Mole Concept

Basic revision of basic concepts. Suitable for IAT, JEE, NEST, NEET, etc. Question mode: Flashcards only. Answer mode: Answer with definition. Good luck with exams!

What is the value of 1 mole?

$$6.022 \times 10^{23}$$

What is the definition of atomic mass unit?

It is $\frac{1}{12}$th of the mass of a single C-12 atom.

What is the value of 1 atomic mass unit (amu) in gram?

$1.67 \times 10^{-24}$ g

How is the value of 1 atomic mass unit in gram related to Avogadro’s number?

1 amu = $\dfrac{1}{N_A}$ g

What is the atomic mass of oxygen?

16 amu

What is the atomic mass of sodium?

23 amu

What is the mass of one mole of oxygen molecules?

16g

What is the mass of one mole of sodium atoms?

23g

How do you calculate the number of moles of a substance when given the mass of the substance and the molar mass of the substance?

$$n=\dfrac{\text{given mass of a substance in (g)}}{\text{molar mass of that substance}}$$

How do you calculate the number of moles of a substance when given the number of particles of that substance?

$$n=\dfrac{\text{number of particles of that substance}}{\text{avogadro number }(N_A)}$$

How do you calculate the number of moles of a gas when given the volume of the gas at STP (standard temperature pressure)?

$$n=\dfrac{\text{volume of gas at STP in (L)}}{22.4\ \text{L}}=\dfrac{\text{volume of gas at STP in (mL)}}{22400\ \text{mL}}$$

What is the law of conservation of mass?

total mass before reaction = total mass after reaction.

What is the law of constant proportion?

All pure samples of the same compound contain the same elements combined in the same proportion by mass.

What is the law of multiple proportions?

When two elements A and B combine to form more than one compound, then the mass of A which separately combines with a fixed mass of B (or vice versa) are in the ratio of fixed whole numbers.

What is the law of reciprocal proportions?

When two elements combine separately (individually) with a fixed mass of a third element, then the ratio of the masses in which they do so is a whole number multiple of the ratio in which they combine with each other.

What is Gay Lussac’s Law of Combining Volume?

Gases combine in a simple ratio of their volume provided all measurements are done at same temperature and pressure.

What is Avogadro’s hypothesis?

Under similar conditions of temperature and pressure, equal volumes of all gases contain equal numbers of molecules.

What is specific gravity of a liquid?

$$\text{specific gravity}=\dfrac{\text{density of liquid}}{\text{density of water}}$$

What is the formula for density of an ideal gas?

$$\text{density}=\dfrac{PM}{RT}$$

Where,

$P$= pressure

$R$ = ideal gas constant

$T$= temperature

$M$= molar mas of that gas

What is the value and unit of ideal gas constant?

$$R=8.314\ \ J\ K^-\ \text{mol}^-$$

How would you calculate the vapour density of a gas when given the density of that gas and density of hydrogen gas at same temperature and pressure?

$$V.D.= \dfrac{\text{density of that gas}}{\text{density of }H_2}$$

How would you calculate the vapour density of a gas when given its molar mass?

$$V.D.=\dfrac{\text{Molar mas of gas}}{2}=\dfrac{M_{\text{gas}}}{2}$$

For a gas at constant temperature and pressure, volume is proportional to the number of moles. Therefore,

$$\text{mole fraction}=\text{volume fraction}$$

Depict this in equation form, given the number of moles and volume of two different gases A and B in the mixture.

$$\dfrac{V_A}{V_A+V_B}=\dfrac{n_A}{n_A+n_B}$$

What is the formula for calculating average molar mass of a mixture of two gases? (2 forms)

$$M_{mix}=\dfrac{\text{total mass}}{\text{total moles}}=\dfrac{m_A+m_B}{n_A+n_B}=\chi_A\cdot M_A+\chi_B\cdot M_B$$

What is the formula for calculating the percentage of an element present in a compound?

$$\text{percentage of element}=\dfrac{\text{no. of atoms}\times \text{atomic mass}}{\text{molecular mass of compound}}\times 100$$

What are the steps for determining the empirical formula of a compound given the percentage composition of its elements?

1. divide percentages of each element by their respective atomic mass to obtain relative moles. this is the ratio, you just need to simplify now

2. identify the smallest result (least number of moles) from the previous step, and divide all results by that value

3. muliply the results from (2) with some number to obtain whole number ratio.

What is the formula for calculating the yield of a chemical reaction?

$$\text{percentage yield}=\dfrac{\text{actual yield}}{\text{calculated yield}}\times 100$$

What is the formula for calculating the percentage purity of a sample?

$$\text{percentage purity}=\dfrac{\text{mass of pure sample}}{\text{total mass of impure sample}}\times 100$$

Which reagent absorbs CO₂ or SO₂ or Cl₂?

KOH solution

Which reagent absorbs O₃?

turpentine oil

Which reagent absorbs O₂?

alkaline pyrogallol

Which reagent absorbs H₂O?

anhydrous CuSO₄ or CaCl₂

Which reagent absorbs NO?

FeSO₄ solution

Which reagent absorbs CO?

ammoniacal Cu₂Cl₂