chapter 8 01 salts final

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IsIrMaNaF/smkI/Salts

Chapter 8: Salts

A. Synthesising Salts ( OOI Tel : 95253

1) The Meaning of Salt. A salt is a compound formed when the hydrogen ion, H+ from acid is replaced by a metal ion or an ammonium ion, NH4

+.

For example,

Acid + Alkali Salt + WaterHCl + NaOH NaCl + H2O

H+ ion is replaced by Na+ ion

Try This !Write the formula of salts formed from each of the following reaction.

a) Sulphuric acid + copper(II) carbonate._______________________________________________

b) Nitric acid + potassium hydroxide solution____________________________________________

c) Hydrochloride acid + ammonium hydroxide solution____________________________________

2) Examples of Salts. Example s of salts formed from their corresponding acids.

Acid Salt Example

Hydrochloric acid Chloride salt

Sulphuric acid Sulphate salt

Nitric acid Nitrate salt

Carbonic acid Carbonate salt

3) Uses of Salts in Daily Life

Field ApplicationAgriculture Ammonium sulphate, (NH4)2SO4 ammonium phosphate,

(NH4)3PO4 are nitrogenous fertiliser. Copper(II) sulphate, CuSO4 and iron(II) sulphate, FeSO4

are used as pesticides to kill pests.Industrial Silver bromide, AgBr is used to make film and

photography paper.Medical Calcium sulphate, CaSO4 is used as plaster to support

broken bones. Potassium manganate(VII) is used as antiseptic on

wounds. Barium sulphate, BaSO4 enable the intestine of

suspected stomach-cancer patients to be seen clearly in X-ray films.

Food Sodium bicarbonate, NaHCO3 is used to raise dough for bread and cake.

Monosodium glutamate (MSG) is used to add flavour to food.

Sodium chloride, NaCl and sodium nitrate, NaNO3

sirManaf/SMKI/salts1

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is used to preserve food such as fish and prawn.


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4) Types of salts Soluble salt – salts that can be dissolve in water at room temperature

Insoluble salt – salts cannot be dissolve in water at room temperature

Solubility is the ability of a compound to dissolve in a solvent. Some salts are soluble in water

while others are not.The solubility of a salt in water depends on the types of cations and anions present.

Try This!1. Determine whether each of the following salt is soluble or insoluble in water.

Salt Solubility ( , X )1. Magnesium chloride2. Lead(II) sulphate3. Calcium carbonate4. Zinc chloride5. Silver chloride6. Potassium carbonate7. Lead(II) nitrate8. Sodium sulphate9. Ammonium chloride10. Barium sulphate11. Copper(II) nitrate12. Copper(II) sulphate13. Copper(II) carbonate14. Iron(II) nitrate15. Iron(III) chloride16. Sodium carbonate17. Ammonium carbonate18. Silver nitrate19. Tin(II) chloride20. Zinc sulphate

2. State whether each of the following salt is soluble or insoluble in water.Formula of Salt Solubility ( , X )1. CaCO3

2. ZnCl2

3. Na2SO4

4. AlCl3

5. K2CO3

6. AgCl7. BaSO4

8. (NH4)2CO3

9. CaSO4

10. PbCl2

sirManaf/SMKI/salts

Salt Solubility in waterSodium, potassium and ammonium salts (Na+, K+, NH4

+)

All are soluble

Nitrate salt (NO3-) All are soluble

Chloride salt (Cl -) All chloride salts are soluble in water

except PbCl2, AgCl and HgCl2

Sulphate salt (SO42-)

All sulphate salts are soluble in water

except PbSO4, CaSO4 and BaSO4

Carbonate salt (CO32-) All carbonate salts are insoluble except

Na2CO3, K2CO3 and (NH4)2CO3

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5) Special Properties of lead(II) chloride and lead(II) iodide

6) Preparation of Salts The method of preparation of a salt depends on the solubility and the type of the salt.

Sodium salts

Potassium salts Acid + alkali salts + water

Ammonium salts

Acid + metal oxide salts + water

Others salts Acid + metal salts + hydrogen gas

Acid + metal carbonate salts + water + carbon dioxide

Try this!Fill in the blank with the suitable reactants

1. ___________________+_________________ sodium nitrate + water

2. ___________________+_________________ magnesium chloride + water

3. ___________________+_________________ zink sulphate + hydrogen gas

4. ___________________+_________________ calcium chloride + water + carbon dioxide


White precipitate of PbCl2

White precipitate dissolves in hot water

White precipitate formed when the water is cooled down.

Yellow precipitate of PbI2

Yellow precipitate dissolves in hot water

Yellow crystals formed when the water is cooled down.

PbCl2 and

PbI2 are soluble in hot water.

Soluble Salts

Acid + alkaliTitration method.

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7) Preparation of Soluble Salts Soluble salts (not Na, K and NH4

+ ) can be obtained from the reaction between:

acid(aq) + metal oxide (s) salt(aq) + water (l)

acid(aq) + metal carbonate(s) salt(aq) + water(l) + CO2(g)

acid(aq) + reactive metal (s) salt(aq) + H2(g)

In the reaction, an excess of an insoluble solid metal oxide, metal carbonate or metal is added to a fixed volume of acid to completely neutralise the acid. The products are salt solution and carbon dioxide gas or hydrogen gas. The unreacted solid can be removed from the salt solution by filtration.

Explain why the salt of sodium, potassium and ammonium cannot be prepared by using the above method?______________________________________________________________________________________________________________________________________________

Try This!1) Write the chemical equation of each of the following reactions.

a) Hydrochloric acid + copper(II) oxide

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b) Nitric acid + lead(II) carbonate

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c) Sulphuric acid + zinc

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d) Hydrochloric acid + magnesium oxide

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e) Nitric acid +calcium carbonate

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f) Sulphuric acid + magnesium

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2) Name a acid and a metal, metal oxide or metal carbonate that can be used to prepare the following

salts.

a) Copper(II) sulphate :__________________________________

b) Lead(II) nitrate :__________________________________


Acid

Salt solution

Unreacted solid

Solid metal, metal oxide and metal carbonate

H2 or CO2

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c) Zinc chloride :__________________________________

3) Complete the following equations.

a) HCl(aq) + PbO(s) ……………….. + ………………….

b) HNO3(aq) + NaOH(aq) ……………….. + ………………….

c) HCl(aq) + NH4OH(aq) ……………….. + ………………….

d) H2SO4(aq) + CuCO3(s) …………… + …………… + ……………

e) HCl(aq) + Na2CO3(s) …………… + …………… + ……………

f) HCl(aq) + Mg(s) ……………….. + ………………….

g) H2SO4(aq) + CuO(s) ……………….. + ………………

h) H2SO4(aq) + NaOH(aq) ……………….. + ………………….

i) HNO3(aq) + PbCO3(s) …………… + …………… + ……………

8) Procedure To Prepare a Soluble Salt (not Na, K or NH4+)

50 cm3 of acid is measured using a measuring cylinder and poured into a beaker. The acid is heated slowly.

Using a spatula, metal / metal oxide / metal carbonate powder is added a little at a time while stirring the mixture with a glass rod.

The addition of the solid powder is stopped when some solids no longer dissolve anymore. (the solid is excess and all the acid is completely neutralised by the solid)

The mixture is filtered to remove the excess solid powder.

The filtrate is transferred to an evaporating dish. The filtrate is heated until saturated. (The filtrate is evaporated to about one-third (1/3) of

the original volume) The saturated solution is then allowed to cool to room temperature and the salt crystals

are formed. The crystals are filtered and rinsed with a little cold distilled water. Salt crystals are then dried by pressing it between filter papers.

Try This! sirManaf/SMKI/salts6

Heating

AcidPowderof :

Metal oxideMetal carbonateMetal

Excess of solid powder

Filtrate (Salt solution)

Heating

Saturated solutionCrystals

Filtrate

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Try this..!

Describe a laboratory experiment how you can prepare the following salts.(a) Copper(II) sulphate (Mastery exercise 8.1)

9) Preparation of Soluble Sodium, Potassium and ammonium Salts Soluble salts of sodium, potassium and ammonium can be prepared by the reaction between an acid and alkali. Acid (aq) + alkali (aq) ---> Salt (aq) + Water (l)

Procedure : Using pipette, 25 cm3 of alkali solution is measured and transferred into a conical flask. Two drops of phenolphthalein are added to the alkali solution. Dilute acid is place in a burette. The initial reading is recorded. Acid is added slowly into the alkali solution while shaking the conical flaks, until the pink

solution turn colourless. The final reading of the burette is recorded. The volume of acid added, V cm3 is calculated. The experiment is repeated by adding V cm3 of acid to 25 cm3 of alkali solution in a

beaker without using phenolphthalein as an indicator. The mixture is transferred into a evaporating dish. The mixture is heated until saturated and the saturated solution is allowed to cool at room

temperature. Salt crystals formed are filtered and rinsed with a little of cold distilled water. Salt crystals are dried by pressing it between filter papers (or in oven)

Try This!1) Name two substances that can be used to prepare the following salts. Write the chemical equation of

each reaction.

a) Sodium sulphate. _____________________________________________________________

b) Potassium nitrate. ____________________________________________________________

c) ammonium chloride. __________________________________________________________

Try this..!

Describe a laboratory experiment how you can prepare the following salts.(a) Sodium Chloride salts (Mastery exercise 8.2)

10) Purification of Soluble Salts The salts formed during preparation of soluble salt contain impurities. Therefore, the soluble salts can be purified through the recrystallisation process.Procedure: Impure salt is placed in a beaker with about 10 cm3 of distilled water. The mixture is stirred while it is heated, and more distilled water is added slowly until all

the salt is dissolved. The hot solution is filtered and transferred into a beaker. The filtrate is heated until it is saturated. (This can be tested by dropping a drop of the

solution on a glass plate. If crystals are formed, then the solution is saturated.) The filtered crystals are rinsed with a little distilled water and dried between two pieces of

filter paper.


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Summarization for preparation of Soluble salt.

11)

Can you find any similarities and differences between method 1 and 2?

12) Preparation of Insoluble SaltsInsoluble salts are prepared through precipitation reaction (or double decomposition reaction).

To obtain the insoluble salt, we need to find two aqueous solutions. One contains of cation Xm+ and the other one contains of anion Yn-. When the two aqueous solutions are mixed together, the insoluble salt, XnYm appears as a precipitate.

For example, if we want to prepare lead(II) chloride, which is insoluble, then the two aqueous solutions required are …………………………….. and ……………………………….

Procedure:1. The two aqueous solutions are added together in a beaker. 2. The mixture is stirred with w glass rod.3. The precipitate of the insoluble salt is formed.4. The insoluble salt is filtered and rinsed with a little distilled water.


Anion(Non-metal ion)

Cation(Metal ion) nn mm

PbCl2

SOLUBLE SALT + SOLUBLE SALT INSOLUBLE SALT + SOLUBLE SALT

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5. The insoluble salt is then presses between two filter papers to dry.

Try This!Name two aqueous solutions that can be used to prepare the following salts.Write the chemical equation of each reaction.

(a) lead(II) sulphate. ________________________________________________________

(b) Silver chloride. __________________________________________________________

(c) Zinc carbonate. __________________________________________________________

(d) Barium sulphate. ________________________________________________________

Describe a laboratory experiment how you can prepare the following salts.(a) Lead(II) iodide salts (Mastery exercise 8.3)

Ionic EquationAn ionic equation only shows the ions that take part in the chemical reaction.

Example 1: Lead(II) nitrate solution is added to sodium chloride solution to form the precipitate of lead(II)

chloride.

Chemical equation:Pb(NO3)2(aq) + 2NaCl(aq) --> PbCl2(s) + 2NaNO3(aq)

Ionic Equation:Pb2+

(aq) + 2Cl- (aq) ----> PbCl2 (s)

Example 2:In the formation of the precipitate of barium sulphate, BaSO4, the chemical equation can be

written: BaCl2(aq) + Na2SO4 (aq) BaSO4(s) + 2NaCl (aq)

Ions ____ + ____ + ____ + ____ BaSO4 + ____ + ____

Ionic equation : ________________________

(shows the ions that take part in the reaction)

Try This!Write the ionic equation of each of the precipitate reactions below.

a) Copper(II) nitrate solution + sodium carbonate solution

b) Zinc chloride solution + lead(II) nitrate solution

c) Dilute sulphuric acid + barium nitrate solution

d) Silver nitrate solution + hydrochloride acid sirManaf/SMKI/salts9

PbCl2

Na+ NO3-

Na+NO3

-

In this reaction, Pb2+ ions combined with Cl- ions to formWhite precipitate of PbCl2.

Na+ ions and NO3- ions do not

take part in the reaction and are free to move in the solution.

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13) Physical Characteristics of Crystals.A salt is mad up of positive and negative ions. When these ions are packed closely with a

regular and repeated arrangement in an orderly manner, a solid with definite geometry

known as crystal lattice is formed.

All crystals have these physical characteristics:

a) Reqular geometry shapes, such as cubic or hexagonal.

b) Flat faces, straight edges and sharp angles.

c) Same angle between adjacent faces.

d) All crystals of the same salt have the same shape although the sizes may be different.

14) Numerical Problems involving stoichiometric reactions in the precipitation of saltsA balanced chemical equation for a reaction in preparation of a salt can be used to calculate

the stoichiometric quantities of the following

Masses of reactants

Volumes and concentrations of reactants

Masses of products

Volumes of products

Question 1:A student prepare copper(II) nitrate, Cu(NO3)2 by reacting copper(II) oxide, CuO with 200 cm3

of 2.0 moldm-3 nitric acid, HNO3. Calculate the mass of copper(II) oxide, CuO needed to react completely with the acid. [Relative atomic mass: Cu, 64 ; O, 16]

Question 2:X cm3 of 0.5 moldm-3 sulphuric acid, H2SO4 is added to 100 cm3 of 1.0 moldm-3 lead(II) nitrate solution to produce lead(II) sulphate, PbSO4.a) Calculate the value of X.b) Calculate the mass of lead(II) sulphate obtained.

[Relative atomic mass: Pb, 20; O, 16; S, 32]


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Question 3:Calculate the minimum volume of 18.25 g dm-3 hydrochloric acid required to react completely with 1.30 g zinc powder. [Relative atomic mass: H = 1; Cl = 35.5 ; Zn = 65]

Question 4:100 cm3 of sulphuric acid is added to excess barium chloride solution. A white precipitate is formed. The maximum of white precipitate formed is 37.28g

a) Named the white precipitate formedb) Calculated the consentration of sulphuric acid used in gdm-3

( Relative atomic mass; H, 1; O, 16; S, 32; Ba, 137 )

Question 5: Barium chloride solution reacts with sulphuric acid as follows:

BaCl2(aq) + H2SO4(aq) BaSO4(s) + 2HCl(aq)a) What volume of sulphuric acid, 1 mole dm-3 is required to reacts with 100cm3 BaCl2 0.5

mole dm-3?b) Calculate the mass of BaSO4 which is formed in this reaction.

(Ba = 137; S = 32 ; O =16)


chapter 8 01 salts final

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