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chemistry > 5: Formulae, Equations and Amounts of Substance > Flashcards

5: Formulae, Equations and Amounts of Substance Flashcards

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1
Q

What is molecular formula

A

The formula that shows the number and type of each atom in a molecule (e.g. C2H4O2)

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2
Q

What is empirical formula

A

The simplest whole number ratio of atoms of each element present in one molecule or formula unit of a compound

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3
Q

How can empirical formula be calculated from mass

A
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4
Q

How can empirical formula be calculated by percentage

A
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5
Q

How can molecular formula be calculated from empirical formula

A
  • Use empirical formula to calulate the relative empirical mass (e.g. C4H10 = (12x4) + (1x 10)
  • Divide the relative formula mass by the relative empirical mass
  • Multiply the elements by the number produced
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6
Q

What is water of crystallisation

A
  • When some compounds can form crystals which have water as part of their structure
  • It is a hydrated compound
  • The compound without water is called anhydrous
  • The conversion of anhydrous compounds and hydrated compounds is reversible by heating hydrated salts or dissolving the anhydrous ones
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7
Q

How to calculate the water of crystallisation

A
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8
Q

What is the ideal gas equation, and what units are used

A
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9
Q

How to convert degrees Celsius to Kelvin

A

+273

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10
Q

How to convert cm3 to m3

A

Multiply by 10^-6

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11
Q

How to convert dm3 to m3

A

Multiply 10^-3

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12
Q

What is the equation for percentage mass of an element

A
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13
Q

What to remember when balancing equations

A
  • Don’t change any formula
  • Put balancing number in front of formula
  • Remener to put state symbols
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14
Q

What to remember when writing ionic equations

A
  • Remember to balance the original equation
  • Spectator ions don’t take part in the equation
  • Only the ions that are reacting
  • Spectator ions can only be cancelled if they are the same on both sides (balanced)
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15
Q

What is a precipitation reaction

A

Two aqueous solutions reacting to form products which include one solid

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16
Q

What is the Avogadro constant

A
  • The number of particles equivalent to the relative atomic mass or molecular mass of a substance
  • 6.02 x 10^23 g mol-1
17
Q

What is the equation for moles

A
18
Q

How can Avogadro’s constant be used to calculate number of particles

A

Number of particles = Avogadro constant x moles of substance

19
Q

How can Avogadro’s constant be used to calculate mass of atoms

A

Mass of atom (g) = relative atomic mass of atom/avogadro constant

20
Q

How can Avogadro’s constant be used to calculate mass of molecules

A

Mass of molecule (g) = relative formula mass of molecule/avogadro constant

21
Q

What is the equation to find concentration

A

Concentration = Moles/Volume

22
Q

How to calculate volume

A

Volume = Number of moles x 24dm3

23
Q

What are random errors and how can they be affected

A
  • Errors that occur by chance and pull the result away from expected in either direction (high or low)
  • Person reading scales badly
  • Instruments scaling system
  • Changes in environment
24
Q

How can the effect of random errors be reduced

A
  • Repeating the experiment
  • Using the mean average of data
  • Ignoring anomalies
25
Q

What are systematic errors with examples

A
  • Errors that occur as a result of a faulty or poorly designed experimental procedure and pull the result away from expected in the same direction (always high or always low)
  • Parallax error, bungs not being efficient
26
Q

How can the effects of systematic errors be reduced

A
  • Setting up the experiment with new equipment
  • Having the experiment done multiple times by different people with different equipment
27
Q

What is the equation for percentage uncertainty

A

Percentage uncertainty = (absolute uncertainty/measured value) x100

28
Q

What is the equation for percentage error

A

Percentage error = (Estimated number - actual number / actual number) x100

29
Q

What is the equation for percentage yield

A

Percentage yield = (actual yield/theoretical yield) x100

30
Q

What are the reason that the percentage yield is under/over 100%

A
  • Under: reaction didn’t go to completion, products were lost, other reactions take place simultaneously
  • Over: Preparing crystals that may be dry still when weighing, impurities
31
Q

What is the equation for atom economy

A
32
Q

What is the atom economy for addition reactions

A

It will always be 100%, as all atoms were used to make the desired product

33
Q

What is atom economy

A

How many of the atoms used in the reaction became the desired product, instead of waste

34
Q

What do titrations measure

A

The concentration of an unknown solution

35
Q

How is a standard solution for a titration prepared

A
  • Weigh out a precise amount of solid
  • Add to a small volume of water to dissolve it
  • Transfer to a volumetric flask
  • Rinse the beaker with distilled water and add to the flask
  • Make the solution up to the maximum mark (bottom of meniscus) of the flask with distilled water
36
Q

Describe the process of a titration

A
  • Measure a known volume of a solution with a volumetric pipette and put it in a conical flask
  • The other solution is put in the burette (usually to 0.00cm3)
  • Indicator is added to the solution in the conical flask
  • Remove the funnel from the burette and measure the initial volume
  • Add small amounts of solution into the conical flask, and swirl
  • Near the end point, place the conical flask on a white tile and add the solution from the burette drop wise
  • Once the colour change has occurred, measure the final volume
  • Repeat multiple times
37
Q

How to obtain results from titration data

A
  • Subtract the initial volume from the final volume
  • Select the data points that are concordant (not including the rough run)
38
Q

What are concordant results

A

Data within 0.1 cm3 of each other

39
Q

Why is the percentage uncertainty double for titration volumes

A

An initial and final volume were taken, so the percentage certainties from both are considered

chemistry (19 decks)

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