Study Material Term 2 Week 8 Level L 2020

Metals

1. List some of the physical properties of the alkali metals.

1. Soft metals.
2. Have low density.
3. Easily cut with a knife.
4. Have shiny lustrous surface when freshly cut.
5. Tarnish quickly on exposure to air.
6. Have low melting compared to other metals (relatively low MP)

2. What flame colours will lithium, sodium and potassium salts give?

Li salt          Na salt              K salt

red flame     yellow flame     Lilac flame

3. Would you classify zinc oxide as acidic, basic or amphoteric?

Amphoteric

4. List some of metal whose oxides may be reduced by heating in a stream of CO gas.

Zn, Fe, Pb, Cu, Ag.

Note:Reactivity series 
   
         Reactivity series wikipedia

5. What kind of ions do the metals and non-metals generally form?Compare the nature of bonding (ionic or covalent) of their compounds.Metals form positive ions ⇒ form ionic bonds in their compounds.
Non-metals can form negative ions ⇒  form ionic bonds in their compounds 
Non-metals can also share electrons forming covalently bonded molecular compounds

6. What will be produced when lithium reacts with oxygen? 
4Li(s) + O₂(g) → 2Li₂O (s)Is the product soluble? Yes, all alkali metal compounds are solubleIs a solution of the product in water acidic or basic? basicWhat will be produced when sodium reacts with water?
 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) 
Is the product soluble? Yes, all alkali metal compounds are soluble
Is the resulting solution acidic or basic? basicWhat will be produced when potassium reacts with chlorine? Potassium chloride

7. What flame color will calcium salts give? Brick red

8. What will be produced when Mg reacts with steam?
 Mg(s) + H₂O(g)➝MgO(s) + H₂(g) What will be produced when Ca reacts with water? 
Ca(s) + 2H₂O(l) →Ca(OH)₂ (s)+H₂(g)What will be produced when calcium or magnesium reacts with oxygen?
2Ca(s) + O₂(g) → 2CaO(s) 2Mg(s) + O₂(g) → 2MgO(s)

9. Write equations for the reaction of zinc with:

 

a) air.

2Zn(s) + O₂(g) ➝2ZnO(s)

b) dil. H₂SO4(aq).

Zn(s) + H₂SO4(aq) ➝ZnSO4(aq) + H₂(g)

 c) steam.
 Zn(s) + H₂O(g) ➝ZnO(s) + H₂(g)

10. Write equations for the reactions that will take place when the following chemicals are heated together. 

a) ZnO and CO 

ZnO(s) + CO(g) ➝ Zn(s) + CO₂(g)

b) Fe₂O3 and H₂

 Fe₂O3(s) + 3H₂(g) ➝ 2Fe(s) + 3H₂O(g)

11. Write equations for the reactions that will take place when the following chemicals are heated.


Cases of thermal decomposition

a) Ca(NO₃)₂ 

2Ca(NO₃)₂(s) Δ→ 2CaO(s) + 4NO₂(g) + O₂(g)

b) Mg(NO₃)₂ 

2Mg(NO₃)₂(s) Δ→ 2MgO(s) + 4NO₂(g) + O₂(g)

c) NaNO₃

2NaNO₃(s) Δ→ 2NaNO₂(s) + O₂(g)

d) Cu(NO₃)₂

2Cu(NO₃)₂(s) Δ→ 2CuO(s) + 4NO₂(g) + O₂(g)

12. What is added to bauxite before the electrolysis process and why?Molten cryolite, Na₃AlF₆ (sodium aluminium fluoride), the cryolite acts as both a solvent to dissolve Al₂O₃ and reduces the melting point of the electrolyte from 2017◦C to 800-1000◦C.


Link here for Electrolysis of aluminium

Note: When asked in an exam, choose the property most relevant to the use. For example, in aircrafts, the most relevant property is low density.

14. Why does aluminium appear to be less reactive than it really is?Aluminum is very reactive. It spontaneously reacts with oxygen of air to produce aluminum oxide which coats the aluminum. Since this oxide layer is inert, aluminum appears to be less reactive than it is.


15. List some of the common uses of zinc.* Making alloys such as brass (an alloy of Cu and Zn) 
* Galvanization
*  Car batteries
*  Sacrificial protection



16. Sodium is produced industrially by electrolysis in a Downs cell. What chemical is added to lower the melting point of the electrolyte? Calcium chloride, CaCl₂



17.

a) What are alloys?

Alloys: are solid solutions (a homogenous mixture) of two or more metals that may contain non- metals as well.

b) Why are they useful?

They combine the properties of their constituents, for eg., an alloy is harder than a pure metal.

c) Why are different metals “blended” into alloys?
Different metals are blended into alloys to produce a metal with the cumulative properties of its constituents.

18. How is copper purified? Give the name of a suitable electrolyte. What are the anode and cathode made of? Write equations for the reactions taking place at each of them.

 Steps: Impure copper is made the anode (connected to the positive terminal of the battery). Pure copper rod is made the cathode (connected to the negative terminal of the battery). 
 Electrolyte: Copper (II) sulphate solution (blue in color)

 Reactions and observations:At anode: Cu(s) → Cu2+(aq) + 2 e- 

Mass of the anode decreases due to the discharge of Cu metal
At cathode: Cu2+(aq) + 2 e- → Cu(s) 


Mass of cathode increases.
Color of the solution stays blue (due to the continuous presence of copper (II) ions).
Anode sludge that is formed below the anode contains solid impurities and can be removed by filtration.

19.  List some of the common uses of copper.

1. Production of electric cables.
2. Production of alloys, such as brass and bronze.
3. In ornamental pieces, machine parts and gears.
4. In steam boilers, cooking utensils and water pipes.

20. What are the colors of copper, copper (I) oxide and copper (II) oxide?

•   Copper:                          pinkish gold
•   Copper (I) oxide:           foxy red 

         Copper (II) oxide:          Black

22. Sodium may be manufactured industrially by electrolyzing molten sodium chloride in the Down process. Write equations, with state symbols, for the half reactions that take place at each electrode


At anode: 2Cl-(l) → Cl₂(g) + 2e- Yellowish green gas evolves at the anode
At cathode: 2Na+(l) + 2e- → 2Na(l) Silvery metal floats on the surface of the electrolyte.



25. All Alkali metals react with water forming a hydroxide solution and hydrogen gas.



27. Write equations for the reactions that will take place when the following chemicals are heated.

a) CaCO3 


CaCO3(s) Δ→ CaO(s) + CO2(g)

b) MgCO3 


MgCO3(s) Δ→MgO(s) + CO2(g)



28. Aluminum may be manufactured industrially by electrolyzing molten aluminum oxide. Write equations, with state symbols, for the half reactions that take place at each electrode.

At anode:
6O2-(l) → 3O₂ (g) + 12e-

At cathode: 

 4Al3+(l) + 12e- → 4Al(l)

Overall reaction:

2 Al₂O₃ (l) → 4Al(l) + 3O₂(g)

29. A tray is to be silver-plated industrially by electrolysis. State the materials (object) used for the anode, cathode and electrolyte.The tray to be plated is made the cathode by connecting it to the negative terminal of the power source.
It is then placed in an electrolyte that contains silver solution.
A rod of pure silver is made the anode by connecting it to the positive terminal of the power source.

30.What will be produced when Mg burns in air? 
Magnesium oxide

What will be observed?

 A brilliant dazzling white flame

What will be produced when Ca reacts with oxygen? 
Calcium oxide

What will be produced when calcium reacts with steam? 
Calcium hydroxide and hydrogen gas

 Write the reaction between sodium metal Na and oxygen gas. 

2Na + ½ O₂ → Na₂O

Describe the structure of alloys.

An alloy is a solid solution of a metal with either other metals or nonmetals as well.
The added atoms can either replace some of the host atoms in the lattice, or occupy the interstices (holes) between neighboring atoms.

. Using the following metals ONLY complete the statements below potassium, calcium, iron, lead

1. a)  This metal reacts with cold water to form a clear solution
2. b)  This metal reacts with cold water to form a milky white solution
3. c)  This metal does not react with cold water but reacts with steam

d)  This metal does not react with water or steam.

Answer

a. potassium: K(s) + H₂O(l) → KOH(aq)
b. calcium: Ca(s) + H₂O(l) → Ca(OH)2(aq)
c. iron: 2Fe(s) + 3H₂O(g) → Fe₂O₃(s) + 3H₂(g) d. lead

Name the products of the thermal decomposition of magnesium hydroxide. Magnesium oxide and water

Briefly describe how sodium is extracted.

1. a)  What chemical is used to manufacture sodium industrially?
2. b)  By what process can sodium be extracted?
3. c)  What is added during the extraction of sodium to lower its melting point?
4. d)  At around what temperature will the process take place?
5. e)  Write an equation to show how sodium is produced.

1. 
   
   Answers
   
   a)  Molten sodium chloride
2. b)  electrolysis
3. c)  Calcium chloride, CaCl₂
4. d)  600°C
   

e)  2NaCl(l) Electrolysis→ 2Na(l) + Cl₂(g)

Give the name of a metal whose carbonate is soluble and one whose carbonate is insoluble. 

Soluble metal carbonates: Sodium and Potassium
Insoluble metal carbonate: Calcium, Magnesium, Aluminum, Zinc, Iron, Lead, Copper

What properties allow aluminium to be used in aircraft manufacture?

1. Low density
2. High tensile strength
3. Resists corrosion

What are the two major metals present in bronze?

 Bronze: copper (Cu) and tin (Sn)

Why does aluminum appear to be less reactive than it really is?

Aluminum is very reactive. It spontaneously reacts with oxygen of air to produce aluminum oxide which coats the aluminum. Since this oxide layer is inert, aluminum appears to be less reactive than it is.



Manufacturing aluminium industrially

1. a)  What chemical is used to manufacture aluminium industrially?
2. b)  What are the formulae and common name of the aluminium ore?
3. c)  What is added to the aluminium ore to remove the impurity that is present along with it?
4. d)  What is added to the aluminium ore to lower its melting point?
5. e)  What is the function of cryolite?
6. f)  At around what temperature will the process take place?
7. g)  Write an equation to show how aluminium is produced?

1. a)  Molten aluminium oxide
2. b)  Al₂O₃.2H₂O
   Common name of ore: Bauxite
   Common name of oxide: Alumina
   
   
   
3. c)  Aluminium is dissolved in sodium hydroxide solution.
4. d)  Cryolite (Na₂AlF6) is added.
5. e)  used to dissolve Al₂O₃ (as a solvent)
   added as a flux that reduces the melting point of the electrolyte from 2017◦C to 800-1000◦C.
6. f)  The operating temperature is 1000°C.

g)

At anode:
6O2-(l) → 3O₂ (g) + 12e-

At cathode: 

 4Al3+(l) + 12e- → 4Al(l)

Overall reaction:

2 Al₂O₃ (l) → 4Al(l) + 3O₂(g)


What properties allow aluminium to be used in overhead cables?

• Excellent electrical conductivity
• Low density
• Resists corrosion

Give the name of a metal whose carbonate is stable to heat. 

21. Sodium carbonate / potassium carbonate