Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (2022)

In chemistry, the molar mass is an important quantity. It measures the mass of a mole of a given substance.

Definition

The molar mass of a given substance is defined as the mass of a sample divided by the moles of that substance in the sample. In other words, it is the mass per mole of a substance.

It is usually denoted by the symbol M.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (1)

Unit

The standard unit is gmol−1. The SI unit is kgmol−1, however, it is very uncommon.

Mole

We know that one mole of a substance consists of 6.022 140 76×1023 elementary particles. This number (aka Avogadro’s constant) is mostly approximated to 6.022×1023. Thus, one mole of carbon contains 6.022×1023 atoms of carbon.

When we say the molar mass of carbon is 12.0gmol−1, it means one mole of carbon weighs 12.01g. In other words, 6.022×1023 atoms of carbon weigh 12.01g.

Important of Molar Mass

In chemistry, calculations are related to chemical reactions and stoichiometry. Calculations often include quantities like molarity, molality, mole fraction, molar volume. All these involve the number of moles. Although there is no direct way to measure the number of moles of any substance, the number of moles can be calculated by knowing the molar mass of the substance. The molar mass links the mass of a substance to its moles. Thus, by knowing the molar mass, we can determine the number of moles contained in a given mass of a sample.

Let me make it more clear with an example of sodium chloride. The molar mass of sodium chloride is known; it is 58.44gmol−1. If we have to measure one mole of sodium chloride, there is no instrument that can directly measures it. But we know 58.44g of sodium chloride is equivalent to one mole of it. So, we measure 58.44g of NaCl with a weight scale, which is equivalent to one of 58.44g. Hence, we have one mole of NaCl measured.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (2)

Some of the important points regarding the molar mass are as follows:

  • It is a bulk property, not atomic property, of a substance.
  • It is an intensive property. So, it does not vary with the size of a sample.
  • It is dependents on percentages of consistents of a sample. Thus, it can vary with a terrestrial location.
  • It is used to convert the mass of a substance to its mole and vice versa.

Atomic Mass and Molar Mass

The atomic mass and the molar mass are confused with one another. But they are two different quantities with a definition. The table below describes the differences between the two.

Table 1: Difference between Atomic Mass and Molar Mass
Atomic MassMolar Mass
The atomic mass is the sum of the mass of protons, neutrons, and electrons.It is the mass of a mole of a substance.
It is denoted by ma.The symbol used for it is M.
It has a unit of the unified mass unit (u) or the atomic mass unit (amu).gmol−1 is the standard unit for the molar mass.
The atomic mass is an atomic property.It is a bulk property.
It does not account for isotopes.The existence of isotopes is accounted for since it is a bulk property.
The atomic mass is constant for a particular isotopic element. It does not vary from sample to sample. For example, the atomic mass of carbon-12 is 12u. This is true for all atoms of carbon-12 in the universe.It could vary from sample to sample depending on the percentages of constituents in the sample.

Average Atomic Mass to Molar mass

If the average atomic mass (ma) or average molecular mass is known, we can convert it into the molar mass (M) with the help of the molar mass constant (Mu).

The average atomic mass is measured in the unified mass unit (u). The unified mass unit is related to the molar mass constant (Mu) by the Avogadro constant (NA).

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (3)

ma is the average atomic mass or the average mass of an atom. So, the mass of a mole of the atom is ma×NA. But this quantity is in the unified mass unit (u). The above equation can convert u to gmol−1.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (4)

Therefore, the average atomic mass divided by one unified mass unit times the molar mass constant results in the molar mass.

The precise value of Mu is 0.999 999 999 65(30)gmol−1. But this value approximately equals 1gmol−1.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (5)

From the above equation, we can say the numeric value of the molar mass and the average atomic mass is approximately equal. This is also true for molecules. The table below lists the elements (and the compounds) with the average atomic mass and the average molar mass.

Table 2: Average Atomic Mass to Molar Mass

Element (or Compund)

Average Atomic Mass (or Average Molecular Mass) (u)

Divide (÷)

Unified Mass Unit (u)

Multiple (×)

Molar Mass Constant (Mu)

Equal to (=)

Molar Mass (1gmol−1)

Hydrogen (H)

1.008u

÷

1u

×

1gmol−1

=

1.008gmol−1

(Video) Percent Composition

Carbon (C)

12.011u

÷

1u

×

1gmol−1

=

12.011gmol−1

Oxygen (O)

15.999u

÷

1u

×

1gmol−1

=

15.999gmol−1

Nitrogen (N)

14.007u

÷

1u

×

1gmol−1

=

14.007gmol−1

Potassium (K)

39.098u

÷

1u

×

1gmol−1

=

39.098gmol−1

Calcium (Ca)

40.078u

÷

1u

×

(Video) GOC 09 | Qualitative & Quantitative Analysis of Organic Compound | Class 11 | JEE | NEET | Pace

1gmol−1

=

40.078gmol−1

Chlorine (Cl)

35.45u

÷

1u

×

1gmol−1

=

35.45gmol−1

Hydrogen Gas (H2)

2.016u

÷

1u

×

1gmol−1

=

2.016gmol−1

Water (H2O)

18.015u

÷

1u

×

1gmol−1

=

18.015gmol−1

Methane (CH4)

16.04u

÷

1u

×

1gmol−1

=

16.04gmol−1

Nitrogen Dioxide (NO2)

46.006u

(Video) Stoichiometry Problems Part I

÷

1u

×

1gmol−1

=

46.006gmol−1

Ammonia (NH3)

17.031u

÷

1u

×

1gmol−1

=

17.031gmol−1

Glucose (C6H12O6)

180.156u

÷

1u

×

1gmol−1

=

180.156gmol−1

Atomic Weight to Molar Mass

The atomic weight (aka relative atomic mass) (Ar) is a dimensionless quantity having the numeric value of the average atomic mass. The average atomic mass and atomic weight are related by the following equation.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (6)

From the above two equations,

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (7)

Therefore, the atomic weight times the molar mass constant results in the molar mass.

So, we can calculate the molar mass of any compound in the same way we calculate the atomic weight from its constituent elements.

Consider an example of glucose. Glucose molecular formula is C6H12O6; it has six carbons, twelve hydrogens, and six oxygens. The molar mass of glucose is the sum of the relative atomic mass of all the atoms in the molecular formula.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (8)
Table 3: Molar Mass of Glucose (C6H12O6)
ElementAtomic WeightMolar Mass (gmol−1)
Carbon (C)12.01112.011
Hydrogen (H)1.0081.008
Oxygen (O)15.99915.999
Molar Mass of Glucose (C6H12O6)180.156

Molar Mass of Mixtures

The molar mass of a mixture is determined using the mole fraction (xi).

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (9)

where: Mmix is the molar mass of a mixture of n components, and xi and Mi are the mole fraction and the molar mass of ith component.

The above formula can also be expressed in terms of the mass fraction wi.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (10)

or

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (11)

Consider a liquid-liquid mixture of water (H2O) and ethanol (C2H6O). Water is 20% and ethanol, 80%.

(Video) Solutions 1 Molarity and Molality

The molar mass of pure water is MH2O.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (12)

Similarly, for ethanol,

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (13)

The molar mass of the mixture is Mmix.

Thus,

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (14) Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (15)

Measurement of Molar Mass

From Atomic Weight

The measurement from the atomic weight is the most reliable and precise method in comparison to others. The atomic weight is determined from the atomic mass and distribution of isotopes. The precision in the molar mass depends upon the precision in the measurement of the atomic weight, which depends on the atomic mass and the percentages of isotopes. Today, with the help of mass spectrometry, we are able to achieve high precision in the atomic mass.

The value of molar mass calculated from the atomic weight are reliable for all practical calculations.

From Vapour Density

The vapour density (ρ) is the mass of vapour to its volume. We are familiar with the ideal gas equation.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (16)

Here, P is the pressure of a gas occupying the volume V at the temperature T. n and R are the moles of the gas and the ideal gas constant.

Now, the number of moles (n) is the mass of the gas divided by the molar mass (M).

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (17)

Using the above two equations,

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (18) Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (19)

If we are able to determine the vapour density of a sample of gas for a known pressure and temperature, we can estimate the molar mass of the vapour from the above equation.

From Freezing-Point Depression

When a non-volatile solute is added into a solvent, the freezing point of the solvent decreases. This decrease is called freezing-point depression. Freezing-point depression ∆TF=TFsolventTFsolution depends on the concentration (molality) of the solute and is governed by the equation below.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (20)

Here, ∆T is freezing-point depression, KF is the solvent dependent cryoscopic constant, b is the molality, and i is the van ‘Hoff factor (number of ions formed after the dissociation of the solute).

For a very dilute solution, Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (21).

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (22) Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (23)

By knowing ∆TF, KF, wsolute, and i, we can determine the molar mass, Msolute.

From Boiling-Point Elevation

Boiling-point elevation is the rise in the boiling point of a solvent due to the presence of a non-volatile solute. Similar to freezing-point depression, the rise in the boiling point depends upon the molality.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (24)

Here, ∆TB=Tsolution−Tsolute is boiling-point elevation, KB is the ebullioscopic constant, b is the molality, and i is the van ‘t Hoff factor.

For a very dilute solution, Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (25)

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (26) Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (27)

By knowing ∆TB, KB, wsolute, and i, we can determine the molar mass, Msolute.

Examples and Calculations

Example 1: To Determine Molar Mass of Oleic Acid

Oleic acid is a odourless fatty acid having a molecular formula of C18H34O2. It has eighteen carbons, thirty-four hydrogens, and two oxygens.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (28)
Table 4: Molar Mass of Oleic Acid, C18H34O2
ElementNumber of AtomMolar Mass (gmol−1)Total
Carbon (C)1812.011216.198
Hydrogen (H)341.00834.272
Oxygen (O)215.99931.998
Molar Mass of Oleic Acid, (C18H34O2)282.468gmol−1

Therefore, the molar of oleic acid is 282.468gmol−1.

Example 2: To Determine Molar Mass of Reinecke’s Salt

Reinecke’s salt is a red crystalline salt with chromium in the centre as shown in the above figure. The chromium atom is surrounded by six nitrogens, four carbons, and four sulphur. The molecular formula is C4H12N7OCrS4.

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (29)
Table 5: Molar Mass of Reinecke's Salt, C4H12N7OCrS4
ElementNumber of AtomMolar Mass (gmol−1)Total
Carbon (C)412.01148.044
Hydrogen (H)121.00812.096
Nitrogen (N)714.00798.049
Oxygen (O)115.99915.999
Chromium (Cr)151.99651.996
Sulphur (S)432.065128.26
Molar Mass of Reinecke’s Salt, C4H12N7OCrS4354.444gmol−1

Example 3: To Determine Molar Mass of Air

Air is a mixture. It mainly consists 79% nitrogen (N2) and (21%) oxygen (O2). Other components are argon (Ar), carbon dioxide, (CO2), water (H2O), helium (He) etc., but these components are in small fraction and can be ignored.

The molar mass of nitrogen (N2) and oxygen (O2) are 28.014gmol−1 and 31.998gmol−1 respectively.

Table 6: Molar Mass of Air
MoleculesFractionMolar Mass (gmol−1)Total
Nitrogen (N2)0.7928.01422.13
Oxygen (O2)0.2131.9985.88
Molar Mass of Air≈28gmol−1

Therefore, the molar of air is 28gmol−1.

Example 4: To Determine Molar Mass of Sodium Chloride Solution

Sodium chloride a common salt. It is white and odourless powder. Consider a solution of 50% NaCl. 100g of the solution consists of 50g of NaCl and 50g of H2O.

The molar mass of water is 2×1.008+15.999=18.015gmol−1 and of sodium chloride is 22.99+35.45=58.44gmol−1.

(Video) Stoichiometry

The molar of the solution is calculated as follows:

Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (30) Molar Mass: Definition, Formula, Mole, Atomic Mass ~ ChemistryGod (31)

Thus, the molar mass of 50% sodium chloride solution is 28gmol−1.

Associated Articles

  • Mole
  • SI unit
  • Atomic mass
  • Atomic weight

FAQs

What is molar mass short answer? ›

It is defined as the mass of substance for a given amount. The amount of molecules or atoms or compounds present in one mole of substance is given by this. Molar mass SI unit is g/mol.

What is the formula of calculating molar mass? ›

Molar mass is the mass (in grams) of one mole of a substance. Molar mass of a compound can be calculated by adding the standard atomic masses (in g/mol) of the constituent atoms. For example: Molar mass of H2O. = 2× atomic mass of hydrogen + 1× atomic mass of oxygen= 2×1 +1×16= 18 g/mol.

What is molar mass 11th class? ›

- Molar mass is the mass of one mole of a given compound or substance. - We know that the number moles of a compound (n) are the ratio of given mass of the compound to the molar mass of the compound and can be expressed as follows.

What is molar mass and atomic mass? ›

Molar mass is the mass of the one mole of the compound whereas atomic mass is the mass of the individual unit of the compound. Basically, molar mass is the mass of an average of many elements of the compound and atomic mass is the mass of the atom.

What is a mole in chemistry? ›

A mole is a very important unit of measurement that chemists use. A mole of something means you have 602,214,076,000,000,000,000,000 of that thing, like how having a dozen eggs means you have twelve eggs. Chemists have to measure using moles for very small things like atoms, molecules, or other particles.

Is atomic mass a unit? ›

Atomic weight is measured in atomic mass units (amu), also called daltons. See below for a list of chemical elements and their atomic weights. … measured in terms of the atomic mass unit, which is defined to be 1/12 of the mass of an atom of carbon-12, or 1.660538921 × 1024 gram.

What is an atomic mass Class 9? ›

Atomic mass can be defined as the total mass of one atom of any given element. The unit of atomic mass is called the unified atomic mass unit (denoted by 'u'). Most of the atomic mass of a substance is made up of protons and neutrons. Therefore, it is almost equal to its mass number.

What is the unit of molar mass? ›

The units for molar mass are, therefore, grams/mole.

How do I calculate moles? ›

The unit is denoted by mol.
  1. The formula for the number of moles formula is expressed as.
  2. Given.
  3. Number of moles formula is.
  4. Number of moles = Mass of substance / Mass of one mole.
  5. Number of moles = 95 / 86.94.

What is mole fraction class 11? ›

Mole fraction of a particular component is defined as the number of moles of the same component of a solution to the total number of moles of all the constituents of the solution. Mole fraction is also known as the amount fraction. The expression of mole fraction of ith component in a solution is: xi=nintotal.

What is molarity in chemistry class 11? ›

Definition: Molarity of a given solution is defined as the total number of moles of solute per litre of solution.

What is the unit of molar mass Class 9? ›

The molar mass of a compound defines the mass of 1 mole of that particular substance and number of grams per mole of a compound. In other words, the molar mass is the total mass of all the atoms in grams that make a mole of a particular molecule. Therefore, the units of molar mass are grams/mole.

What is the mass of an atom? ›

The atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as daltons, D). The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope.

How do you find the atomic mass of Class 11? ›

To obtain the atomic mass of a particular atom, you simply add the number of protons and the number of neutrons present in the atom. For example, consider an oxygen atom having 8 electrons, 8 protons and 8 neutrons. Simply add 8 protons and 8 neutrons to obtain the atomic mass of oxygen.

What are 4 types of moles? ›

There are 4 common types of moles: congenital moles, dysplastic nevi, acquired nevi, and spitz nevi. Below are the differences between each.

What is the symbol of mole? ›

This number is also known as the Avogadro number and is denoted by , SI unit symbol is “mol”.

Who discovered mole? ›

A mole of any substance or particles is defined exactly as a constant, 6.02214076×1023 particles or we can call this as Avogadro's Number, which may be atoms, molecules, ions or electrons. The word mole is coined by the chemist Wilhelm Ostwald.

What is a molecule class 9? ›

A group of two or more than two atoms of the same or different elements that are chemically bonded together is called a molecule. For example, two atoms of hydrogen and one atom of oxygen react with each other and form one molecule of water.

What is an ion Class 9? ›

Answer : (a) An electrically-charged atom (or group of atoms) is called an ion. it is formed by the loss or gain of an electron by an atom. Ions are of two types: cations and anions. For example, A sodium ion (Na+ ) is formed when a sodium atom loses one electron.

What is the symbol for mass? ›

Mass (symbolized m) is a dimensionless quantity representing the amount of matter in a particle or object. The standard unit of mass in the International System (SI) is the kilogram (kg).

What are the first 20 elements? ›

Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, and Calcium are metals in the first twenty elements. Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Phosphorous, Sulphur, Chlorine, and Argon are the non-metals in the first twenty elements.

What are the 118 elements called? ›

118 Elements and Their Symbols and Atomic Numbers
Name of the ElementSymbol of the ElementAtomic Number
SodiumNa11
MagnesiumMg12
AluminiumAl13
SiliconSi14
69 more rows

What is the 30 elements? ›

The Elements, sorted by Atomic Number
Atomic NumberSymbolName
30ZnZinc
31GaGallium
32GeGermanium
33AsArsenic
76 more rows

What means molar mass? ›

The molar mass/molecular weight is actually the sum of the total mass in grams of the atoms present to make up a molecule per mole. The unit of molar mass is grams/mole.

Is mole a unit? ›

The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 x 1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol1 and is called the Avogadro number.

What is the value of 1 mole? ›

The value of the mole is equal to the number of atoms in exactly 12 grams of pure carbon-12 (12 g C = 1 mol C atoms = 6.022 × 1023 C atoms). Here some of the language of the current SI definition is incorporated.

What is no of moles? ›

The number of moles of a substance equals the ratio of its given mass in a chemical reaction to the mass of one mole of that substance. It can be interpreted as the number of moles possible for that given mass of the substance. It is denoted by the symbol n and its unit of measurement is mol.

How many atoms are in a mole? ›

The value of the mole is equal to the number of atoms in exactly 12 grams of pure carbon-12. 12.00 g C-12 = 1 mol C-12 atoms = 6.022 × 1023 atoms • The number of particles in 1 mole is called Avogadro's Number (6.0221421 x 1023).

How many grams are in a mole? ›

There are three steps to converting grams of a substance to moles: ▪ Step 1: Determine how many grams of a substance are in the problem. Use the periodic table to check the atomic mass, this is the number of grams per mole → 1 mole of Aluminum is 26.982 g ▪ Written as a fraction this is …

What is the unit of molality? ›

The SI unit of molality is moles per kilogram (mol/kg). For example, a solution whose molality is given as 6 mol/kg is stated as 6 molal or 6 m.

What is mole fraction unit? ›

Mole fraction is a unit of concentration, defined to be equal to the number of moles of a component divided by the total number of moles of a solution. Because it is a ratio, mole fraction is a unitless expression.

What means mole fraction? ›

Definition of mole fraction

: the ratio of the number of moles of one component of a solution or other mixture to the total number of moles representing all of the components.

What is molarity and its unit? ›

Molarity: The number of moles of solute per litre of solution. Unit of Molarity is moles/litre or M.

What is molality in chemistry? ›

Molality is defined as the “total moles of a solute contained in a kilogram of a solvent.” Molality is also known as molal concentration. It is a measure of solute concentration in a solution. The solution is composed of two components; solute and solvent.

What is molality class XI? ›

Molality: It is defined as the moles of the solute present in 1kg of the solvent. It is denoted by 'm'. Molality(m)=Mass of solvent in KgNumber of moles of solute.

What is mass made of? ›

Ordinary matter is made from atoms. The mass of atoms is overwhelmingly concentrated in their nuclei. The surrounding electrons are of course crucial for discussing how atoms interact with each other — and thus for chemistry, biology, and electronics. But they provide less than a part in a thousand of the mass!

How do atoms exist Class 9? ›

Atoms exist in free states in the form of molecule. Molecule may be formed by the combination of two or more similar atoms of an element, such asoxygen molecule is formed by the combination of two oxygen atoms, molecule of hydrogen which is formed by the combination of two hydrogen atoms.

Who discovered atomic mass? ›

The first scientists to measure atomic mass were John Dalton (between 1803 and 1805) and Jons Jacoband Berzelius (between 1808 and 1826). Early atomic mass theory was proposed by the English chemist William Prout in a series of published papers in 1815 and 1816.

How do you find the average atomic mass of an isotope in Class 9? ›

Hint: To calculate the average atomic mass, multiply the fraction by the mass number for each isotope, then add them together.

How do you find the atomic mass of the first 20 elements? ›

A simple way to get atomic mass of first 20 elements of the periodic table

How do you calculate mass number? ›

Together, the number of protons and the number of neutrons determine an element's mass number: mass number = protons + neutrons. If you want to calculate how many neutrons an atom has, you can simply subtract the number of protons, or atomic number, from the mass number.

What is molar mass class 9th? ›

Molar mass of a substance is that mass of the substance which contains one mole of substance. In simple terms, it is the weight of one mole of substance. To calculate the molar mass, the atomic mass of each substance is multiplied with the subscript of that element in the chemical formula.

What is molecular mass Class 9? ›

Molecular mass or molecular weight is the mass of a molecule. “The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance”. It is expressed in the atomic mass unit(u).

What is the unit of molar mass? ›

The unit to measure the mass of the compound is gram. The unit to measure the molar mass of the compound is grams per mole or g/mol. The molar mass is defined as the mass of 1mol, which is in the SI measured in g/mol.

What is an atom Class 9? ›

Explanation: An atom is the smallest unit of an element. In an atom, subatomic particles like protons and neutrons are present inside the nucleus and negatively charged electrons are present in the extranuclear part.

What is a chemical formula Class 9? ›

- A chemical formula is defined as a collection of chemical symbols that is used to show the elements present in any compound and its proportion. -For example: The chemical formula of water is H2O . It says that two hydrogen atoms combine with one oxygen atom to form one molecule of water.

How do you find a mole of Class 9? ›

The number of moles of a substance in a given pure sample can be represented by the following formula:
  1. n = N/NA ...
  2. Molar mass of a Substance = (Mass of the Substance in grams)/(Number of Moles) ...
  3. Number of Moles = (Mass of the Sample)/(Molar Mass) ...
  4. Number of Atoms or Molecules = (Number of Moles)*(6.022*1023)

What is a Valency class 9? ›

Valency is simply equal to the number of electrons gained, lost or shared by an atom of an element to achieve the nearest noble gas configuration. For example, the valency of sodium (Na) is 1, magnesium (Mg) is 2, Chlorine (Cl) is 1 etc.

What is the gram atom definition? ›

Definition of gram-atomic weight

: the mass of one mole of an element equal in grams to the atomic weight. — called also gram-atom.

What is an ion Class 9? ›

Answer : (a) An electrically-charged atom (or group of atoms) is called an ion. it is formed by the loss or gain of an electron by an atom. Ions are of two types: cations and anions. For example, A sodium ion (Na+ ) is formed when a sodium atom loses one electron.

What is molecular mass Toppr? ›

The molecular mass of a substance is the sum of atomic masses of all the atoms in a molecule of the substance. It is used for those substances whose constituent particles are molecules.

What means molar mass? ›

The molar mass/molecular weight is actually the sum of the total mass in grams of the atoms present to make up a molecule per mole. The unit of molar mass is grams/mole.

Is mole a unit? ›

The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 x 1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol1 and is called the Avogadro number.

What is the value of 1 mole? ›

The value of the mole is equal to the number of atoms in exactly 12 grams of pure carbon-12 (12 g C = 1 mol C atoms = 6.022 × 1023 C atoms). Here some of the language of the current SI definition is incorporated.

What is called atom? ›

atom, smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. As such, the atom is the basic building block of chemistry.

What is a molecule class 7? ›

A group of two or more than two atoms of the same or different elements that are chemically bonded together is called a molecule. For example, two atoms of hydrogen and one atom of oxygen react with each other and form one molecule of water. Suggest Corrections.

Who discovered atom? ›

John Dalton (1766-1844), a great chemist, really started the modern atomic hypothesis. His atom however was like a solid billiard ball.

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