The raw materials used for the manufacture of Portland cement are
- A.Lime, silica and sulphur dioxide
- B.Lime, silica and carbon dioxide
- C.Lime, silica and alumina
- D.Lime, silica and boric acid
Correct answer
Explanation
The correct answer is C, Lime, silica and alumina. Portland cement is made by heating a mix of limestone, which supplies lime, with clay, which supplies silica and alumina.
The raw materials are ground together and burnt in a rotary kiln at about 1,400–1,500 °C. The heat drives off carbon dioxide from the limestone and fuses the lime with silica, alumina and some iron oxide to form hard lumps called clinker. The clinker is ground to a fine powder with a little gypsum, which slows down the setting so the cement can be worked. The main compounds formed are calcium silicates and calcium aluminate. It is called Portland cement because, once set, it looks like the Portland stone of England; Joseph Aspdin patented it in 1824.
A is wrong: sulphur dioxide is not a raw material of cement.
B is wrong: carbon dioxide is given off when limestone is heated; it is not added.
D is wrong: boric acid is used in some glasses, not in cement.
Exam tip: cement, limestone plus clay; gypsum is added to slow setting.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →