Topic 5-Formulae, Equations & Amounts of Substances Flashcards
Give the definition of the Empirical Formula
The smallest whole number ratio of the atoms of each element in a compound.
If you have 5cm, how many dm will you have?
0.005dm
What does Avogadro’s constant tell you? What is the figure?
The number of particles in a mole, 6.02 x 10^23
Give the definition for the molecular formula.
The molecular formula gives the actual numbers of atoms of each type of element in a molecule.
What is a base?
Bases are substances that act as the opposite of acids, they also release hydroxide ions in aqueous solutions.
A solution of sodium hydroxide is described as having a concentration of 0.4 mol dm-3. Explain what this means.
0.4 mols of sodium hydroxide are dissolved in every dm3 of solution.
What number must you add to the degrees in C to get the degrees in Kelvin?
273
What equation can you use for % uncertainty?
(uncertainty/measurement) x 100 x no.of measurements
What will form when a reactive metal + acid react?
Salt + Hydrogen
What will form when you react an acid and a base?
Salt + water
What reactants will produce salt + water + carbon dioxide?
Acid + carbonate
Define the concentration of a solution.
How many moles/grams are dissolved per 1dm”3
What are the units for concentration?
g dm-3
or
mol dm-3
What type of reaction has taken place if two aqueous solutions react to form a solid?
A precipitation reaction i.e solid precipitate has formed.
What is the only thing ionic equations show?
Only the reacting particles (and products they form)
Define Molar gas volume.
The space one mole of gas occupies at a certain temp and pressure.
What is the volume of 1 mol of gas at room temperature and pressure?
24dm”3 mol-1
What is the volume of 1 mol of gas at standard temperature and pressure?
22.4dm”3 mol-1
What is the IDEAL gas equation?
PV=nRT
What is a hazard?
Anything that has the potential to cause harm or damage.
What is risk?
The probability of someone or something being harmed if they are exposed to the hazard
Define systematic error
These errors are the same every time you repeat the experiment e.g. set up of equipment.
Define a random error
These errors are different every time you repeat the experiment e.g. error reading burette.
Which type of error can be reduced by repeating the experiment?
The random errors.
If the conical flask is washed out between each titrations, will this effect the moles?
No this has NO EFFECT on mols.
How will the experiment be affected if the pipette is washed out with water before each titration?
It will dilute what is in the conical flask so titres will be smaller.
What effect will completely filling the volumetric flask rather than it only being to the graduation line, have?
Solution in the burette will be too dilute therefore titre will be larger than it should be.
How do you know what is ionic?
which ions become disassociated
Roughly-
Metal (or ammonium) compounds. Acids in solution = ionic (only split up ions if it’s aqueous)
anything else e.g. insoluble salts. = not ionic
How do ionic equations for acids and metal hydroxides differ?
All ions disassociate so in the end its always a reaction between
H + OH –> H2O
What happens in ionic equations for the reaction between acids and metal carbonates?
It will ALWAYS be
CO3 + 2H —-> CO2 + H2O
Even in net ionic equations, only which type of element should have a charge?
AQUEUOUS atoms are only ever written with a charge.
Leave gases and solids neutral!!!
What should you do with the conical flask to ensure the results of the experiment aren’t affected
rinse with distilled or deionised water.
Equation for atom economy?
mass of atoms in desired product/
mass in all reactants x100
Equation for percentage yield?
actual yield/ maximum theoretical yield x 100
Define “mole”
One mole is the amount of substance that contains the same number of particles as the number of carbon atoms in 12g of C12.
What can you know about an equation involving a basic oxide?
That a basic oxide acts oppositely to an acid
When are your results labelled as “concordant”
When they are within 0.1 of each other (NOT INCLUDING ROUGH TITRE)
In a question you know that two compounds are in a 1:1 ratio. How do you work out the percentage yield of the compound?
As it is in 1:1 ratio, this mean that the THEORETICAL YIELD is equal to this number of mols. Then rearrange the equation.
Define the term ‘mole’
One mole is amount of substance that contains that contains the same number of particles as the number of carbon atoms in exactly 12g of carbon 12
What are the units for molar mass?
g mol-1
LITERALLY MR THINK G / MOL
Explain 3 actions the technician might take in the procedure just before the end point of titration to ensure end point accurate
- White tile to accurately see point of colour change
- Drop by drop when closer to rough titre TO AVOID OVERSHOOTING
- swirl to ensure all alkali and acid react.
In a question where they use a 100cm3 solution and then only put 10cm3 into conical flask remember…..
To divide the moles by 10!
10/100 of solution so not representational of just 10!
How does a graph show direct proportion?
Straight line through origin.
Why would you add a pinch of Xcarbonate to acid before the reaction
To saturate solution with CO2.
What happens to a solution during a dilution?
Will increase the volume, and decrease the concentration but the moles will stay the same.
What is 1000 mg in g?
1g = 1000mg
How many kg in 1 tonne?
1000kg
