C3 - Quantitative Chemistry Flashcards
Moles
What should you always show when answering questions about moles?
Your working!!
Moles
What is relative formula mass?
The relative mass of a chemical compound (sum of the atomic masses within the compound)
Moles
True or false: Mr means RFM
True
Moles
What does Ar mean?
The atomic mass of a particle
Moles
How do you work out the percentage of an element in a compound?
Mass of element (Ar) / Mr (RFM) of compound x 100
Moles
How do you work out the RFM of a substance?
Sum of the Ar of each element in compound
Moles
What are moles a measure of?
How many particles there are in a substance
Moles
How many particles does 1 mole of a substance contain?
6.02 x 10 to the power 23
Moles
What is avogadro’s constant?
6.02 x 10 to the power 23 (how many particles there are in 1 mole of a substance)
Moles
The mass of 6.02 x 10 to the power 23 particles of a substance is equal to the _____ of that substance in grams
RFM
Moles
Derive the equation for moles in any way you want
Mass = moles x RFM because moles is how many lots of RFM there are
Moles
What is the symbol for moles and the symbol for mass?
m - mass
n - moles
Moles
True or false: moles are measured in grams
False - they are measured in moles
Moles
Have you done practice questions using moles?
Yes
Moles
What is the law of the conservation of mass?
No atoms are created or destroyed in a chemical reaction, they only join together in different ways
Moles
True or false: the law of the conservation of mass is useful to remember when doing worksheets about moles
True
Moles
What is a molar reacting ratio?
The number of moles of each particle there are in a balanced equation
Moles
What is relative atomic mass?
The average mass of an element (total mass of all isotopes of an element/number of atoms of that element)
Total mass of all isotopes = abundance of isotope x mass of isotope (obviously)
Limiting reagents
What is a limiting reagent?
The reactant that is completely used up first and therefore limits the amount of product formed
Limiting reagents
How do you work out which particle is the limiting reagent in a chemical reaction?
Compare the actual molar ratio to the theoretical molar ratio
Moles
How do you answer a question asking you to find the missing mass of a substance in a chemical reaction
- Check if equation is balanced - Balance equation if not balanced
- Work out how many moles of each substance has been used in the experiment
- Use the molar ratio to find out how many moles of the missing substance should be used
- Convert moles back to mass
(This should all be common sense and effortless in an exam)
Empirical formula + yield + atom economy
What is empirical formula?
The simplest molar ratio of atoms in a compound
Empirical formula + yield + atom economy
What is the empirical formula of C2H8?
CH4 (methane)
Empirical formula + yield + atom economy
How do you work out the empirical formula from given masses of elements in a compound?
Work out the molar quantity of both elements and then simplify the ratio of moles between them
Empirical formula + yield + atom economy
What is the % Yield in an experiment?
Actual mass of a substance actually produced compared to how much could be theoretically produced in a perfectly balanced equation
Empirical formula + yield + atom economy
How do you calculate % yield?
Actual mass/ theoretical mass x 100
Empirical formula + yield + atom economy
How do you calculate theoretical mass?
Moles present x RFM of a substance
Empirical formula + yield + atom economy
What is atom economy?
The proportion of atoms that are useful products in an equation
Empirical formula + yield + atom economy
How do you calculate atom economy?
RFM of useful products / RFM of total reactants x 100 as a percentage
Empirical formula + yield + atom economy
When a question states ‘a compound contains 75% carbon and 25% hydrogen - find the empirical formula’ what does the percentage mean?
The percentage of mass taken up by each element
(Which means to find the empirical formula you have to divide by the RFM to find the molar ratio between them!!)
Empirical formula + yield + atom economy
What is the molecular formula
The actual number of atoms in a compound (the opposite of the empirical formula)
Empirical formula + yield + atom economy
How do you work out the molecular formula from the mass of a given compound and it’s empirical formula?
Mass / RFM and then find real molar ratio in that compound, multiply molar ratio found by the empirical formula and write as you would an empirical formula (C3H6 for example)
Empirical formula + yield + atom economy
What are 3 reasons why yield might not be 100%
Reaction is reversible (it reaches a state of equilibrium before fully reacting)
Other side reactions occur
Som product was lost (for example as gas in air)
Concentration
What is concentration
The amount of a substance in a given area
Concentration
How do you calculate concentration
Mass/ volume
Concentration
What is concentration measured in?
g/dm3 (decimetres cubed)
Concentration
What is 1 litre in decimetres cubed?
1 dm3
Concentration
What is 1 ml in cm3
1 centimetre cubed
Concentration
What is a solution?
Mix of solute and solvent
Concentration
What is a solute
A substance that can be dissolved in a solution
Concentration
What is a solvent
Something capable of dissolving a solute
