Flashcards in Acid and Base Titrations Deck (27):
What is concentration?
It is defined as the amount of solute in a specified amount of solution
How is the concentration of a solution expressed?
Mol/l, g/l, p.p.m, % w/v, % v/v, % w/w
What is a primary standard solution?
It is a water soluble substance that is stable and available in pure form and can be used to make a solution of known concentration
What is a standard solution?
Is a solution whose concentration is accurately known
What does 1M solution contain
1 mole of a solute dissolve in 1 litre of a solution
How is a standard solution prepared
Using a primary standard or by titrating with another solution
What unit of concentration is particularly useful for very dilute solutions?
P.p.m , if concentration of fluoride in a water sample is 2 p.p.m that means that there are 2mg of fluoride ion in every litre of water
What is required to make standard solutions?
Primary standard solution
What care just be taken when making up a standard solution?
Volumetric flask - when filled to calibration mark at temp states, it contains specific known volume
Analytical balance - extremely accurate to measure solute
Wash bottle - no solution is lost
How is a solution of known concentration made up?
-solute is weighed accurately and transferred to clean beaker + small volume of pure water added [wash bottle]
-the mixture is stirred with stirring rod in order to dissolve properly [washbottle]
-poured into volumetric flask using funnel [washbottle with beaker and funnel]
-flask filled to within about 1cm3 of calibration mark and water then added in drops until bottom of meniscus rests on the calibration mark
-flask sealed with stopper and inverted to make sure it is homogenous
What water is added when making standard solution?
Deionised water or pure water
Give an example of a standard solution?
How is the concentration of a solution found?
By titrating with standard solution
Precautions to ensure accurate titration results
-burette is washed out with pure water and then solution it is to contain
-solution added using beaker and funnel
-tap of burette is opened briefly to fill the part of the burette below the tap [displaces air]
-burette filled up until the label of the liquid is above the 0cm3 mark
-tap is opened of burette to ensure its at definite mark
-burette readings taken at eye level : bottom of meniscus read
-pipettes washed with pure water and then solution to be contained [conical with only water]
-indicator either weak acids or weak bases adding too much with affect accuracy
-conical flask swirled and any solution on sides can be washed down using water bottle
-mean of titres is result
Why is a burette more accurate than a graduated cylinder
Markings easier to read
Why is the funnel removed after filling burette?
To control flow - may be drops
Why can't standard solutions be prepared directly?
They are not readily available in pure form
What's the objective of standardisation?
To find its concentration accurately
What three things are needed to find unknown concentration?
-balanced equation - mole ratio
-concentration of one of the reagents
-volume of both reagents
Standardisation of hydrochloric acid using a standard solution of sodium carbonate what indicator is used?
Methyl orange = yellow to peach/pink
Hydrochloric acid/sodium hydroxide titration and then in making salt sodium chloride, indicator?
Methyl orange = yellow - peach/pink
How do you obtain a sample of salt from hydrochloric acid and sodium carbonate titration?
-place 25cm3 of the sodium hydroxide solution in a beaker with no indicator
-using results from earlier, add enough hydrochloric acid to neutralise it
-gently hear solution until all water has been evaporated. Sample of sodium chloride will remain
Applications of acid-base titrations
Find concentration of everyday materials, the concentration of the weak acid in vinegar ethanoic acid found by titrating against sodium hydroxide
Determination of concentration of ethanoic acid in vinegar, indicator?
Phenolphthalein - pink=colourless
Why is diluted vinegar used?
Acid in vinegar is too concentrated. If undiluted vinegar was used, small acid titration volume would result and increase percentage error
Determination of the amount of water of crystallisation in hydrated sodium carbonate, indicator?
Methyl orange - yellow = pink/peach