Module 2: Chapter 3 (Amount of substance) Flashcards Preview

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How is mol calculated?

amount, n = mass, m / molar mass, M


How is the number of 'particles' calculated?

n x Na (6.02 x 10^23)


What is the molecular formula?

the number of atoms of each element in a molecule


What is the empirical formulae?

the simplest whole-number ration of atoms in each element in a compound


What is the water of crystallisation?

- Many crystalline solids are hydrated, water molecules are incorporated into their crystalline structure
- this water is known as the water of crystallisation


What is the approach to calculating the formula of a hydrated solid?

- subtract mass of crucible & anhydrous salt from mass of crucible; hydrated salt and use answer to calculate the moles of water
- subtract the mass of crucible from mass of crucible & anhydrous salt and use the answer to calculate the number of moles in the salt
- divide the moles of water by the moles of the compound


What is the equation to calculate mol of a gas at RTP?

mol (n) = volume of gas (dm^3) / 24dm^3


What is the ideal gas equation?

pV = nRT

p -> pressure (Pa)
V -> volume (m^3)
n -> moles of gas
R -> ideal gas constant (8.314)
T -> temperature (Kelvin)


How do you convert between Pa and KPa?

Pa -(÷1000)-> KPa
KPa -(x1000)-> Pa


How do you convert between cm^3, dm^3 and m^3?

cm^3 -(÷1000)-> dm^3 -(÷1000)-> m^3
m^3 -(x1000)-> dm^3 -(x1000)0-> cm^3

cm^3 -(÷1 000 000)-> m^3
m^3 -(x1 000 000)-> cm^3


How do you convert between K and Celsius?

C -(+273)-> K
K -(-273)-> C


What is the concentration of a solution?

The concentration of a solution tells us the amount of solute in a particular volume of solution


How is concentration calculated?

concentration (moldm^-3) = mol (n) / volume (dm^3)


How do you convert between conc in gdm^-3 and moldm^-3?

gdm^-3 -(÷Mr)-> moldm^-3
moldm^-3 -(xMr)-> gdm^-3


What is meant by the 'amount of substance'?

- n
- counts the number of particles in a substance measured in the unit mole, mol.


Explain what a mole is

One mole is the amount of a substance that contains 6.02x10^23 particles (Avogadro constant)


What is Avogadro's constant?

Is 6.02x10^23 mol^-1, the number of particles in each mole of carbon-12
- C-12 is the standard measurement of relative atomic masses


What is Molar Mass, M?

- molar mass is the mass per mole of a substance
- the units of molar mass are gmol^-1


What is molar gas volume?

- the molar gas volume Vm is the volume per mole of gas molecules at a stated temperature and pressure
- volume of gas depends on the pressure and temperature, most experiments are at RTP


What is meant by RTP?

- RTP is about 20 degrees celcius and 101 kPa (1 atm)
- at RTP 1 mole of gas molecules has a volume of approx 24.0 dm^3
- therefore at RTP the molar gas volume = 24.0 dm^3


What is meant by the term hydrated?

a crystalline compound containing carbon and hydrogen only


What does anhydrous mean?

containing no water molecules


How do you calculate percentage yield

actual yield / theoretical yield


Why is theoretical yield hard to achieve?

- reaction may not have gone to completion
- other reactions may have taken place alongside the reaction (side reactions)
- purification of the product may result in the loss of some product


How is atom economy calculated?

Mr of desired products / Mr of all reactants


What are reactions with high atom economies?

- produce a large proportion of desired products and a few unwanted products
- are important for sustainability as they make the best use of natural resources