Chapter 8-Reactivity trends Flashcards by Ben Taylor-Rose

How do group 2 elements react with oxygen?

They tarnish with air to form a coating of the metal oxide or when heated in pure oxygen burn vigorously to produce a white ionic oxide

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What is general equation for group 2+ Oxygen?

2M(s) + O₂(g) –> 2CaO(s)

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What colour flame does magnesium+oxygen produce?

Bright white

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What colour flame does calcium+oxygen produce?

Orange

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What colour flame does strontium+oxygen produce?

Orange-red

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What colour flame does barium+oxygen produce?

Green

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What does a group 2 metal + water produce?

A metal hydroxide + hydrogen

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What is the general equation for group 2 + water?

M(s) + 2H₂O(l) –> M(OH)₂(aq) + H₂(g)

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Further down group 2 what happens to the reaction with water?

It gets more vigorous

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What does magnesium requre to react with water and why?

It requires steam as it reacts very slowly with cold water

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What is the formula for magnesium reacting with steam?

Mg(s) + H₂O(g) –> MgO(s) + H₂

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What does a group 2 metal and an acid produce?

Salt and Hydrogen

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What is the general equation for a group 2 metal reacting with hydrochloric acid?

M(s) + 2HCl(aq) –> MCl₂(aq) + H₂(g)

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What is the general equation for a group 2 metal oxide reacting with water?

MO(s) + H₂O(l) –> M(OH)₂(aq)

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What happens down group 2 for metal oxides?

Solubility increases

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What happens down a group 2 for metal hydroxides and what does this do?

Solubility increases and causes the solutions to be more alkaline as more OH⁻ ions are released into the water.

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Why down group 2 are metal hydroxides more soluble?

Down the group the ions get larger with the same charge so have a lower charge density
These ions have less ‘pulling power’ on OH⁻ ions so more get released into the water making it more soluble

What are some uses of group 2 hydroxides?

Ca(OH)₂ -used in agriculture to neutralise acid soils
Mg(OH)₂ -used in toothpaste and indigestion tablets as an antacid
Both are weak alkalis and are not as caustic as sodium hydroxide

What does a group 2 oxide + acid make?

Salt + water

What is the general equation of a group 2 oxide + acid?

MO(s) + 2HCl(aq) –> MCl₂ (aq) + H₂O

What are some properties of group 2 carbonates?

Insoluble in water
Undergo thermal decomposition to oxide and carbon dioxide
React with acids to produce a salt, water and carbon dioxide

What is the general formula for the thermal decomposition of group 2 metal carbonates?

MCO₃ (s) –> MO(s) + CO₂(g)

What happens down the group to do with the thermal decomposition of group 2 carbonates?

They become more stable and are more difficult to decompose

Why does it become more difficult to thermally decompose carbonate ions down group 2?

The smaller the positive ion, the higher the charge density so greater pulling power on carbonate ion (on the oxygen)
As ions get larger, charge densitry decreases, so you have to heat the compound more to persuade the CO₂ to leave the MO

What happens when carbon dioxide and excess carbon dioxide is bubbled through limewater?

* Carbon dioxide turns solution cloudy/milky-forms insoluble calcium carbonate precipitate * Excess carbon dioxide reacts with calcium carbonate and water to form a clear solution of calcium hydrogen carbonate

What happens to the solubility of group 2 sulfates down the group?

* Decreases * Cation gets larger so has a lower charge density-less attracted to polar water molecules

What is a use for the insolubility of group 2 Carbonates?

* The barium swallow * Barium is unsoluble so won't dissolve as well as being radioopaque-shows clearly on a radiograph so can map organs

What is the state and colour of flourine at RTP?

* Gas * Pale yellow

What is the state and colour of chlorine at RTP?

* Gas * Yellow green

What is the state and colour of bromine at RTP?

* Liquid * Red-brown

What is the state and colour of iodine at RTP?

* Solid * Grey

How can we tell apart solutions of bromine and iodine assuming they look very similar (brown)?

* Dissolving Bromine in cyclohexane creates a orange layer above aqueous layer * Dissolving Iodine in cyclohexane creates a violet layer above aqueous layer

Why do halogens dissolve more easily in cyclohexane than water?

Halogens are a non-polar molecule and so is cyclohexane

What happens to reactivity down group 7?

Atomic radius increases, increasing shielding, decreasing in power to attract an electron to form a negative ion (less nuclear attraction), decrease in reactivity

What is the redox reaction of halogens?

Cl₂ + 2e⁻ --> 2Cl (reduction)

What reaction can occur between halogens and halide compounds?

A displacement reaction whereby the more reactive halogen displaces the other (cyclohexane can be added after to confirm the less reactive halogen left in the test tube.

How can chlorine be used to treat water?

It is added to kill bacteria as it reacts with water to form HClO (a weak bleach).

What is the disproportionation reaction of chlorine and water?

Cl₂(aq) + H₂O(l) --> HCl(aq) + HClO(aq)

What are the pros of using chlorine to treat water?

* Kills bacteria * Ensures water is fit to drink * Can help those in third world countries (little risk)

What are the cons of using chlorine to treat water?

* Is a toxic gas * Causes respiritory problems in low quantities * Large concentrations can be fatal * Can react with methane to form chlorinated hydrocarbons-can cause cancer

How is bleach formed?

Sodium hydroxide reacts with chlorine to form a solution containing lots of ClO⁻ ions to form-used in household bleach.

What is the disproportionation reaction to form bleach?

2NaOH(aq) + Cl₂(aq) -->NaCl + NaClO + H₂O