Concentration of a solution can be expressed in : 1. Molarity 2. Molality Select the answer using the code given below:
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Correct answer
Explanation
The correct answer is C, Both 1 and 2. Molarity and molality are both standard ways of stating how much solute is present in a solution. Molarity (M) is the number of moles of solute dissolved in one litre of solution, so a 1 M solution of sodium chloride has 58.5 g of the salt in one litre of solution. Molality (m) is the number of moles of solute dissolved in one kilogram of solvent. Because volume changes with temperature while mass does not, molality stays the same when a solution is heated or cooled, but molarity changes slightly. Other ways to express concentration include mass percentage, mole fraction, normality and parts per million (ppm), used for very dilute solutions such as pollutants in water. Option A is wrong because molality is also a unit of concentration. Option B is wrong because molarity is the most common unit of all. Option D is wrong because both are accepted measures. Exam tip: molarity is per litre of solution and depends on temperature; molality is per kilogram of solvent and does not.
Practice Questions
View allWhich of the following statements about electromagnetic waves, sound waves and water waves is/are correct ? 1. They exhibit reflection 2. They carry energy 3. They exert pressure 4. They can travel in vacuum Select the correct answer using the code given below :
- A.1,2 and 3
- B.2 and 4
- C.1 and 3 only
- D.1 only
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All three kinds of wave reflect, carry energy and exert pressure, but only electromagnetic waves can travel through a vacuum.
Read the full explanation →Which one of the following is NOT the unit of energy?
- A.Joule
- B.Watt-hr
- C.Newton-metre
- D.kg-metre/sec²
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A kilogram-metre per second squared is mass times acceleration, which is force; it is the newton, not a unit of energy.
Read the full explanation →To protect steel and iron from rusting, a thin layer of which one of the following metals is applied?
- A.Magnesium
- B.Zinc
- C.Aluminium
- D.Lead
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Coating iron or steel with a thin layer of zinc is called galvanisation, and it is the most common way to protect them from rusting.
Read the full explanation →In an electric circuit, a wire of resistance 10 Ω is used. If this wire is stretched to a length double of its original value, the current in the circuit would become :
- A.half of its original value.
- B.double of its original value.
- C.one-fourth of its original value.
- D.four times of its original value.
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Stretching the wire to twice its length makes its resistance four times larger, so at the same voltage the current falls to a quarter.
Read the full explanation →Which one of the following scientists mentioned that an electron in an atom could revolve in certain stable orbits without the emission of radiant energy ?
- A.Ernest Rutherford
- B.J.J. Thomson
- C.Niels Bohr
- D.Albert Einstein
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In his 1913 model of the atom, Bohr proposed that electrons move in certain fixed orbits, called stationary states, in which they do not radiate energy.
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