3 Amount of substance Flashcards
Explain Avagadro’s constant. (1 mark)
The number of particles contained in one mole of any substance.
How do you calculate the number of moles something? (1 mark)
moles= mass/Mr or molar mass
What is molar mass? (1 mark)
The mass (in grams) in each mole of a substance.
What is a molecular formula? (1 mark)
The number of atoms of each element in a molecule.
What is an empirical formula? (1 mark)
The simplest whole number ratio of atoms of each element in a compound.
Define relative molecular mass (Mr). (2 marks)
Relative molecular mass is the mass of a molecule relative to 1/12th of the mass of a carbon-12 atom.
Define relative formula mass. (2 marks)
Relative formula mass is the mass of a formula unit relative to 1/12th of the mass of a carbon-12 atom.
What does it mean if a salt is hydrated? (1 mark)
Water molecules are part of their crystalline structure.
What are two assumptions that decrease the accuracy of experimental formula of hydrated salts? (2 marks)
All the water has been lost
No further decomposition of the salt
What are the two equations for concentration?
conc= mol/vol
conc=mass/vol
What is a standard solution? (1 mark)
A solution of known concentration.
What is molar gas volume? (2 marks)
The volume per mole of gas molecules at a stated temperature and pressure.
State the ideal gas equation. (2 marks)
pV=nRT
What are the units for the ideal gas equation? (3 marks)
p- Pascals (Pa)
V- Metres cubed (m3)
n- Moles (mol)
R- 8.31 Jmol-1K-1 (the ideal gas constant)
T- Kelvin (K)
What are the values of room temperature and pressure (RTP)? (2 marks)
293K/298K or 20/25 degrees celcius
101kPa or 1atm
Explain what the term stoichiometry means. (1 mark)
The ratio of the amount, in mol, of each substance in an equation.
What is the equation for percentage yield? (1 mark)
= (actual yield/theoretical yield) x 100
What is the limiting reagent? (1 mark)
Th reactant that is not in excess.
What is the equation for atom economy? (1 mark)
= (Mr of desired products/Mr if all products) x 100
How is relative formula mass calculated? (1 mark)
By adding together the relative atomic masses of the elements in the empirical formula.
How do you convert between mol/vol and mass/vol? (1 mark)
mol/vol= (mass/vol)/Mr
Identify a compound of calcium that could be used to convert a soil pH from 5.8 to 7.5. (1 mark)
Ca(OH)2
or CaO
A salt has empirical formula H4N2O3, suggest the formulae of the ions present in this salt. (2 marks)
NH4+
NO3-
