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CHEMISTRY as - ocr a > Chapter 8 > Flashcards

Chapter 8 Flashcards

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1
Q

What is a reducing agent

A

An element that reduces other substances by losing electrons to another species

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2
Q

group 2

Redox reactions with oxygen

A

2Mg + O2 —> 2MgO

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3
Q

group 2

Redox reactions with water

A

Forms alkaline hydroxide and hydrogen

Mg + 2H2O —> Mg(OH)2 + H2

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4
Q

group 2

Redox reactions with dilute acids

A

Metal + acid —> salt + hydrogen

Mg + HCl —> MgCl + H2

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5
Q

Why does reactivity increase down group 2

A

The ionisation energies decrease down the group

Because attraction between nucleus and outer electrons decrease

  • atomic radius increase
  • more shielding

Less energy needed to remove electron
More easily lost
More reactive

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6
Q

group 2

Redox reactions with

Metal oxides and water

A

Releases hydroxide ions, OH-
Forming alkaline solutions

MgO (s) + H2O —> Mg2+(aq) + 2OH-(aq)

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7
Q

Since group 2 hydroxides are only slightly soluble in water

What happens when the solution becomes saturated

A

Further metal and hydroxide ions will form a solid precipitate

Mg2+ (aq) + 2OH- (aq) —> Ca(OH)2

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8
Q

What is the solubility of hydroxides in water

A

down a group

Alkalinity increases
Solubility increases
pH increases
More OH- ions

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9
Q

Testing the solubility and alkalinity if group 2 down a group

A

1) add partial of each group 2 oxide to water
2) shake mixture
3) insufficient water to dissolve all metal hydroxide, undissolved white solid at bottom - saturated solution
3) measure pH

Should increase down group

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10
Q

How can metal hydroxides be used in everyday

A

Used to neutralise acidic fields
Ça(OH)2 (s) + H+ (aq)—> Mg2+(aq) + 2H2O

Used in antacids for treating acid indegstion
CaCO3 (s) + HCl (aq) —> CaCl2 (aq) + H2O + CO2
Mg(OH)2

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11
Q

Boiling point trend for

Halogens

A

Boiling points increase down group
Because

More electrons
Stronger London forces
More energy required to break London force

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12
Q

Halogens are oxidising agents - reduced

Definition

A

Substance that has the ability to oxidise other substances by gaining electrons

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13
Q

How do displacement reactions show the reactivity of halogens

Halogen reactivity decrease down a group

A

1) a solution of each halogen is added to aqueous solutions of the other halides

If the halogen added is more reactive than halide then

2) a reaction takes place - displacing
3) the solution changes colour

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14
Q

Colours of halogens in water

A

I2 - brown
Br2- orange
Cl2 - pale green

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15
Q

Bromine and iodine colours are similar

How to overcome confusion

A

Add a non polar solvent = cyclohexane
Shake

Halogens dissolve more readily
Colours are easier to tell apart

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16
Q

Halogen colours in cyclohexane

A

I2- pale green
Br2- orange
Cl2- violet

17
Q

Equation of displacement between

Cl and Br

A

Cl2 + Br- —> Cl- + Br2 (aq)

18
Q

What about fluorine and astanine

A

Fluorine - Pale yellow gas

Reacts with all substances it comes into contact with

Astanine - has not been seen

It’s radioactive and decays rapidly

19
Q

Trend in reactivity in halogens

A

Halogens react by gaining electrons
As you go down the group tendency to gain a electron decreases
Because

Atomic radius and shielding increases
Less nuclear attraction to capture an electron from another species
Reactivity decreases

20
Q

What is disproportionation

Example

A

Redox reaction in which the same element is both oxidised and reduced

Chlorine with water and cold dilute sodium hydroxide

Chlorine with dilute sodium hydroxide
- dissolve more readily than in water

Cl2 + 2NaOH -> NaClO + NaCl + H2O

21
Q

Identifying a carbonate

A

Add dilute nitric acid (HNO3)

Bubble gas through limewater (Ca(OH)2)

CO2 (g) + Ca(OH)2 —> CaCO3 (s) + H2O

White precipitate - milky

22
Q

Identifying sulfate

A

Add barium chloride to a solution

If white precipitate formed then sulfate is present

Ba2+ + SO42- —> BaSO4

23
Q

Identifying halides

Aqueous silver ions react with halide ions to from precipitate

A

0) add dilute nitric acid - remove ions that might interfere
1) add silver nitrate AgNO3 To solution
2) White cream yellow - Cl2, Br2, I2 precipitate formed
3) add aqueous ammonia to gets solubility
4) dissolves in :
Cl2 - dilute ammonia
Br2 - concentrated ammonia
I2 - insoluble in concentrated

24
Q

Correct order for analysing unknot inorganic compound

A

Carbonate CO3 2-
Sulfate SO4 2-
Halide Cl-

25
Q

Why is there an order for tests

A

You have to carry out carbonate before sulfate

  • because it is the only one with effervescence
  • barium carbonate also forms a white precipitate

Do halide last
- Ag2CO3 + Ag2SO4 will both form precipitates

26
Q

Testing for a mixture of ions

Carbonate test

A

Complete until effervescence stops
Carbonate ions will be removed

Use dilute HNO3

27
Q

Testing for a mixture of ions

Sulfate test

A

Add excess Ba(NO3)2
Filter out white precipitate

Can’t use BaCl2 - will show in halide test

28
Q

Testing for a mixture of ions

Halide test

A

Add AgNO3

Add NH3 to confirm

29
Q

Testing for cations

NH4 +

Aqueous ammonium ions will react with hydroxide ions

A

1) add NaOH to solution of ammonium ions
2) ammonium gas produced
3) mixture is warmed to release gas
4) test gas with moist pH indicator paper

Ammonia is alkaline
Will turn paper blue

30
Q

Why does chlorine have a lower boiling point than iodine

A

The strength of the London forces between molecules of chlorine is weaker than the forces between iodine

Because
The size and relative mass of chlorine is less than iodine
And contains fewer electrons

31
Q

Melting point of metals across period

A

Metal melting points increases across a period
Giant metallic structure with metallic bonding
Increases because metallic bonding increases across period,

Because of
Increasing positive charge
More delocalised electrons
Decreasing atomic radius

32
Q

Melting point of giant covalent structures

A

Have the highest melting point
Strong covalent bonds holding together atoms
Large energy needed to overcome bonds

33
Q

Simple molecules boiling point across period

A

Bp depends on strength of London forces between the molecules
London forces are weak, easily overcome
Bp are very low
Bigger molecules with more atoms means stronger London forces

Sulfur is biggest so has strongest London forces and highest bp
Argon is lowest because exists as monoatomic with very weak London forces

34
Q

State the effect of using cyclo hexane

A

Halogen will dissolve
Form a separate layer
Yellow will be organic - bromine
Brown will be violet - iodine

35
Q

Benefits of chlorine

A

Kills disease causing microorganism
Stops further reinfection
Makes water safe
Prevents algae, bad taste and smell

36
Q

Risks of chlorine

A

Respiratory irritant
If reations with organic hydrocarbons - chlorinated hydrocarbons cause cancer
Chemical burns

37
Q

What are 2 alternatives of using chlorine to treat water

A

Ultraviolet and ozone

38
Q

Benefits and disadvantages of ozone

A

Strong oxidising agent
Kills diseases causing microorganisms

Expensive to produce
Short half life
Not permanent

39
Q

Benefits and disadvantages of uv

A

Kills microorganisms - damaging DNA
Ineffective in cloudy water
Won’t stop from being contaminated further down

CHEMISTRY as - ocr a (15 decks)

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