Past Paper Questions Flashcards
Purpose of Bunsen valve at end of delivery tube
Prevent water from entering delivery tube from water bath
Reason for having boiling tube at certain angle in decomposition
Prevent heating of certain reactant/ mixing of reactant and catalyst
Benefit of using solid catalyst
More easily separated from reactants
Where does water go in and out of reflux condenser
Water in at bottom and out at top
How does starch show colour change
With slight excess of iodine will form complex with starch which is blue-black, from pale yellow
What is inverse of ln
e to the power of
How to find relative abundances for mass spectrum
Divide percentages by smallest one to find ratio
Why use fresh hydrochloric acid in flame test
the acid can become contaminated with residue from previous tests
Appearance of substances when being dried with drying agent
Cloudy to clear
What happens if iodine clock reaction carried out without sodium thiosulfate
Changes colour straight away
Why are metals malleable
Layers of metal ions can Slide Over each other and there are always electrons between layers preventing repulsion between ions in one layer and another
Why can a much less exo student value not be due to measurement uncertainties
Student value much less negative indicating a systematic error, uncertainties will give values scattered about the true value rather than consistently below it meaning cannot explain the discrepancy
When is best buffer solution formed with weak acid and strong base
When weak acid has been half neutralised
Purpose of trial titration
To find the approximate end point
If drawing burette value what must you include
Meniscus with bottom of it touching value
What does drying agent do
Removes/absorbs water
Why use a copper beaker instead of glass when measuring enthalpy change of combustion
Because copper is a better conductor of heat so more of the heat transferred to the water, value more exo and closer to true value
Why would a hydrated compound form a colourless solution on gentle heating
Solid dissolves in water of crystallisation
Do tertiary, secondary or primary halogenoalkanes precipitate faster
Tertiary
How to draw carboxylic acid group in skeletal formula
Do not show carbon, just double bond to oxygen and hydroxyl group
How to calculate percentage uncertainty for using 25cm3 twice which has uncertainty of 0.04cm3
0.04 x 2 / 50 X 100
General formula for cycloalkenes
CnH2n-2
How to ensure concen of propanone and acid are constant during clock reaction
Use a much higher concen of propanone and acid than iodine
How to measure electrical conductivity of metal
Connect to battery (long and short line next to each other) and ammeter and measure current
