WAJAF4 Chemistry 2010 CHAPTER 8: SALT
CHAPTER 8 : SALTS
- SYNTHESISINGSALTS
Learning Outcomes
You should be able to:
state examples of salts used in daily life,
explain the meaning of salt
identify soluble and insoluble salts,
describe the preparation of soluble salts,
describe the purification of soluble salts by recrystallisation,
list physical characteristics of crystals,
describe the preparation of insoluble salts,
write chemical and ionic equations for reactions used in the preparation of salts,
design an activity to prepare a specified salt,
construct ionic equations through the continuous variation method
solve problems involving calculation of quantities of reactants or products in stoichiometric reactions
Activity 1: Meaning and uses of Salts
1. A salt is an ……………………..……… formed when the ……………….. ion, from an …………… is replaced by a ……………. ion or an …………………..ion.
- Example of salts : Complete the table below
Acid / Formula of acid / Salt / Formula / Cation / Anion
Sodium chloride / NaCl / Na+ / Cl-
Potassium carbonate / K2CO3
Copper(II) sulphate / CuSO4
Ammonium nitrate / NH4NO3
Magnesium nitrate / Mg(NO3)2
Sodium ethanoate / CH3COONa
3. Match the following salts with their uses.
Salts / UsesBarium sulphate BaSO4 / / Fungicide
Calsium sulphate CaSO4 / / Bleaching agent
Iron sulphate FeSO4 / / Paint for yellow line on road
Ammonium nitrate NH4NO3 / / X-ray ‘meals’ in hospital
Copper(II) sulphate CuSO4 / / Nitrogenous fertilizer
Sodium chloride NaCl / / Toothpaste
Sodium hydrogen carbonate / / Iron tablets, for anaemia patient
Sodium nitrite NaNO2 / / Baking powder
Sodium hypochlorite NaOCl / / Preserve food
Tin(II) fluoride SnF2 / / A flavouring
Lead(II) chromate PbCrO4 / / Plaster of Paris for broken bone
Activity 2 : Identify soluble and insoluble salt.
Fill in the blanks with the correct word(s)
- All ………………. , ………………., and …………………. salts are soluble in water.
- All ………………. salts are soluble in water.
- All sulphate salts are soluble in water except …………….. sulphate, …………. sulphate and ………… sulphate.
- All chloride salts are soluble in water except …………….. chloride , …………. chloride and ………… chloride.
- All carbonate salts are insoluble in water except …………….. carbonate, …………. carbonate and ………… carbonate
6. State whether each of the following salt is soluble or insoluble in water
No / Formula of Salt / Solubility ( , X ) / No / Formula of Salt / Solubility ( , X )1 / PbCO3 / 21 / MgCO3
2 / NaCl / 22 / KCl
3 / CaSO4 / 23 / (NH4)2SO4
4 / AgNO3 / 24 / Cu(NO3)2
5 / K2CO3 / 25 / SnCO3
6 / FeCl3 / 26 / CaCl2
7 / Na2SO4 / 27 / BaSO4
8 / NH4NO3 / 28 / KNO3
9 / CuSO4 / 29 / Ag2CO3
10 / PbCl2 / 30 / MgCl2
11 / ZnCO3 / 31 / ZnSO4
12 / Ca(NO3)2 / 32 / Ba(NO3)2
13 / Na2CO3 / 33 / FeCO3
14 / AgCl / 34 / NH4Cl
15 / PbSO4 / 35 / Fe(NO3)3
16 / Pb(NO3)2 / 36 / MgSO4
17 / (NH4)2CO3 / 37 / BaCO3
18 / HgCl2 / 38 / ZnCl2
19 / Na2SO4 / 39 / FeSO4
20 / NaNO3 / 40 / Mg(NO3)2
Activity 3: Write chemical and ionic equations for reactions used in the preparation of soluble salts
- Complete these general equation for preparing soluble salts.
a. metal + acid …………… + …………………….
b. metal oxide (or metal hydroxide) + acid …………… + ……………………
c. alkali + acid …………… + …………………….
d. metal carbonate + acid …………… + ……………… + ……………………….
- Using the general equations in question 1, complete the following chemical equation. It may also be necessary to balance the equation.
a. Mg + H2SO4 …………… + …………………….
b. (i) CuO + HCl …………… + ……………………
(ii) Zn(OH)2 + HNO3 ...... + ......
c. NaOH + HCl ………………….. + ……………………….
d. MgCO3 + H2SO4 …………… + ……………… + ……………………….
- Deduce the identity of the acid, metal, salt, or other product by filling in the missing details in this table of preparation of soluble salt
Method of Preparation / Reactants / Salt Formed / Other Product
a)metal + acid / Magnesium + ……………… / Magnesium chloride / Hydrogen
b)metal oxide + acid / Copper(II) oxide + sulphuric acid / ……………………… / …………….
c)metal carbonate + acid / ……………… + ……………… / Zinc sulphate / Water + …………….
……………..
d)metal hydroxide + acid / ……………… + ……………… / Potassium nitrate / ……………
f) alkali + acid / ……………… + ……………… / Sodium chloride / ……………
- Name the reactants which are needed to prepare the following soluble salts:
(a)Copper(II) sulphate : ……………………………………………………………………………..
(b)Zinc chloride: …………………………………………………………………………….
(c)Potassium nitrate: ……………………………………………………………………………..
(d)Ammonium sulphate: ……………………………………………………………………………..
(e)Magnesium nitrate: ……………………………………………………………………………..
5. Rewrite each of the following chemical equation as ionic equation. Shown below is an example where a chemical equation can be simplified into an ionic equation.
Example : Chemical equation : Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)
Zn + 2H+ + SO42- Zn2+ + SO42- + H2
(s) (aq) (aq) (aq) (aq) (g)
Ionic equation : Zn(s) + 2H+(aq) Zn2+(aq) + H2(g)
a. Chemical equation :Mg(s) + 2HCl(aq) MgCl2(aq) + H2O
Ionic equation : ......
b. Chemical equation :MgO(s) + 2HCl(aq) MgCl2(aq) + H2O
Ionic equation : ......
c. Chemical equation : NaOH (aq) + HNO3(aq)NaNO3(aq) + H2O(l)
Ionic equation : ......
d. Chemical equation : CuCO3(s) + H2SO4(aq) CuSO4(aq) + CO2(g) + H2O(l)
Ionic equation : ......
Activity 4 :Write out the procedure for the preparation of soluble salts of sodium, potassium and ammonium
Soluble salt / Sodium Chloride, NaClName two chemical substances to prepare the salt /
- …………..…………………………..
- ………………………………………
Chemical equation
Procedure: (Diagram) / Description
Describe the physical characteristics of the crystals that you obtained
Activity 5 :Write out the procedure for the preparation of soluble salts (not sodium, potassium or ammonium salt)
Soluble salt / Copper(II) sulphate, CuSO4Name two chemical substances to prepare the salt / 1. …………..…………………………..
- ………………………………………
Chemical equation
Procedure: (Diagram) / Description
Describe the purification process of the crystals
Activity 6: Write chemical and ionic equations for reactions used in the preparation of insolublesalts
- Insoluble salts can be prepared by ………………….. method through …………………………….. reaction. In this reaction, two different aqueous solution mutually exchange their …….. to form
………………………….
Soluble salt solution + Soluble salt solution Insoluble salt MX
containing cation M+ containing anion X-
Chemical equation : AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
Ionic equation : Ag+(aq) + Cl- (aq) AgCl(s)
- Preparation of insoluble salts
Example 1: Barium sulphate,
Solution 1: ……………………………………... Solution 2: ……….………………………………….
Chemical equation : ………………………………………………………………..……………………..
Ionic Equation : …………………………………………………………………………………………….
Observation : White precipitate formed
Example 2: Copper(II) carbonate, CuCO3
Solution 1: ……………………………………..Solution 2: ……………………………………….
Chemical equation : …………………………………………………………………………………….
Ionic Equation : ………………………………………………………………………………………….
Observation : ……………….. precipitate formed
Example 3: Lead(II) chromate(VI),
Solution 1: ……………………………………..Solution 2: …………………………………….
Chemical equation : ………………………………………………………………………………….
Ionic Equation : ………………………………………………………………………………………..
Observation : ……………….. precipitate formed
Activity 7 :Describe the preparation of insoluble salts
Name two chemical substances to prepare the salt /
- …………..…………………………..
- ………………………………………
Chemical equation
Ionic equation
Procedure: (Diagram) / Description
Activity 8 : Construct ionic equation for the formation of lead(II) chromate through the continuous variation method,
Figure 1
Figure 1 shows seven test tubes for the reaction between lead(II) nitrate Pb(NO3)20.5 mol dm-3and potassium chromate(VI) K2CrO4 0.5 mol dm-3.
(a) Calculate the number of moles of lead(II) nitrate Pb(NO3)2 and potassium chromate(VI) K2CrO4 used in test tubes 1-7. Using a ruler, measure the height of lead(II) chromate(VI) precipitate formed. Record all these in Table 1as well as complete Table 1.
Test Tube / 1 / 2 / 3 / 4 / 5 / 6 / 7Volume of Pb(NO3)2/cm3 / 5.0 / 5.0 / 5.0 / 5.0 / 5.0 / 5.0 / 5.0
No of mole of Pb(NO3)2
Volume of K2CrO4/cm3 / 1.0 / 2.0 / 3.0 / 4.0 / 5.0 / 6.0 / 7.0
No of mole of K2CrO4
Height of precipitate / cm
Colour of solution above precipitate
Table 1
(b)Based on Table 1, draw a graph of the height of the precipitate against volume of lead (II) nitrate solution on the graph paper.
(c)On the graph that you have drawn in (b),
(i) mark and write the minimum volume of potassium chromate(VI) solution needed for complete reaction with 5.0 cm3 of lead(II) nitrate solution 0.5 mol dm-3.
(ii) Calculate the number of moles of chromate(VI) ions that has reacted with 1 mole of Pb2+. ions.
(iii) Write the formula of lead(II) chromate.
………………………………………………………………………………………………………………
(iv) Write the ionic equation for the formation of lead(II) chromate(VI).
………………………………………………………………………………………………………………
(d)What can you observed about the height of the precipitate in Figure 1?
………………………………………………………………………………………………………………
……………………………………………………………………………………………………………..
(e)What is your inference based on your answer in (d)?
……………………………………………………………………………………………………………….
……………………………………………………………………………………………………………….
……………………………………………………………………………………………………………..
Activity 9 : Solve problems involving calculation of quantities of reactants or products in stoichiometric reactions
Example 1 : A student prepares copper (II) nitrate by reacting copper (II) oxide with 100 cm3
1.5 mol dm-3 nitric acid. Calculate the mass of copper (II) oxide need to react
completely with the acid. [Relative atomic mass: Cu, 64 ; O, 16]
Solution :
Chemical equation : CuO + 2HNO3 Cu(NO3)2 + H2O
Mole ratio : 1 mole 2 mole 1 mole 1 mole
Number of moles of HNO3 = 1.5 x 100 = 0.15 mol
1000
Mole ratio of CuO : HNO3 = 1 : 2
Number of mole of CuO = 1 x 0.15 = 0.075 mole
2
Mass of CuO = 0.075 x (64 + 16) = 6 g
Question :
1Excess zinc powder is added to react completely with 50of 2.0hydrochloric acid.
(a)Write an ionic equation for the reaction between zinc and hydrochloric acid.
(b)Calculate the number of moles of hydrochloric acid used.
(c)Calculate the volume of hydrogen gas liberated at room conditions.
[Molar volume: 24]
2Excess of magnesium carbonate powder, MgCO3, is reacted with 100 cm3 of a 1 mol dm-3 sulphuric acid H2SO4 , What is the mass of magnesium sulphate formed?
[Relative atomic mass : Mg =24, O=16, S = 32 ]
- 0.12 g of magnesium reacts with excess hydrochloric acid to produce hydrogen gas. Given that the relative molecular mass of H=1, Mg = 24, CI =35.5 and 1 mol of gas occupies 24 dm3 at room temperature and pressure.
Fnd the (a) mass of salt formed (b) volume of gas produced
Example 2 : A sample of insoluble lead (II) sulphate is prepared by mixing 50 cm3 of 1.0 mol dm-3
lead (II) nitrate solution and y of 1.5 mol dm-3sulphuric acid.
[Relative atomic mass: O, 16 ; S, 32 ; Pb, 207]
(a)Calculate the volume, y, of the sulphuric acid needed to react completely with the
lead (II) nitrate solution.
Solution :
Chemical equation : Pb(NO3)2 + H2SO PbSO4 + 2 HNO3
Mole ratio : 1 mole 1 mole 1 mole 2 mole
Number of moles of Pb(NO3)2 = 1.0 x 50 = 0.05 mol
1000
Mole ratio of Pb(NO3)2 : H2SO4 = 1 : 1
Number of mole of H2SO4reacted = 0.05 mol
1.5 x y = 0.05 mole
1000
y = 0.05 x 1000 = 33.33 cm3
1.5
(b)Calculate the mass of lead (II) sulphate obtained.
Solution :
Number of mole of PbSO4 = Number of moles of Pb(NO3)2 = 0.05 mol
Mass of PbSO4 = 0.05 x (207 + 32 + 4 x 16) g
= 15.15 g
Question
4. A sample of insoluble silverchloride is prepared by mixing 50of 1.0 mol dm-3silver nitrate solution and zof 0.5 sodium chloride solution.
[Relative atomic mass: Ag 108; Cl 35.5]
(a)Write the chemical equation for the reaction between silver nitrate and sodium chloride.
(b) Calculate the volume, z, of the sodium chlorideneeded to react completely with the silver
nitrate solution.
(c)Calculate the mass of silverchloride obtained.
B. SYNTHESISING QUALITATIVE ANALYSIS OF SALTS
Learning Outcomes
You should be able to:
state examples of salts used in daily life,
explain the meaning of salt
identify soluble and insoluble salts,
describe the preparation of soluble salts,
describe the purification of soluble salts by recrystallisation,
list physical characteristics of crystals,
describe the preparation of insoluble salts,
write chemical and ionic equations for reactions used in the preparation of salts,
design an activity to prepare a specified salt,
construct ionic equations through the continuous variation method
solve problems involving calculation of quantities of reactants or products in stoichiometric reactions
Activity 10 : Qualitative Analysis
- Qualtitative analysis of a salt is a chemical technique used to identify the …….. that are present in a salt by analysing its ………………. and ……………………. properties.
- Make inferences on the following substances based on their colour: (use formula of substance when writing your answer. Make it is correct!)
Colour (solid or solution) / Substance or cation or anion
Green powder / Salt: Cation
Blue powder / Cation:
Brown powder / Cation:
Black powder / Two metal oxides:
Yellow powder when hot and white when cold
Brown powder when hot and yellow when cold
Blue solution / Cation:
Pale green solution / Cation:
Brown solution / Cation:
Solid : White
Solution : colourless / 6 cations :
Solid : White
Solution : colourless / 4 anions :
3. Complete the following table
Salts / Solubility in water / ColourInsoluble / white
Copper(II) carbonate
Iron(II) sulphate
Soluble / Brown
Lead(II) sulphate
Magnesium carbonate
Zinc chloride
Ammonium carbonate
Insoluble / Yellow
Activity 11 : Confirmatory Tests for gases,
Complete the observation for the confirmatory test for gases
Gas / Method / Diagram / ObservationCarbon dioxide / Bubble the gas produced into lime water
Heating
Carbonate
salts /
Oxygen / Insert a glowing splinter into the test tube /
Nitrogen dioxide / Observe the colour of gas produced. Bring a piece of moist blue litmus paper to the mouth of the test tube /
Chlorine / Observe the colour of the gas.
Bring a piece of moist blue litmus paper to the mouth of the test tube /
Ammonia / Dip a glass rod into concentrated hydrochloric acid and bring a drop of acid to the mouth of the test tube
/place moist red litmus paper at the mouth of the test tube / / .
Hydrogen / Bring a lighted splinter to the mouth of the test tube.
Mg + HCl release hydrogen gas /
Hydrogen chloride / Dip a glass rod into concentrated ammonia solution and bring a drop of ammonia to the mouth of test tube /
Activity 12 : Action of Heat On Carbonate Salts
Carbonate salts (except Na+ & K+ ) decompose on heating giving off carbon dioxide gas and residue metal oxide
Activity : Complete the chemical equation and observation for the action of heat on carbonate salt
Carbonate salt / Action of heatPotassium carbonate K2CO3 , Sodium carbonate Na2CO3 / Not decompose by heat
Metal Carbonate metal oxide + carbon dioxide
Calcium carbonate / CaCO3 CaO + CO2
Observation : White solid formed. Gas liberated turn lime water chalky
Magnesium carbonate / MgCO3 ……….. .. + …. ………
Observation : ……………………………………………….
……………………………………………………………….
Aluminium carbonate / Al2(CO3)3 ……….. .. + …. ………
Observation : ……………………………………………….
……………………………………………………………….
Zinc carbonate / ZnCO3 ……….. .. + …. ………
Observation : ……………………………………………….
……………………………………………………………….
Lead(II) carbonate / PbCO3 ……….. .. + …. ………
Observation : ……………………………………………….
……………………………………………………………….
Copper(II) carbonate / CuCO3 ……….. .. + …. ………
Observation : ……………………………………………….
……………………………………………………………….
Activity 13 : Action of Heat On Nitrate Salts
Nitrates Salts - Decompose on heating liberate nitrogen dioxide gas and oxygen gas except NaNO3 and KNO3 which liberate oxygen gas only
Activity:Complete the chemical equation and observation for the action of heat on nitrate salt
Nitrate salts / Action by HeatMetal Nitrate metal nitrite + oxygen
Potassium nitrate / 2KNO3 2 KNO2 + O2
Observation : white solid formed, gas released relighted glowing splinter
Sodium nitrate / 2NaNO3 ……….. .. + …. ………
Observation : ………………………………………………………..
……………………………………………………………………….
Metal Nitrate metal oxide + nitrogen dioxide + oxygen
Calcium nitrate / 2Ca(NO3)2 2CaO + 4NO2 + O2
Observation : white solid formed, Brown gas which turns moist blue litmus red released. Another gas released relighted glowing splinter
Magnesium nitrate / Mg(NO3)2 ……….. .. + …. ……… + ……………
Observation : ………………………………………………………..
……………………………………………………………………….
Zinc nitrate / Zn(NO3)2 ……….. .. + …. ……… + ……………
Observation : ………………………………………………………..
……………………………………………………………………….
Lead(II) nitrate / Pb(NO3)2 ……….. .. + …. ……… + ……………
Observation : ………………………………………………………..
……………………………………………………………………….
Copper(II) nitrate / Cu(NO3)2 ……….. .. + …. ……… + ……………
Observation : ………………………………………………………..
……………………………………………………………………….
Activity 14 : Confirmatory Tests for Anions,
1. Write the ionicequation for thefollowing reactions.
2. Which anion produce the following observations?
a) b)
c) d)
Activity 15: Reaction of Cations with alkali solution
1. Positive ions are identified by their reactions with a. sodium hydroxide NaOH solution
b. Ammonia solution NH3
- In these reactions, the cations (positive metal ions) produce different coloured precipitate which may or may not be soluble in excess alkali
Look for
precipitate
State whether each of the following precipitate is soluble or insoluble in excess alkali.
NaOH solution / Ammonia Solution NH3A little / In excess / A little / In excess
Soluble ( , X ) / Soluble ( , X )
Ca2+ / White precipitate / No change
Zn2+ / White precipitate / White precipitate
Al 3+ / White precipitate / White precipitate
Pb 2+ / White precipitate / White precipitate
Mg2+ / White precipitate / White precipitate
Cu 2+ / Blue precipitate / Blue precipitate
Fe 2+ / Green precipitate / Green precipitate
Fe 3+ / Brown precipitate / Brown precipitate
Which anion produces the following observations?
a)
b)
Activity 16 :Confirmatory Tests for Fe2+, Fe3+, Pb2+ and NH4+
(A)The table shows how confirmatory tests are conducted for ammonium ion, NH4+ , Iron(II) ion, Fe2+ , Iron(III) ion, Fe3+ , and lead(II) ion, Pb2+ . Complete the confirmatory tests and observation.
Cation / Name of Reagent / Observation/ Add a few drops of ……………………
to the test tube containing 2 cm3 of lead(II) nitrate solution (ions)
Add 2 cm3 of distilled water and boil the mixture. Cool the contents using running water from the tap. / ……………… precipitate is formed
which ………………..in the hot water
and is ……………… on cooling
/ Add a few drops of ……………………
to the test tube containing 2 cm3 of iron(II) sulphate solution (ions) / ……………….. precipitate is formed
/ Add a few drops of ……………………
to the test tube containing 2 cm3 of iron(III) sulphate solution (ions) / ……………….. solution is formed
/ Add a few drops of ……………………
to the test tube containing 2 cm3 of ammonium chloride solution ( ions) / ……………….. precipitate is formed
The diagram below shows the flow chart for the chemical test of Fe2+ ions and Fe3+ ions.
Based on the flow chart, explain how to differentiate Fe2+ ions and Fe3+ ions.
………………………………………………………………………………………………………….
………………………………………………………………………………………………………….
………………………………………………………………………………………………………….
………………………………………………………………………………………………………….
Activity 17 :Qualitative analysis to identify salts
(A).Identify the salt S1
The following tests were carried out to identify salt S1. Based on the observations given for each test, state its inference. Finally, identify salt S1
Test / Observation / Inference1. Heat S1 strongly in a test
tube. Identify any gas
liberated. / Brown gas and gas relight a glowing splinter liberated.
Residue is brown when hot and yellow when cold
2. Dissolve a spatulaful of
S1 in distilled water.
Divide into four portions and carry out the following tests: / Residue dissolve in acid to produce colourless solution
(a) add solution until excess. / White precipitate, dissolve in excess NaOH solution
(b) add solution until
excess / White precipitate, insoluble in excess ammonia solution
(c) add potassium iodide
solution / Yellow precipitate formed
(d)add dilute ,
followed by
solution. Carefully add about 1of oncentrated
/ Brown ring formed
(A).Conclusion for salt S1 : …………………………………………………………………….
(B).Identify the salt S2
The following tests were carried out on an aqueous solution of salt S2. Based on the observations given for each test, state its inference. Finally, identify salt S2.
Test / Observation / Inference1. Pour about 2of S2
into a test tube. Add
solution until excess / White precipitate, dissolve in excess NaOH solution
2. Pour about 2of S2
into a test tube. Add
solution until excess / White precipitate, dissolve in excess ammonia solution
3. Pour about 2of S2 into a test tube. Add dilute , followed by silvernitrate, solution / No change
4. Pour about 2of S2 into a test tube. Add dilute HCl solution, then add BaCl2solution / White precipitate
(B).Conclusion for salt S2 : ……………………………………………………………………..
Activity 18 :plan qualitative analysis to identify anions
Rajoo works in a laboratory. He noticed that there are two large bottles. However both the labels have fallen off. He found four labels beside the bottles. i.e ‘Sodium Chloride Solution’, ‘Sodium Carbonate Solution’, ‘Sodium Sulphate Solution’and ‘Sodium Nitrate Solution’. So he has to carry out confirmatory test to identify the anion in both the solutions.
Complete the graphic organizers describing four tests and their results. The charts can then be used by Rajoo to distinguish which bottle contains which solution.
CHART A: SODIUM CARBONATE AND SODIUM NITRATE
CHART B: SODIUM CHLORIDE AND SODIUM SULPHATE
1