Amount Of Substance Flashcards
Avogadro constant definition
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)
Molar concentration definition
Molar concentration is the number of moles of a solute per litre of solution. (mol dm-3)
Concentration definition
Concentration is amount per unit volume. (usually mol dm-3 but could be g dm-3)
Stoichiometry definition
Stoichiometry is the ratio in which reactants react and products are produced, in whole numbers.
What is the law of conservation of mass?
The Law of conservation of mass states that mass cannot be created or destroyed.
Definition of limiting reactants
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.
Definition of empirical formula
The Empirical formula shows the simplest ratio of atoms of each element present in a compound.
Molecular formula definition
The Molecular formula is the actual number of atoms of each element present in one molecule of a compound.
Standard conditions definition
Standard conditions are 100kPa pressure and 298K temperature. (0oC = 273K)
Titrations definition
Titration is a technique used to find the concentration of an unknown solution by adding a known solution.
Endpoint definition
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.
Equivalence point definition
The equivalence point of a titration is the point at which equal moles of acid and alkali are present.
Titre definition
The titre is the amount of solution added to reach the endpoint.
Acid definition
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)
Alkali definition
An alkali is a base which dissolves in water. It gives a pH of >7.
Indicator definition
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
Strong acid/ alkali definition
A strong acid/alkali dissociates or ionises fully in solution in water to give H+ / OH- ions.
Weak acid/ alkali definition
A weak acid/alkali dissociates or ionises partially in solution in water to give H+ / OH- ions.
Standard solution definition
A standard solution is one of a known concentration.
Primary standard definition
A primary standard is a substance that is suitable for making a standard solution. (high molar mass, high solubility, stable, not hygroscopic)
Yield definition
The Yield of a reaction is the amount of product you get from the reaction.
Atom economy definition
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.
What is the moles formula?
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
Definition of 1 mole
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
What is the formula for number of particles?
Number of particles = n x L
Where n is number of moles, and L is avogadro’s constant
Molar mass definition
Molar mass is the mass per mole of a substance. The units of molar mass are gmol^-1 (worked out by finding the RAM)
What is the formula for moles using molar mass and mass?
n = m/M
Where n is number of moles, m is mass in grams and M is molar mass
What is the ideal gas equation?
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
What are acids also known as ?
Proton donors
What are bases also known as?
Proton acceptors
What are some examples of acid?
- HCl
- HNO3
- H2SO4
- CH3COOH
What is meant by concentrated acid?
Have more H+ ions than diluted acids ( same definition with alkalis, but with OH- ions)
What are some examples of bases?
- NaOH
- Ca(OH)2
- KOH
- NH3
What is the formula to find moles in a solution?
n = CV
Where n is mol, C is concentration and V is volume
How do you convert from cm3 to dm3?
Divide cm3 by 1000
How do you find concentration with only mass and volume?
C = g/dm3
Where C is concentration, g is mass and dm3 is volume
What are the methyl orange colour changes in acids and alkalis?
Red in acid, yellow in alkali
What are the phenolphthalein colour changes in acids and alkalis?
Colourless in acid, and pink in alkali
What equipment is needed for titration practicals?
- suction bulb
- pipettes
- beaker
- burette
- conical flask
- graduated volumetric flask
- stopper
Spectator ions definition
Spectator ions are not included in ionic equations because the ions do not change
Errors because of the apparatus in titration
Errors because of the apparatus- burettes and pipettes measure volumes to certain degrees of accuracy-
Calculate % error if volume was 12mL & 24mL
Errors because of poor technique
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
What to remember for the exam on titration
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
