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5.3 Reactions and Envrionmental Issues. SNC2P. Treating Car Exhaust. 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O(g). This equation represents the complete combustion of gasoline. Gasoline reacts with oxygen to produce carbon dioxide and water.

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treating car exhaust
Treating Car Exhaust

2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(g)

This equation represents the complete combustion of gasoline. Gasoline reacts with oxygen to produce carbon dioxide and water.

Incomplete combustion can result in carbon (C) (soot),carbon monoxide (CO), and nitrogen oxides (NO2 and NO3)to be released and enter the air.

treating car exhaust cont d
Treating Car Exhaustcont’d
  • Incomplete combustion can cause gasoline vapours to enter the exhaust.
  • Usually nitrogen gas is not very reactive. But in the presence of hot temperature nitrogen can react with oxygen gas (O2).
  • Thus some vapours can include nitric oxides (i.e. NO, NO2) which contributes to smog and formation of ozone (O3).
treating car exhaust cont d1
Treating Car Exhaustcont’d
  • A catalytic converter can be used to reduce the emissions released form the car’s exhaust.
  • All chemicals being released from the exhaust pass through the converterbefore being released into the atmosphere.
mechanism of the converter
Mechanism of the Converter
  • The metals on the surface of the converter cause a displacementreactionto occur.
  • The reactants(NO, NO2) change intolessreactiveproducts(N2 and O2).
  • Thesereactions are also able to convertunburnedgasolineCO2 and H2O.
  • The surface area of the converter must alsobelargesothatthereis a greater surface on which the reactioncanoccur.
recovering gold
Recovering Gold
  • The gold must beremovedfrom the rock throughchemicalreactions.
  • To remove the gold, the chemicalreactionsusuallyinvolvecyanide (CN-) and zinc metal (Zn).
  • CN- is a toxiccompound and thuscanbeharmful to the environment.

Gold is a highlydesirablemetalthatcanberemovedusingdifferentchemicalreactions.

recovering gold cont d
Recovering Gold cont’d

4Au(s) + 8NaCN(aq) + O2(g) + 2H2O(l) 4Na[Au(CN)2](aq) + 4NaOH(aq)

  • Leachingis a processused to retrieve gold. The processrequirescyanide (CN-).
  • The rockcontaining gold must first becrushed and the powder must be place into piles to furtherbecrushed.
  • NaCN solution issprayed onto the piles of powder in order to turn gold into an aqueous solution.
  • This enables the gold to bedrainedaway.

This diagramillustrates the gold « heaps » (piles of rock powder) whichisthensprayedwith CN- aqueous solution.

recovering gold cont d1
Recovering Gold cont’d
  • Zn powdercanthenbeadded to the aqueouscyanide solution.
  • The zinc is more reactivethen the gold in the activityseriesand thusis able to displace the gold and bind to CN-.

Othermetalsthat are more reactivethen Au canalsobeused for thisdisplacementreaction.

Gold isnowretrievedfrom the aqueous solution in a solid state.

2Na[Au(CN)2](aq) + Zn(s) 2NaCN(aq) + Zn(CN)2(aq) + 2Au(s)

cleaning and disinfecting pools
Cleaning and Disinfecting Pools

A variety of compounds containing chlorine (Cl) are used to prevent the growth of bacteria and other organisms in the water in swimming pools and hot tubs.

Care must be taken when using these chemicals to ensure that they are effective in disinfecting the water but remain safe for the users.

household hazardous product symbols hhps
HouseholdHazardous Product Symbols (HHPS)

Precautions must be taken when using household chemicals. When mixed, reactions could occur that might be detrimental to the user’s health.

bleach and ammonia
Bleach and Ammonia
  • Whenbleachis mixed withammonia (NH3) itcancreate a toxicproduct.
  • BleachcontainsNaClO (sodium hypochlorate). WhenNaClOcombines withNH3 (ammonia) chlorinegasisproduced.

2NH3(aq) + 2NaClO(aq) 2NaONH3 (aq) + Cl2(g)

Chlorinegas (Cl2) istoxic, killingbacteria. If itistooconcentrateditcan cause damage to the respiratory system wheninhaled.

bleach and ammonia1
Bleach and Ammonia

Two other ammonia and bleach reactions produce toxic compounds called chloramines (NCl3(g) and NH2Cl(g)).

A) NH3(aq) + 3NaClO(aq) 3NaOH(aq) + NCl3(g)

B) NH3(aq) + NaClO(aq) NaOH(aq) + NH2Cl(g)

Chloramines are formedwhen one or more hydrogenatoms are removedfromnitrogen and replacedwithchlorine.

Chloramines are highlytoxic and may cause skin and eye irritation. If inhaleditcanalso cause irritation in the respiratory tract.