AE 1 Flashcards
Outline the steps to prepare and test a natural indicator
- Place shredded cabbage into a pestle.
- Add a large pinch of sand and 10 mL of ethanol into the pestle.
- Grind the mixture using a mortar until the ethanol has become intensely coloured.
- Decant the solution into a small beaker.
- Prepare 10-fold serial dilutions of 1 molL-1 HCl and 1 molL-1 NaOH in separate test tubes.
- Add three drops of the indicator solution into each test tube.
What are the variables of the practical:preparing and testing a natural indicator
Independent variable: pH of the solution in each test tube.
Dependent variable: Colour of the solution in each test tube after the indicator was put in.
Controlled variable: The amount of indicator used and the amount of HCl and NaOH in each test tube.
What are the results of the practical:preparing and testing a natural indicator
acidic ———————–>basic
red >purple> blue> green >yellow
State the range (number of colour) of methyl orange
Low ph to high
red to yellow
3.1 to 4.4
State the range (number of colour) of methyl red
Low ph to high
red to yellow
4.8-6.0
State the range (number of colour) of bromothymol blue
Low ph to high
yellow to blue
6.0-7.6
State the range (number of colour) of phenol red
Low ph to high
yellow to red
6.8-8.4
State the range (number of colour) of phenophthalein
Low ph to high
colourless to pink
8.2-10
State the range (number of colour) of litmus
Low ph to high
red to blue
5-8
Describe the everyday uses of indicators in sol testing
o A small sample of soil is mixed with universal indicator solution.
o BaSO4 is sprinkled onto the surface
o BaSO4 provides a neutral white background which contrasts the colour of the indicator solution seeping through from the soil.
o The colour is matched to a pH value on a pH chart.
Soil testing is important as pH of soil affects nutrient availability.
o In agriculture, this affects the productivity and yield.
o pH is determined to affect which plants can be grown as each plant is only suitable in certain conditions.
Describe the everyday uses of indicators in swimming pools
o Collect sample of pool water.
o Place drops of indicator in sample (as recommended).
o Use white background to match the colour chart.
o pH can be lowered or raised using substances such as HCl or Na2CO3.
o It is important to maintain pH of swimming pools close to 7.4 to avoid irritation of the eyes and mucous membranes.
o It is kept at 7.4 as it is more basic which prevents algae and bacteria from growing.
Describe the everyday uses of indicators in aquarium waters
o pH may be affected by respiration, decay of biological matter (produces acids) and carbonates leaching from decorations such as coral and gravel (raised pH).
o Certain species of fish may favour or can only prosper in certain pH ranges.
o Indicators can be used to ensure aquarium water lies in a suitable range.
What is the trend of basic oxides and acidic oxides in the periodic table
o Non-metals on the RHS of the periodic table are acidic and covalent.
o Metals on the LHS tend to form basic oxides.
Generally the more EN the element, the more acidic its oxide.
o Oxides of elements near the semi-metal region of the periodic table can react with both acids and bases. These oxides are known as amphoteric oxides. Examples include: Al2O3, ZnO and Cr2O3.
o However, these substances do not contain ionisable protons (H+) and hence cannot be amphiprotic (substances which can donate or accept protons).
Define Lechats
When a chemical system at equilibrium is disturbed, the system will shift to a new equilibrium by undergoing a reaction which minimises the effect of the disturbance.
What is a dynamic equilbrium
o Dynamic Equilibrium: Microscopic changes which balance out to produce no overall net change at a macroscopic level.
Carbon dioxide dissolves in water and reacts to form carbonic acid, H2CO3.
CO2(aq) + H2O(l) ⇌ H2CO3(aq)
What happens when the bottle is opened for the first time
(decrease in pressure), therefore Increase in CO2 will be seen as many gas bubbles will rise to the surface (effervescence)
shifts left
Carbon dioxide dissolves in water and reacts to form carbonic acid, H2CO3.
CO2(aq) + H2O(l) ⇌ H2CO3(aq)
What happens when an open bottle eventually goes flat and is no longer fizzy.
Decrease in [CO2(g)]
CO2(g) escapes and hence bubble form and escapes
shifts left
Carbon dioxide dissolves in water and reacts to form carbonic acid, H2CO3.
CO2(aq) + H2O(l) ⇌ H2CO3(aq)
What happens when a cold bottle is placed on a desk and allowed to warm up.
increase in temperature shifts left, little bubbles produced
Carbon dioxide dissolves in water and reacts to form carbonic acid, H2CO3.
CO2(aq) + H2O(l) ⇌ H2CO3(aq)
What happens when the volume of CO2 is increased
shifts left
An increase in volume means there is a decrease in pressure. Thus the equilibrium will shift to the side with more gas moles to minimise the disturbance, thus favouring the reverse reaction.
What are the natural sources of sulfur dioxide
Geothermal hot springs and volcanoes
Natural decay of vegetation land, wetlands and oceans.
What are the industrial sources of sulfur dioxide
Burning of fossil fuels
S(s) + O2(g) → SO2(g)
Smelting of Metals
CuS(s) + O2(g) → Cu(s) + SO2(g)
What are the natural sources of NOx
Lightning
O2 + N2(g) → 2NO(g) (needs condition >1000 OC)
2NO(g) + O2(g) → 2NO2(g) (reacts with air)
micro-organisms feed on nitrogenous material is soils to produce N2O
What are the industrial sources of NOx
Combustion of fossil fuels in motor vehicle
Combustion in oil and coal electrical power plants
What are two environmental effects of acid rain
Damage to forest (trees die from nutrient deficiency rather than direct)- bad for environment in general and can affect agricultural purposes.
increase in lake acidity (kills fish and hence disrupts food chains)
What are two societal effects of acid rain
Erosion of irreplaceable marble and limestone buildings.
H2SO4(aq) + CaCO3(s) → CaSO4(s) + H2O(l) + CO2(g)
Photochemical smog- hazy, irritates eyes and hard to breathe
What are the problems associated with SO2 and NOx
o Sulfur oxides are irritating gases which present a major health risk, especially for people with respiratory disorders.
o Nitrogen oxides are important components in formation of photochemical smog and acid rain.
o Sulfur dioxide, sulfur trioxide and nitrogen dioxide are acidic oxides which combine with water to produce acid rain.
How can sulfur dioxide emissions be reduced
o Reducing sulfur content of fuels (OZ coal)
o Using a scrubber to remove sulfur dioxide
Scrubber passes gaseous emissions through a slurry of lime (CaO), which neutralises the sulfur dioxide to form calcium sulfite
SO2(g) + CaO(s) CaSO3(s)
How can nitric oxide emissions be reduced
o Catalytic converters catalyse decomposition of NO back to N2¬ and O2, and also decompose carbon monoxide into carbon dioxide
o Rhodium or platinum catalyst
2NO(g) + 2CO(g) N2(g) + 2CO2(g)
State the equations in how acid rain is formed
2NO2(g) + H2O(l) → HNO3(aq) + HNO2(aq)
SO2(g) + H2O(l) → H2SO3(aq)
what are the evidence that show an increase in atmospheric concentration of sulfur and nitrogen
and what are the problems with the evidence shown
o Direct: chromatographs show an increase since 1970s.
o Indirect: samples extracted from ice cores from 1700s
o Knowledge from NOx and SO2 from things such as a cars. An increase in cars results to an increase in sulfur and nitrogen. (industrial revolution)
o Measurements of effects of increased areas of acid rain and photochemical smog.
Problems with Evidence
o It only showed from 1970s and onwards.
o Evidence on Antarctica might not reflect levels worldwide or concentrated areas may only be generally geographically localised to a specific region.
Outline the steps in the practical:use of pH meters/probes and indicators to distinguish between acidic, basic and neutral chemicals
- Rinse the pH probe with distilled water.
- Calibrate the pH probe using standard buffer solutions with pH 4, 7 and 10.
- Place a small amount of the solution to be tested into a beaker.
- Insert the pH probe into the substances and record the pH of the solution.
- Rinse the pH probe with distilled water and repeat steps 3, 4 and 5.
What is the funky name for citric acid
2-hydroxypropane-1,2,3-tricarboxylic acid
Identify examples of naturally occurring acids and their chemical composition
citric acid: (2-hydrohypropane-1,2,3-tricarbocylic acid)- C6H8O7: found in citric fruits such as lemon and orange.
Acetic acid: CH3COOH - Acetic acid is produced naturally through bacterial fermentation which is oxidised to acetic acid.
Identify examples of naturally occurring bases and their chemical composition
Calcium carbonate: (CaCO3)- found in limestone.
Ammonia: (NH3) Certain organisms can produce ammonia from atmospheric nitrogen.
What is the difference between strength and concentration of an acid
o Strength depends on the identity of the substance and its degree of ionisation in water.
o Concentration is the amount of acid in a given volume of a solution.
How do you convert [H] to pH
-log (H)
How do you convert pH to [H]
10^(-pH)
How do you convert [H] to [OH]
[H] x [OH] = 10^-14
How do you convert pH to pOH
pH + pOH = 14
State two reasons in which acids are used as food preservatives.
o Used as opposed to bases because they taste better. E.g. lactic acid, acetic acid and citric acid.
o Used as a preservative- destroys microorganisms involved in decomposition; oxidation is limited and it cannot survive in low pH.
Outline what Lavoisier (1776) proposed
o He concluded an acid must contain oxygen.
o He was wrong when HCl(l) was discovered to have no oxygen and reacted in water to produce acidic solutions.
Outline what Davy (1815) proposed
o Noted that all known acids contained a hydrogen that could be displaced by a reaction with a metal.
outline three things arrhenius (1884) proposed
o Defined acids as a molecule or a polyatomic ion with a H in its formula and dissociates in water to produce hydrogen ions, H+(aq).
o A base was defined as a molecule or ion with OH in its formula and dissolves in water to produce hydroxide ions, OH-(aq).
o He noted the strongest acids produced the strongest degree of dissociation.
What are the limitations to arrhenius’ definition
o His definition however, could not explain the basic nature of substances such as ammonia which did not contain hydroxide ions in their formulae, but behaved like bases.
o He could not explain why some salts were basic or acidic.
o His definition only covered acids and bases in aqueous solution, hence could not explain the role of the solvent.
what is BL propose
o Acids were proton donors and bases were proton acceptors.
o A proton was defined as a hydrogen ion.
Outline how BL’s definition affected Arrhenius’s definition
o BL did not contradict Arrhenius’ definition, it only generalises it. I.e. it allowed for more species to be defined as an acid or a base.
o It could explain the basic nature of substances like ammonia. Ammonia dissolves in water and reacts with a water molecule to produce NH4+(aq) and a hydroxide OH-(aq).
what is an amphiprotic substance
o A molecule that can act as a proton acceptor and a proton donor is amphiprotic
