Chemistry · Some Basic Concepts Of Chemistry · NEET
Yes, they are equal. This is because 1 cm³ = 1 mL exactly. So a density of 1.25 g/cm³ is the same as 1.25 g/mL. NEET questions freely swap these two, so never let the different label confuse you — treat them as identical.
NCERT says density tells us how closely particles are packed. If density is more, the particles are packed more closely together. So a solid like iron has high density (particles tightly packed), while a gas has very low density (particles far apart). Same idea: solids > liquids > gases in density for most substances.
The true SI unit of density is kg/m³ (mass in kg, volume in m³). But this gives huge numbers — water is 1000 kg/m³. Chemists prefer g/cm³ because the numbers are small and easy: water is just 1 g/cm³. Both are correct; g/cm³ is simply more convenient in the lab.
Multiply by 1000. Reason: 1 g = 10⁻³ kg and 1 cm³ = 10⁻⁶ m³, so 1 g/cm³ = 10⁻³ kg ÷ 10⁻⁶ m³ = 10³ kg/m³. Example: water 1 g/cm³ = 1000 kg/m³. Iron 7.87 g/cm³ = 7870 kg/m³.
Density is a DERIVED unit, not a base unit. It is built from two base quantities — mass (kg) and length/volume (m³). The seven SI base units (kg, m, s, A, K, mol, cd) are the fundamental ones; density comes from combining mass and volume, so it is derived.
No. Density is a property of the substance itself, not of how much you have. If you take 10 g of water or 100 g of water, the density stays 1 g/cm³. This is because when mass increases, volume increases in the same ratio, so mass ÷ volume stays constant. This is why density is called an intensive property.
The density of a 1 M solution of a compound X is 1.25 g mL⁻¹. The molality of the solution is (molar mass of X = 85 g mol⁻¹)
The density of a 2 M aqueous solution of NaOH is 1.28 g cm⁻³. The molality of the solution is (molar mass of NaOH = 40 g mol⁻¹)
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Density = Mass ÷ Volume. You can rearrange it as Mass = Density × Volume, which is the form most used in NEET molarity and molality problems.
The SI unit is kilogram per cubic metre, written kg/m³ or kg m⁻³. Chemists more often use g/cm³ (equal to g/mL) because the numbers are smaller and easier.
Water has a density of about 1 g/cm³ (1 g/mL), which equals 1000 kg/m³. This makes water a handy reference value to remember for NEET.
Density is an intensive property. It does not depend on how much of the substance you take — a drop of water and a bucket of water have the same density.
Because it is made by combining two things: mass (a base quantity) and volume (which comes from length, a base quantity). It is not one of the seven SI base units, so it is derived.
