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Chemistry A-level (edexcel) > Amount Of Substance > Flashcards

Amount Of Substance Flashcards

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1
Q

Avogadro constant definition

A

The Avogadro constant (L) is the number of atoms, molecules, ions or other chemical entities in one mole of a substance. L = 6.02 x 1023 (it’s in your data book)

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2
Q

Molar concentration definition

A

Molar concentration is the number of moles of a solute per litre of solution. (mol dm-3)

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3
Q

Concentration definition

A

Concentration is amount per unit volume. (usually mol dm-3 but could be g dm-3)

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4
Q

Stoichiometry definition

A

Stoichiometry is the ratio in which reactants react and products are produced, in whole numbers.

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5
Q

What is the law of conservation of mass?

A

The Law of conservation of mass states that mass cannot be created or destroyed.

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6
Q

Definition of limiting reactants

A

Limiting reactants are reactants that restrict the amount of product that a reaction can produce. Usually (at least) one reactant will be in excess (too much) and another will be limiting.

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7
Q

Definition of empirical formula

A

The Empirical formula shows the simplest ratio of atoms of each element present in a compound.

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8
Q

Molecular formula definition

A

The Molecular formula is the actual number of atoms of each element present in one molecule of a compound.

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9
Q

Standard conditions definition

A

Standard conditions are 100kPa pressure and 298K temperature. (0oC = 273K)

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10
Q

Titrations definition

A

Titration is a technique used to find the concentration of an unknown solution by adding a known solution.

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11
Q

Endpoint definition

A

The endpoint of a titration is the point at which enough of the solution from the burette has been added to react completely with the unknown solution.

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12
Q

Equivalence point definition

A

The equivalence point of a titration is the point at which equal moles of acid and alkali are present.

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13
Q

Titre definition

A

The titre is the amount of solution added to reach the endpoint.

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14
Q

Acid definition

A

An acid is a substance which forms solutions with a pH of <7, and is a “proton donor” (provides H+ ions in solution in water)
A base is a substance which will act as a “proton acceptor” for an acid (accepts H+ ions)

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15
Q

Alkali definition

A

An alkali is a base which dissolves in water. It gives a pH of >7.

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16
Q

Indicator definition

A

An indicator is something that changes colour to show the progress of a chemical reaction. It is a weak acid that changes colour depending if it is in acid or alkaline conditions

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17
Q

Strong acid/ alkali definition

A

A strong acid/alkali dissociates or ionises fully in solution in water to give H+ / OH- ions.

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18
Q

Weak acid/ alkali definition

A

A weak acid/alkali dissociates or ionises partially in solution in water to give H+ / OH- ions.

19
Q

Standard solution definition

A

A standard solution is one of a known concentration.

20
Q

Primary standard definition

A

A primary standard is a substance that is suitable for making a standard solution. (high molar mass, high solubility, stable, not hygroscopic)

21
Q

Yield definition

A

The Yield of a reaction is the amount of product you get from the reaction.

22
Q

Atom economy definition

A

The Atom economy of a reaction is a measure of how many atoms (in terms of atomic mass) in reactants end up in your desired product.

23
Q

What is the moles formula?

A

Number of moles in an atom = mass in grams/ molar mass* of atoms

*molar mass can be worked out by finding the RAM of an element/ formula

24
Q

Definition of 1 mole

A

1 mole is the amount of substance that contains the same number of particles as the number of carbon atoms in 12g of Carbon-12

25
Q

What is the formula for number of particles?

A

Number of particles = n x L

Where n is number of moles, and L is avogadro’s constant

26
Q

Molar mass definition

A

Molar mass is the mass per mole of a substance. The units of molar mass are gmol^-1 (worked out by finding the RAM)

27
Q

What is the formula for moles using molar mass and mass?

A

n = m/M

Where n is number of moles, m is mass in grams and M is molar mass

28
Q

What is the ideal gas equation?

A

PV = nRT

P is pressure (Pa, kPa or Nm^-2)
Volume in dm^3 or cm^3
Temperature in kelvin (add 273 to degrees C)
Gas constant is 8.31J/K/mol

29
Q

What are acids also known as ?

A

Proton donors

30
Q

What are bases also known as?

A

Proton acceptors

31
Q

What are some examples of acid?

A
  • HCl
  • HNO3
  • H2SO4
  • CH3COOH
32
Q

What is meant by concentrated acid?

A

Have more H+ ions than diluted acids ( same definition with alkalis, but with OH- ions)

33
Q

What are some examples of bases?

A
  • NaOH
  • Ca(OH)2
  • KOH
  • NH3
34
Q

What is the formula to find moles in a solution?

A

n = CV
Where n is mol, C is concentration and V is volume

35
Q

How do you convert from cm3 to dm3?

A

Divide cm3 by 1000

36
Q

How do you find concentration with only mass and volume?

A

C = g/dm3
Where C is concentration, g is mass and dm3 is volume

37
Q

What are the methyl orange colour changes in acids and alkalis?

A

Red in acid, yellow in alkali

38
Q

What are the phenolphthalein colour changes in acids and alkalis?

A

Colourless in acid, and pink in alkali

39
Q

What equipment is needed for titration practicals?

A
  • suction bulb
  • pipettes
  • beaker
  • burette
  • conical flask
  • graduated volumetric flask
  • stopper
40
Q

Spectator ions definition

A

Spectator ions are not included in ionic equations because the ions do not change

41
Q

Errors because of the apparatus in titration

A

Errors because of the apparatus- burettes and pipettes measure volumes to certain degrees of accuracy-
Calculate % error if volume was 12mL & 24mL

42
Q

Errors because of poor technique

A

Errors because of poor technique- common mistakes are
- not rinsing out the burette and pipette with the correct solutions
-not ensuring that there is no air below the tap in the burette
-getting air bubbles in the stem of the pipette
- not swirling the flask after each addition of solution from the burette
- not shaking the solution in the standard flask thoroughly
- running in the solution from the burette too quickly and overshooting the endpoint

43
Q

What to remember for the exam on titration

A

Record titres to 2dp with last number ending in 0 or 5
Ensure you have at least 2 titres to 0.1cm3 of each other
Never use your rough value in working out the mean titre
Calculate mean titre to 2dp

Chemistry A-level (edexcel) (3 decks)

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