Acids, bases and salt Flashcards
what happens to acids when they dissolve in water
they produce H+ ions
what happens to alkalis when they dissolve in water
they produce OH+ ions
what are the properties of acids
all acids dissolve in water
pH of less than 7
turn blue litmus red
give a red colour with universal indicator
what are the properties of alkalis
all alkalis dissolve in water
pH greater than 7
turn red litumus blue
give a blue colour with universal indicator
what acid is present in citrus fruits
citric acid
what acid is present in fizzy drinks
carbonic acid
what acid is present in vinegar
ethanoic acid
what is an acid
a proton donor
what is a base
a proton acceptor
why are fizzy drinks acidic
carbon dioxide reacts with water in the drink to give carbonic acid
what are bases
any substance that reacts with an acid ,forming a salt and water e.g. metal oxides and metal hydroxides
acid + base =
salt + water
what is the neutralisation reaction
H+ + OH- = H2O
the lower the pH
the more acidic the solution
the higher the pH
the more alkaline the solution
what colour is methyl orange in acidic solutions
red
what colour is methyl orange in alkaline solutions
yellow
what colour is phenolphthalein in acidic solutions
colourless
what colour is phenolphthalein in alkaline solutions
pink
what colour is universal indicator in acids
red or orange
what colour is universal indicator in alkali
blue or purple
how to measure pH of a solution
pH meter or universal indicator
what is a strong acid
an acid which completely dissociates into its H+ ions when it dissolves in water
what is a weak acid
an acid which only partially dissociates into its ions when it dissolves in water and most of the acid remains as unchanged molecules so conc of H+ ions is low
what is a concentrated acid
a concentrated acid contains a large mass of acid dissolved in a given volume of water
what is a dilute acid
a dilute acid contains a small mass of acid dissolved in a given volume of water
how do you dilute a concentrated acid
add the acid to the water slowly and NEVER the other way around
why should acid always be added to water and not the other way around
if water is added to acid, the heat produced causes the mixture to boil and the liquid spills out whereas if the acid is added to water the water will absorb the heat generated and the mixture will not boil
concentration in g dm^3 =
mass of solute / volume of solution
what happens if the conc of hydrogen ions is increased by a factor of 10
the pH decreases by 1
what happens if the conc of hydrogen ions is decreased by a factor of 10
the pH increases by 1
metal + acid =
salt + hydrogen
what do you see when a metal reacts with dilute acid
the metal dissolves because it reacts with the acid
fizzing is seen
the reaction mixture gets warmer
what is the test for hydrogen
test the gas with a lighted splint
a squeaky pop is heard
acid + alkali =
salt + water
what do we observe in acid-alkali neutralisation reactions
the reaction mixture gets warmer
acid + base =
salt + water
metal carbonates + acid =
salt + water + carbon dioxide
observations when a metal carbonate reacts with a dilute acid
the solid dissolves because it reacts with the acid
fizzing/effervescence
what is the test for carbon dioxide
bubble the gas into limewater
the limewater turns cloudy
what are the solubility rules
all sodium, potassium and ammonium salts are SOLUBLE
all nitrates are SOLUBLE
common chlorides, bromides and iodides EXCEPT silver and lead are SOLUBLE
common sulfates except lead, calcium and barium are SOLUBLE
common carbonates and hydroxides excpet sodium, potassium and ammonium are INSOLUBLE
What is a precipitate
a solid which forms when two solutions are mixed
how to make insoluble salts by precipitation
mix together solutions of silver nitrate and sodium chloride in a beaker, then filter the mixture to get the precipitate
the insoluble salt, silver chloride remains in the filter paper
pour a little distilled water over the residue in the funnel to remove impurities
carefully remove the filter paper with silver chloride and dry in a warm oven
what do you do in a neutralisation reaction to make soluble salts
metals/metal oxide/metal carbonate + acid
how do you make soluble salt by neutralisation
take 25cm^3 of hot sulfuric acid in a beaker
add small amounts of zinc oxide (with a spatula) to the acid and stir
continue to add small amounts of zinc oxide until all the acid is used up
filter the mixture to remove the excess zinc oxide
heat the filtrate gently until most of the water evaporates and crystals appear around the edges
leave it to cool at room temp and allow crystals to form
dry the crystals between filter papers
how do you get large crystals
heat the evaporating basin using a water bath
what do you do in a titration to make soluble salts
acid + alkali
how do you get a soluble salt using titration
fill the burette with HCL to eye level
record the initial volume of acid in the burette
pipette out sodium hydroxide into a conical flask and add a few drops of the indicator, phenolphthalein. The solution in the flask turns pink
add the acid slowly from the burette while swirling the flask until the end point is reached
the end point is when the solution changes from pink to colourless
record the final volume of acid in the burette
calculate the titre (end reading - start reading)
use the burette to add this volume of acid to the alkali without the indicator
heat the solution gently till most water evaporates
leave it to cool at room temp and crystals will form
dry the crystals between filter papers
why is a pipette used instead of a measuring cylinder in titrations
a pipette provides more accurate and repeatable measurements
why must the titration be repeated
to improve the reliability of the investigation
to identify anomalous results
to be able to calculate an average value using concordant results
how do you make sure that the titration is carried out correctly
read the volume of acid from the bottom of the meniscus
repeat the titration until concordant results are obtained
add the HCL dropwise towards the end point
place a white tile under the conical flask to see the end point clearly
what are the reasons why a student’s mean titre is different from the accurate value
the student did not read the volume from the bottom of the meniscus
the jet of the burette was not filled
there was an error in the judgment of colour change at the end point
there was an airlock below the tap in the burette
what are concordant titres
within + or - 0.10 cm^3
