Acids, Bases and Salts

Question 1

What is an indicator

Answer 1

an indicator is a substance that is one colour in acids and a different colour in alkalis

Question 2

Litmus Solution

Answer 2

acid - red/orange
neutral - purple / no change
alkali - darker purple / blue

Question 3

phenolphthalein

Answer 3

acid - colourless
neutral - colourless
alkali - pink

Question 4

methyl orange

Answer 4

acid - pink / red
neutral - orange
alkali - yellow

Question 5

what causes acidity

Answer 5

hydrogen ion

Question 6

universal indicator is a measure of

Answer 6

concentration of hydrogen ions. 1 is 10x more conc. than 2, 100x more than 3 etc

Question 7

salts are

Answer 7

ionic substances where hydrogen is replaced by other positive ions

Question 8

acids are

Answer 8

substances that contain hydrogen and have a pH of less than 7 when dissolved in water

Question 9

difference between hydrogen chloride gas and hydrochloric acid

Answer 9

gas - covalently bonded HCl molecules
acid - H+ and Cl- ions in solution

Question 10

What happens when an acid is dissolved in water

Answer 10

Arrhenius acids dissolve in water to form hydrogen ions

Question 11

Concentrated and dilute

Answer 11

amount of acid molecules dissolved in a volume of water

Question 12

strong and weak

Answer 12

how many of the acid molecules have split into ions ( dissociation or ionisation )

Question 13

Strong

Answer 13

all molecules have dissociated

Question 14

weak

Answer 14

small proportion of molecules have dissociated ( shown by reversible arrow )

Question 15

why is hcl more dangerous than methanoic acid

Answer 15

higher proportion of acid molecules dissolved have dissociated, forming a higher conc. of H+ ions

Question 16

What are bases

Answer 16

substances that can neutralise acids. often hydroxides or metal oxides

Question 17

what are alkalis

Answer 17

sub group of bases, all soluble in water, hydroxides.
Dissolve in water to form hydroxide ion, which causes alkalinity

Question 18

Example of a weak alkali

Answer 18

ammonia

Question 19

acid + reactive metal

Answer 19

metal salt + hydrogen

gold, platinum, silver and copper are unreactive so dont work this way

effervescence, exothermic, ‘dissolves’

Question 20

base + acid

Answer 20

metal salt + water

solid base - dissolves on heating
soluble base - exothermic

Question 21

metal carbonate + acid

Answer 21

metal salt + water + carbon dioxide

effervescence, ‘dissolves’

Question 22

ammonia + acid

Answer 22

ammonium salt

exothermic

Question 23

ionic equations

Answer 23

write balanced equation

rewrite equation separating ions ( not covalent )

cancel ions appearing on both sides

write out ionic equation

Question 24

ionic equation metal + acid

Answer 24

metal + H+ = metal ion + hydrogen

Question 25

ionic equation base + acid

Answer 25

OH- + H+ = H2O O2- +2H+ = H2O

Question 26

ionic equation metal carbonate + acid

Answer 26

CO3 + 2H+ = H2O + CO2

Question 27

ionic equation ammonia + acid

Answer 27

NH3 + H+ = NH4

Question 28

ionic equation acid + hydrogencarbonate

Answer 28

H+ + HCO3 = CO2 + H2O

Question 29

What is a neutralisation reaction

Answer 29

acid + alkali salts form

Question 30

When to use excess base

Answer 30

soluble salt but no potassium, sodium, ammonium base is insoluble but salt is soluble

Question 31

excess base method

Answer 31

add excess base to alkali to ensure it all reacts heat to speed reaction filter out unreacted base heat the filtrate to make a hot saturated solution leave to cool and crystallise use metal oxide and acid

Question 32

how to test is solution is saturated

Answer 32

dip in glass rod and blow on it crystals formed = saturated

Question 33

Anhydrous v Hydrated

Answer 33

anhydrous = contains no water of crystallisation hydrated = water molecules are ' locked' in the solid structure

Question 34

when to use titration

Answer 34

soluble salts of sodium, potassium and ammonium

Question 35

titration method

Answer 35

measure 25. cm3 of alkali with glass pipette and place in conical flask and add indicator ( phenolphthalein ) put acid in biurette and record starting value ( aim for 0 ) add acid to alkali slowly and swirl conical flask to make sure they react when the acid is nearly neutralised add the alkali a drop at a time until indicator changes colour record volume of alkali used repeat with no indicator with same volumes heat mixture and evaporate until saturated leave to crystallise filter off crystals and leave to dry use Naoh, KOH, nh3 + acid

Question 36

when to use precipitation

Answer 36

insoluble salt

Question 37

precipitation method

Answer 37

mix two soluble solutions together - one containing positive ion and one containing negative ion. filter solution. residue is the insoluble salt. rinse off impurities with distilled water leave to dry use metal nitrate + sodium salt

Question 38

why does silver chloride change colour when left to dry

Answer 38

silver ions gain electrons in light, so change colour. hence why silver solutions is kept in brown bottles

Question 39

ionic equation for precipitation reaction

Answer 39

metal ion + eg. sulphate = metal eg.sulphate

Question 40

three salts which are always soluble

Answer 40

sodium, potassium, ammonium

Question 41

which chlorides are soluble

Answer 41

all except silver and lead

Question 42

which sulphates are soluble

Answer 42

all except barium, lead and calcium

Question 43

nitrates are always...

Answer 43

soluble

Question 44

which carbonates and hydroxides are soluble

Answer 44

only sodium, potassium, ammonium