Which one of the following is NOT present in cement?
- A.2CaO·SiO₂
- B.3CaO·SiO₂
- C.4CaO·SiO₂
- D.3CaO·Al₂O₃
Correct answer
Explanation
The correct answer is C, 4CaO·SiO₂. There is no compound with the formula 4CaO·SiO₂ in Portland cement; the four main compounds of cement clinker are dicalcium silicate, tricalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite. Cement is made by heating limestone with clay in a rotary kiln to about 1,500 °C. The clinker that forms is ground with a little gypsum. Tricalcium silicate (3CaO·SiO₂) gives early strength, dicalcium silicate (2CaO·SiO₂) adds strength slowly over weeks, tricalcium aluminate (3CaO·Al₂O₃) reacts fastest with water, and tetracalcium aluminoferrite (4CaO·Al₂O₃·Fe₂O₃) contributes colour. Gypsum is added to slow down the setting caused by the aluminate. Option A is wrong because dicalcium silicate is a major compound of cement and gives long-term strength. Option B is wrong because tricalcium silicate is the largest single compound in cement and gives early strength. Option D is wrong because tricalcium aluminate is present and is responsible for the quick initial setting. Exam tip: cement = C₃S, C₂S, C₃A, C₄AF; gypsum slows setting.
Practice Questions
View allThe rate of evaporation of liquid does not depend upon
- A.temperature
- B.its surface area exposed to the atmosphere
- C.its mass
- D.humidity
Show answer
Evaporation is a surface process, so its rate depends on conditions at the surface of the liquid, not on how much liquid there is in total.
Read the full explanation →Which one of the following is considered as a compound ?
- A.Silicon
- B.Tin
- C.Sugar solution
- D.Calcium carbonate
Show answer
Calcium carbonate, CaCO3, is a compound because calcium, carbon and oxygen are chemically combined in it in a fixed ratio.
Read the full explanation →'Altitude sickness' is caused at high altitude due to
- A.high partial pressure of oxygen
- B.low partial pressure of oxygen
- C.low level of haemoglobin
- D.high partial pressure of carbon dioxide
Show answer
As one climbs, air pressure falls, so each breath delivers oxygen at a lower partial pressure and less of it passes from the lungs into the blood.
Read the full explanation →Which one of the following is not a characteristic of a compound?
- A.Composition is variable.
- B.All particles of compound are of only one type.
- C.Particles of compound have two or more elements.
- D.Its constituents cannot be separated by simple physical methods.
Show answer
A compound always has a fixed composition by mass, so a variable composition is a property of mixtures, not compounds.
Read the full explanation →A positively charged particle (alpha-particle) is projected towards west in a horizontal plane. It is deflected towards north in the same plane by a magnetic field. Which one among the following is the direction of the magnetic field?
- A.Towards south
- B.Towards east
- C.Vertically downwards
- D.Vertically upwards
Show answer
The magnetic force on a moving charge is F = q(v × B), and only an upward field turns a westward-moving positive charge towards the north.
Read the full explanation →