atoms. molecules and stoichometry

Question 1

what is an atom

Answer 1

smallest particle into which an element can be divided without losing its identity

Question 2

what is a molecule

Answer 2

a group of atoms held by covalent bonds which is capable of independent existence in a compound

Question 3

what is relative atomic mass

Answer 3

the average mass of one atom of the element compared to 1/12 the mass of an atom of 12C isotope expressed on the 12C scale

Question 4

what is the formula for Ar

Answer 4

average massof one atom of an element/1/12 x mass of one atom of 12C

Question 5

what is relative molecular mass

Answer 5

the average mass of one molecule of the substance to 1/12 the mass of an atom of 12C isotope being expressed on the 12Cscale

Question 6

what is the formula for relativemolecular mass(Mr)

Answer 6

average mass of one molecule in a substance/1/12 x mass of one atom of 12C

Question 7

what is relative isotopic mass

Answer 7

the mass of one atom of the isotope compared to 1/12 the mass of an atom of 12C isotope, expressed on the 12C scale

Question 8

what is the formula for relative isotopic mass (RIM)

Answer 8

mass of one atom of the isotope/1/12 x mass of one atom of 12C

Question 9

what are moles

Answer 9

• mole is the unit of the amount of substance
• one mole of a substance contains as many particles of that substance as there are atoms of carbonin 12 grams of 12C
• when mole is used, the particles must be stated (atoms, molecules, ions or electrons)
• 1 mole of any substance has a mass in grams automatically equal to its Ar or Mr

Question 10

what is the avogadro constant

Answer 10

• number of entities in sample or amount of substance in sample
• had been determined to experimentally have a value of 6.02x10^23 per mole
• one mole of any substance is the amount of substance containing a number of particles equal to the avogadro constant

Question 11

what is empirical formula

Answer 11

simplest formula which shows the ratio of the atoms of the different elements in the compound

Question 12

what is molecular formula

Answer 12

shows the actual number of atoms of each element present in one molecule of a compound

Question 13

what is the molar volume of gases

Answer 13

• 1 mole of any gas occupies a volume of 22.4 dm3 at s.t.p o 24 dm3 at r.t.p
• equal volume has same moles but different mass

Question 14

what is s.t.p

Answer 14

• standard temperature and pressure
• 0 degrees celcius
• 1 atm pressure

Question 15

how may the concentration of an aqueous solution be expressed

Answer 15

• either as mass of solute per dm3 (gdm^-3)

- or mole of solute perdm3 (moldm^-3)

Question 16

what happens to moles after dilution

Answer 16

-when a given volume of solution is diluted, the number of mles of solute remains unchanged after dilution