Topic 4 Flashcards by Edith Hamilton

What is the trend for solubility of group 2 hydroxides

Increases down the group

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How does the solubility of group 2 hydroxides relate to the alkaline pH

The maximum alkaline pH increases down the group

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What is the definition of thermal stability

It is a measure of extent to which a compound decomposes when heated

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What is the trend for reactivity with oxygen and group 2

Reactivity increases down Group 2, becomes more vigorous

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What is the trend for reactivity with chlorine and group 2

Reactivity increases down Group 2, becomes more vigorous

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What is the trend for reactivity with water and group 2

Reactivity increases down Group 2, magnesium reacts very slowly

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General equation for group 2 and water

M(s) + 2H2O(l) –> M(OH)2(aq) + H2(g)

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General equation for group 2 and chlorine

M(s) + Cl2(g) –> MCl2 (s)

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General equation for group 2 and oxygen

2M(s) + O2(g) –> 2MO(s)

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What is the difference in the reaction with calcium and water compared with other group 2 metals

Calcium hydroxide is only slightly soluble in water, so it forms a precipitate
Ca(OH)2 is a solid

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How is the reaction of a group 2 metal different with steam than water

M(s) + H2O(g) –> MgO(s) + H2(g)
- A metal oxide is formed and hydrogen gas is formed

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General equation for group 2 oxides with water

MO(s) + H2O(l) –> M(OH)2(aq)

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Equation for milk of magnesia with stomach acid

Mg(OH)2 + 2HCL –> MgCl2 + 2H2O

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Why does milk of magnesia not pose a health risk

Due to the low solubility of magnesium hydroxide it means the concentration of OH- ions is very low

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What is the reaction between a group 2 oxide or hydroxide with acid called

A neutralisation reaction

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Trend of solubility in group 2 sulfates

decreases down the group

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How can the presence of sulfate ions in aqueous solution be shown

By adding a solution containing barium ions, usually barium chloride or nitrate

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What must be present in the solution to prevent barium carbonate from forming as a white precipitate

Hydrogen ions

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Why are Group 1 carbonates more thermally stable than Group 2 carbonates

Group 2 ions have a larger charge, 2+ compared to group 1 1+
Group 2 ions polarise/distort the carbonate ion more effectively
Weakening the C=O bond

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Explain whether magnesium carbonate is more or less thermally stable than barium carbonate

Magnesium carbonate is less thermally stable, as it decomposes easier than barium carbonate
- this is because the Mg2+ ion is smaller
- so it has a higher charge density
- meaning it is more likely to distort the carbonate ion
- and weaken the C=O bonds within the carbonate ion

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How would you compare the thermal stability of two Group 2 nitrates

Heat them up and see which produces brown fumes first
use a light sensor to measure colour of gas
same heat applied
same amount of nitrates in each test tube
safety precaution of a fume cupboard

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How to do a flame test?

Using a platinum or nichrome wire
Clean wire with HCL
Dip wire into the sample of the compound
Hold the wire into the blue flame of the bunsen burner

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What are possible problems with a flame test?

Many compounds contain small amounts of sodium compound impurities, its intense colour can mask the other colours
describing colours can be subjective

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What colour does metal cation lithium produce in the flame test?

Red

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What colour does metal cation sodium produce in the flame test?

Yellow

What colour does metal cation potassium produce in the flame test?

Lilac

What colour does metal cation rubidium produce in the flame test?

red/purple

What colour does metal cation caesium produce in the flame test?

blue/violet

What colour does metal cation beryllium produce in the flame test?

NO COLOUR

What colour does metal cation magnesium produce in the flame test?

NO COLOUR

What colour does metal cation calcium produce in the flame test?

brick red

What colour does metal cation stronium produce in the flame test?

crimson red

What colour does metal cation barium produce in the flame test?

apple green

What causes the colours in a flame test?

Electrons absorb energy and move to higher energy levels, 'excited state' this movement is immediately followed by the return of the electron to its ground state which releases energy, which if corresponds to the visible light spectrum then we can see it.

What is the usual test for ammonium ions in a solid or solution?

Add sodium hydroxide solution Warm the mixture

What does the reaction of ammonium ions, adding sodium hydroxide solution and warming the mixture do, and how does this test for ammonium ions

NH4+ OH- --> NH3 + H2O --> ammonia can usually be detected by its strong smell --> damp red litmus paper can also be used and it turns blue

What is another test that can be done to test for ammonium ions

Hydrogen chloride gas reacts with ammonia to form white fumes of ammonium chloride NH3 + HCL --> NH4Cl

Why do melting and boiling points increase as you go down group 7

As the number of electron increases down the group, this increases the strength of the London forces and the size of electron cloud

What is the trend of reactivity in group 7

They decrease in reactivity, this can be linked to decreasing electronegativity

Which halogens displace other halogens

Chlorine displaces bromine and iodine Bromine displaces iodine

What organic solvent is ideal to add when doing halogen displacement reactions as the halogens colour change is more easy to see

Cyclohexane

What colour is chlorine in cyclohexane

Pale green

What colour is bromine in cyclohexane

Orange

What colour is iodine in cyclohexane

Purple or violet

Why is chlorine the most reactive out of bromine and iodine

1. It is the smallest atom, so the incoming electron gets closer and is more attracted by the protons in the nucleus 2. It has the smallest number of complete inner energy levels of electrons, so incoming electrons experience least repulsion

What things can chlorine be used for

- bleach - weed killer - disinfectant

How do halide ions and halogen molecules act in redox reactons

Halide ions act as as reducing agents halogen molecules act as oxidising agents

What are the three possible products from the reduction of sulfuric aicd

- sulfur dioxide - sulfur - hydrogen sulfide

How do we know that to get the product of hydrogen sulfide we need the strongest reducing agent

As the oxidation number of sulphur has been reduced the most from +6 to -2

Observations of sodium halides when concentrated sulfuric acid is added

NaCl - misty fumes NaBr - Brown fumes, choking smell NaI - purple fumes or black solid, rotten egg smell

Steps to test for halide ions in solution

1. Add dilute nitric acid to remove any carbonate ions 2. Add silver nitrate to form precipitates 3. Add dilute aqueous ammonia 4. Add concentrated aqueous ammonia

What colour precipitates do the halide ions make

Chloride ions --> white precipitate Bromide ions --> Cream precipitate Iodide ions --> Yellow precipitate

Results of the halide ions when adding dilute aqueous ammonia

Chloride ions are SOLUBLE Bromide ions are INSOLUBLE Iodide ions are INSOLUBLE

Results of the halide ions when adding concentrated aqueous ammonia

Chloride ions are SOLUBLE Bromide ions are SOLUBLE Iodide ions are INSOLUBLE

What acid does hydrogen fluoride form when reacting with water

Hydrofluoric acid

What acid does hydrogen chloride form when reacting with water

Hydrochloric acid

What acid does hydrogen bromide form when reacting with water

Hydrobromic acid

What acid does hydrogen iodide form when reacting with water

Hydriodic acid

How do you test for the presence of Sulfate ions

- Add HCL - Add Barium chloride - A white precipitate may form

How do we know that iodide ions are the strongest reducing agent when using sulfuric acid

Hydrogen iodide reduces sulfur the most from +6 to -2, H2S Hydrogen Bromide reduces sulfur from +6 to +4, SO2 Hydrogen Chloride doesn't reduce sulfur

Why is HCl a good conductor of electricity but hydrogen chloride is not

The covalent bond in hydrogen chloride changes to an ionic bond in aqueous solution making HCL a good conductor of electricity

What colour is Fe(II)

Green

What colour is Fe(III)

Brown

What colour is Colbalt(II)

Blue

How do you collect a dry, solid sample

1. Cool off reaction mixture 2. Filter off less soluble parts 3. Dry between filter paper

Why is a nichrome wire used for a flame test and not iron

- Nichrome doesn't produce any colour during the flame test - Nichrome is inert so won't react with oxygen like iron

Why is fresh hydrochloric acid used to clean the wire in a flame test

Old acid may have become contaminated with residue from previous tests

Why is HCL used in a flame test

forms volatile chlorides

Products of group 2 carbonates thermal decomposition

Metal oxide and Carbon dioxide