Atomic structure and quantitative chemistry

Question 1

For an atom on the periodic table, what does the larger number represent?

Answer 1

The mass number; the number of protons plus neutrons.

Question 2

For an atom on the periodic table, what does the smaller number represent?

Answer 2

The atomic number; the number of protons.

Question 3

What is the relative atomic mass of a proton?

Answer 3

1.

Question 4

What is the relative atomic mass of a electron?

Answer 4

Very small (1/2000).

Question 5

What is the relative atomic mass of a neutron?

Answer 5

1.

Question 6

Atoms of the same elements with different numbers of neutrons are known as what?

Answer 6

Isotopes.

Question 7

The relative atomic mass of an atom of an element is relative to what?

Answer 7

The 12^C atom.

Question 8

The relative atomic mass displayed on a periodic table is an average of what?

Answer 8

An average of the relative atomic mass for the isotopes of that element.

Question 9

Relative formula mass of a compound is what?

Answer 9

The relative atomic masses of all the atoms in the compound combined.

Question 10

The relative formula mass of a substance in grams is known as what?

Answer 10

A mole of that substance.

Question 11

Elements and compounds can be detected accurately by using what type of methods?

Answer 11

Instrumental methods.

Question 12

Advantages of using instrumental methods:

Answer 12

Accurate.
Sensitive.
Rapid.
Small samples required.

Question 13

An example of a use of chemical analysis.

Answer 13

Eg: identifying additives in food.

Question 14

Artificial colours in foods can be detected and identified by what method?

Answer 14

Paper chromatography.

Question 15

Gas chromatography (GC) can be linked to what to help identify substances?

Answer 15

A mass spectrometer making GC-MS a method of identifying substances.

Question 16

How does GC-MS work?

Answer 16

Gas chromatography allows for the separation of a mixture of compounds.
The time taken for a substance to travel through the column can be used to help identify the substance.
The output of the GC can be linked to a MS which can be used to identify the substance.
MS can also give the relative molecular mass of each substance in the column.

Question 17

Molecular ion peaks on a graph from a MS show what?

Answer 17

The relative molecular mass of the substance.

Question 18

Number of peaks on a GC graph show what?

Answer 18

The number of substances present.

Question 19

Position of a peak on a GC graph shows what?

Answer 19

Retention time of the substance which can be used to identify the substance as different substances have different retention times.

Question 20

The percentage of an element in a compound can be calculated how?

Answer 20

RFM of compound/RAM(RFM) of element x100

Question 21

Empirical formula of a compound can be found how?

Answer 21

Find the mass of each reactant.
Find the molar mass of each.
Find the number of moles for each.
Then do the amount for each divided by the smallest amount out of each of them.
Left with a ratio.

Question 22

What is empirical formula?

Answer 22

The simplest whole number ratio of elements in a compound. This can be the same as the actual number of atoms but not always.

Question 23

How do you calculate masses of reagents/products?

Answer 23

E - check it is a balanced equation.
M - calculate moles of substance you know.
R - find reacting ratio of two things in question.
M - find mass of unknown in grams.

Question 24

True or false, in a chemical reaction atoms can be gained or lost.

Answer 24

False, in a chemical reaction atoms can neither be created nor destroyed, they may however be used in another chemical reaction at the same time.

Question 25

Reasons why never 100% yield in a chemical reaction:

Answer 25

Reaction may not be completed as it may be reversible.
Some of the product may be lost when it is separated from reaction mixture.
Some reactants may react in different ways from the expected reaction.

Question 26

Amount of product obtained is known as the…

Answer 26

…yield.

Question 27

When yield is compared to the maximum yield it is known as the what?

Answer 27

Percentage yield.

Question 28

What is the term used to describe a reaction where the products of the reaction can react to produce the original reactants?

Answer 28

Reversible reactions.

Question 29

A reversible reaction can be shown in the form:

Answer 29

A + B Equilibrium symbol C + D

Question 30

Example of a reversible reaction:

Answer 30

Eg:

Ammonium Chloride Equilibrium symbol Ammonia + Hydrogen Chloride