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All acids ____ when dissolved in water
dissociate to produce H+ ions
All alkalis___when dissolved in water
dissociate to produce OH- ions
why is universal indicator not used in titration
gradual colour change, can’t see exact point it neutralises
Methyl orange - colour in acidic solution + alkaline solution
acidic = red
alkaline = yellow
litmus - colour in acidic solution + alkaline solution
acidic = red
alkaline = blue
Phenolphthalein - colour in acidic solution + alkaline solution
acidic = colourless
alkaline = pink
What Ph values are acidic?
6→0
neutral PH
7
what PH values are alkaline
8→14
what is a strong acid?
A strong acid dissociates 100% when added to water
what is a weak acid?
only partially dissociates therefore far fewer H+ ions
definition/ characteristics of an Acid
dissociate in water to produce H+ ions
PH value below 7
An acid is a proton donor
Definition of a base
neutralise acids to form salt
proton acceptors
Alkali definition
soluble bases
produce OH- ions in water
PH value greater than 7
Acid + base →
salt + water
Acid + metal →
salt + hydrogen
Acid + carbonate →
salt + water + carbon dioxide
Acid + Ammonia →
ammonia salt
What are the 2 methods of making salts when the salt is soluble?
titration (uses 2 solutions)
Adding solid base to acid (aq + s)
how to do a titration to obtain a salt
PART 1
pipette 25cm3 of solution 1(named in exam) into a conical flask + indicator
fill burette with 2nd solution - note starting vol
add 1 to 2, swirling
stop when 1 drop changes colour
note volume added - repeats, mean
do again without indicator adding volume calculated
PART 2
heat in evaporating basin to get SOME of the water
allow to cool, so crystals form
filter to obtain crystals
dab between paper towels
how to get salt through solid base + acid
PART 1
add solid base to acid
stop when solid base no longer reacts (excess)
filter to remove excess base
PART 2 (same as titration)
heat in evaporating basin to get SOME of the water
allow to cool, so crystals form
filter to obtain crystals
dab between paper towels
how to obtain salt when salt is insoluble?
precipitation (aq + aq → s + aq)
how to do precipitaton
mix 2 solutions that contain ions of insoluble salt
e.g Metal ion needed (NO3) aq
(group 1) non metal ion needed
filter to get insoluble salt
wash with distilled water
dab to dry
group 1 solubility
ALL soluble
nitrates solubility
soluble
chlorides solubility
soluble except AgCl and PbCl2
sulfates solubility
soluble except BaSO4, CaSO4 and PbSO4
carbonates solubility
insoluble, except sodium carbonate, potassium carbonate and ammonium carbonate
hydroxides solubility
insoluble except sodium hydroxide and potassium hydroxide and calcium hydroxide(slightly soluble)
write a balanced symbol equation for the reaction between copper oxide and sulfuric acid
CuO(s) + H2SO4 (aq)→ CuSO4 (aq)+ H2O(l)
copper oxide/sulfuric acid practical
why was a measuring cylinder used to measure acid, not burette/pipette
you do not need a precise measurement of HCl - copper added in excess
copper oxide/sulfuric acid practical
why was the acid warmed?
to increase rate of reaction
copper oxide/sulfuric acid practical
why was acid not allowed to boil?
safety reasons - so it doesn’t get on skin
copper oxide/sulfuric acid practical
why was excess copper oxide used?
to ensure all the HCl is reacted/neutralised so the salt is pure
copper oxide/sulfuric acid practical
why is it important to remove excess copper oxide
to ensure we get pure CuSO4 crystals
copper oxide/sulfuric acid practical
why did you leave the sopper sulfate on the windowsill to crystallise, instead of just heating it to boil off all the water
Hydrated Copper sulfate crystals contain water. heating to dry would give anhydrous copper sulfate (white powder)
how to prepare a sample of pure, dry lead (II) sulfate
Add 75 cm3 of lead nitrate and 75 cm3 potassium sulfate to a beaker. Mix the solutions with a glass rod until a precipitate forms.
Put the filter paper in the funnel and place it over the conical flask.
Pour the mixture from the beaker into the funnel.
Use distilled water to wash any solid left in the beaker into the funnel. Wash the filtrate with distilled water. will remove traces of potassium nitrate.
Transfer the filtrate onto an evaporating dish and leave on windowsill
filter out crystals, dab between paper towels to dry
Universal indicator colour - acid/alkali
acid - red
alkali - purple
(scale)