C2.3 - Atomic Structure, Analysis and Quantitative Chemistry Flashcards
Which number is usually shown on the top of an element in the periodic table?
The Mass Number
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
Negligible
What is the mass number?
The total number of protons and neutrons in an atom.
What are isotopes?
Atoms of the same element that have different numbers of NEUTRONS.
What is the relative mass of an element compared to?
The C12 isotope
What is the Relative Formula Mass?
The sum of the relative atomic masses of the atoms shown in the formula.
How would you describe one mole of a substance?
The relative formula mass f a substance, in grams.
How can elements and compounds be detected and identified?
Using instrumental methods.
What are the advantages of instrumental methods?
They are accurate. sensitive and rapid and are useful when the amount of a sample is very small.
How can artificial colours in foods be detected?
Using paper chromatography.
What does gas chromatography allow?
The separation of a mixture of compounds.
How does gas chromatography work?
- Different substances, carried by a gas, travel through a column packed with solid material at different speeds, so that they become separated.
- The number of peaks on the output of a gas chromatograph shows the number of compounds present.
- The position of the peaks indicates retention time.
Why is a mass spectrometer linked to a gas chromatography column?
- It can be used to identify the substances leaving the end of the column.
- It can also give the relative molecular mass of each of the substances separated in the column, because the molecular mass is given by the ion peak.
How can the percentage of an element in a compound be calculated?
From the relative mass of the element in the formula and the relative formula mass of the compound.
How is the empirical formula calculated?
From the masses or percentages of the elements in a compound.
How can the masses of reactants and products be calculated?
From balanced symbol equations.
Why may it not be possible to obtain 100% yield in a chemical reaction?
- The reaction may not go to completion because it is reversible
- Some of the product may be lost when it is separated from the reaction mixture
- Some of the reactants may react in different ways from the expected reaction
What is the amount of product obtained called?
The yield
What is the percentage yield?
When the yield is compared with the maximum theoretical amount as a percentage.
What is a reversible reaction?
When the products of the reaction can react to produce the original reactants.
