Required Practicals (Paper 1) Flashcards
Describe how you would use metal oxide/carbonate and dilute acid to make pure, dry crystals
- use metal oxide/carbonate and dilute acid
- add dilute acid to a beaker
- heat sulfuric acid with bunsen burner
- add metal oxide (or small ribbons of magnesium if that is what question required) one spatula at a time
- stir
- continue adding until magnesium oxide is in excess
- filter
- using a filter paper and funnel
- to remove excess magnesium oxide
- pour solution in an evaporating basin
- warm/heat the solution in an evaporating basin using a water bath/electric heater to evaporate the solution
- to point of crystallisation
- leave to cool and crystallise (overnight) at room temperature
• pat dry with filter paper
this is probably the best method out of all of them, so remember these points and choose this when revising over heating half solution, etc
Describe a method to determine the reacting volumes of solutions of a strong acid by titration, when given the strong alkali’s volume
1. Use the pipette and pipette filler to add 25 cm3 of alkali (e.g. sodium hydroxide) to a conical flask.
- Add a few drops of indicator p**henolphthalein and put the conical flask on a white tile.
- Fill the burette with acid (e.g. HCl) and record the starting volume.
- Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix
- When colour starts to change, add drop by drop for accuracy
- Stop adding the acid when the end-point is reached (when the indicator first permanently changes colour to pink). Record the final volume reading.
- Repeat steps 1 to 5 until you get concordant titres/results
- Caclaulte mean
there is some additional info for this practical covered in 4.2.5 (Titrations)
In a titration, why should a burette and pipette be washed out with their solutions before an experiment?
Washing removes any chemicals that have been left behind after another experiment
which might react with the substances in the experiment
and produce erroneous (wrong) results
What is the purpose of a rough titration?
to determine the approximate value of the end point
which saves having to add the reagent drop by drop from the beginning
however, the rough titration overshoots the end point and the is not normally used
Why shouldn’t universal indicator be used in a titration?
A sharp colour change is needed to correctly indicate the end point
universal indicator includes a mixture of indicators, so the colour change would not be sharp enough
What colours are alkalis and acids with phenolphthalein indicator?
Alkali - pink
Acid - colourless
With phenolphthalein indicator, what colour change will be observed when acid is used to neutralise (so added to) an alkali?
pink to colourless
and inverse
Describe a method to investigate the variables that affect temperature changes in reacting solutions with 2 solutions e.g. acid and alkali
1. Choose independent variable (likely stated in question) e.g. concentration of one of the reactants, or the type of acid/alkali being used (for neutralisation if alkali), or the type of metal/metal carbonate being used (for displacement)
- Place the polystyrene cup inside the glass beaker to make it more stable.
- Measure an appropriate volume of each liquid, eg 25 cm3.
- Place one of the liquids in a polystyrene cup.
- Record the temperature of the solution.
- Add the second solution and record the highest or lowest temperature obtained.
- Change your independent variable and repeat the experiment.
similar for reacting solutions of acid plus metals, acid plus carbonates, neutralisations (above), displacement of metals (but need solid method which is on anotehr card for some of these)
Describe a method to investigate the variables that affect temperature changes in reacting solutions with a solid and solution e.g. metal and acid
- Choose independent variable e.g. the surface area of the solid, or the type of acid being used, or the type of metal being used
- Place the polystyrene cup inside the glass beaker to make it more stable.
- Measure an appropriate volume of the solution, eg 25 cm3.
- Measure an appropriate mass of the solid, or select a suitable sized piece of metal.
- Place the solution in a polystyrene cup.
- Record the temperature of the solution.
- Add the solid and record the highest or lowest temperature obtained.
- Change your independent variable and repeat the experiment.
What is the difference between precise and accurate measurements?
An accurate result is one close to the true value
Precise measurements are ones in which there is very little range about the mean value, it measures random errors
Is analysis by titration enough to decide whether the champagne is safe to drink?
Don’t know - insufficient evidence to decide
3 marker
Describe a method to determine the position of an unknown metal on the reactivity series
- add unknown metal to copper sulfate solution
- measure temperature change
- place metals in order of temperature change
When measuring temperature change, what would be a better alternative to a glass beaker? Why?
Use a polystyrene cup
To prevent heat/energy loss/transfer
(as better insulator)
An experiment measured the reactivity of metals through temperature change with copper sulfate solution; suggest an improvement to this experiment
replace the copper sulfate solution with a compound of (silver) sulfate, which is less reactive than copper
3 reasons
Why is a burette used?
- Can add named substance in small increments
- Can measure variable volumes
- More accurate than measuring cylinder
