amount of substance Flashcards
what is the relative atomic mass?
the average mass of the isotopes for an element on a scale of which a carbon-12 atom has a mass of exactly 12 units
what is the equation for the relative atomic mass of an element?
average mass of one atom of an element x 12 // mass of one atom of C12
what is the definition of relative molecular mass or Mr?
the average mass of one molecule on a scale of which a carbon- 12 atom has a mass of exactly 12 units
what is the equation for the relative molecular mass of a molecule?
average mass of a molecule x 12 // mass of one atom of C12
when is the term relative formula mass used?
for ionic compounds because they don’t exist as molecules
what is the avogadro’s constant?
the number of atoms in 12g of Carbon 12
what is a mole?
the amount of substance that contains 6.022 x 10^23 particles
what is the value of avogadro’s constant?
6.022 x 10^23
what is the moles equation?
moles= mass/Mr (mass of one mole)
what does the concentration of a solution tell us?
how much solute is present in a known volume of solution
what are concentrations of solutions measured in?
mol/dm^3
what is the equation for how to work out the number of moles in a solution?
number of moles in solution=
concentration(mol/dm^3) x volume (dm3)
what is Boyle’s law?
the product of pressure and volume is constant as long as the temperature remains constant
pressure x volume = constant
what is Charles’ law?
volume is proportional to temperature as long as pressure remains constant
volume/ temp = constant
what is Gay-Lussac’s law (also called the constant volume law)?
pressure is proportional to temperature as long as volume remains constant
pressure/ temp = constant
what does combining Boyle’s, Charles’ and Gay- Lussac’s laws result in?
pressure x volume/ temperature = constant for a fixed mass of gas
what is the ideal gas equation in words?
pressure x volume = number of moles x gas constant x temperature
what is the ideal gas equation in symbols?
P x V = n x R x T
what is the ideal gas equation in units?
Pa x m^3 = mol x JK^-1mol^-1 x K
what is always the value of R (gas constant)?
8.31 JK^-1mol^-1 (always given this)
what unit does temperature always need to be changed to in ideal gas equations?
Kelvin
on the kelvin scale, where is 0 Degrees Celsius?
273k
so you always add 273 to the temp
what is the empirical formula?
the formula that represents the simplest whole number ratio of the atoms of each element present in a compound
what is the molecular formula?
the number of atoms of each element in one molecule
how do we find the empirical formula of a compound from its composition by percentage or mass?
- write out the mass or percentage of each element
- divide each mass or percentage by the Ar of the element (not Mr)
- divide by smallest number
what is the atom economy?
a measure of what proportion of the products of a reaction as the desired product and how much is waste. The higher the atom economy, the less waste that is produced.
what is the equation for atom economy?
mass of desired product from equation/ total mass of products
ALL MULTIPLIED BY 100%
OR
Mr of desired product/ Mr of total products
what is the percentage yield?
the amount of product obtained compared to the theoretical mass of the product
what is the equation for percentage yield?
mass of product obtained/ maximum theoretical mass of product
ALL MULTIPLED BY 100
what are reasons for percentage yield not being 100%?
-reversible reaction
-some product may be lost when it is separated from the reaction mixture
-some of the reactants may react in other reactions(side reactions)
what is the formula for nitrate?
NO3-
what is the formula for sulfate?
SO4 2-
what is the formula for carbonate?
CO3 2-
what is the formula for hydrogen carbonate?
HCO3 -
what is the formula for hydroxide?
OH-
what is the formula for phosphate?
PO4 3-
what are the formulas for zinc and silver?
Zn2+
Ag+
what are spectator ions?
some ions which aren’t involved in the reaction when ionic compounds are dissolved in water
spectator ions do not change state!
what does an ionic equation show?
only shows the species that are involved in the reaction
what is the rule for deciding who gets to be in the ionic equation?
if you don’t change state…. you’re not invited to the party!
how can you use Avogadro’s constant to convert between number of particles and number of moles?
number of particles= number of moles x Avogadro’s constant
how do we calculate uncertainty of equipment in chemistry?
uncertainty x number of readings/ value
ALL X100
how do we get a concentration in mol/cm3 into g/dm3?
x Mr
how do we convert cm3 into dm3?
divide by 1000
how do we convert dm3 to m3?
divide by 1000
how do we convert cm3 to m3?
divide by 1 mil
How much space does 1 mole of a gas occupy at room temp and pressure?
24dm3
what are some rules to remember how acids react in titrations?
Monoprotic acids contain one H+ ion per unit (eg HCL, HNO3) react with NaOH in 1:1
Diprotic acids contain two H+ ions per unit (eg H2SO4) react with NaOH in ratio 1:2
triprotic acids contain three H+ ions per unit (eg H3PO4) react with NaOH in 1:3
describe how to prepare 250cm3 of an aqueous standard solution of an acid?
-use a weighing boat and spatula to weigh out (on a 2 d.p. mass balance) 2.00g of the solid acid.
-pour the 2g of solid into the beaker and ensure to weight the boat before and after pouring out contents to calculate exactly how much solid has been used.
-add approx 100cm3 of distilled water. keep stirring with glass rod to ensure all acid is dissolved
-use a funnel to pour the solution into a 250cm3 volumetric flask
-use distilled water to add the washings and make the solution up to the 250cm3 mark. Use a dropping pipette when you get close to the mark.
-invert the volumetric flask multiple times with the cap on to mix the solution
state one advantage of using a conical flask rather than beaker for a titration?
less chance of splashing because of the narrow neck when swirling solution
explain the importance of percentage yield?
helps us get as much product as possible in a reaction/ efficient conversion of reactants to products
explain the importance of atom economy?
maximising mass of reactants that end up in the desired product/ minimising amount of by-products
