Making Standard Solutions Flashcards
what is a standard solution
a solution whose concentration is accurately known
what is the easiest way to prepare a standard solution
- to dissolve a known mass of a substance into water
- to have a known volume of the solution
what is the name of the substance that is dissolved into the water
primary standards
what should primary standards ideally be in terms of their level of reactivity
- they should be chemically stable
- not absorb water from the atmosphere
- should quickly react with other substances when used in titrations
what should primary standards ideally be in terms of availability
they should be available in a high degree of purity
what should primary standards ideally be in terms of their solubility and molar mass
- they should be soluble in water
- and should have a high molar mass as solids
what are examples of two solutions that are used in titrations despite not being primary standard substances
- hydrochloric acid
- sodium hydroxide
why is hydrochloric acid not considered a primary standard
- because it only exists in gaseous and aqueous states
- meaning it cant be a solid even though it has a high molar mass
why is sodium hydroxide not considered a primary standard despite being able to be a solid
- it absorbs water vapour and carbon dioxide from the atmosphere
- meaning it isnt chemically stable
what does it mean for a substance to be chemically stable
it doesnt decompose or react with substances in the air
why is weighing sample of sodium hydroxide solution a problem despite it being able to be accurately weighed
- because it can react with water and CO2 in the atmosphere
- you cant be certain about what is being weighed
- as there are unknown masses of water and CO2 in it
what is sulfamic acid
- a readily available primary standard for use in acid-base titrations
- that has the necessary characteristics
if sulfamic acid has the formula NH2SO3H, what is its molar mass
97gmol-1
you have 250cm3 of 0.1M of sulfamic acid. how would you calculate its mass
- moles = concentration x volume
- 0.25 x 0.1 = 0.025 mols
- mass = moles x Mr
- 0.025 x 97 = 2.4g
what apparatus do you need for making a standard solution of sulfamic acid
- safely glasses and a lab coat
- an accurate balance (+- 0.001g)
- weighing bottle
- spatula
- 250cm^3 beaker
- 250cm^3 volumetric flask
- wash bottle with deionised water
- small funnel
- glass stirring rod
now that you have calculated the rough mass of sulfamic acid, what is the first step in the experiment
- adding between 2.3 and 2.5g of sulfamic acid to the weighing bottle
- in order to weigh accurately
what do you after you have weighed the weighing bottle with the sulfamic acid
- transfer as much as possible of the acid into a beaker
- then reweigh the weighing bottle
what do you then add to the beaker
- 100cm^3 of deionised water
- stir with the rod until all the sulfamic acid has dissolved
what do you do the stirring rod after you have used it
- wash traces of the solution on the rod into the beaker
- using deionised water
how would you then transfer the solution in the beaker into the volumetric flask
by placing a funnel into the neck of the volumetric flask
what do you do to the beaker after this
- you wash the beaker with the wash bottle
- and transfer the rinsings into the volumetrc flask
why is even more deionised water added to the flask after all of this
to make the graduation mark exactly on the flask
how would you then make a uniform solution in the flask
by putting a stopper on the flask several times and inverting it
