mole concept and stoichiometry

Question 1

define relative atomic mass (Ar)

Answer 1

the relative atomic mass of an atom is the average mass of one atom of that element compared to 1/12 of the mass of one carbon-12 atom

Question 2

formula of relative atomic mass

Answer 2

average mass of one atom of the element / 1/12 the mass of an mass of an atom of carbon-12 (Ar has no unit)

Question 3

why are some Ar values of some elements not whole numbers?

Answer 3

relative abundance of all the isotopes of the elements. The amount of an isotopes in an element expressed in percentage

Question 4

define relative molecular mass (Mr)

Answer 4

The relative molecular mass of a molecular substance is the average mass of one molecules of that element or compoundto 1/12 of the mass of one carbon-12 atom

Question 5

formula of relative molecular mass

Answer 5

average mass of one molecule of an element or a compound / 1/12 mass of an atom of carbon-12 (Mr has no unit)

Question 6

what is a mole?

Answer 6

1. a unit measurement for very small particles such as atoms, molecules, ions and electrons
2. represented by mol
3. a mole of a substance contains the same number of particles as the number of atoms in 12g of carbon-12

Question 7

avogadro’ s number

Answer 7

one mole of any substance contains 6x10 23 particles -> avogadro’s constant

Question 8

how to calculate number of particles?

Answer 8

no. of particles= no. of mass x 6x10 23

Question 9

how to calculate number of moles?

Answer 9

number of particles / 6 x 10 23

Question 10

what is a molar mass?

Answer 10

the mass of one mole of any substance
1. they have the same numerical value as Ar
2. the unit for molar mass is g/mol

Question 11

how to calculate number of moles of a substance?

Answer 11

mass of the substance in g / molar mass of the substance in g/mol

Question 12

relationship between number of moles, mass and molar mass.

Answer 12

mass / moles l molar mass

Question 13

how to find the percentage composition of a compound?

Answer 13

percentage by mass of an element in a compound= Ar of the element x number of atoms of the element in the formula / Mr of the compound x 100%

Question 14

what is a empirical formula?

Answer 14

1. simplest formula of a compound
2. shows the types of elements present in the compound
3. shows the simplest ratios of the different types of atoms in the compound

Question 15

what is a molecule formula?

Answer 15

it shows the exact number of atoms of each element in a molecule

Question 16

avogadro’ s law

Answer 16

equal volumes of all gases, under the same temperature and pressure, contain the same number of particles. [same no. of moles of particles]

Question 17

what is molar gas volume ?

Answer 17

one mole of any gas occupies 24 dm3 at room temperature and pressure. 24 dm3 is called the molar volume of a gas at rtp.

Question 18

formula for no. of moles of gas? [in dm3]

Answer 18

volume of gas in dm3 /24dm3

Question 19

formula for no. of moles of gas? [in cm3]

Answer 19

volume of gas in cm3 / 24 000cm3