TOPIC 5: FORMULAE, EQUATIONS AND AMOUNTS OF SUBSTANCES Flashcards
What is Avogadro’s number?
6.02 x 10^23
How do i calculate number of moles given number of particles
Moles= Number of particles you have/Number of particles in a mole (Avogadros number)
Define molar mass
The relative molecular mass
Two equations for moles
- Concentration x volume
2. Mass/Mr
2 Equations for concentration
- Concentration=mass of substance/volume
2. Concentration=moles/volume
When a base reacts with an acid what does it form
A salt and water
How to calculate number of moles of a gas
volume in dm3/Molar gas volume
What is the Molar gas volume at Room temperature
24 dm^3mol^-1
Ideal Gas Equation and define each term
PV=nRT
P= Pressure V= Volume N= Number of moles R= gas constant T= Temepraure in Kelvin
What is the gas constant?
8.31 J k^-1
Describe the colour change for methyl orange
From an Acid to an alkali it turns from yellow to red
Describe the color change for phenolphthalein
From an Acid to an Alkali it turns from red to colourless
How to calculate percentage uncertainty
Uncertainty/Reading x 100
what is the uncertainty
Resolution/2
How to work out Total uncertainty of an experiment
- Find the percentage uncertainty for each bit of equipment
- Add the individual percentage uncertainties
- Take this uncertainty and take it from the result
Equation for percentage yield
actual yield/theoretical yield x 100
Equation for atom economy
Atom economy = Relative formula mass of desired products / Relative formula mass of all reactants x 100
What is the molar mass
The same as the relative molecular mass but instead molar mass has units gmol -1
What is the empirical formula
Gives the smallest whole number of ratio of atoms of each element in a compound
What is the molecular formula
Gives the actual numbers of atoms of each type of element in a molecule
How to calculate the percentage composition of an element
Percentage composition of element = Total mass of element in compound/ Total mass of compound x 100
What happens in a precipitation reaction
If two aqueous compounds react together and one of the products forms as a solid a precipitation reaction takes place
How do you use the ideal gas equation to work out the molar mass of an unknown volatile liquid
- Put a known mass of the liquid in a flask then attach it to a sealed gas syringe
- Gently warm the apparatus in a water bath until the liquid completely evaporates
- Record the volume of gas in the syringe and the temperature of the water bath
- Use the ideal gas equation to work out the number of moles of the liquid in your sample and use the equation moles= mass/mr to find mr
How can we reduce percentage uncertainty
If we use a larger volume of liquid for example percentage uncertainty will be lower
What is a systematic error
They are the same every time you repeat an experiment and can be caused by an error due to the set-up
What is a random error and how do we reduce it
An error that make the results a bit different when you repeat and experiment. Repeating the exepriemtn and calculating a mean will reduce the effect of random error
What is meant by the theoretical yield
The mass of product that should be made in a reaction if no chemicals are lost in the process
What is the atom economy for addition reactions
- 100 % as the reactants combine to form a single product and no atoms are wasted
What is the atom economy and percentage yield in substitution reactions
- The atoms of the reactant are swapped and you get the desired product and the bi-product
- Substitution reactions have a high percentage yield and low atom economy as a bi-product is formed
