Atomic structure, analysis and quantitative chemistry Flashcards
What are the mass of subatomic particles and what is an atoms mass number?
proton and neutrons have a mass of 1, electrons have negligible mass
total number of protons and neutrons is called the atoms mass number
What is relative atomic mass and what are isotopes?
atoms of the same elements can have a different number of neutrons, these are the isotopes of the elements
The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element.
What is relative formula mass and moles?
the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
the relative formula mass of a substance, in grams, is known as one mole of that substance
What are the advantages of detecting elements/compound using instrumental methods?
accurate, sensitive and rapid
useful when the amount of the sample is small
How can chemical analysis be used in food?
identify additives in food
artificial colours can be detected by paper chromatography
some substances are better at dissolving in the water than bonding with the paper, as a result some substances move further
What is gas chromatography?
gas chromatography allows the separation of a mixture of compounds as they travel at different sppeds
the time taken for a substance to travel through the column can be used to help identify the substance
the gas chromatography column can be linked to a mass spectrometer, which can be used to identify the substances leaving the column
the mass spectrometer can give the relative molecular mass of the substances
How can the percentage of an element in a compound found?
(relative atomic mass / relative formula mass) x 100
How is empirical formula of a compound calculated?
1) find masses
2) find the atomic mass (Ar) of each element
3) divide masses by Ar
4) find the ratio (divide by smallest value)
[e.g.
3.2g of sulfur reacts with oxygen to produce 6.4g of sulfur dioxide
mass of oxygen reacted = 6.4 - 3.2 = 3.2
- 2/32 = 0.1
- 2/16=0.2
1:2 ratio, SO2]
How can you calculate mass of reactants and products from a balanced equation?
1) work out the Mr of the compounds, shows how much of one compound is needed to produce another
e. g.
CaCO3 -> CaO + CO2
if we have 50g of CaCO3, how much CaO can we make?
Mr of CaCO3 = 40 + 12 + 3(16) = 100
Mr of Cao = 40 + 16 = 56
therefore, 100g of CaCO3 would yield 56g of CaO
100 / 2 = 50, as we are given 50g of CaCo3 we must divide 56 by 2, 56 / 2 = 28
the mass of CaO would be 28g
Why is not always possible to obtain the calculated amount of a product?
the reaction may not be completed as it is reversible, some products can react to produce the original reactants
some of the product may be lost when it is separated from the reaction mixture
some of the reactants may react in different ways to the expected raction
How do you work out percentage yield?
(actual mass of product / theoretical mass of product) x 100
