5: Formulae Flashcards
How many particles are in a mole?
6.02 x10^23
What is the symbol for moles?
n
What is the name of the constant for the number of particles in a mole?
Avogadro’s constant, L
What is the equation for moles using just number of atoms?
Moles = Number of particles / number of particles in a mole
What is molar mass, M?
Mass per mole
Same as the relative atomic mass (Mr)
What is the moles equation?
Moles = Mass / molar mass
How would you calculate the number of atoms in something?
Number of atoms = Moles x Avogadros constant
What is concentration?
The number of moles dissolved in 1 dm3
What is 1 dm3 equivalent to?
1 litre
What is the concentration equation for moles?
Moles = Concentration x Volume
What is the concentration equation for mass?
Mass = Concentration x Volume
What is the unit for concentration?
Mol dm-3
or g dm-3
What is empirical formula?
Smallest whole number ratio of atoms in a compound
How do you work out the empirical formula from experiment data?
Work out how many moles of each product
Divide by the smallest
Ratio must be whole, and is number of atoms in empirical formula
How would you work out empirical formula from percentages?
Work out moles as if there is 100g of product and do the same
What is the equation for percentage composition?
Percentage composition of X = mass of element in compound / total mass of compound x 100
What is shown in ionic equations?
Reacting particles and what is formed
How do you determine what to include in ionic equations?
Write out all ions on both sides
Cancel any ions that occur on both sides
What is a spectator ion?
An ion that is in the reaction but is not changed
What is reaction stoichiometry?
Ratios of reactants and products
number before
What are the 4 state symbols?
s = solid l = liquid g = gas aq = aqueous (solution in water)
What occurs in displacement reactions?
More reactive element reacts to take the place of less reactive element
What occurs when an acid reacts with a base?
Acid + Base -> Salt + Water
2H+ + 2OH- -> 2H2O
What occurs when an acid reacts with a carbonate?
Acid + CO3- -> Salt + Water + CO2
2H+ + CO3 2- -> H2O + CO2
What is the volume equation?
Moles = Volume in dm3 / molar gas volume
What is the molar gas volume at room temp. & pressure?
24 dm3 mol-1
What is the molar gas volume at standard temp. & pressure?
22.4 dm3 mol-1
How can you find the volume of a gas?
Collecting gas in a gas syringe
Displacing water from measuring cylinder
What is the ideal gas equation?
pV = nRT p = pressure (Pa) V = volume (m3) n = moles R = 8.31 J K-1 mol-1 T = Temperature (K)
How do you convert degrees Celsius to kelvin?
K = C + 273
What is the gas constant?
R = 8.31 J K-1 mol-1
How do you convert cm3 to m3?
m3 = cm3 x 1/1000000
How do you convert dm3 to m3?
m3 = dm3 x 1/1000
How would you use the ideal gas equation to work out the molar mass of an unknown, volatile liquid?
Put a known mass of liquid in flask Attach sealed gas syringe Warm until fully evaporated Record volume of gas and temp. Use equation to work out how many moles and then molar mass
What is a hazard?
Anything that has potential to cause harm or damage
What is a risk?
Probability of someone being harmed
What is a standard solution?
A solution that has a known concentration
What is the function of a burette?
Measure different volumes and let you add solution drop by drop
What is the function of a pipette?
Measure only one volume of solution
How do you use a pipette?
Fill the pipette to just above the line and take out of solution and drop to line for exact measurement
Give the steps to do a titration
Measure alkali of unknown conc. using a pipette
Add a few drops of an indicator such as phenolpthalein
Rinse & fill a burette with the standard solution
Perform rough titration to estimate end point until permanent change
Perform accurate titration until 2 cm3 of end point then add acid by drop
Work out acid to neutralise acid, the titre
Repeat until titres are concordant (within 0.1 cm3 of eachother)
What are the two main indicators for acid/alkali reactions?
Methyl orange - yellow to red when adding acid to alkali
Phenolphthalein - red to colourless when adding acid to alkali
How can you obtain g dm-3 from the mol dm-3?
g dm-3 = mol dm-3 x Mr
What is the calculation for volume?
volume (cm3) = moles x 1000 / concentration
What are the assumptions of an ideal gas?
There are no (or negligible) intermolecular forces between the gas molecules
The volume occupied by the molecules is negligible relative to the volume of the container
Temp is proportional to average kinetic energy of molecules
All collisions are perfectly elastic (no loss of kinetic energy)
Pressure is due to collisions between molecules and wall of the container
Molecules behave as rigid spheres
Which gases behave like ideal gases?
Those which are well above their boiling points
Nitrogen, oxygen, hydrogen and noble gases
How do you convert different volumes?
1 m3 = 1000 dm3 = 1000000 cm3
