Chemistry EMPA Written Task Flashcards
What test would you use just to identify a simple acid?
Universal indicator
- result= red
Test for primary alcohol?
Reagent: acidified potassium dichromate + low temperature (to prevent further oxidation into a secondary alcohol = carboxylic acid
colour changes from orange> green (colour of reduced chronium lll ions)
OR
purple> colourless (with potassium manganate Vll)- colour of reduced manganate ll ion).
Test for a secondary alcohol?
Reagent: acidified potassium dichromate + refluxed (further oxidised) = ketone
colour changes from orange> green (colour of reduced chronium lll ions)
OR
purple> colourless (with potassium manganate Vll)- colour of reduced manganate ll ion)
Test for a tertiary alcohol?
Reagent: no visible colour change because in tertiary alcohols the carbon carrying the hydoxyl (OH) group is not bonded to any hydrogen atoms. So there are no C-H bonds to break and the C-C bonds would require too vigorous conditions to break.
why is starch added to bread to absorb water vapour?
To stop the acid reacting with the sodium hydrogencarbonate beforehand.
Sodium hydrogencarbonate produces CO2 in baking powder. What is the advantage of an acid?
The acid neutrilises/reacts with NaHCO3 to produce CO2.
Studies have shown tartaric acid can cause paralysis and ultimately death. Why is this not an issue in baking powder?
Because acid is only going to be used in small quantities in baking powder.
Improvements to techniques in the experiment (Section C)
- Wash the rod into the flask (after stirring)
- Wash beaker into flask (after pouring solution into flask)
- Wash funnel into flask (after filtering through contents)
- Shake/mix final solution.
How do you obtain an average titre from a titration?
Do further titrations to produce two concordant results
- Add together the 2 most concordant results and divide by 2
- exclude other results before calculating average.
Barium chloride is added to magnesium sulfate until no more white precipitate was formed and the mixture was filtered. What 2 main ions were involved in the filtrate?
Cl- (Barium chloride) and Mg2+ (Magnesium sulfate)
Why would you use an excess of a solution instead of a solution (reagent) instead of a solid- could be other way round
To ensure all the compound was reacted/
To ensure all the residue was pure (reacted)
To seperate two reactants where one of them is soluble?
add cold water and filter it out
When it says work out percntage by mass?
do mass = moles x Mr then TIMES BY !00
why is a solution filtered to remove soluble impurities before calculating mass?
it could affect the mass of a precipitate
why is magnesium hydroxide used instead of magneium caebonate to neutrilsie stomach acid?
It proudces less gas in the stomach (C02) so less wind
