8.. Flashcards
Bronsted-Lowry Theory
defines acids and bases in terms of proton transfer between chemical compounds
Bronsted-Lowry acid
species that gives away a proton
Bronsted-Lowry base
species that accepts a proton using its lone pair of electrons
conjugate acid-base pairs
is two species that are different from each other by H+ ion
amphiprotic
species that can act both as a proton donor and acceptor
amphoteric
compounds that has both acidic and basic characters
- When the compound reacts with an acid, it shows that it has basic character
- When it reacts with a base, it shows that it’s acidic
reactions between metals and acids
acid+metals –> salt+hydrogen
- extent of reaction depends on the reactivity of the metal and strength of acid
reactions between metals and oxides
acid + metal oxide → salt + water
reactions between acid and metals hydroxides
acid + metal hydroxide → salt + water
reactions between metals and carbonates
acid + metal carbonate → salt + water + carbon dioxide
reactions between metals and hydrogencarbonates
acid + metal hydrogencarbonate → salt + water + carbon dioxide
neutralization
A neutralisation reaction is one in which an acid (pH <7) and a base/alkali (pH >7) react together to form water (pH = 7) and a salt
common indicators
Litmus, Methyl orange, Phenolphtalein
color change for Litmus paper
color in acid - pink
color in alkali - blue
color change for methyl orange indicator
color in acid - red
color in alkali - yellow
color change for Phenolphtalein indicator
color in acid - colorless
color in alkali - pink
how to convert between pH and conc of H+ ions
pH of acids
0-7
conc of H+>conc of OH
pH of bases
7-14
conc of OH- > conc of H+
Kw
10^-14
universal indicator
acid - red
basic - violet
strong acids
dissociates almost completely in aqueous solutions
- HCl (hydrochloric acid), HNO3 (nitric acid) and H2SO4 (sulfuric acid)
- irreversible reactions
weak acids
weak acid is an acid that partially (or incompletely) dissociates in aqueous solutions
- organic acids (ethanoic acid), HCN (hydrocyanic acid), H2S (hydrogen sulfide) and H2CO3 (carbonic acid)
- equilibrium
Strong bases
base that dissociates almost completely in aqueous solutions
- group 1 metal hydroxides such as NaOH (sodium hydroxide)
- irreversible reactions
weak bases
base that partially (or incompletely) dissociates in aqueous solutions
- NH3 (ammonia), amines and some hydroxides of transition metals
- equilibrium
strong acids produce _________ conjugate bases
weak
weak acids produce _______ conjugate bases
strong
how can strong and weak acids be distinguished
- pH values
- electrical conductivity
- reactivity
electrical conductivity of strong acids vs weak acids
- ## strong acids have a higher concentration of H+, so they conduct electricity better
reactivity of strong acids vs weak acids
- strong and weak acids of the same concentrations react differently with reactive metals
- this is bc the concentration of H+ is greater in strong acids compared to weak acids
- ## The greater H+ concentration means that more H2 gas is produced in a shorter time
acid deposition
- Rain is naturally acidic because of dissolved CO2 which forms carbonic acid
H2O (l) + CO2 (g) ⇌ H2CO3 (aq) - Carbonic acid is a weak acid and dissociates in the following equilibrium reaction giving a pH of 5.6
H2CO3 (aq) ⇌ H+ (aq) + HCO3- (aq)
For that reason acid rain is defined as rain with a pH of below 5.6
Acid deposition includes all processes by which acidic components leave the atmosphere
- This could be gases or precipitates
There are two types of deposition: wet acid deposition and dry acid deposition
- Wet acid deposition refers to rain, snow, sleet, hail, fog, mist and dew
- Dry acid deposition refers to acidic particles and gases that fall to the ground as dust and smoke
- Acid deposition is formed when nitrogen or sulfur oxides dissolve in water to form HNO3, HNO2, H2SO4 and H2SO3
Formation of sulfur based acids
- fossil fuels are often contaminated with small amounts of sulfur impurities
- when these contaminated fossil fuels are combusted, the sulfur in the fuels get oxidised to sulfur dioxide
- sulfur dioxide may be further oxidised to sulfur trioxide
- the sulfur dioxide and trioxide then dissolve in rainwater droplets to form sulfurous acid (H2CO3) and sulfuric acid (H2CO3)
- these acids are components of acid rain which has several damaging impacts on the environment
formation of acid rain by nitrogen oxides
- the temperature in an internal combustion engine can reach 2000 °C
- nitrogen and oxygen, which at normal temperatures don’t react, comine to form nitrogen monoxide
- nitrogen monoxide reacts further forming nitrogen dioxide
- nitrogen dioxide gas rects with rain water to form a mixture if nitrous and nitric acids, which contribute to acid rain
- lightning can also trigger the formation of nitrogen monoxide and nitrogen dioxide in the air
- -
effects of acid deposition on materials
- acid deposition can react with metals and rocks (limestone) causing buildings and statues to get damaged
- limestone and marble both contain CaCO3
- calcium carbonate reacts with sulfuric or nitric acids causing stoneworks to corrode or weaken
- metallic structures, such as iron bridges, are vulnurable to corrosion by wet and dry deposition forming the salt of the metal
what is the effects of acid deposition on plants
- Apart from acid deposition directly falling on leaves and killing plants, acid particulates can block stomata ( plant pores) and prevent gaseous exchange
- Acid rain can fall on soils and release important minerals such as magnesium, calcium and potassium which are leached (washed out) from soils and are therefore unavailable to plants
- Aluminium ions released from rocks are toxic to many plants and damage their roots
acid deposition effects on water
- When acid rain falls on rivers and lakes the pH can fall to levels that are unable to support life
- Below about pH 4, aluminium ions are released from rocks when they are held as aluminium hydroxide
- Alumnium ions are toxic to fish as they damage the gills and prevent fish from efficiently absorbing oxygen
- Nitrate ions from nitric acid in acid rain can contibute to over-fertilization of waterways and lead to eutrophication
- Eutrophication is excessive algal growth that results in oxygen depletion and stagnation of waterways
acid deposition effects on human health
- no direct impact on skin
- however, acid particulates in the air can increase the risk of respiratory diseases
- When acid rain comes into contact with metal pipes there is an increased risk that toxic metal ions will be released into the water supply such as Cu2+, Al3+ and Pb2
2 ways to reduce sulfur oxide emissions
- removal of sulfur from fossil fuels can either take place pre-combustion or post-combustion
- SO2 and SO3 are both acidic and toxic
- sulfur dioxide is produces naturally during volcanic eruptions
- large quantities have been emitted by burning coal, oil and natural gas
reducing sulfur oxides via pre-combustion
- Pre-combustion takes place for coal and petroleum, altough it is expensive to remove all the sulfur, so a small percentage often remains
- essential to remove most of the sulfur as it damamges the workings of the internal combustion engines
- sulfur is removed by reacting it with hydrogen - hydrodesulfurization
- sulfur is recovered and used in the manifacture of sulfuric acid
reducing sulfur oxides via post-combustion
- carried out in a coal fired power stations
- the waste gases from burning the coal contain sulfur dioxide
- the waste gases are passed through a wet slurry of calcium oxide and calcium carbonate which react with SO2 and produce calcium sulfate
- calcium sulfate is also known as gypsum and is used to make plsterboard and other useful building materials
