acids, bases and salts Flashcards
metal + acid ->
metal + acid -> salt + h2 gas
metal oxide/hydroxide + acid ->
metal oxide/hydroxide + acid -> salt + water
metal carbonate + acid ->
metal carbonate + acid -> salt + water + carbon dioxide
acid + ammonia solution (NH3) ->
acid + ammonia solution (NH3) -> ammonium salt
ONLY ONE PRODUCT
ionic equation for metal oxide + acid reactions
O2- + 2H+ -> H2O
ionic equation for metal hydroxide + acid
OH- + 2H+ -> h2o
ionic equation for metal + acid
metal + H+ -> metal ion + h2
ionic equation for acid + ammonia
H+ + NH3 -> (NH4)+
ionic equation for metal carbonates and acids
(CO3)2- + 2H+ -> CO2 + h2o
what salts are soluble?
- all nitrates
- all sodium, potassium and ammonium salts, carbonates and hydroxides
- most chlorides (except silver and lead)
- most sulfates (except barium, lead and calcium)
what salts are insoluble?
- most carbonates and hydroxides (except sodium, ammonium and potassium)
- barium, lead and calcium sulfate
- silver and lead chloride
what are the 3 ways to make salts?
- excess base
- titration
- percipitation
when should you use percipitation to make salts and what solutions should be used?
- when the salt produced is insoluble
- …nitrate and sodium… if in doubt*
when should excess base method be used?
when the salt is soluble but not a sodium, potassium or ammonium salt
in the excess base method, what solutions should be used?
appropriate acid + insoluble base eg oxide, hydroxide or carbonate
when should titration be used?
when making soluble, sodium,potassium or ammonium salts
what solutions should be used to make salts through titration ?
appropriate acid + appropriate hydroxide (or carbonate)
What is an indicator?
An indicator is a substance that shows the presence of acids or alkalis
What is a universal indicator?
A mixture of several different indicators that can indicate the strength of acids and alkalis
How can indicators be used?
Indicators can be used in solution or dried onto paper to make test papers
What color does red litmus paper turn in the presence of an alkali?
Blue
What color does blue litmus paper turn in the presence of an acid?
Red
What color does phenolphthalein turn in an acidic solution?
Colorless
What color does phenolphthalein turn in an alkaline solution?
Pink
What color does methyl orange turn in an acidic solution?
Red
What color does methyl orange turn in an alkaline solution?
Yellow
What color does universal indicator turn in acid?
Red
What color does universal indicator turn in a neutral substance ?
Green
What color does universal indicator turn in a strong alkali?
Blue
Fill in the blank: The strength of acids and alkalis is measured on the _______.
[pH scale]
what colour does litmus solution turn in a neutral substance?
purple
what colour does red litmus paper turn in a neutral substance?
stays red
what colour does blue litmus paper turn in a neutral substance?
stays blue
what colour does phenolphthalein turn in a neutral substance?
stays colourless
what colour does methyl orange turn in a neutral substance?
yellowey orange
what is an acid?
a substance containing hydrogen, with a pH of less than 7
what causes acidity?
H+ ion
what are salts?
ionic substances where hydrogen has been replaced by other positive ions (usually metal cations)
how does the pH scale work?
as concentration of hydrogen ions increases by a factor of 10 , the pH decreases by 1
eg pH1 contains 10 x as many H+ than pH2 (10x as acidic), 100 x as acidic than pH3 etc.
How does water as a solvent affect the acidic properties of an acid?
water is a polar molecule so it separates the acidic molecule into its ions, including the H+ ion (which gives an acid its acidity)
arrhenius definition of an acid
acids are substances that when disolved in water produce H+ ions
what are concentrated vs dilute acids/alkalis?
refers to the amount of acid molecules dissolved in water (concentration of the acid)
what are strong acids?
acids that will completely dissaciote in water all the acid molecules break up and form H+ eg HCl
what are weak acids?
acids where only a small proportion of the molecules dissaciote into H+ (meaning the solution contains undissociated molecules and some ions) - only partially dissaciate eg ethanoic acid
what is dissasociation/ionisation?
refers to how many of the acid molecules have been split apart into ions
what are bases?
substances that can neutralise acids, normally metal (hydr)oxides
what are alkalis?
soluble bases, bases that dissolve/react with water to produce OH- ions
what causes alkalinity?
OH- ions
how does ammonia react with water?
reversible reaction which leads to a low concentration of OH- ions, so ammonia is a weak alkaline solution of pH12
method for writing ionic equations (5 steps)
- write balanced symbol equation
- rewrite equation separating ions in ionic compounds and acid
- remove spectator ions (those that don’t change charge)
- write out ionic equation
- check charges are balanced on both sides
what is a neutralisation reaction?
H+ ions from the acid and OH- ions from the alkali combine to form neutral water
what is titration?
lab technique where 2 solutions are mixed to determine the exact volume of each which react together eg when exactly neutralizing an acid with a base to make a salt
titration method (8 steps)
- fill the burette with acid with the tap closed, then open the tap to fill the nozzle of the burette and record the start volume
- use a glass pipette and pipette filler to collect some base and add to a conical flask.
- add phenolphthalein indicator to the base in the conical flask - it will be pink in the alkaline conditions
- start running the acid into the conical flask by opening the tap of the burette. stop when the indicator turns colourless
- refill the burette anc clean the conical flask. repeat whole experiment with same values but without any indicator
- pour your solution containing the salt
- heat the solution to evaporate away some of the water (not all! - some is water of crystallization)
- leave to cool and crystallize, forming your salt
chemical test for hydrogen
if hydrogen is present in a test tub, a lit splint placed in the test tube will make a ‘squeaky pop’
chemical test for carbon dioxide
bubble CO2 through limewater and it will turn cloudy
what is a neutralisation reaction?
a reaction between an acid and base where OH- and H+ ions react to form neutral water
how do you obtain a dry salt from a solution? (5)
- concentrate solution util it becomes saturated (test by dipping hot glass rod and blowing on it to see if crystals form)
- stop heating, allow solution to cool
- filter to remove most of the water
- wash crystals with water
- dry crystals with funnel paper and leave to fully form in a warm dry space
