Making-salts IGCSE Chemistry

8/19/2019 Making-salts IGCSE Chemistry

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Making salts


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What are salts?

Salts are the compounds formed when acids are neutralised

Acids can be neutralised by reaction with

Bases (or alkalis)

Carbonates

Acids will even react with M!A"S to make salts

What are acids?

Acids are chemicals whose p#s are less than $ i%e% & ' %

Acids are chemicals that produce # ions when added to water+

Common stron* acids include

#+,-.C#".-/C AC/,

S0"1#0-/C AC/,

2/!-/C AC/,

#Cl

# S.

#2.

2 4

3


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What are bases?

Bases are chemicals that 20!-A"/S acids

i%e% $%3 ' 34

Soluble bases are known as

to make a SA"! and WA!-

A"5A"/S

!hey have p# values 6-A!- than $

!hey are usually

M!A" .7/,S

M!A" #+,-.7/,S

e%*% ma*nesium o8ide

e%*% copper(//) o8ide

M*.

Cu.

e%*% sodium hydro8ide

e%*% calcium hydro8ide

2a.#

Ca(.#) 2

Ammonia 2#3 is an alkaline *as


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Makin* saltsSalts that we make must be 10-

i%e% we are tryin* to make C-+S!A"S (solids)

sodiumchloride

coppersulphate

2aCl CuS.4

!hese two e8amples are produced when a solution 9A1.-A!S

So both of these salts are S."0B" in water

Most salts are S."0B" in water Most bases (and carbonates) are /2S."0B" in water

!his is very useful when tryin* to make salts by reactin* acids


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Makin* soluble saltsBefore makin* salts it is important to know if the salt is soluble or not

A set of S."0B/"/!+ -0"S can be appliedCreatin* S."0B/"/!+ -0"S

!he simplest way is to ima*ine every chemical as bein* soluble %%%%%%%%

and then remember the e8ceptions

Compounds are looked at by referrin* to either the CA!/.2 or A2/.2part of the name

e%*% sodium chloride can be

either a S.,/0M compound

or a C#".-/, compound

e%*% copper(//) sulphate can beeither a C.11-(//) compound

or a S0"1#A! compound


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S."0B/"/!+ -0"S

CA!/.2 -0"S

all S.,/0M: 1.!ASS/0M and AMM.2/0M compounds are S."0B"

!here are no other rules for CA!/.2S

sodium bromide

potassium sulphate

ammonium carbonate

2aBr

5 S.2 4

(2# ) C.4 2 3

is S."0B"

is S."0B"

is S."0B"


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A2/.2 -0"S!here are many more anion rules

A""2/!-A!S 2.3

-are soluble

C#".-/,SB-.M/,S/.,/,S

Cl-

Br-

/-

are solubleare solubleare soluble

e8cept silver chloride: silver bromide ; silver iodide

S0"1#A!S S.42- are soluble

e8cept barium sulphate ; lead sulphate

CA-B.2A!S C. 32- are /2soluble

e8cept sodium carbonate: potassium carbonate ; ammonium carbonate

are /2soluble

e8cept sodium hydro8ide: potassium hydro8ide ; ammonium hydro8ide

A""

#+,-.7/,S ' .# (and .7/,S ' . )2--

; lead chloride: lead bromide ; lead iodide

#A"/,S


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S0MMA-+ !AB"

CA!/.2S.,/0M

1.!ASS/0M

AMM.2/0M

S."0B/"/!+S."0B"

S."0B"

S."0B"

A2/.2 S."0B/"/!+ 7C1!/.2

2/!-A!

#A"/,<

S0"1#A!

CA-B.2A!#+,-(.7/,)

S."0B"

S."0B"

S."0B"

2.2

S/"9- #A"/,

BA-/0M S0"1#A!S.,/0M: 1.!ASS/0M ; AMM.2/0M

CA-B.2A!S (soluble)

S.,/0M: 1.!ASS/0M ; AMM.2/0M#+,-.7/,S (soluble)

#A"/,< ions are chlorides: bromides ; iodides (= fluorides)

/2S."0B"

/2S."0B"


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Which salts are soluble?0se the table to help you decide if the named salt is soluble or insoluble

>inc nitrate ' soluble Why? /t is a 2/!-A!

sodium carbonate ' soluble Why? /t is a S.,/0M compound

calcium carbonate ' insoluble Why? /t is a CA-B.2A!

copper sulphate ' soluble Why? /t is a S0"1#A!barium sulphate ' insoluble Why? /t is BA-/0M S0"1#A!

iron bromide ' soluble Why? /t is a B-.M/,

silver iodide ' insoluble Why? /t is S/"9- /.,/,

potassiumhe8acyanoferrate ' soluble Why? /t is a 1.!ASS/0Mcompound

ammonium carbonate ' soluble Why? /t is an AMM.2/0Mcompound


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Makin* soluble saltsSoluble salts are made by reactin* the appropriate acid with

a BAS: a CA-B.2A! or occasionally the M!A"

!o make a 2/!-A! use 2/!-/C AC/,

!o make a S0"1#A! use S0"1#0-/C AC/,

!o make a C#".-/, use #+,-.C#".-/C AC/,

Besides makin* a SA"!S other products are also made dependin* onwhat the acid reacts with

Acids react with bases to make a SA"!S and WA!-

AC/, = BAS SA"! = WA!-

Acids react with carbonates to make a SA"!S : WA!- ; C.2AC/, = BAS SA"! = WA!- = C.

2

Acids react with metals to make a SA"!S ; #+,-.62

AC/, = M!A" SA"! = #+,-.62


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Makin* soluble salts/n almost all of these cases the metal: base or carbonate will be /2S."0B"

!his makes it easier to make a pure sample of the saltSolids (/2S."0B") material can easily be removed by /"!-A!/.2

usin* a funnel and filter paper

Crystals can be obtained by 9A1.-A!/26

off some (or all) of a solvent


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Makin* copper sulphate crystalsWhat acid needs to be used? S0"1#0-/C AC/,

What can it react with? either a BAS C.11- .7/,

or C.11- CA-B.2A!

Copper metal will 2.! react with acids

C.11- .7/, = S0"1#0-/C AC/, C.11- S0"1#A! = WA!-

2 4

Cu. = # S. CuS. = # . 4 2

C.11- CA-B.2A! = S0"1#0-/C AC/, C.11- S0"1#A! = WA!- = CA-B.2 ,/.7/,

2 4CuC. = # S. CuS. = # . = C.

4 23 2


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Makin* copper sulphate crystals

1our @& cm of sulphuric acid into a 3&&ml beaker

Warm *ently on a tripod and *au>e until it be*ins to

S!AM 2.! B./"

Carefully remove the beaker from the *au>e and put it onto a MA!

Add C.11- .7/, one spatula at a time

Stir with a *lass rod

/f the solid dissolves add more: stirrin*: until no more dissolves

What does this mean? A"" the acid has -AC!,

!he solid should have settled to the B.!!.M%

(/f usin* C.11- CA-B.2A! do 2.! warm the acid)

!he solid is 02-AC!, copper o8ide or carbonate

What is the solid?

!his is often described as bein* /2 7CSS


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Makin* copper sulphate crystals

ilter the mi8ture carefully into an evaporatin* dish

2ow evaporate half the volume%%%% and leave to stand

!his produces beautiful

of C.11- S0"1#A!

' makin* sure 2. black copper o8ide passes throu*h

B"0 crystals


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Makin* sodium chloride crystals

Sodium chloride is a S."0B" salt

What acid needs to be used? #+,-.C#".-/C AC/,What can it react with? either a BAS S.,/0M #+,-.7/,

or S.,/0M CA-B.2A!

' 2a.#' 2a.#

!his is S."0B"

!his is also S."0B"

2a C.

S.,/0M #+,-.7/, = #+,-.C#".-/C AC/, S.,/0M C#".-/, = WA!-

2a.# = #Cl 2aCl = # . 2

S.,/0M CA-B.2A! = #+,-.C#".-/C AC/, S.,/0M C#".-/, = WA!- = CA-B.2 ,/.7/,

2

2a C. = #Cl 2aCl = # . = C.23 2


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Makin* sodium chloride crystalsWe cannot use the previous techniue of addin* an insoluble base to the acid

/t is important the e8act volume of acid needed to neutralise the alkali is known

@ml of the acid is measure out usin* a measurin* cylinder

and poured into a conical flask

An indicator e%*% 1henolphthalein can be added

Sodium hydro8ide is poured into a B0-!!

!he startin* volume is recordedSodium hydro8ide is carefully added byopenin* the tap and allowin* it into the flask

!he indicator will turn 1/25

-ecord this new volume

Calculate the volume of sodium hydro8ide added

-epeat the e8periment usin* this volume and the same volume of acid

without the indicator

vaporate to obtain crystals of sodium chloride


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Makin* insoluble compounds

/nsoluble compounds CA22.! be made by reaction of an acid with

an /2S."0B" BAS or CA-B.2A! When the acid meets the insoluble compound an impervious coat forms

preventin* further reaction

!o make an insoluble compound !W. solutions must be mi8ed!he insoluble compound immediately forms%

!his is known as a 1-C/1/!A!Choosin* the solutions

• "ook at the 2AM of the insoluble compound

• "ook at the CA!/.2 (first part of the name)

•

Choose a solution containin* this ion• "ook at the A2/.2 (second part of the name)

• Choose another solution containin* this ion


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7AM1" "A, S0"1#A!

•

"ook at the CA!/.2• Choose a solution containin* this ion

• "ook at the A2/.2 (S0"1#A!)

• Choose a solution containin* this ion

("A,)("A, nitrate)

2itrates are A"WA+S soluble

(sodium S0"1#A!)

Sodium compounds are A"WA+S soluble

• Mi8 the solutions and observe the chan*es

A W#/! precipitate should be seen

• write a W.-, D0A!/.2

"A, nitrate = sodium S0"1#A!

= sodium nitrate"A, S0"1#A!


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7AM1" "A, /.,/,

•


• "ook at the A2/.2 (/.,/,)


("A,)("A, nitrate)

2itrates are A"WA+S soluble

(potassium /.,/,)

1otassium compounds are A"WA+S soluble


A +"".W precipitate should be seen


"A, nitrate = potassium /.,/,

"A, /.,/, = potassium nitrate


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7AM1" A"0M/2/0M #+,-.7/,

•


• "ook at the A2/.2 (#+,-.7/,)


(A"0M/2/0M)(A"0M/2/0M sulphate)

Sulphates are usually soluble

(sodium #+,-.7/,)

sodium compounds are A"WA+S soluble


A W#/! precipitate should be seen


Aluminium sulphate = sodium #+,-.7/,

A"0M/2/0M #+,-.7/, = sodium sulphate


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1urifyin* insoluble compounds

/nsoluble compounds are prepared as precipitates

!o obtain a pure dry sample you need to '

• filter the mi8ture: keepin* the residue

• the residue will be wet and have soluble impurities

• keep the residue on the filter paper and rinse with distilled water

or suee>e between wads of filter paper

• scrape the residue onto a watch *lass and place into an ovento dry (@& C)

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Making-salts IGCSE Chemistry