Salts-Answer chemistry

7/29/2019 Salts-Answer chemistry

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CHAPTER 8: SALT

ANSWERS

Activity 1

1. ionic compound, hydrogen , acid , metal , ammonium

2.

Acid Formula of acid Salt Formula Cation Anion

Hydrochloric acid HCl Sodium chloride NaCl Na+ Cl-

Carbonic acid H2CO3 Potassium carbonate K2CO3 K+ CO3

2-

Sulphuric acid H2SO4 Copper(II) sulphate CuSO4 Cu2+ SO4

2-

Nitric acid HNO3 Ammonium nitrate NH4NO3 NH4+ NO3-

Nitric acid HNO3 Magnesium nitrate Mg(NO3)2 Mg2+ NO3

-

Ethanoic acid CH3COOH Sodium ethanoate CH3COONa Na+ CH3COO

-

2. ( any other correct answer can be accepted)

Salt Uses

Barium sulphate BaSO4 X-ray meals in hospital

Calsium sulphate CaSO4 Plaster of Paris for broken bone

Iron sulphate FeSO4 Iron tablets for anaemia patient

Ammonium nitrate NH4NO3 Nitrogenous fertilizer

Copper(II) sulphate CuSO4 Fungicide

Sodium chloride NaCl A flavouring agent

Sodium hydrogen carbonate Baking powder

Sodium nitrite NaNO2 For preserving food/ food preservative

Sodium hypochlorite NaOCl Bleaching agent

Tin(II) fluoride SnF2 Toothpaste

Lead(II) chromate PbCrO4 Paint for yellow line on road

Activity 2

1. sodium, potassium and ammonium.

2. nitrate

3. lead(II), barium and calcium sulphate

4. lead(II), argentums and mercury(I) chloride

5. sodium, potassium and ammonium carbonate

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CHAPTER 8: SALT

6

No Formula of

Salt

Solubility ( , X ) No Formula of Salt Solubility ( , X )

1 PbCO3 X 21 MgCO3 X

2 NaCl 22 KCl 3 CaSO4 X 23 (NH 4)2SO4 4 AgNO3 24 Cu(NO3)2 5 K2CO3 25 SnCO3 X6 FeCl 3 26 CaCl 2 7 Na2SO4 27 BaSO4 X8 NH4NO3 28 KNO3 9 CuSO4 29 Ag 2CO3 X10 PbCl 2 X 30 MgCl 2 11 ZnCO3 X 31 ZnSO4 12 Ca(NO3)2 32 Ba(NO3)2 13 Na2CO3 33 FeCO3 X14 AgCl X 34 NH 4Cl 15 PbSO4 X 35 Fe(NO3)3 16 Pb(NO3)2 36 MgSO4 17 (NH 4)2CO3 37 BaCO3 X18 HgCl 2 X 38 ZnCl 2 19 Na2SO4 39 FeSO4 20 NaNO3 40 Mg(NO3)2

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CHAPTER 8: SALT

Activity 3

1. a. metal + acid salt + hydrogen

b. metal oxide (or metal hydroxide) + acid salt + water

c. alkali + acid salt + water

e. metal carbonate + acid salt + carbon dioxide + water

2. a. Mg + H2SO4 MgSO4 + H2

b. (i) CuO + 2HCl CuCl2 + H2O

(ii) Zn(OH)2 + 2HNO3 Zn(NO3)2 + 2H2O

c. NaOH + HCl NaCl + H2Od. MgCO3 + H2SO4 CaSO4 + CO2 + H2O

3.

Method of Preparation Reactants Salt Formed Other

Product

a) metal + acid Magnesium + hydrochloric

acid

Magnesium chloride Hydrogen

b) metal oxide + acid Copper(II) oxide + sulphuricacid

Copper(II) sulphate water

c) metal carbonate +

acid

Zinc carbonate + sulphuric

acid

Zinc sulphate Water +

carbon

dioxide

d) metal hydroxide +

acid

Potassium hydroxide + nitric

acid

Potassium nitrate Water

e) alkali + acid Sodium hydroxide +

hydrochloric acid

Sodium chloride Water

4.

(a) Copper(II) sulphate : Copper(II) oxide / hydroxide / carbonate + sulphuric acid

(b) Zinc chloride : Zinc / (zinc oxide / hydroxide / carbonate) + hydrochloric acid

(c) Potassium nitrate : potassium hydroxide + nitric acid

(d) Ammonium sulphate : aqueous ammonia + sulphuric acid

(e) Magnesium nitrate : Magnesium / (magnesium oxide / hydroxide / carbonate) +

nitric acid

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CHAPTER 8: SALT

5. a. Mg(s) + 2H+(aq) Mg2+(aq) + H2 (g)

b. MgO(s) + 2H+(aq) Mg2+(aq) + H2O (l)

c. OH-(aq) + H+(aq) H2O (l)

d. CuCO3(s) + 2H+(aq) Cu2+(aq) + CO2(g) + H2O (l)

Activity 4

Name of solution : sodium hydroxide and hydrochloric acid

Chemical equation : NaOH + HCl NaCl + H2O

Procedure :

1. A pipette is used to transfer 25.0 3cm of sodium hydroxide solution to a conical flask. 2 to 3

drops of phenolphthalein is added.

2. A burette is filled with hydrochloric acid and record the initial burette reading.

3. Titration is carried out carefully by slowly adding the acid into the conical flask and the flask is

shaken well.

4. The acid is added continuously until the indicator turns from pink to colourless. The final burette

reading is recorded.

5. The volume of acid used to neutralize 25.0 3cm of the alkali is determined. (let the volume be V

3cm )

6. 25.0 3cm of the same sodium hydroxide solution is pipetted into a conical flask. No indicator is

addeded.

7. From the burette, exactly V 3

cmof hydrochloric acid is added to the alkali and is shaken well.

8. The contents of the conical flask is poured into an evaporating dish.

9. The solution is heated gently to evaporate most of the water to produce a saturated solution.

10. The hot saturated salt solution is cooled for crystallization to occur.

11. The sodium chloride crystals is filtered, and the salt is rinsed with a little distilled water.

12. The crystals are dried by pressing them between filter papers

Salt crystal characteristic

Flat surfaces, straight edges and sharp angles

Fixed geometrical shape

Fixed angles between two neighbouring surfaces

Crystals of some substance have same hapes but maybe in different sizes

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CHAPTER 8: SALT

Activity 5

Name of chemical : copper(II) oxide and sulphuric acid

Chemical equation : CuO + H2SO4 CuSO4 + H2O

Procedure :

1. 50 3cm of sulphuric acid 1 mol dm-3 is poured into a beaker. The acid is warmed.

2. By using a spatula, copper(II) oxide powder is added bit by bit into the acid. The mixture is stirred

well.

3. Copper(II) oxide is added continuously until some of it no longer dissolves.

4. The unreacted copper(II) oxide is removed by filtration

5. The filtrate is filtered into an evaporating dish. The solution is heated gently to produce a

saturated salt solution.

6. The saturated solution is cooled until crystals are formed.

7. The copper(II) nitrate crystals are filtered, and are then rinsed with a little distilled water.

8. The crystals are dried by pressing them between filter papers

9. Purification process Recrystallisation

The copper(II) sulphate crystals are placed in a beaker.

Enough distilled water is added to cover the crystals. The solution is gently heated and stirred

with a glass rod. Water is added bit by bit until all the crystals are dissolved.

Impurities is removed by filtration and filtrate is poured into an evaporating dish.

The solution is heated gently to evaporate most of the water to produce a saturated solution.

The hot saturated salt solution is cooled for crystallization to occur.

The copper(II) nitrate crystals are filtered, and the salt is rinsed with a little distilled water.

The crystals are dried by pressing them between filter papers

Activity 6

1. Precipitation, double decomposition reaction, ions , precipitate

2. Example 1: Barium sulphate,4

BaSO

Solution 1: Barium chloride/nitrate Solution 2: sodium/potassium sulphate

Chemical equation : BaCl2 + Na2SO4 BaSO4 + 2NaCl

Ionic Equation : Ba2+ + SO42- BaSO4

Example 2: Copper carbonate, CuCO3

Solution 1: copper(II) nitrate/sulphate/chloride Solution 2: Sodium/potassium carbonate

Chemical equation : Cu(NO3)2 + Na2CO3 CuCO3 + 2NaNO3

Ionic Equation : Cu2+ + CO32- CuCO3

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CHAPTER 8: SALT

Observation : green precipitate formed

Example 3: Lead(II) chromate(VI), 4PbCrO

Solution 1: lead(II) nitrate Solution 2: Sodium/potassium chromate(VI)

Chemical equation : Pb(NO3)2 (aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)

Ionic Equation : Pb2+ (aq) + CrO42- (aq) PbCrO4 (s)

Observation : yellow precipitate formed

Activity 7

Name of solution : lead(II) nitrate and Sodium/potassium iodide

Chemical equation : Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq)

Procedure :

1. 50 cm3 of 0.5 mol dm-3 lead(II) nitrate solution is poured into 50 cm3 of 1.0 mol dm-3

potassium iodide in a beaker

2. The mixture is stirred with a glass rod

3. A yellow precipitate of lead(II) iodide is formed immediately

4. The resulting mixture is then filtered

5. The yellow precipitate is rinsed with distilled water to remove impurities

6. The yellow solid, lead(II) iodide is then pressed between a few pieces of filter papers to be

dried

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CHAPTER 8: SALT

Activity 8

Test Tube 1 2 3 4 5 6 7

Volume 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 0.0025

Volume of K2CrO4 /cm3 1.0 2.0 3.0 4.0 5.0 6.0 7.0

No of mole of K2CrO4 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035

Height of precipitate / cm 0.45 0.90 1.40 1.90 2.30 2.30 2.30

Colour of the solution

above the precipitate

Colourless Yellow

(b)

(c) (i) 5 cm3

(ii) 0.0025 mole of chromate(VI) ions that has reacted with 0.0025 mole of Pb 2+. ions.

1 mole of chromate(VI) ions that has reacted with 1 mole of Pb2+. ions.

(iii) PbCrO4

(iv) ionic equation : Pb2+ + CrO42- PbCrO4

(d) The height increase from test 1 to 5 and become constant from test tube 5 to 7.

(e) In test tube 1-4, there are excess lead(II) ions, so more precipitate are formed when

increasing volume of CrO42- solution added. In test tube 5-7 all the lead(II) ions had reacted

with chromate(VI) ions, so the amount of precipitate formed is the same.

Activity 9 : Solve problems involving calculation of quantities of reactants or product in

stoichiometric reactions

1 (a) Zn + 2HCl ZnCl2 + H2

(b) No of mole of HCl = 2.0 x 50 = 0.1 mol

1000

7

Volume of potassium chromate(VI) / cm3

Height of precipitate / cm

1 2 3 4 5 6 7


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CHAPTER 8: SALT

(c) Mole ratio HCl : H2 = 2 : 1

No of mole of H2 = 1/2 x 0.1 = 0.05 mol

Volume of H2 = 0.05 x 24 dm3

= 1.2 dm3

2 (a) No of mole of H2SO4 = 1.0 x 100 = 0.1 mol

1000

(b) Mole ratio H2SO4 : MgSO4 = 1 : 1

No of mole of MgSO4 = 0.1 mol

Mass of MgSO4 = 0.1 x (24 + 32 + 4x16) g

= 12.0 g

3.a) No of mole of Mg = 0.12 = 0.005

24

No of mole of MgCl2 = 0.005

Mass of MgCl2 = 0.005 x (24 + 2 x 35.5)

= 0.475 g

b) No of mole of H2 = 0.005 mole

Vol of H2 = 0.005 x 24 dm3

= 0.12 dm3 or 120 cm3

4. (a)AgNO3 + NaCl AgCl + NaNO3

(b)

Number of moles of AgNO3 = 1.0 x 50 = 0.05 mol

1000

Mole ratio of AgNO3 : NaCl = 1 : 1

Number of mole of NaCl = 0.5 x z = 0.05 mole

1000

Z = 0.05 x 1000 = 100 cm3

0.5

b) Number of mole of AgCl = Number of moles of AgNO3 = 0.05 mol

Mass of AgCl = 0.05 x (108 + 35.5) g

= 7.175 g

Activity 10 : Qualitative Analysis

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CHAPTER 8: SALT

1. ions, physical and chemical properties.

2.

Colour (solid or solution) Substance or cation or anion

Green powder CuCO3 , Fe2+

Blue powder Cu2+

Brown powder Fe3+

Black powder CuO, MnO2

Yellow powder when hot and white when cold ZnO

Brown powder when hot and yellow when cold PbO

Blue solution Cu2+

Pale green solution Fe2+

Brown solution Fe3+

Solid : White

Solution : colourless

Cation : Ca2+ , Al3+ , Mg2+ , Pb2+ , Zn2+ ,

NH4+

Solid : White

Solution : colourless

Anion : Cl- , CO32- , SO42-, NO3-

3. Complete the following table

Salts Solubility in water Colour

Lead(II) chloride, silver chloride, barium

sulphate, lead(II) sulphate and calcium

sulphate

Insoluble white

Copper(II) carbonate Insoluble green

Iron(II) sulphate soluble green

Iron(III) salts except carbonate Soluble Brown

Lead(II) sulphate Insoluble white

Magnesium carbonate Insoluble white

Zinc chloride soluble white

Ammonium carbonate soluble white

Lead(II) iodide / chromate(VI) Insoluble Yellow

Activity 11 : Confirmatory Tests for gases,

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CHAPTER 8: SALT

Activity 12 : Action of Heat On Carbonate Salts

Carbonate salt Action of heat

Magnesium carbonate MgCO3 MgO + CO2

Observation : White solid formed. Gas liberated turn lime water

chalky

Aluminium carbonate Al2(CO3)3 Al2O3 + 3CO2

Observation : White solid formed. Gas liberated turn lime water

chalky

Zinc carbonate ZnCO3 ZnO + CO2

Observation : The residue is yellow when hot and white when

cold. Gas liberated turn lime water chalky

Lead(II) carbonate PbCO3 PbO + CO2

Observation : The residue is brown when hot and yellow whencold. Gas liberated turn lime water chalky

Copper(II) carbonate CuCO3 CuO + CO2

Observation : Black solid formed. Gas liberated turn lime water

chalky

Activity 13 : Action of Heat On Nitrate Salts

Nitrate salts Action by Heat

Sodium nitrate 2NaNO3 2 NaNO2 + O2

Observation : white solid formed, gas released relighted glowing

splinter

Magnesium

nitrate

2Mg(NO3)2 2MgO + 4NO2 + O2

Observation : white solid formed, Brown gas which turns moist blue

litmus red released. Another gas released relighted

glowing splinter

Zinc nitrate 2Zn(NO3)2 2ZnO + 4NO2 + O2

Observation : The residue is yellow when hot and white when cold.,

Brown gas which turns moist blue litmus red released.

Gas ObservationCarbon dioxide lime water turn milky/chalky

Oxygen glowing splinter will be relightedNitrogen dioxide Brown gas, blue litmus paper change to red

Chlorine Greenish yellow gas The colour of litmus paper change from blue

red

whiteAmmonia white fume formedRed litmus paper change to blue.

Hydrogen 'pop' sound is heardHydrogen chloride white fume formed

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CHAPTER 8: SALT

Another gas released relighted glowing splinter

Lead(II) nitrate 2Pb(NO3)2 2PbO + 4NO2 + O2

Observation : The residue is brown when hot and yellow when cold,

Brown gas which turns moist blue litmus red released.

Another gas released relighted glowing splinter

Copper(II) nitrate 2Cu(NO3)2 2CuO + 4NO2 + O2

Observation : black solid formed, Brown gas which turns moist blue

litmus red released. Another gas released relighted

glowing splinter

Activity 14 : Confirmatory Tests for Anions,

1. Ionic equation : 2H+ + CO32- H2O + CO2

Ionic equation : Ag+ + Cl- AgClIonic equation : Ba2+ + SO42- BaSO4

2. Which anion produce the following results?

Salt K1 sulphate ion

Salt K2 chloride ion

Salt K3 nitrate ion

Salt K4 carbonate ion

Activity 15 : Reaction of Cations with alkali solution

1.

NaOH solution Ammonia Solution NH3

A little In excess A little In excess

Soluble ( , X ) Soluble ( , X )Ca2+ White precipitate X No change Zn2+ White precipitate White precipitate Al 3+ White precipitate White precipitate XPb 2+ White precipitate White precipitate XMg2+ White precipitate X White precipitate X

Cu 2+ Blue precipitate X Blue precipitate X

Fe 2+ Green precipitate X Green precipitate X

Fe 3+ Brown precipitate X Brown precipitate X

2. Salt K5 - Inference 1 ammonium ion

Inference 2 Zinc, aluminium and lead(II) ions

Inference 3 magnesium or calcium ions

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CHAPTER 8: SALT

Salt K6 Inference 4 calcium ion

Inference 5 Zinc ion

Inference 6 magnesium , aluminium and lead(II) ions

Activity 16 : C onfirmatory Tests for Fe2+, Fe3+, Pb2+ and NH4+

(A)Cation Name of Reagent Observation

+2Pb Potassium iodide solution Yellow , dissolve , reappear

+2Fe Potassium hexacyanoferrate(III) Dark blue

+3Fe Potassium thiocyanate solution Blood red solution

NH4+ Nessler reagent Brown

(b) Pour 2 cm3 of iron(II) sulphate solution and 2 cm3 of iron(III) chloride solution into two test

tubes respectively. Then add a few drops of potassium hexacyanoferrate(II) solution to two

test tubes, Fe2+ ions solution will form light blue precipitate whereas Fe3+ ions solution will

form dark blue precipitate [All correct to score 1 mark, can use any other reagent]

or

Pour 2 cm3 of iron(II) sulphate solution and 2 cm3 of iron(III) chloride solution into two test

tube respectively. Then add a few drops of potassium thiocyanate solution to two test tubes,

there is no change in Fe2+ ions solution whereas Fe3+ ions solution will form blood red

solution.

Activity 17 : Structured qualitative analysis to identify salts

(A). Identify the salt S1

Test Inference

Step 1. Nitrogen dioxide gas, oxygen gas released.

Residue is lead(II) oxide

2 Fe2+, Fe3+ or Cu2+ ions may not be present

(a) Zn2+ , Al3+ or Pb2+ ions may be present

(b) Pb2+ or Al3+ ion may be present

(c) Confirm lead(II), Pb2+ ions present

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CHAPTER 8: SALT

(d) Confirm nitrate , NO3- ions present

Salt S1 is lead(II) nitrate

(B). Identify the salt S2

Test Inference

1. Zn2+ , Al3+ or Pb2+ ions may be present

2. Zn2+ ions may be present

3. Cl- ions not present

4. SO42- ions may be present

. Conclusion for salt S2 : zinc sulphate

Activity 18 : plan qualitative analysis to identify anions

All answers must be correct to score one mark for each chart.

CHART A: SODIUM CARBONATE AND SODIUM NITRATE

13

Test 1

Add dilute 3HNO

(any acid)

Result 1Effervescence

Result 1

No change


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CHAPTER 8: SALT

CHART B: SODIUM CHLORIDE AND SODIUM SULPHATE

14

Test 2add dilute H2SO4 followedby FeSO4 solution.

Carefully add 1 3cm of

concentrated H2SO4

Test 3

Add dilute 3HNO ,followed by silver nitrate,

3AgNO solution

Test 4Add dilute HCl, followed

by barium chloride,BaCl2 solution

SODIUMC

A

RBONATE

SODIUMN

ITRATE

Result 2

No change

Result 3

No change

Result 4No change

Result 2

Brown ring

Result 3

No change

Result 4

No change

Test 1

Add dilute 3HNO(any acid)

Result 1

No change

Result 1

No change


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CHAPTER 8: SALT

15

Test 2add dilute H2SO4 followedby FeSO4 solution.

Carefully add 1 3cm of

concentrated H2SO4

Test 3

Add dilute 3HNO ,

followed by silver nitrate,3

AgNO solution

Test 4Add dilute HCl, followed by

barium chloride,BaCl2 solution

SODIUM

CHLORIDE

SODIUM

SULPHATE

Result 2

No change

Result 3White

precipitate

Result 4

No change

Result 2

No change

Result 3No change

Result 4

Whiteprecipitate

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Salts-Answer chemistry