Chapter 8 - Reactivity Trends Flashcards
What are group 2 metals called?
Alkaline earth metals
What type of agent are group 2 metals known as?
Reducing agents
How do group 2 metals work as reducing agents?
Each metal atom is oxidised, losing two electrons to form 2+ ions which causes another species to gain these electrons and so get reduced
What is formed when a group 2 metal reacts with oxygen?
Metal oxide
What is formed when a group 2 metal reacts with water?
Metal hydroxide + hydrogen gas
What is formed when a group 2 metal reacts with dilute acids?
Salt + hydrogen gas
Why does reactivity increase down group 2 metals?
- Atomic radius increases
- More inner shells so heleiding increases
- Nuclear attraction decreases so less energy to lose electrons
- Formation of 2+ ions requires input of two ionisation energies
Ionisation energies ________ down group 2 elements
Decreases
Group 2 elements become _________ reducing agents down the group
Stronger
What happens when a group 2 oxide reacts with water?
Hydroxide ions released to form alkaline solutions of the metal hydroxide
What is the equation for reaction between calcium oxide and water?
CaO(s) + H2O(l) -> Ca2+ (aq) + 2OH- (aq)
What is formed when a solution of calcium oxide reacting with water becomes saturated?
Calcium hydroxide precipitate
Ca(OH)2
Solubility of group 2 hydroxides _________ down the group so resulting solutions contain _________ OH- ions and are more _________. Which means pH _________
Increases
More
Alkaline
Increases
Compare the solubilities of Mg(OH)2 and Ba(OH)2
Mg(OH)2 very slightly souble in water -> low OH- concentration in solution so pH ~ 10
Ba(OH)2 much more soluble in water -> greater OH- concentration in solution so pH ~ 13
What are the uses of calcium hydroxide, Ca(OH)2? Give equation
Agriculture - added to fields to increase pH of acidic soils by neutralising the acids in soil
Ca(OH)2 (s) + 2H+ (aq) -> Ca2+ (aq) + 2H2O (l)
What are the uses of magnesium hydroxide Mg(OH)2? Give equation
Medicine - treatment for acid indigestion by neutralisation
Mg(OH)2 (s) + 2HCl (aq) -> MgCl2 (aq) + 2H2O (l)
What are the uses of calcium carbonates, CaCO3? Give equation
Medicine - treatment for acid indigestion by neutralisation
CaCO3 (s) + 2HCl (aq) -> CaCl2 (aq) + 2H2O (l) + CO2 (g)
Trend in boiling point of halogens down the group?
Increases
Why does boiling point increase down group 7 halogens?
- More electrons
- Stronger London forces
- More energy required to break intermolecular forces
What type of agent are group 7 halogens known as?
Oxidising agents
How do group 7 halogens work as oxidising agents?
Each halogen atom is reduced, gaining one electron to form 1- ions which causes another species to lose this electron and so get oxidised
What happens in a displacement reaction of halogens?
More reactive halogen displaces halide from solution
Colours of Cl2, Br2 and I2 solution in water?
Pale green
Orange
Brown
Colours of Cl2, Br2 and I2 solution in cyclohexane?
Pale green
Orange
Violet
What can displace I-?
Chlorine and bromine
What can displace Br-?
Chlorine
What can displace Cl-?
Nothing
More reactive halogen gets __________ (________ electrons)
Reduced
Gains
Explain why reactivity decreases down the group 7 halogens?
- Atomic radius increases
- More inner shells so heleiding increases
- Nuclear attraction decreases so harder to gain electron
Halogens become _______ oxidising agents down the group
Weaker
What is disproportionation?
Redox reaction in which the SAME element is both reduced and oxidised
Give the equation for chlorine purifying water?
Cl2 + H2O -> HClO + HCl
Why is chlorine reacting with cold, dilute aqueous sodium hydroxide a better bleach than reacting chlorine with water?
Chlorine has a low solubility in water, so reacting with NaOH allows for a larger concentration of chlorate ions which act as a bleach
Give the equation for the reaction between chlorine with cold, dilute aqueous sodium hydroxide?
Cl2 + 2NaOH -> NaClO + NaCl + H2O
Which ion acts as a bleach?
Chlorate (I) ions, ClO-
What are the benefits and risks of using chlorine in water treatment?
Benefits - kills bacteria
Risks - hazards of toxic chlorine gas and formation of chlorinated compounds
How is the carbonate test is carried out?
Add dilute HNO3 to solution being tested
What is the positive result for a carbonate test?
Effervescence (bubbles) to indicate the release of a gas (CO2)
How can the gas of a positive carbonate test be tested?
Bubble through limewater, it will turn cloudy in the presence of CO2
Barium sulfate is ___________ in water
Insoluble
How is sulfate test carried out?
Add Ba(NO3)2 to solution being tested
What is a positive result for a sulfate test?
White precipitate
How is halide test carried out?
Add AgNO3 (aq) to aqueous solution of sample being tested
What is the positive result of a halide test if CHLORINE is present?
White precipitate which is soluble in dilute NH3 (aq)
What is the positive result of a halide test if BROMINE is present?
Cream precipitate which is soluble in concentrated NH3 (aq)
What is the positive result of a halide test if IODINE is present?
Yellow precipitate which is insoluble in concentrated NH3 (aq)
Give the ionic equation for reaction of CHLORINE with AgNO3?
Ag+ + Cl- -> AgCl
Give the ionic equation for reaction of BROMINE with AgNO3?
Ag+ + Br- -> AgBr
Give the ionic equation for reaction of IODINE with AgNO3?
Ag+ + I- -> AgI
What is the sequence of tests for anions?
- Carbonate test
- Sulfate test
- Halide test
Why is carbonate test carried out before the sulfate and halide test?
BaCO3 and AgCO3 are both insoluble in water and form precipitates so carbonate ions need to be removed first
Why is sulfate test carried out before the halide test?
AgSO4 is insoluble in water and will form a precipitate so sulfate ions need to be removed first
In a mixture of ions why should HNO3 be used in the carbonate test and not H2SO4 or HCl?
Would affect sulfate and halide test otherwise
In a mixture of ions why should Ba(NO3)2 be used in the sulfate test and not BaCl2?
Would affect halide test otherwise
How is the test for ammonium ions, NH4+ carried out?
Add NaOH to solution being tested and warm it
What is the positive result from ammonium ion test?
Moist pH indicator paper will turn blue in the presence of ammonia gas
Give the equation for the ammonium ion test?
NH4+ + OH- -> NH3 (g) + H2O (l)