Moles And Chemical Calculations

Question 0

Define atomic mass

Answer 0

The number of protons and neutrons in the nucleus of an atom

Question 1

Define atomic number

Answer 1

The number of protons found in the nucleus of an atom

Question 2

Define relative atomic mass (RAM or Ar)

Answer 2

The average mass of the naturally occurring isotope of the element relative to the mass of an atom of carbon-12, which is given a mass of exactly 12.

Question 3

Define relative molecular mass , Mr (RMM) / relative formula mass (RFM)

Answer 3

The mass of a molecule of the compound relative to the mass of an atom of carbon-12, which is given a mass of exactly 12.

Question 4

Isotopes

Answer 4

Atoms of the same element which have the same number if protons but a different number of neutrons.

Question 5

Relative isotopic mass

Answer 5

Is the mass of the isotopic of an elements relative to 1/12 of the mass of a carbon-12 atoms.

Question 6

Mike

Answer 6

The amount of substance that has the same number of particles (atoms, molecules, ions etc) as the there are in exactly 12g of carbon-12 (6.023 x 10^23)

Question 7

Molar mass (g mol^-1)

Answer 7

The mass of one mole of a compound, expressed in grams. This one mole of carbon-12 has a mass of exactly 12g. One mole of sodium-23 has a mass of 23g and so on.

Question 8

Avogadro’s number

Answer 8

The number of particles in a mole I.e. 6.023 x 10^23 = 1 mole

Question 9

What is a weighted average?

Answer 9

For example, in any sample of chlorine, some atoms have a relative mass of 35 and others have a relative mass of 37. A simple average of 35 and 37 would be 36 but there aren’t equal numbers of c35 and c37 so it doesn’t work.
The weighted value is the average made of one atom.

Question 10

How do you work out the weighted average?

Answer 10

Eg 
35^Cl = 75%
37^Cl = 25%
Total mass of 100 atoms = (35x75)+(25+75) 
= 3550
The av. mass of one atom= 3550/100
=35.5

Question 11

How to work out the relative formula mass.

Answer 11

Add up the relative atomic masses.
Eg: MgCO3
RFM = 24+12 + (3x16)
= 84

Question 12

How to find the percentage composition if a compound

Answer 12

1. Find the RFM of the whole compound.
2. Find the RAM of what you are finding the composition of.
3. Divide the RAM by a the RFM and X 100

Question 13

Formula for mass (g)

Answer 13

No. of moles X mass of 1 mole (g)!

Question 14

What is the formula for no. of molee

Answer 14

Mass (g) / mass of 1 mole (g)