2. Chemistry Of The Elements

Question 0

What is the test for hydrogen?

Answer 0

There will be a ‘squeaky pop’ when a splint is put into the gas

Question 1

What is the test for oxygen?

Answer 1

A glowing splint will be relighted

Question 2

What is the test for carbon dioxide?

Answer 2

Lime water will turn cloudy if the gas passed through it is carbon dioxide

Question 3

What is the test for ammonia?

Answer 3

Damp red litmus paper will turn blue

Damp universal indicator will turn purple

Question 4

What is the test for chlorine?

Answer 4

Damp litmus paper will be bleached white

Question 5

What are the tests for the anions?

Answer 5

Cl-, Br- and I-, using dilute nitric acid and silver nitrate solution

Chloride ions + nitric acid + silver nitrate > white precipitate (silver chloride)
Bromide ions + nitric acid + silver nitrate > cream precipitate (silver bromide)
Iodide ions + nitric acid + silver nitrate > yellow precipitate (silver iodide)

SO4 2- (sulphate ions) using dilute hydrochloric acid and barium chloride solution

SO4(2-) + HCl + Ba(2+) > white precipitate (barium sulphate)
iii) CO3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved
Carbonate + acid > salt + water + carbon dioxide
Carbon dioxide produced will turn lime water cloudy

Question 6

What are the tests for the cations?

Answer 6

Li+, Na+, K+, Ca2+ using flame tests

Lithum: red
Sodium: orange (so strong can mask other colours)
Potassium: lilac
Calcium: brick red

NH4+, using sodium hydroxide solution and identifying the ammonia evolved

NH4 + OH > NH3 + H2O
ammonium ions + hydroxide ions > ammonia + water
ammonia (pungent smelling gas) turns red litmus paper blue

Cu2+, Fe2+ and Fe3+, using sodium hydroxide solution

Copper(ii) sulphate + sodium hydroxide > blue precipitate
Iron(ii) sulphate + sodium hydroxide > green precipitate
Iron(iii) sulphate + sodium hydroxide > brown precipitate

Question 7

What is the sacrificial protection of iron in terms of the reactivity series?

Answer 7

Sacrificial is covering a metal with a more reactive metal. What this means is water and/or air will react with the more reactive metal instead of the one underneath.

Question 8

describe how the rusting of iron may be prevented by grease, oil, paint, plastic and galvanising

Answer 8

Grease, oil, paint and plastic prevent air and/or water from coming into contact with iron. This means the reaction that rusts iron can’t occur.

Galvanising is coating in zinc. This Zinc react in the air to form ZnCO3 which prevents air and/or water from coming into contact with the iron.

Question 9

Describe the conditions under which iron rusts

Answer 9

Water and oxygen are needed to rust iron: iron that reacts with these becomes hydrated iron(iii) oxide.

Question 10

Define the terms:

redox
oxidising agent
reducing agent

Answer 10

In a redox reaction, a more reactive metal gains an oxygen from a less reactive metal which looses it.
i.e. a more reactive metal is oxidised and a less reactive metal is reduced.

The reducing agent is the more reactive metal which reduces the other metal.

The oxidising agent is the less reactive metal which allows the other metal to be oxidised.

Question 11

What is oxidation?

What is reduction?

Answer 11

oxidation is the gain of oxygen, but the loss of electrons

reduction is the loss of oxygen, but the gain of electrons

Question 12

deduce the position of a metal within the reactivity series using displacement reactions between metals and their oxides, and between metals and their salts in aqueous solutions

Answer 12

A metal oxide or a metal salt dissolved in water:

introduce a more reactive metal and it will displace the current one
introduce a less reactive metal and no displacement will take place

From this you can deduce which metals are more and less reactive.

Question 13

describe how reactions with water and dilute acids can be used to deduce the following order of reactivity: potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper

Answer 13

potassium, sodium, lithium and calcium all react with water and acids

magnesium, zinc and iron all react with acids (and very slowly with water.)

copper doesn’t react with either.

The more vigorous the reaction the more reactive the metal. The more things a metal will react with, the more reactive the metal.

Question 14

describe a physical test to show whether water is pure.

Answer 14

If water is pure it will boil at exactly 100° and freeze at exactly 0°

Question 15

describe the use of anhydrous copper(II) sulfate in the chemical test for water

Answer 15

anhydrous copper sulphate will become hydrous copper sulphate when it is reacted with water.

So if anhydrous copper sulphate goes from white to blue in the presence of a liquid it will be water.

Question 16

describe the reactions of dilute hydrochloric and dilute sulfuric acids with magnesium, aluminium, zinc and iron

Answer 16

acid + metal > salt + hydrogen

For example:
magnesium + hydrochloric acid > magnesium chloride + Hydrogen
Mg + 2HCl > MgCl2 + H2

Question 17

describe the combustion of hydrogen

Answer 17

The combustion of hydrogen is its reaction with oxygen.
Water is created. and a lot of energy.

4H + O2 > H2O

Question 18

How does carbon dioxide contribute to climate change?

Answer 18

Carbon dioxide prevents heat leaving the earth’s atmosphere in rays that the earth emits.
Significant amounts of green house gasses will warm up the earth, changing the climate.

Question 19

explain the use of carbon dioxide in carbonating drinks and in fire extinguishers, in terms of its solubility and density

Answer 19

Carbon dioxide is dissolved into drinks at a high pressure, this makes CO2 bubbles in fizzy drinks.

Some fire extinguishers have CO2 in, because it is denser than air it will fall over the fire creating a barrier between the air and fire: the fire can’t burn with out the oxygen in the air.

Question 20

describe the properties of carbon dioxide, limited to its solubility and density

Answer 20

It is denser than air.

It is soluble in water at a high pressure.

Question 21

describe the formation of carbon dioxide from the thermal decomposition of metal carbonates such as copper(II) carbonate

Answer 21

When metal carbonates are heated they become carbon dioxide and a metal.

For example:
copper carbonate > copper oxide + carbon dioxide
CuCO3 > CuO + CO2

Question 22

describe the laboratory preparation of carbon dioxide from calcium carbonate and dilute hydrochloric acid

Answer 22

calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide

CaCO3 + 2HCl → CaCl2 + H2O + CO2

Question 23

describe the reactions of magnesium, carbon and sulfur with oxygen in air, and the acid-base character of the oxides produced

Answer 23

The two non-metals burn in air- giving out heat and light- to bond with oxygen.
They become non-metal oxides, which are, by nature, acids.

Magnesium will burn in air to from a metal-oxide.

Question 24

describe the laboratory preparation of oxygen from hydrogen peroxide, using manganese(IV) oxide as a catalyst

Answer 24

hydrogen peroxide is put in a conical flask with manganese(IV) oxide as a catalyst. Plus there could be some water to diloute the hydrogen peroxide.

Hydrogen peroxide > water + oxygen
2H2O2 > 2H2O + O2

You can then collect oxygen by downwards displacement method.

Question 25

explain how experiments involving the reactions of elements such as copper, iron and phosphorus with air can be used to investigate the percentage by volume of oxygen in air

Answer 25

Copper, iron and phosphorus all react with air.

If you know the volume of air that you have, then react it with on of these, then re measure the volume of air; what has been lost is all oxygen that reacted.

Question 26

What are the percentages of gases in the air?

Answer 26

About 78% nitrogen

About 21% oxygen

About 1% other gases (argon, carbon dioxide)

Question 27

understand these displacement reactions as redox reactions.

Answer 27

When a more reactive halogen displaces a less reactive one this is a redox reaction.

This means that one element has been reduced (gained something) and one has been oxidised (lost something.)

OILRIG helps to remind you how redox reactions go:

Oxidation
Is
Lost
Reduction
Is
Gain

Question 28

describe experiments to demonstrate that a more reactive halogen will displace a less reactive halogen from a solution of one of its salts

Answer 28

A more reactive halogen will displace a less reactive one that is bonded as a salt. This will only happen if the salt is dissolved in water or a gas.

Question 29

explain, in terms of dissociation, why hydrogen chloride is acidic in water but not in methylbenzene

Answer 29

Water (H2O) is a polar molecule.
Methylbenzene is a non-polar molecule.
Hydrogen chloride is a polar molecule.

Polars only dissolve in polars.
When hydrogen chloride is dissolved you get +H ions.
These are acidic.

Question 30

describe the relative reactivities of the elements in Group 7

Answer 30

As you go down group 7, the reactivity decreases

At the top, the positive charge of the proton in the nucleus is close to the surface (as there are few shells) this makes it easy for them to pull in the one electron they need to become stable, meaning they are very reactive.

Lower down where there are more shells the pull of the proton is further from the surface making it less easy to pull in another electron.

Question 31

What is the difference between hydrogen chloride gas and hydrochloric acid?

Answer 31

Hydrogen chloride gas is HCl

Hydrochloric acid is hydrogen chloride dissolved in water. The two ions become detached leaving Cl- and H+ ions. H+ is acidic, hence the term acid.

Question 32

make predictions about the properties of other halogens in this group(group 7)

Answer 32

We would expect …

the colour to keep getting darker
the melting and boiling points to get higher
…further down the group.

Question 33

What are the colours and physical states of the elements (group 7) at room temperature?

Answer 33

Fluorine………….. Gas……….. yellow
Chlorine…………. Gas……….. yellow-green
Bromine…………. Liquid…….. red-brown
Iodine……………. Solid………. purple
Astatine…………. Solid………. black

Question 34

describe the relative reactivities of the elements in Group 1

Answer 34

Group one elements get more reactive the further down the group.

Question 35

explain the relative reactivities of the elements in Group 1 in terms of distance between the outer electrons and the nucleus.

Answer 35

Group one elements are more reactive further down the group.

Group one elements need to loose an electron- the one on the outer shell- to react. Electrons are held to an atom by the protons in the nucleus. If an electron is close to the nucleus the force holding it in will be very strong, if it is further away it will be weaker.

So bigger atoms (towards the bottom of the group) with the outer orbital far from the nucleus will loose their electron more easliy: this means they react more easily/quickly/more/vigorously.

Smaller atoms with the electron closer to the pull of the nucleus (at the top of group one) will be less reactive as it takes more to loose the electron.

Question 36

describe the reactions of these elements with water and understand that the reactions provide a basis for their recognition as a family of elements

Answer 36

The group one elements- lithium, sodium, potassium- are easily identifiable as the same group due to the fact that they all react vigorously with water (clearly due to the fact they have similar electronic configurations.)

The reactions that occur are huge- they get bigger further down the group. Hydrogen gas is produced as well as metal hydroxide.

Question 37

Describe the noble gases (Group 0) and explain their lack of reactivity in terms of their electronic configurations.

Answer 37

Nobel gasses are inert, this means they do not react. The reason for this is because they are stable: meaning they have a full outer shell, so they do not need to loose or gain electrons.

Question 38

why do elements in the same group of the Periodic Table have similar chemical properties?

Answer 38

Metals in the same group have the same number of electrons on their outer shell.
This means they will behave in a similar way; they will react and bond similarly.

For example in group one, the elements all form -1 ions as they each loose one electron to become stable (to have a full outer shell.)

Question 39

explain the classification of elements as metals or non-metals on the basis of their electrical conductivity and the acid-base character of their oxides

Answer 39

Metals are all conductors. Metals form metal-oxides which are alkaline.

Nonmetals don’t conduct. They form nonmetal-oxides which are acidic.