M3 Chapter 8 - Reactivity Trends Flashcards by Zafar Rizvi

What is a reducing agent?

An element that itself is oxidised to reduce another species.

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What is the most common type of reaction for group 2 elements?

Redox Reactions.

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Group 2 Metal + Oxygen –> ?

Metal Oxide

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Give an example of the previous reaction..

2Mg (s) + O2(g) –> 2MgO(s)

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Prove that the previous reaction was a redox reaction.

Mg was oxidised to +2
O was reduced to -2

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How do Group 2 Metals react with water?

Group 2 Metal + Water –> Alkaline Hydroxide + H2.

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How does reactivity change down Group 2?

Reactivity increases down the group.

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Metal + Acid –> ?

Salt + Hydrogen

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What type of reaction is this?

Redox reaction.

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How does reactivity change for this reaction?

Down group 2 the trend in reactivity remains the same. Therefore, the trend in reactivity remains increasing down the group.

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Why is the trend of ionisation energy inversely proportional to the reactivity of group 2 elements?

The ionisation energies decrease down the group due to the attraction between the nucleus and outer electrons. Due to a similar reason, since reactions occur due to electrons, the ability for group 2 elements to lose electrons increases down the group therefore, these are inversely proportional.

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Group 2 Oxide + Water –> ?

Metal Hydroxide

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CaO + H2O –> ?

Ca2+ (aq) + 2OH-
Ca2+(aq) + 2OH - –> Ca(OH)2

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Are these Metal Hydroxides soluble in water?

Yes they are soluble

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How does solubility change for hydroxides down the group?

Down the group, solubility increases.

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Down group 2, how does Solubility, pH and alkalinity change?

Down the group they all increase.

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How would you test this trend for alkalinity?

Add spatula of Group 2 oxides to water in a test tube.
Shake mixture to ensure dissolvinf occurs.
Measure the pH of each solution. The alkalinity will be seen to increase down the group.

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How can Ca(OH)2 be used as bases as a real world application?

Calcium Hydroxide = Used in agriculture to increase the pH of acidic soils. This is because the Ca(OH)2 reacts with protons (acids) to make Ca2+ and 2H2O.

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How can Mg(OH)2 be used as bases as a real world application?

The Mg(OH)2 can be used as antacids to treat indigestion. Calcium Carbonate can also be used to acheive the same. Mg(OH)2 + 2HCl –> MgCl2 + 2H2O.

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List 3 physical properties of Group 2 metals.

High melting and boiling points
Low density metals
Form colourless (white) compounds

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The highest energy electrons of group 2 metals are in which subshell?

S subshell

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Does reactivity increase or decrease down group 2?

Increases down group 2
Electrons are lost more easily due to larger atomic radius and more shielding

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What happens to the first ionisation energy as you go down group 2? Why?

Decreases due to:
- Increased shielding (more filled electron shells)
- Increased atomic radius (weaker attraction between outer electrons and nucleus hence less energy required to remove electron)

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What type of reaction is the reaction between group 2 elements and oxygen?

Redox reaction

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Write an equation for the reaction of Calcium and Oxygen.

2Ca(s) + O2(g) --> 2CaO(s)

What are the products when group 2 elements react with water?

Hydroxide and Hydrogen Gas

Which group 2 element does not react with water?

Beryllium

Which group 2 element reacts very slowly with water?

Magnesium

What type of reaction is the reaction between group 2 metal and water?

Redox Reaction

Write an equation for the reaction of Barium and Water.

2Ba(s) + 2H2O(l) --> Ba(OH)2(aq) + H2(g)

What is oxidised and what is reduced in a reaction between group 2 metals and water?

Metal = Oxidised Water = Reduced

What are the products when a group 2 element reacts with an dilute acid?

Salt and Hydrogen Gas

Write an equation for the reaction of calcium and hydrochloric acid.

2Ca(s) + 2HCl(aq) --> 2CaCl(s) + H2(g)

What is formed when group 2 oxides react with water?

Metal Hydroxide

Write an equation for the reaction between a group 2 oxide and water.

MO(s) + H2O(l) --> M(OH)2 (aq)

What group 2 metal oxide is insoluble in water?

Beryllium Oxide

What is the trend in hydroxide solubility down group 2?

Increases down the group. Mg(OH)2 is slightly soluble Ba(OH)2 creates a strong alkaline solution

What is Ca(OH)2 used for? Write an equation related to one of its uses.

Used to neutralise soil Ca(OH)2(aq) + 2HCl(aq) -> H2O(l) + CaCl2 (aq)

What is Mg(OH)2 used for?

Milk of magnesia - antacid to treat indigestion, heartburn etc.

What is calcium carbonate used for?

Present in limestone and marble Used in building construction

What is the drawback of using calcium carbonate in construction? Write a related equation.

Group 2 Carbonates react with acids CaCO3 + HCl --> H2O(l) + CO2(g) + CaCl2 (aq)

What group elements are referred to as halogens?

Group 7

List two properties of halogens.

- Low melting and boiling points - Exist as diatomic molecules

What is the trend in boiling point down group 7? Why?

- Increases down the group - Because size of atom increases due to more occupied electron shells meaning stronger london forces of attraction between molecules, take more energy to break.

What is the trend in reactivity down group 7? Why?

- Reactivity decreases This is because atomic radius increases, electron shielding increases both meaning that the ability to gain electron and form 1- ion decreases.

What is the trend in oxidising ability down the group? Why?

Decreases down the group (oxidising ability means how easily it itself can be reduced ie: gain electrons) Due to this: Cl has the fewest occupied electron shells meaning the greatest force of attraction between outer electrons and nucleus meaning easiest to gain electrons and be reduced. (Best oxidising agent is chlorine)

What is the trend in REDUCING ability for the halides down the group? Why?

Increases down the group (Cl- weakest, I- strongest). Because I- has most occupied electron shells meaning outer electrons further away from nucleus. This means weakest force of attraction between outer electrons and positive charge of nucleus hence most easily oxidised ie: losing an electron.

When a more reactive halogen displaces a less reactive halide, what is the reaction called?

Displacement Reaction

What is the colour of chlorine in water?

Pale Green

What is the colour of bromine in water?

Orange

What is the colour of iodine in water?

Brown

What is the colour of chlorine in cyclohexane?

Pale Green

What is the colour of bromine in cyclohexane?

Orange

What is the colour of iodine in cyclohexane?

Violet

Out of the 3 halides Cl-, Br- and I-, which can be oxidised by chlorine?

Br- and I- ions.

Write the equation for chlorine oxidising bromide ions.

Cl2(aq) + 2Br-(aq) --> 2Cl-(aq) + Br2 (aq)

Write the equation for Cl2 oxidising 2I-.

Cl2(aq) + 2I-(aq) --> 2Cl- (aq) + I2(aq)

Out of the 3 halides, Cl-, Br- and I-, which can be oxidised by bromine?

Only I- ions

Write the equation for bromine oxidising iodide ions.

Br2(aq) + 2I- (aq) --> 2Br-(aq) + I2(aq)

Out of the 3 halides Cl-, Br- and I-, which one of these can be oxidised by iodine?

None.

Define disproportionation.

The oxidation and reduction of the same element in a redox reaction.

What is the equation for the reaction of Cl2 with water?

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

What type of reaction is the reaction of chlorine with water?

Disproportionation. Chlorine is both oxidised and reduced.

Why is chlorine added to drinking water?

Kills bacteria in the water making it safer to drink

What are the two forms of the Chlorate ion?

ClO- (Chlorate I) and ClO3- (Chlorate V)

What is the equation for forming bleach?

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

What are anions also known as?

Negative Ions

Test for Carbonate? (CO32-)

- Add strong acid to sample - Collect gas produced - Pass through limewater to see if CO2.

What are the observations for a positive test of carbonate ions (CO32-)?

Fizzing Limewater turns cloudy

Write an equation for the carbonate ion test.

CO32-(aq) + 2H+(aq) --> H2O (aq) + CO2 (g)

Test for sulfate ions? (SO42-)?

Add dilute HCl and BaCl2 to sample

What are the observations for a positive test of sulfate ions (SO42-)?

White precipitate of Barium Sulfate is produced.

Write an equation for the sulfate ion test.

So42-(aq) + Ba2+(aq) --> BaSo4(s)

What do you use to test for halide ions?

Acidified AgNo3 (Silver Nitrate)

Why do you add HNO3 to test for halide ions and not HCl?

To remove CO32- Adding HCl would add Cl- ions, giving a false positive result.

How can you test for a halide ion?

- DIssolve sample in water - Add AgNo3(aq) (Aqueous silver Nitrate) - Record colour change - If difficult to distinguish, add aqueous ammonia. First add dilute ammonia, then concentrated ammonia. - Note the solubility of the precipitate.

Write the result and equation for the Cl- test.

White Precipitate, soluble in dilute aqueous ammonia. Ag+(aq) + Cl-(aq) --> AgCl(s)

Write the result and equation for Br- test.

Cream Precipitate, soluble in concentrated aqueous ammonia only. Br- (aq) + Ag+(aq) --> AgBr(s)

Write the result and equation for I- test.

Yellow Precipitate, insoluble in concentrated and dilute aqueous ammonia. Ag+(aq) + I- (aq) --> AgI(s)

When testing for carbonate, sulfate and halide ions, in which order should the tests be carried out and why?

1. Carbonate Test 2. Sulfate Test 3. Halide Test Because barium ions form insoluble precipitates of BaCO3 and silver ions form insoluble precipitates of Ag2SO4.

What are cations also known as?

Positive ions.

How can you test for ammonium ions (NH4+)?

Add NaOH (Sodium Hydroxide) to the sample and warm it. Test the gas produced with red litmus paper.

What are the observations for positive ammonium ions test?

Red litmus paper has turned blue Ammonia has a pungent smell

Write the equation for ammonium ions test.

NH4+(aq) + OH-(aq) --> NH3(aq) + H2O(aq)