3. AMOUNT OF SUBSTANCE Flashcards
Define Empirical formula
The simplest whole number ratio of atoms of each element present in a compound
Define Anhydrous
Containing no water molecules
Define Relative molecular mass
The weighted mean mass of a molecule of a compound compared with 1/12th of the mass of an atom of carbon-12
Define Relative formula mass
The weighted mean mass of the formula unit of a compound compared with 1/12th of the mass of an atom of carbon-12
Define concentration
The amount of solute, in moles, dissolved in 1dm^3 (1000cm^3) of solution
Define Standard solution
A solution of known concentration
Define Limiting reagent
The reactant that is not in excess, which will be used up first and stop the reaction
What are the 3 equations for working out amount (mol)?
n = m/M
n = cV
n = V(dm^3)/24.0 ONLY USE IF ‘AT RTP’ IS MENTIONED IN THE QUESTION
What is the ideal gas equation?
pV = nRT
p = pressure / Pa
V = volume / m^3
n = amount / mol
R = ideal gas constant (8.31Jmol^-1K^-1)
T = temperature / K
What is the equation for percentage yield?
Percentage yield = actual yield / theoretical yield x 100%
What is the equation for atom economy?
Atom economy = sum of molar mass of desired products / sum of molar mass of all products x 100%
How do you convert from moldm^-3 to gdm^-3?
x by relative formula mass (gmol^-1)
How do you convert from gdm^-3 to moldm^-3?
÷ by relative formula mass (gmol^-1)
How do you convert from cm^3 to dm^ to m^3?
cm^3 -> dm^3 = x10^-3
dm^3 -> m^3 = x10^-3
cm^3 -> m^3 = x10^-6
How do you convert from ˚C to K?
+273
How do you work out empirical formula?
- Calculate moles of each element, n = m/M
- Divide each mol by the smallest mol
- Once each element has the smallest whole number write the formula
How do you prepare a standard solution?
Dissolve an exact mass of the solute in a solvent and make up the solution to an exact volume
What are the standard room temperature and pressure values?
20˚C
101kPa (1atm)
Why may the theoretical yield be difficult to achieve?
- The reaction may not have gone to completion
- Other reactions may have taken place alongside the main reaction
- Purification of the product may result in the loss of some product
What is the limiting reagent?
The reactant that is not in excess, which will be used up first and stop the reaction
Why are reactions with high atom economies good?
- they make processes more efficient
- they preserve raw materials
- they reduce waste
