Chapter 8 Reactivity Trends Flashcards
what is a reducing agent?
an element that reduces another species
what type of reaction is common for group 2 metals?
redox ( oxidisation)
what is the general formula for a reaction between group 2 metal and oxygen?
MO
what are the products of a group 2 metal reacting with water?
An alkaline hydroxide = M(OH)2 + h2
what is the equation for a redox reaction between a metal and a acid
metal + acid —- salt + hydrogen
does reactivity increase or decrease down group 2 elements?
reactivity increases
why does reactivity increase down group 2?
more shells so larger atomic radius and increased shielding affect reducing nuclear attraction to outermost electron therefore reducing ionisation energy
what is the equation for group 2 oxides reacting with water?
CaO + H2O —— Ca^+2 + 2OH-
how are group 2 hydroxides formed?
Ca+2 + 2OH- ——– Ca(OH)2
are group 2 hydroxides soluble?
they are slightly soluble and increase solubility down the group with a solution containing more OH so is more alkaline
what are the uses of group 2 compounds?
Calcium Hydroxide is added to fields as lime to increase pH of acidic soils by neutralising acid and forming water
Ca(OH)2 + 2H2 —— Ca+2 + H20
Group 2 bases are used as antacids for treating acid indigestion using mangenium and calcium carbonates with suspension of magnesium hydroxide
Mg(OH)2 + 2HCl ——– MgCl2 + H20
CaCO3 + 2HCL ——– CaCl2 + H20 + CO2
which halogens are gas, liquid or solid?
Fluorine - pale yellow gas
chlorine - plae green gas
bromine - red-brown liquid
iodine - shiny grey black solid
At - never seen
why does halogens boiling point increase down the group?
more electrons so stronger london forces therefore more energy needed to break intermolecular forces as a result boiling point increases
what is the redox reaction for halogen?
Cl2 + 2e —— 2Cl-
each halogen atom gains an electron to become reduced forming halide ion. Halogen is an oxidising agent as it has oxidised another species
what is a halogen-halide displacement reaction?
halogen displaces halide from solution causing solution to change colour
what does a halogen-halide displacement reaction show?
shows that reactivity of halogens decrease down the group
what colour is formed from bromine formation?
orange
what colour is formed from iodine formation?
violet
can a chloride react with Bromine?
no
can a bromide react with chlorine?
yes
can an iodide react with both chlorine and bromine?
yes
why does reactivity and tendency to gain electron decrease down the halogen group?
atomic radius increases and more inner shells so shielding increases which reduces nuclear attraction to gain electron from other species therefore reactivity decreases
what is disproportionation?
a redox reaction where the same element becomes both oxidised and reduced
what is the equation for chlorine with water?
Cl2 + h20 —— HClO + HCL
disproportionation takes place
what is the equation for chlorine with cold dilute sodium hydroxide?
Cl2 + 2NaOH —— NaClO + NaCl + h2O
what are the benefits and risks for chlorine use?
Benefits:
-kills bacteria in water
-reduces diseases like Typhoid and Cholera in water
Risks:
-it is a respiratory irritant
-toxic gas
- chlorine in water can react with hydrocarbons to form chlorinated hydrocarbons which may cause cancer
what is the test for halide ions?
halide ions react with silver ions to form precipitates of silver halides
Ag+ + X- —— AgX
how are reducing ability of halide ions shown?
shown by reacting halides with sulfuric acid
Chlorine ions cannot reduce H2SO4
bromines ions can reduce h2so4 to so2
2h+ + h2so4 + 2br- ———– so2 + br2 + 2h2o
iodine reduces so2 to s and further reduces to hydrogen sulfide h2s
What observation is shown if a solution containing iodide ions is added to silver nitrate
Cream precipitate
What is the order of reactivity of halogens
cl>I>br
When bromine is displaced it forms brown colour. When iodine is displaced it forms brown colour. How are these differentiated
Add organic solvent such as solvent which makes iodine from orange to violet . Chlorine remains green and bromine remains brown
