acids, bases and salts

Question 1

what is an acidic solution

Answer 1

a solution with pH less than 7

the lower the pH the stronger the acid

Question 2

what is an alkaline solution

Answer 2

A solution with a pH more than 7

the higher the pH, the stronger the alkali

an alkali is a base dissolved in water

Question 3

what is the pH of a neutral solution

Answer 3

pH 7

Question 4

what ions do acids contain

Answer 4

hydrogen ions, H+

Question 5

what do alkalis contain

Answer 5

hydroxide ions, OH-

Question 6

what is a strong acid

Answer 6

an acid which completely dissociates to release H+ ions in an aqueous solution

Question 7

what is a weak acid

Answer 7

an acid which partially dissociates to release h+ ions in a aqueous solution

Question 8

what is a strong base

Answer 8

A base which completely dissociates to release OH- (hydroxide) ions in an aqueous solution

Question 9

what is a weak base

Answer 9

a base which partially dissociates to release OH- ions in an aqueous solution

Question 10

what is the product formed when a metal is added to a dilute acid

Answer 10

acid + metal –> salt + hydrogen

generally the more reactive the metal in the reactivity series, the faster the reaction

Question 11

what are the three neutralisation reactions of dilute acids

Answer 11

acid + alkali –> salt + water

acid + base –> salt + water

acid + metal carbonate –> salt + water + carbon dioxide

the composition of salt formed depends on the acid used and the positive ions in the base, akali or carbonate

Question 12

what is neutralisation

Answer 12

the reaction of hydrogen ions with hydroxide ions to form water

hydrogen + hydroxide –> water

H+ + OH- –> H2O

Question 13

how can you test for the presence of carbonates

Answer 13

carbonates react with dilute acids to form carbon acids

the gas formed from this reaction can be bubbles through lime water; if limewater turns cloudy, the gas is CO2

Question 14

how to prepare salt from a metal or insoluble base / carbonate

Answer 14

STEP 1

excess metal / base / carbonate is added to the acid to make sure all the acid has reacted and been used up

heating and stirring help the process

for metals and metal carbonates the fizzing stops when all the acid has been used up

STEP 2

the mixture is filtered using a filter funnel and filter paper

the excess solids remains in the filter paper. the salt solution passes through into the evaporating basin

STEP 3

the salt crystals are collected from the solution by evaporation

large crystals - evaporate water slowly near a radiator or window ledge

small crystals - use a bunsen to evaporate 2/3 of water quickly, before allowing to crystalise naturally

Question 15

what are the names of the salts formed from:
hydrochloric acid
nitric acid
sulfuric acid

Answer 15

hydrochloric acid produces chlorides

nitric acid produces nitrates

sulfuric acid produces sulfates

Question 16

what is the test for sulfate ions

Answer 16

first add dilute hydrochloric acid, followed by barium chloride solution

a white precipitate will form if sulfate ions are present in the solution

Question 17

what is titration used for

Answer 17

a method to prepare solutions of soluble salts

to determine the relative and actual concentrations of solutions of acids/alkalis

Question 17

how do you calculate the concentration of a solution

Answer 17

concentration = mol ÷ volume

the units of concentration are mol dm-3

Question 18

what does the concentration of an acid / base refer to

Answer 18

the amount of substance present - the number of moles of acid/base in a solution

Question 19

what does the strength of an acid / base refer to

Answer 19

the strength refers to the degree of ionisation of the acid or base - how readily the acid releases hydrogen (H+) ions or how readily the base releases hydroxide (OH-) ions

Question 20

outline how to perform a titration

Answer 20

measure exactly 25cm3 of alkali into a clean conical flask

add a few drops of indicator (2-3) to the flask

place the flask onto a white tile

fill the burette with acid

slowly add the acid from the burette to the alkali until the indicator changes colour
this is the end point of the reaction

record the volume of acid added to the flask

repeat steps 1-6 without using the indicator and addin the same volume of acid from the burette

the salt crystals are collected from the solution by evaporation

Question 21

what is a precipitate

Answer 21

two solutions containing salts combining together to form an insoluble salt

Question 22

how are insoluble salts prepared

Answer 22

mixing - the two soluble salt solutions are mixed

filtration - the insoluble precipitate is separated from the mixture by filtration. the precipitate is separated from the mixture by filtration. the precipitate stays behind in the filter paper, while the solution passes through

washing and drying - water can not dissolve the precipitate - it is insoluble - but it can wash of any remaining impurities. the filter paper is then removed, opened out the precipitate is dried in a oven