5. Formula and amounts (CONCENTRATION + TITRATION)
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What is an acid
a solution with a pH below 7 and is a proton donor - releases H+ ions
What is a base
A proton accepter - accepts H+ ions
What is an alkali
A base that has been dissolved in water
What is the difference between weak and strong acid/alkali
A strong solution fully ionises in aqueous solutions to give H+ ions and OH- ions A weak solution only partially ionises in aqeous solutions
How to go from cm3 to dm3
divide by 1000
How to go from cm3 to m3
Divide by 1000 000
How to go from dm3 to m3
Divide by 1000
What is 1 cm3 the same as
1 ml –> so 1 dm3 is the same as one Litre
Phenolphthalein in acid
Colourless
Phenolpthalein in alkali
Pink
Methyl orange in acid
Orange In excess acid = red
Methyl orange in alkali
Yellow
Why is it good to wash out pipette and burette with the acid / alkali before the titration
Ensures the titration is done with a known concentration of the acid / alkali Also so water doesn’t dilute the solution
Why must you remove the funnel from the top of the burette before the titration
Drops of acid could fall into the burette so then you don’t know how much was added
During the titration the student washed the inside of the conical flask containing the alkali with some distilled water. Suggest why this washing does not give an incorrect result.
Water does not change the number of moles of the alkali present
What are concordant results
Results within 0.1 cm3 of each other
Explain 4 actions you would take in a titration to ensure the end point is accurate just before the end point titration is reached
Add drop by drop to avoid ‘overshooting to the end point’ Swirl to ensure all acid and alkali react Rinse the sides with deionised water between additions to rinse all reactants into the solution so all can react Use a white tile to clearly see colour change
What is a standard solution
A solution with a known concentration