Moles and equations Flashcards
All relative masses are compared to ‘the standard’ which is:
1/12th the mass of a carbon-12 atom.
What is the relative isotopic mass?
The relative isotopic mass is mass of an isotope compared with 1/12th the
mass of carbon-12.
What is the relative atomic mass?
The relative atom mass is the weighted mean mass of an atom compared with 1/12th of the mass of carbon-12.
What is the equation for calculating Ar?
Ar = (M1A1)+(M2A2)/A1+A2
What is amount of substance?
Refers to the quantity of a substance that is present in a sample.
The number of particles in the Avogadro constant is:
6.02x10^23
What is the equation for calculating the number of particles using the Avogadro constant?
No. of particles = no. mol (n) x Na (Avogadro)
What is molar mass, Mr?
Molar mass is the mass per mole of a substance.
What are the units for molar mass?
g mol-1
What is the equation for calculating the number of moles from mass?
No. of moles = mass / molar mass
The empirical formula is:
The simplest whole number ration of atoms of each element present in a compound. (always used for giant structures).
The molecular formula is:
The actual number of atoms of each element in a molecule.
What are the 3 instructions to show how to determine the molecular formula from the empirical formula?
- Calculate the molar mass (Mr) of the empirical formula unit.
- Divide the molar mass (Mr) of the compound by the molar mass (Mr) of the empirical formula unit.
- Multiply the empirical formula by this amount to work out the molecular formula.
What is the molar gas volume?
The volume per mole of gas.
What is the volume per mole of gas at RTP?
Approx 24.0dm3 mol-1
RTP is:
20oC and 101KPa
What is the equation for calculating the number of moles of gas at RTP when the volume of gas is in cm3?
No. of moles of gas in mol = Volume of gas in cm3 / 24000 cm3
What is the equation for calculating the number of moles of gas at RTP when the volume of gas is in dm3?
No. of moles of gas in mol = Volume of gas in dm3 / 24 dm3
What is the ideal gas equation?
PV=nRT
P= pressure Pa
V= volume m3
n= moles mol
R= ideal gas constant 8.314
T= temperature K
Conversion:
oC to K
+273
Conversion:
K to oC
-273
Conversion:
KPa to Pa
x1000
Conversion:
Pa to KPa
/1000
Conversion:
cm3 to m3
/1000000
Conversion:
m3 to cm3
x 1000000
Conversion:
dm3 to m3
/1000
Conversion:
m3 to dm3
x1000
The concentration of a solution is:
The moles of solute per unit volume of solvent.
What is the equation for calculating the number of moles of solution?
n = c x v (in dm3)
Conversions:
cm3 to dm3
dm3 to cm3
/1000
x1000
What is a standard solution?
A standard solution is a solution of a known concentration.
What are the 3 instructions to show how to determine the mass of solute needed to make up a standard solution?
- Consider volume + concentration of solution needed.
- Work out the amount (in mol) of solute needed.
- Convert this amount of solute into mass in g to weigh out.
What is mass concentration?
Mass concentration is the mass of solute dissolved in 1 dm3 of solution.
What is the equation for calculating mass concentration?
Mass concentration = mass of solute (in g) / volume (in dm3)
Conversions:
moldm-3 and gdm-3
gdm-3 to moldm-3
x RFM
/RFM
What does stoichiometry mean?
Stoichiometry means the ratio of moles in an equation (balancing numbers).
What are the 3 steps for many mole calculations?
- Calculate the number of moles of the chemical you are given most information about. ‘Calculate the n of the one you know’.
- Use the stoichiometry of the balanced equation to determine the number of moles of the other chemical you have been asked about.
- Answer the question asked. e.g Calculate the volume of oxygen or the mass of magnesium oxide etc.
A reactant is in excess if:
There are more moles of it than are needed to react completely with another reactant.
A limiting reagent is a reactant that:
A reactant that is not in excess will get used up in the reaction and stop the reaction. This is the limiting reagent.
Hydrated salt:
Hydrated salt contains some water as part of its structure. e.g MgCl2.7H20
Anhydrous salt:
Anhydrous salt is a salt that has no water as a part of its structure. e.g MgCl2
What is water of crystallisation?
Water of crystallisation is the water present in hydrated salts, it is the .H20 part.
Heating to constant mass is:
Used to remove water of crystallisation.
What is the equation for calculating percentage uncertainty?
percentage error = error x no of readings for measured value / measured value x 100
Number of readings:
1. Burette
2. Change in temperature
3. Change in mass
4. Volumetric flask
5. Pipette
- 2
- 2
- 2
- 1
- 1
What is the percentage yield if all the reactants in a reaction are converted into products?
100%
What are three reasons why chemical reactions might not produce 100% yield?
- Might not have all reacted.
- Escape of products or reactants.
- Some reactants may be lost during transfer of apparatus.
What is the equation for percentage yield?
% yield = actual amount in mol of products / theoretical amount in mol of product x 100
What is the equation for atom economy?
Atom economy = sum of Mr desired products / sum of Mr of all products x 100
High atom economy is important in industry because:
Less wastage, more sustainable
A low atom economy can be improved by:
Make both products desired products.
What do chemists in industry need to consider when thinking about the sustainability of a chemical process?
- Starting materials
- Energy costs
- Percentage yield
