc. x new vol
This is then rearranged as required

36
Q

Saturated solution definition?

A

A chemical solution containing the maximum concentration of a solute dissolved in the solvent at a particular temperature. No more solute will dissolve.

37
Q

Supersaturated solution meaning?

A

A solution that contains a higher that saturation concentration of solute. Any slight disturbance causes crystallisation of excess solute

38
Q

Solubility definition?

A

A chemical property referring to the ability for a given substance to dissolve in a solvent

39
Q

Precipitate meaning?

A

Insoluble solid that forms during a chemical reaction and separates out in solution

40
Q

How to test if chloride ions are present?

A

First silver nitrate: white precipitate
Then dilute ammonia: precipitate disappears
Then concentrated ammonia: N/A

41
Q

How to test if bromide ions are present?

A

First silver nitrate: cream precipitate
Then dilute ammonia: precipitate remains
Then concentrated ammonia: precipitate disappears

42
Q

How to test if iodide ions present?

A

First silver nitrate: yellow precipitate
Then dilute ammonia: precipitate remains
Then concentrated ammonia: precipitate remains

43
Q

How to test for carbonate ions?

A

Add dilute HCl acid to sample
If effervescence observed carbonate is likely
Transfer gas to limewater, if cloudy CO2 is present

44
Q

How to test for sulfate ions?

A

Add barium chloride to sample.
If present white barium sulfate precipitate will form

Fundamentals Of Chemistry (10 decks)

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