Chemistry · Some Basic Concepts Of Chemistry · NEET
You use the TOTAL. Mass of solution = mass of solute + mass of solvent. This is the number one mistake students make. If you dissolve 2 g of salt in 18 g of water, the solution mass is 2 + 18 = 20 g, NOT 18 g. So mass percent = (2 / 20) x 100 = 10%. Always add the solute mass into the bottom of the fraction.
Step 1: mass of solute = 2 g. Step 2: mass of solution = 2 + 18 = 20 g. Step 3: mass percent = (2 / 20) x 100 = 10%. This is the exact example from NCERT and the answer is 10% w/w. Notice you did not need any molar mass - mass percent uses only masses in grams.
No. Mass percent does NOT depend on temperature. This is a very common NEET question. When you heat a solution, its volume expands but its MASS stays the same (mass is conserved). Since mass percent uses only masses (grams), heating does not change it. Molarity DOES change with temperature because it uses volume (litres), and volume expands on heating. So molarity is the odd one out - it is the only temperature-dependent term among molality, mole fraction, and mass percent.
Mass percent (w/w %) = grams of solute per 100 grams of solution; it uses only mass, so it has no units and never changes with temperature. Molarity (M) = moles of solute per litre of solution; it uses volume and moles, so it changes with temperature. Use mass percent when the problem gives you masses in grams. Use molarity when the problem gives volume of solution and you need moles.
Because you divide mass by mass (grams / grams), the units cancel out. What is left is just a ratio, and multiplying by 100 turns it into a percentage. That is why a mass percent is written as a plain number with a % sign, like 10% or 69%, with no g, mol, or L attached.
It means every 100 g of that acid solution contains 69 g of pure HNO3 and 31 g of water. This is exactly the kind of data NCERT gives you (69% HNO3, density 1.41 g/mL) so you can then convert to molarity. The trick: take 100 g of solution as your basis, because that makes the solute mass equal to the percent number directly.
Which of the following concentration terms is dependent on temperature?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Mass percent = (mass of solute / mass of solution) x 100, where mass of solution = mass of solute + mass of solvent. It is also called weight percent or w/w %.
Yes. Mass percent, weight percent, and w/w % all mean the same thing: grams of solute per 100 grams of solution.
No. Since you divide mass by mass, the units cancel. Mass percent is just a number with a % sign.
Because it uses only mass, and mass never changes when you heat or cool a solution. Only volume changes with temperature, so only volume-based terms like molarity are affected.
Mass of solution = 2 + 18 = 20 g, so mass percent = (2 / 20) x 100 = 10%. This is the standard NCERT example.
