Unit notes and practice questions
Everything here is for unit 5 of the Grade 10 Chemistry textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.
The cards filed under this chapter on the Grade 10 Chemistry page. Open one at a time.
When you use it
Use when outlining the industrial steps of the Contact Process for sulfuric acid manufacturing.
Watch out
Never write sulfur trioxide reacting directly with water in the Contact Process. It must first be absorbed into concentrated sulfuric acid to form oleum, which is then diluted.
Drafted from Grade 10 Chemistry, pages 201-236, then checked twice before it went up
When you use it
Use this formula to calculate the mass percent of pure gold from a given carat value.
Watch out
Pure gold is 24 carats. Do not divide the carat value by 100.
Drafted from Grade 10 Chemistry, pages 201-236, then checked twice before it went up
| Element | Chief Ore or Source | Industrial Extraction Method |
|---|---|---|
| Aluminum | (Bauxite) | Hall-Héroult process (Electrolysis with ) |
| Iron | (Hematite) | Blast furnace reduction using |
| Copper | (Chalcopyrite) | Roasting, smelting, and electrolytic refining |
| Sulfur | Underground elemental deposits | Frasch process using superheated water |
| Chlorine | (Brine) | Electrolysis of concentrated aqueous |
When you use it
Use this table to identify raw ores and corresponding extraction processes for major metals and nonmetals.
Watch out
Cryolite is not the aluminum ore. It is an additive that lowers the melting point of alumina from 2045 °C to 1000 °C.
Drafted from Grade 10 Chemistry, pages 201-236, then checked twice before it went up
10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.
Question 1
Solder, which is commonly used to join electrical wires and resistances, is an alloy composed of:
Answer: A 67% tin and 33% lead
Why
According to the textbook, solder (also called fuse metal) has a composition of 67% tin and 33% lead, giving it a lower melting point than pure tin.
Question 2
According to the reactivity series of metals, which metal is the strongest reducing agent?
Answer: A Potassium
Why
Metals at the very top of the reactivity series lose electrons most readily and are the strongest reducing agents. Potassium sits at the top of the series, while gold sits at the bottom as the weakest.
Question 3
Why is white phosphorus always stored under water in the laboratory?
Answer: A It spontaneously ignites in the presence of oxygen.
Why
White phosphorus is very reactive and bursts into flames spontaneously when exposed to air (oxygen). Storing it under water prevents it from contacting oxygen.
Question 4
In the industrial extraction of aluminum by the Hall-Héroult process, cryolite (Na3AlF6) is added to aluminum oxide to:
Answer: A reduce its melting point from 2045 °C to 1000 °C
Why
Cryolite is added to Al2O3 to lower its extremely high melting point from 2045 °C to 1000 °C and to provide a good electrically conducting medium.
Question 5
A goldsmith in Addis Ababa crafts traditional jewelry using 18 carat gold. What is the mass percent of pure gold in this 18 carat alloy?
Answer: A 75.00%
Why
Pure gold is 24 carats (100%). An 18 carat alloy contains 18 parts gold out of 24 parts by mass: (18 / 24) * 100 = 75.00%.
Question 6
In the blast furnace during iron extraction, what is the primary role of limestone (CaCO3)?
Answer: A It decomposes to CaO, which acts as a flux to remove silica impurities as slag.
Why
Limestone decomposes into calcium oxide (CaO), which reacts with sand/silica (SiO2) to form molten calcium silicate (CaSiO3), known as slag.
Question 7
Which setup of electrodes and electrolyte is used during the electrolytic refining of blister copper?
Answer: A Anode: impure copper; Cathode: pure copper; Electrolyte: copper sulphate solution with dilute sulphuric acid
Why
During copper refining, a thick block of impure copper serves as the anode, a thin strip of pure copper acts as the cathode, and acidified copper sulphate solution serves as the electrolyte.
Question 8
Which statement correctly describes the allotropes of sulphur?
Answer: A Rhombic sulphur is the most stable form, while monoclinic sulphur is stable only above 95.3 °C.
Why
Rhombic sulphur (α-sulphur) is the most stable form at room temperature. Monoclinic sulphur (β-sulphur) is stable only above 95.3 °C; below this temperature it converts back to rhombic sulphur.
Question 9
A maintenance crew repairing steel parts uses the thermite welding process. Which mixture of substances is ignited in this process?
Answer: A Powdered aluminum and iron(III) oxide
Why
Thermite is a mixture of powdered aluminum and iron(III) oxide (Fe2O3). When ignited, aluminum reduces the iron oxide, producing molten iron at around 3000 °C.
Question 10
Which steel-making method forces a mixture of powdered calcium oxide (CaO) and oxygen gas directly onto the surface of molten pig iron, completing the conversion in only 20 to 25 minutes?
Answer: A Basic Oxygen Process
Why
The Basic Oxygen Process uses a high-speed blow of oxygen gas and powdered CaO directly on molten pig iron. The intense exothermic reactions keep the charge molten and finish the process in 20 to 25 minutes.
The app holds 12 questions on this unit, marked as you go. These are the first 10.
Unit 5 runs from page 201 to page 236 of the Ministry of Education edition.
Ministry of Education edition, English, 307 pages
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