Reactivity trends Flashcards
(26 cards)
what is the outer shell electron configuration for group 2 elements? and what happens to the electron configuration when they react?
s2
2 electrons are lost and s orbital is unoccupied
this is oxidation
write an equation for the reaction of calcium with oxygen
what would you observe
2Ca + O2 -> 2 CaO
you would observe a bright red flame and white powder is produced
write an equation for calcium with water
what would you observe?
Ca + 2H2O -> Ca(OH)2 + H2
bubbles of gas are produced. the water turns cloudy as calcium hydroxide is only partially soluble
write equations for reactions of calcium with HCl, then H2SO4
what would you observe?
Ca + 2HCl -> CaCl2 + H2
Ca + H2SO4 -> CaSO4 + H2
the calcium dissolves and bubbles of gas are produced
Explain the trend in reactivity in terms of the first and second ionisation energies of Group 2 elements down the group.
Reactivity increases down group 2. Ionisation energies decrease down the group because atomic radius increases and shielding also increases. The attraction between the nucleus and the outer electrons decreases.
Describe the trend in solubility of group 2 oxides as you go down the group.
pH of resulting solutions?
trend in alkalinity?
-oxides become more soluble as you go down the group
11-14
become more alkaline
Group 2 compounds tend to be bases. (e.g. calcium and magnesium hydroxides and calcium carbonate) Give some uses of group 2 compounds that rely on their basicity. Include equations.
Calcium hydroxide is added to soil to decrease acidity. The calcium hydroxide neutralises the acid in the soil.
Ca(OH)2 + 2H+ -> Ca2+ + 2H2O
Group 2 bases are used for treating indigestion. They neutralise excess acid in the stomach
CaCO3 + 2HCl > CaCl2 + CO2 + H2O
Mg(OH)2 + 2HCl >MgCl2 + 2H2O
Describe and explain the trend in the boiling points of Cl2, Br2 and I2, in terms of induced dipole–dipole interactions (London forces)?
Boiling points increase as you go down the group. This is because there are more electrons and therefore bigger London forces between the molecules. These stronger forces need more energy to overcome.
what is the outer shell electron configuration that all halogens have?
p5
what happens to the electrons when the halogens react with a metal?
halogen gains an electron
new configuration is p6
Predict what you would see, give the full balanced equation and ionic equation for the reaction between chlorine water and potassium bromide
Cl2 + 2KBr > Br2 + 2KCl
Cl2 + 2Br- > Br2 + 2Cl-
Predict what you would see, give the full balanced equation and ionic equation for the reaction between bromine and potassium chloride
no reaction would take place
Predict what you would see, give the full balanced equation and ionic equation for the reaction between bromine and sodium iodide
Br2 + 2NaI > I2 + 2NaBr
Br2 + 2I- > I2 + 2Br-
Describe and explain the trend in reactivity down group 7 (Hint - in terms of attraction, atomic radius and electron shielding?)
Reactivity decreases down group 7. The group 7 elements react by gaining an electron. As you go down the group, atomic radius increases, shielding increases and the attraction of the nucleus for an incoming electron decreases.
define disproportionation
a reaction where an element is both oxidised and reduced.
equation to show how chlorine is used in water purification and explain how it is an example of disproportionation
Cl2 + H2O > HClO + HCl
Disproportionation is a reaction where an element is both oxidised and reduced.
Chlorine is oxidised from an oxidation number of 0 in Cl2 to an oxidation number of +1 in HClO and chlorine is reduced from an oxidation number of 0 in Cl2 to an oxidation number of -1 in HCl
Write an equation to show how chlorine reacts with cold, dilute aqueous sodium hydroxide, to form bleach.
Define disproportionation and explain how this reaction is an example of it
Cl2 + 2NaOH > NaClO + NaCl + H2O
Disproportionation is a reaction where an element is both oxidised and reduced.
Chlorine is oxidised from an oxidation number of 0 in Cl2 to an oxidation number of +1 in NaClO and chlorine is reduced from an oxidation number of 0 in Cl2 to an oxidation number of -1 in NaCl
List and describe the benefits of chlorine use in water treatment and contrast with associated risks?
Chlorine kills harmful bacteria in water. This makes water safe to drink and reduces the incidence of water-borne diseases such as typhoid and cholera. However, chorine can react with hydrocarbons in the water forming chlorinated hydrocarbons which are carcinogenic. The overall risk to health of not adding chlorine to water is much greater than the risk caused by low levels of chlorinated hydrocarbons.
What reagents can be used to identify solutions of aqueous anions of Cl-, Br- and I-? \
Describe how you would carry out these tests, what you would expect to see and write full balanced and ionic equations for the reactions.
acidified silver nitrate can be used to identify halide ions. these tests can be further confirmed by the addition of dilute and concentrated ammonia solution
AgNO3(aq) + NaCl(aq) > AgCl(s) + NaNO3(aq) WHITE
Ag+ + Cl- > AgCl
AgNO3(aq) + NaBr(aq) > AgBr(s) + NaNO3(aq) CREAM
Ag+ + Br- > AgBr
AgNO3(aq) + NaI(aq) > AgI(s) + NaNO3(aq) YELLOW
Ag+ + I- > AgI
what reagent used to identify carbonate ions? and positive results
add an acid
bubbles of gas
balanced and ionic equations for carbonate test
Na2CO3 + 2HCl >2NaCl + CO2 + H2O
CO32- (aq) + 2H+ (aq) > CO2 (g) + H2O (l)
what reagents are used to identify sulphate ions?
add barium chloride or barium nitrate
positive result: white precipitate
full and ionic equations for sulphate test
Na2SO4 (aq) + BaCl2 (aq) à BaSO4 (s) + 2NaCl (aq) SO42- + Ba2+ à BaSO4 (s)
what reagents are used to identify ammonium ions and positive result?
Add sodium hydroxide and warm gently with a damp piece of red litmus paper held over the test tube
damp red litmus paper turns blue
