elements of life activities

2Salters Advanced Chemistry, Pearson Education Ltd 2008. © University of York.

T his document may have b een altered from the orig inal.

IntroductionNo one yet has been able to look inside atoms to see what they are really like.

T he typ ic al p ic tu re of an atom we hav e in ou r minds is neither ‘the tru th’ nor

‘the rig ht answer’ – it is a g ood working model whic h help s to ex p lain many

p henomena.

M u c h ev idenc e has been g athered to su p p ort the c u rrent model of an atom.

T he model may c hang e as more ev idenc e c omes to lig ht, and it is v ery likely to

bec ome more detailed.

W e c an sometimes ex p lain thing s u sing only a simp lifi ed model of the atom.

T hinking of atoms as tiny sp heres is su ffi c ient to ex p lain the states of matter ( the

p rop erties of solids, liq u ids and g ases) – bu t this model is not detailed enou g h

to ex p lain why metals tend to reac t with non-metals. M odels c an be simp le or

elaborate, dep ending on the job they need to do. K eep this in mind as you r

ideas and u nderstanding of c hemistry dev elop .

W h a t y ou doH ow has the c u rrent model of the atom dev elop ed? M any sc ientists c ontribu ted

to the seq u enc e of g athering knowledg e abou t the atom, bu t some made

p artic u larly imp ortant disc ov eries – they were:

Y ou will need to work in a g rou p of three for this ac tiv ity.

1

one c hoic e.)

2 P rep are a series of P owerP oint® slides on the sc ientist you hav e c hosen. Y ou r

p resentation shou ld c ov er the following p oints:

U se su itable tex tbooks, mag az ine artic les or the Internet to help you to fi nd

the information you need. Y ou c ou ld start by searc hing the S alters’ A dv anc ed

inc lu de and what to leav e ou t as a g rou p .

3 T he members of you r g rou p shou ld now deliv er their p resentations to the

rest of the c lass – make su re the rep orts are p resented in c hronolog ic al

order.

4 A t the end of the ac tiv ity ev eryone in the c lass will need notes on you r

p resentations – p rep are handou ts of you r g rou p ’s set of p resentations.

In this activity you will learn how some of our

id eas ab out atomic structure have d evelop ed .

H O W D O W E K N O W

A B O U T A T O M S ?

EL 1 .1

984_01_SAC SP_EL.indd 2 16 /4/08 15 :5 2:3 4

3Salters Advanced Chemistry, Pearson Education Ltd 2008. © University of York.This document may have been altered from the original.

IntroductionYou are going to carry out a quantitative investigation – trying to answer, as

accurately as possible, a question which begins ‘How much … ?’ A titr ation is a

method of quantitative analysis that can be used when two solutions react

together. O ne solution of a known concentration is placed in a burette – the

second solution is placed in a conical fl ask. The solution in the burette is run

into the fl ask until just enough has been added for the reaction to be complete.

An indicator is often added to show when the reaction has finished, but this is

not necessary if the reaction is accompanied by a very obvious colour change. An

analysis involving a titration is sometimes called a volumetr ic analy s is .

H ow it w ork s

In this investigation, you are going to find out how much iron there is in a

solution of an iron(II) salt by titrating the solution with potassium

manganate(V II) solution.

The salt is called hydrated iron(II) ammonium sulfate, which contains F e

ions, as its name suggests. These react with the MnO 4− ions in the potassium

manganate(V II), as shown in the equation below:

5 F e (aq) MnO 4−(aq) (aq) 5 F e (aq) Mn (aq) 4H O (l)

pale deep light colourless

green purple brown

This looks rather complicated, but it tells you that the colour of the potassium

manganate(V II) disappears as it reacts with the F e (aq) ions. This provides a

way of deciding when the titration is complete because when all the F e (aq)

ions are gone just one dr op more of potassium manganate(V II) solution will

make the titration mixture turn pale purple.

conical fl ask

volumetric fl ask

pipette

)

)

CARE Take care when pouring potassium manganate(VII) solution as it stains the hands. W ear protectiv e glov es if necessary .

R e q uire m e nts

IRRITA N T

d ilu te s u lfu r ic a c id

HARMFUL

ir o n (II) a m m o n iu m s u lfa te s o lid

WEAR EYE

P RO T EC T IO N

CARE E y e protection must b e worn.

This activity introduces you to the technique of

titration – one method of quantitative analysis.

Y ou will learn how to perform a titration and

mak e use of accurately calibrated apparatus.

Titration will be used in later modules.

HOW MUCH IRON IS

IN A SAMP LE OF AN

IRON COMP OUND?

EL1.2

984_01_SAC SP_EL.indd 3 16/4/08 15:52:36


This document may have been altered from the original.

What you do1 Weigh a clean, dry weighing bottle accurately. Add about 5g of iron(II)

ammonium sulfate to the bottle and record the mass of the bottle plus

sulfuric acid,

transferring the washings to the beaker each time. It is important that all the

solid goes into the beaker.

2 of sulfuric acid into the beaker – but do not fill

the beaker more than half full. Stir the acid and the solid together with a

glass rod until you are sure that all the solid has dissolved.

3

the dilute sulfuric acid and transfer the washings to the volumetric flask.

Then rinse the funnel with a small amount of the acid. This technique

ensures that all the iron compound from the beaker is transferred to the

volumetric flask.

4

below the graduation mark. Now add more acid slowly from a clean

dropping pipette until the bottom of the meniscus is just touching the

graduation mark. Stopper the flask and invert it several times to mix the

solution.

5 of the solution from the

volumetric flask and transfer it to a conical flask.

6 beaker to fill a burette with the potassium

the beaker to make sure the jet is full of solution – ask your teacher for help

if an air bubble stays in the jet. B e careful how you turn the burette tap –

some burettes have tapered keys which leak if they are used wrongly. If you

are not sure, ask your teacher for advice on how to use a burette correctly.

7

.

8 Add small volumes of potassium manganate(VII) solution from the burette to

the solution in the conical flask, swirling the flask after each addition. The

purple colour of the MnO4−(aq) ions will disappear as they react with the

Fe (aq) ions. The e n d p o in t of the titration is when you fi rst get a

permanent faint purple colour from excess manganate(VII) ions.

9

have run out into the flask. This first attempt will be a roug h titration but it

will give you a general idea of where the end point comes.

10 D o several further accurate titrations, in which you approach the end point

adding the manganate(VII) solution drop by drop, until you have three

.

Recording your results

mass of weighing bottle and solid = _ _ _ _ _ _ _ g

mass of weighing bottle = _ _ _ _ _ _ _ g

mass of solid = _ _ _ _ _ _ _ g

Titration Roug h 1 2 3 4 5

final burette reading/cm3

initial burette reading/cm3

titre/cm3

Average titre = _ _ _ _ _ _ _ cm

EL1.2 H ow much iron is in a sample of an iron compound?

984_01_SAC SP_EL.indd 4 16/4/08 15:52:36

5

Using your results

11 Work out the average of your three closest figures for the volume of

number of decimal places.

12 You will learn how to do calculations following titrations in the E lem ents

fr om th e S ea module. For the moment, simply multiply the volume of

the mass (mg) of iron(II) ions pipetted into the conical flask each time.

13 of solution in the volumetric

flask.

14

ammonium sulfate that you used.

15

crystals.

16 The percentage of iron in a pure sample of hydrated iron(II) ammonium

sulfate crystals, Fe(NH4) (SO4) ·6 H

result for the percentage of iron in the compound.

E v aluating your results and p rocedures

In any analysis involving a titration, there are errors or uncertainties related to

the precision of the equipment used. The glassware has been designed so that, if

it is used appropriately, the precision errors are:

Volumetric or standard flask (class B) volumetric flask is

filled correctly (i.e. the bottom of the meniscus rests on the calibration line)

Burette (class B) – one drop from a burette has a volume of approximately

P ipette (class B) pipette is used correctly (i.e. it is allowed to

Procedural errors can arise if your practical technique is not good – a good

technique would include the following:

between titrations

from the burette is added drop by drop, with swirling, as the end point is

reached

manganate(VII)) only the minimum number of drops is added each time.

How much iron is in a sample of an iron compound? EL1.2

Q uestions

1 F ill in the following table for your ex periment.

Q uantity measured % error

M ass of iron compound weighed on balance

2 5 0 cm3 solution made up in volumetric fl ask

2 5 cm3 solution delivered by pipette

Y our average titre delivered by burette

2 Which of the stages in your procedure do you think could have led to errors? In each case, say whether it would make the result higher or lower.

3 Which of all the sources of error that you have identified is likely to have most impact on your overall result?

percentage error = error_ _ _ _ _ _ _

reading × 1 0 0

It is important to repeat a titration several times to check that your results are reliable. A fter calculating the average titre, you should correct the value to an appropriate number of decimal places.

Salters Advanced Chemistry, Pearson Education Ltd 2008. © University of York.This document may have been altered from the original.

984_01_SAC SP_EL.indd 5 16/4/08 15:52:36



IntroductionWhen metal compounds are placed in a Bunsen flame, the electrons in the metal

atoms absorb energy and are promoted to higher (excited) energy levels. The

electrons then emit energy as they fall back to lower energy levels – this energy

is emitted in the form of radiation, some of which is in the visible part of the

spectrum. The radiation is emitted at specific frequencies and if the emission

spectrum of a metal is examined closely, it is found to be made up of a series of

lines. Using only our eyes, we see the predominant colour resulting from the

main frequencies at which each type of metal atom emits the radiation.

What you doYou are going to look at the light emitted when metal compounds are put into a

Bunsen burner flame. You will capture an image of the colours with a mobile

phone camera or digital camera. You will use these images to create a

PowerPoint presentation in which you describe and explain the visible emission

spectra of some metals.

1 L ight your Bunsen burner and adjust the flame until no yellow colour

appears in it.

2 Select one of the splints that has been soaked in a metal compound solution

overnight.

3 Hold the splint in the Bunsen flame long enough to observe the colour that

it imparts to the flame, but do not allow the splint to burn.

4

colour accurately.

5

holds the splint in the flame while the other takes a photograph of the

colour.

6

P reparing your P owerP oint presentation

7 Download the images from your camera onto a computer.

8 Use these images, and the ideas you have met during your study of this

topic, to produce a PowerPoint presentation which will:

when they are heated in a Bunsen burner flame

the formation of atomic emission spectra.

In this activity you will have an opportunity to

view the visible lig ht emitted when some metal

compounds are heated. This visible radiation is

part of the emission spectra of the metals.

INVESTIG ATINGVISIBLE EMISSION

SPECTRA

EL1.3

®)

solutions:

Requirements

HARMFUL

b arium chloride

WEAR EYE

PROTECTION

CARE Eye protection must be worn.

984_01_SAC SP_EL.indd 6 16/4/08 15:52:37


Introduction

radioactive isotope decays in a random manner regardless of what other nuclei

are doing. We can’t predict when a particular nucleus will decay but we can

predict that half the radioactive nuclei in the sample will decay in a fixed time –

the radioactive half-life.

In this simulation of radioactive decay, you will drop a cardboard tray

containing pieces of pasta onto a table. This causes some of the pasta to change

from lying on their sides to standing on one of their flat ends – this is a random

process, in a similar way that radioactive decay is a random process. We are

going to take the pieces of pasta lying on their sides to represent radioactive

nuclei, and the pieces which stand on a flat end to represent a radioactive

nucleus which has decayed.

What you do1

cardboard tray.

2 Swirl the tray to get the pasta into a single layer – make sure that all the

number of pieces of pasta in a table like the one opposite – this is most ®.

3

4

and enter this number in the table.

5

6 Plot a graph, using the computer package if possible, of unchanged pasta

(represents the number of undecayed radioactive nuclei) in the sample

against the ‘drop number’ (represents time).

7 Share your results with other groups of students so that you can find a class

average for the number of ‘undecayed nuclei’ at each stage – draw another

graph using the average figures.

In this activity you will use pasta to simulate

radioactive decay – this will enable you to

practise working out radioactive half-lives.

SIMULATINGRADIOACTIVE DECAY

EL1.4

Requirements

Drop number

Unchanged p asta

Pastaremov ed

0 0

1

2

3

4

5

6

7

8

9

10

Questions

1 Work out three values of ‘radioactive half-life’ based on the graph drawn using your own data.

2 What do you notice when you compare the half-life values?

3 U se the graph drawn using the class average values to work out three values of the half-life. How do these values compare with each other and with the values found from your own graph?

984_01_SAC SP_EL.indd 7 16/4/08 15:52:37



What you doThe statements in the table below refer to the formation of ions, using sodium and chlorine as examples.

1

Statement True False

a A sodium atom spontaneously loses an electron to get a full shell of electrons

b An N a7− ion is more stable than a sodium atom because it has a full shell of electrons

c A C l7+ ion is just as stable as a C l− ion because they both have a full shell of electrons

d Each proton in the nucleus of an atom attracts one specific electron

e Energy is req uired to remove an electron from an atom

f When an atom is ionised, it req uires even more energy to remove a second electron

g If you remove an electron from a sodium atom you can never put it back

hO nce you have removed one electron from a sodium atom you can’t remove another because that would mean it no longer had a full electron shell

iS olid sodium chloride contains pairs of sodium and chloride ions which are kept together by their opposite charges

j When sodium chloride dissolves, the solution contains molecules of sodium chloride

Table 1

Particle Electron arrangement

N a 2.8.1

N a+ 2.8

N a7− 2.8.8

C l 2.8.7

C l− 2.8.8

C l7+ 2.8

2

each other why you have chosen your particular answer and agree between you what your group thinks is the best answer

for each statement.

3 Your teacher will help you to compare your group’s answers with the answers chosen by other groups. Be prepared to

explain why your group has chosen answers, and also be ready to challenge other groups if you think that your answer is

more appropriate than theirs.

4 Write down how you have modified your original ideas about why atoms form ions after talking and listening to other

students.

In this activity you can check and clarify your

ideas about why some atoms form ions.

WHY DO ATOMS FORM IONS?

EL2.1

984_01_SAC SP_EL.indd 8 16/4/08 15:52:37


What you do1 Blow up the balloons and tie the necks – do not blow them up too hard or

you will not be able to twist them.

2 Twist one of the balloons in the middle. It now represents two electron pairs

balloon resembles the space occupied by a pair of electrons, and the balloon

lobes push each other out of the way – just as electron pairs repel one

another. You can see that the ‘balloon molecule’ takes the linear shape you

).

3 Twist a second balloon in the middle, and then twist the middle of this

balloon several times around the middle of the first balloon to represent

four

the twist to lubricate the join.

a What shape does the ‘molecule’ made in step 3

of a molecule with such a shape.

4 Now, get a third balloon – twist it in the middle and twist it around the

middle of the ‘molecule’ you made in step 3. Again, make sure the balloons

are twisted round each other several times. Now you have a representation

of a molecule with six electron pairs round a central atom.

b What shape does the ‘molecule’ made in step 4


5 Now comes the exciting bit – get a pin and pop one of the balloon lobes. If

you did your twisting well, the air won’t escape from the other half of the

popped balloon, and you will have five ‘electron pairs’.

c What shape does the ‘molecule’ made in step 5


6 Pop two more lobes to get three ‘electron pairs’.

d What shape does the ‘molecule’ made in step 6


7 Summarise your findings in a table like the one below. When you draw the

diagrams, represent the electron pairs with lines or wedges, as shown in

C hemical Ideas 3.2.

Requirements

The shapes adopted by twisted balloons can

closely resemble the shapes of molecules. You

have to be careful if this modelling process is to

work well.

SHAPES OF MOLECULES:

BALLOON MOLECULES

EL2.2(1)

Figure 1 Two electron pairs round a central atom.

Figure 2 Four electron pairs around a central atom.

Number of electron pairs round central atom

Shape Bondangles

Diagram Ex ample

984_01_SAC SP_EL.indd 9 16/4/08 15:52:38



What you do1 Working in pairs, draw the dot–cross diagram for each of the following

4 H O NH NH4 5 6 SiH4

2 Write the following headings across the top of a piece of A4 paper (landscape

format):

3 Place your dot–cross cards under that heading on the piece of paper. Now

match the other cards with your dot–cross diagrams to show the formula,

4 Discuss the placing of the cards with your partner, then compare your card

arrangements with those of other pairs of students. Are there any ideas you

are not sure about?

5 Finally, construct a table to summarise the information shown by your cards.

Requirements

In this part of the activity you will draw

dot–cross diagrams for simple molecules and

ions and use them to predict molecular shapes

and bond angles.

SHAPES OF MOLECULES: SHAPESAND BOND ANGLES

EL2.2(2)

984_01_SAC SP_EL.indd 10 16/4/08 15:52:38


Shapes of molecules: shapes and bond angles EL2.2

Linear Tria n g u la r p la n a r Te tra h e dra l

Te tra h e dra l Te tra h e dra l Tria n g u la r p y ra m id

V - s h a p e d V - s h a p e d Tria n g u la r b ip y ra m id

Oc ta h e dra l 9 0 ° 9 0 ° a n d 1 20 °

1 0 9 ° 1 0 9 ° 1 0 9 °

1 0 9 ° 1 0 9 ° 1 0 9 °

1 20 ° 1 8 0 ° B C I3

B e C I2 C H4 H2O

N H3 P C l5

S C I2 S C I6 S iH4

N H4

+

984_01_SAC SP_EL.indd 11 16 /4/08 15 :5 2 :3 9



What you do1 For each of the substances named in the table, describe its structure and

p rop erties by choosing one of the resp onses from each of S ections A – D and

p utting tick s, , in the ap p rop riate box es.

2

differences betw een them and decide on any chang es y ou think y ou should

mak e to y our orig inal g rid.

3

any chang es that are necessary and mak e a note of any features that y ou

w ere less certain about. T his w ill serv e as a reminder for y ou to focus on

these p oints w hen y ou rev ise this top ic in the future.

Me th a n e Ir o n Dia m o n d So d iu m c h lo r id e

A: Str u c tu r e

Giant lattice (metallic)Giant s tru ctu re (io nic)Giant s tru ctu re (co v alent netw o rk )S imp le mo lecu lar

B: Me ltin g te m p e ra tu r e

H ig hL o w

C: So lu b ility in w a te r

S o lu b leIns o lu b le

D: Co n d u c tio n o f e le c tr ic ity

C o nd u cts as a s o lid and w h en mo ltenC o nd u cts in s o lu tio n and w h en mo ltenD o es no t co nd u ct electricity

In this activity you will summarise the physical

properties of d ifferent types of structures.

W HAT TY PE O F PRO PERTIES

DO DIF F EREN TSTRUCTURES HAV E?

EL 2.3

984_01_SAC SP_EL.indd 12 16/4/08 15:52:39


IntroductionThe checklist below covers the key points in Chemical Storylines EL1 and

EL2.

The statements listed correspond to learning outcomes in the specifi cation

for the AS examinations. They are listed in the order in which they occur in this

modules.

Y ou will probably have made summary notes of the main ideas that you have

met. N ow is a good time to make sure that your notes cover all the points you

need. If you feel that you are not yet able to meet the req uirements of all of the

statements in the list, you should look again at the areas concerned, seek help

from your teacher if necessary and develop your notes accordingly.

M ost of the points are covered in Chemical Id eas, with supporting

information in Chemical Storylines or the activitites. H owever, if the main

source of information is in a storyline or an activity this is indicated.

What you do

column that best represents your current ability to do what is described:

A – I am confi d ent that I can d o this

B – I need help to clarify my id eas on this

C – I am not yet ab le to d o this.

Y ou will be sharing this information with your teacher so that you can work

together to improve your understanding.

At the end of Chemical Storylines EL1 and EL2 you should be able to: A B C

levels; compare and contrast the features of these spectra:– similarities – both line spectra, lines in same position for a given element, lines become closer at higher

freq uencies, sets of lines representing transitions to or from a particular level– differences – bright/coloured lines on a black background or black lines on coloured/bright background

in the spectra, E = h

Z = 3 6

, and radiations

that the half-life is fi x ed for any given isotopeActiv ity EL1.4

and pressure) and understand that this is how certain elements are formed

uses

damage

continued

This activity helps you check your knowledge

and understanding of the topics that you have

covered in C hemical S torylines E L 1 and E L 2 .

CHECK YOURK NOWLEDG E AND UNDERSTANDING

(PART 1)

EL2.4

984_01_SAC SP_EL.indd 13 16/4/08 15:52:39



EL2.4 Check your knowledge and understanding (part 1)

sophisticated models Activity EL1.1

relative atomic mass, relative formula mass and relative molecular mass

dative covalent bonds, and be able to describe a simple model of metallic bonding

characteristic of giant lattice (metallic, ionic, covalent network) and simple molecular structure typesActivity EL2.3

CH4, N H3, H2O and SF 6) and ions (such as N H4+) with up to six outer pairs of electrons (any combination of

bonding pairs and lone pairs) Activity EL2.2

984_01_SAC SP_EL.indd 14 16/4/08 15:52:39


Introduction

Magnesium sulfate can be made in the laboratory in the reaction between

magnesium carbonate and dilute sulfuric acid:

SO 4( aq) MgSO 4 O ( l)

What you doM ak ing hydrate d m ag ne s ium sulfate crys tals ( E p s om salts )

1 sulfuric acid into a

beaker.

2 W eigh approximately 6 g of magnesium carbonate – this is more than is

needed to react with all of the acid so you don’t need to weigh it accurately.

3 Add spatula measures of the solid magnesium carbonate to the acid and stir

until all visible signs of reaction have stopped.

4 Support a filter funnel in a clamp and place an evaporating basin underneath

it.

5 P repare a filter paper, put it into the filter funnel and filter the mixture from

the beaker.

6 Heat the filtrate in the evaporating basin to reduce it to about one-third of its

original volume – do NO T heat to dryness. (CAR E There may be

considerable ‘spitting’.) Wear goggles and heat gently.

7 P ut the evaporating basin in a safe place, covered by a dry filter paper, to

allow the solution to crystallise – this may take a day or two.

8

absorbent tissues and then allow the crystals to air dry.

A nalys ing m ag ne s ium sulfate crys tals

The magnesium sulfate crystals you have made have the formula MgSO 4·xH O .

W hen they are heated, water of crystallisation is driven off leaving anhydrous

magnesium sulfate, MgSO 4.

MgSO 4·xH O ( s) MgSO 4 xH O ( g)

B y weighing the hydrated and anhydrous magnesium sulfate before and after

IRRITA N T

sulfuric acid

beaker

measuring cylinder

)

CARE When heating the hydrated magnesium sulfate, there can be considerable ‘spitting’. Goggles should be worn and the B unsen burner fl ame should be turned down as low as possible.

R e q uire m e nts

WEAR EYE

P RO T EC T IO N

CARE E ye protection must be worn.

Epsom salts are widely sold as a mild laxative –

they are hydrated magnesium sulfate. In this

activity you will make magnesium sulfate

crystals and then analyse them to fi nd out their

exact formula.

MAKING AND ANALYSING EPSOM

SALTS

EL3

984_01_SAC SP_EL.indd 15 16/4/08 15:52:39



of the magnesium sulfate. This will allow you to determine the exact formula for

the crystals. As you carry out steps 9–12, record your results like this:

mass of crucible = _ _ _ _ _ _ _ g

mass of magnesium sulfate in the magnesium sulfate crystals = _ _ _ _ _ _ _ g

mass of water in the magnesium sulfate crystals = _ _ _ _ _ _ _ g

9 Weigh a clean, dry crucible and record its mass.

10 Put some of the dry crystals of hydrated magnesium sulfate you have made

11 Heat the crucible gently for about a minute, and then more strongly for a

further 5 minutes (although you should try and keep the heat as low as

possible). You may see the crystals appear to ‘melt’. The liquid is likely to

‘spit’ as the water of crystallisation is driven off (CARE Wear goggles). You

will need to use the crucible lid to prevent loss of solid. Allow the crucible to

cool and then reweigh it, recording your mass.

12

– heating a substance until its mass remains the same is called ‘heating to

constant mass’.

Q uestions

1 What is meant by the terms:a hydratedb anhydrousc water of crystallisation?

2 Why is it necessary to heat the hydrated magnesium sulfate to constant mass?

3 Calculate the relative formula masses of:a magnesium sulfate (M gSO4)b water.

4 a Calculate the number of moles of magnesium sulfate in the crystals you weighed out.

b Calculate the number of moles of water in the crystals.

5 a Calculate the number of moles of water which are combined with 1 mole of magnesium sulfate in the crystals.

b What is the exact formula for the magnesium sulfate crystals?

EL3 M aking and analysing Epsom salts

984_01_SAC SP_EL.indd 16 16/4/08 15:52:40


What you doReaction of the elements w ith w ater

1 beaker with water. Use a pair of tweezers to select a small

piece of calcium metal (CARE Avoid skin contact) and add it to the water.

2 Observe what happens to the contents of the beaker. When the reaction

seems to be over, test the pH of the mixture using universal indicator

solution. Make a note of your observations.

3

(CARE Barium and its compounds are harmful. Do not swallow any. Barium

is kept under oil or liquid paraffin. You will need to dry your piece of metal

on filter paper before using it.)

a Use a reference book to find out what the products are in these reactions.

Then summarise your results in a table like the one below.

b Make a note of any common properties of these

metals and the compounds produced from them.

c Make a note of any patterns you can spot in your

results.

S olub ilities of the hydrox ides and carb onates

In this part of the experiment you will be looking to see whether precipitates

form when you add drops of solutions of sodium carbonate and sodium

4 You will be given a worksheet with boxes on which to place drops of

it is not already laminated.

5

6

appropriate column.

d

– magnesium ribbon

– calcium

– barium

)

)

)

)

)

)

Requirements

HIGHL Y

F L A M M A B L E

calcium

WEAR EYE

PROTECTION

CARE Eye protection must be worn.

This activity introduces you to some of the

chemistry of these elements and g ives you

p ractice at sp otting p atterns and look ing for

g eneralisations in your results.

INVESTIG A TINGTHE C HEMISTRY OF G ROU P 2 ELEMENTS

EL4 .1

CORROSIVE

s o d iu m h y d r o x id e s o lu tio n

u n iv e r s a l in d ic a to r s o lu tio n

HIGHL Y

F L A M M A B L E

b a r iu m

HIGHL Y

F L A M M A B L E

HARMFUL

Me ta l Ob s e r v a tio n w h e n m e ta l a d d e d to w a te r

C h e m ic a le q u a tio n

p H o f m ix tu r e p r o d u c e d

ma g nesium

984_01_SAC SP_EL.indd 17 16 /4/08 15 :5 2 :41



Table 1 Reactions of Group 2 metal ions in solution

So

luti

on

of

hyd

roxi

de

ion

s

So

luti

on

of

carb

on

ate

ion

s

So

luti

on

of

mag

nes

ium

ion

s

So

luti

on

of

calc

ium

ion

s

So

luti

on

of

stro

nti

um

ion

s

So

luti

on

of

bar

ium

ion

s

EL4.1 Inv estigating th e ch emistry of Group 2 elements

984_01_SAC SP_EL.indd 18 16/4/08 15:52:41


IntroductionThe naturally occurring form of most elements is made up of a mixture of

isotopes of the element. F or example, natural chlorine is made up of the

isotopes

atoms of chlorine

S o the r ela tiv e a tom ic m a ss of chlorine = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The relativ e atomic mass ( Ar) of a naturally occurring element ( the form of

the element that normally tak es part in chemical reactions) is the w eighted

mean of the mass numb ers of the stab le isotopes of the element. The mass

numb ers and relativ e ab undances of the stab le isotopes can b e found from the

mass spectrum of the element.

W h a t y ou do

This activity shows how a mass spectrometer

can b e used to give information ab out isotopes.

Y ou will use mass spectra data to determine the

relative ab undances of the isotopes of an

element and then calculate its relative atomic

mass.

ISOTOPICAB UND ANCE AND RELATIVE ATOMIC

MASS

EL4.2

The peak heights of a mass spectrum are often adjusted so that the most

differentiation b etw een the peak intensities.

1 M easure the peak height for each isotope of k rypton and calculate its relativ e

ab undance in natural k rypton. U se these data and the mass numb ers of the

isotopes to calculate the relativ e atomic mass ( Ar) of k rypton.

2 D raw the mass spectrum you w ould expect to ob tain for naturally occurring

chlorine.

Fig ure 1 The mass spectrum of krypton.

100

8 0

6 0

4 0

2 0

0

4 0 8 0 9 05 0 6 0 7 0

m/z

Inte

nsi

ty /

%

984_01_SAC SP_EL.indd 19 16/4/08 15:52:42



What you doYou need to download and print, or draw, graphs of the melting temperatures

and boiling temperatures of the elements from hydrogen to argon.

To download a graph, fi nd an Internet site that provides information about

the P eriodic Table. A good example is www.webelements.org – a site designed

and developed at the University of Sheffi eld. N avigate through the site until you

reach a graph showing the information you are looking for. It may contain

information about more elements than those you need but that is fi ne. P rint

copies of the graphs.

welcome.htm). This interactive P eriodic Table allows you to select the data you

need and plot your own graph, which you can then print.

If you cannot download and print off a graph from the Internet, you will need

to fi nd the req uired information from a chemistry data book. In this case, use

spreadsheet software to allow you to show the data graphically and to print a

hard copy.

This activity helps you to identify how the

melting and boiling temperatures of elements

change across a row in the P eriodic Table.

PATTERNS INTHE PHYSICALPROPERTIES OF

ELEMENTS

EL4.3

Q uestions

1 On your graphs, indicate which elements are from Period 1 , which are from Period 2 and which are from Period 3 .

2 F or each graph, describe the patterns that you observe across each period.

3 H ow do the patterns across Period 2 compare to those across Period 3 ?

4 E x plain how your graphs show ‘periodicity’.

5 F or each graph, note which group of elements appear at:a the peaksb the troughs.

6 Part of the boiling temperature graph is shown below. L abel the point you think represents the element sodium. E x plain how you arrived at your answer.

Successive elements in the Periodic Ta b le

Bo

ilin

g t

emp

erat

ure

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IntroductionThe checklist below covers the key points in Chemical Storylines EL3 to EL5 .

The statements listed correspond to learning outcomes in the specification

for the AS examinations. They are listed in the order in which they occur in this

modules.

You will probably have made summary notes of the main ideas that you have

met. Now is a good time to make sure that your notes cover all the points you

need. If you feel that you are not yet able to meet the requirements of all of the

statements in the list, you should look again at the areas concerned, seek help

from your teacher if necessary and develop your notes accordingly.

Most of the points are covered in Chemical Id eas, with supporting

information in Chemical Storylines or the activities. H owever, if the main

source of information is in a storyline or an activity this is indicated.

What you do

column that best represents your current ability to do what is described:

A – I am confi d ent that I can d o this

B – I need help to clarify my id eas on this

C – I am not yet ab le to d o this.

You will be sharing this information with your teacher so that you can work

together to improve your understanding.

At the end of Chemical Storylines EL3 to EL5 you should be able to: A B C

relative atomic mass, relative formula mass and relative molecular mass

molecular formulae and percentage composition

– calculate relative atomic mass and the relative abundance of isotopes– work out the relative molecular mass of molecules

according to their common properties

the properties of an element in this group

temperature Activity 4.3

levels or electron shells) and vice versa

Group 2:– reactions of the elements with water– acid–base character of the oxides and hydroxides– thermal stability of the carbonates– solubilities of hydroxides and carbonates Activity 4.1

from their atomic mass order and how subseq uent research validated this knowledge

validity of a discovery Chemical Storylines EL4

This activity helps you check your knowledge

and understanding of the topics that you have

covered in C hemical S torylines E L 3 to E L 5 .

CHECK YOURK NOW LEDGE AND UNDERSTANDING

(PART 2)

EL5

984_01_SAC SP_EL.indd 21 16/4/08 15:52:43

elements of life activities

Documents

su p p ort

p henomena

r p resentations p rep

c lass

c hang e

p ic tu

odels c

c u rrent model