Chapter 2 - Atoms, Ions and Compounds

Question 1

Mass Defect

Answer 1

Due to strong nuclear forces in the nucleus that are holding together the protons and neutrons, creating a loss of their mass instead.

Question 2

What is the mass of 1 atom of Carbon

Answer 2

1.992646 * 10(-26) kg

Question 3

Relative isotopic mass

Answer 3

The mass of an isotope relative to 1/12th the mass of an atom of C-12

Question 4

Relative atomic mass

Answer 4

The weighted mean mass of an atom of an element relative to 1/12th the mass of an atom of C-12.

Question 5

Mass spectrometer

Answer 5

1. Sample is placed
2. Sample is vaporised
3. An electrically heated metal coil gives off a stream of electrons that collides with the atoms. It leaves positively charged ions
4. The ions are accelerated. The heavy ions move slower, and the lighter ones move faster.
5. The ions are detected on a mass spectrum as a mass-to-charge ratio. The greater the abundance, the larger the signal.

Question 6

Mass-to-charge ratio

Answer 6

relative mass of an ion/ relative charge on ion

Question 7

Fragmentation of ions

Answer 7

A process that occurs inside the mass spectrometer. Atoms are hit against fast electrons.
M (g) + e- -> M+ (g) = 2e-

M+ is a molecular ion.
If a covalent bond in the molecular breaks, fragmentation happens. This produces an ion and a free radical (an atom with an unpaired electron.it is very reactive)
Only the ions are attracted to the charge plates.

Question 8

Mass spectogram

Answer 8

The peak on the furthest right side on the x axis is the mass of the element.

Question 9

What is the charge of a proton

Answer 9

+1.602 * 10(-19) C

Question 10

What is the charge of electrons

Answer 10

• 1.602 *10(-19) C

Question 11

How to work out the relative atomic mass using %

Answer 11

(% * isotope) + (% * isotope)/ 100

Question 12

metal ions

Answer 12

They are on the left of the periodic table

They lose electrons to form cations

Question 13

non-metal ions

Answer 13

They are on the right of the periodic table. They gain electrons to form anions.

Question 14

why are the neutrons important

Answer 14

they hold the nucleus together. Because all the protons will continue to repel each other.

Question 15

Heavy water

Answer 15

They contain the 2H isotope, referred to as deuterium. Heavy water has a higher melting and boiling point, along with a much higher density.

Question 16

atomic mass unit

Answer 16

The mass of a carbon-12 isotope is exactly 12 atomic mass units.
The standard mass for atomic unit is 1u, the mass of 1/12 of an atom of carbon. Therefore, 1u = a proton or a neutron.

Question 17

What does the weighted mean mass take into consideration

Answer 17

% abundance of each isotope

relative isotopic mass of each isotope

Question 18

How can you determine the relative atomic mass of a metal

Answer 18

You know that 1 mole of any gas will always occupy 24dm3 of volume. We can use this to figure out what metal is being used. If a group 1 metal reacts with water, this happens:
2M + 2H20 -> 2MOH + H2
The hydrogen gas can be collected over water because it’s not very soluble (cannot dissolve in the water)
It can be bubbled through a trough and into a measuring cylinder, where it can displace the water. The volume of gas can be measured and the identity of the metal can be found.

Question 19

Method for determining the relative atomic mass of a metal

Answer 19

1. set up apparatus
2. make sure that the 250cm3 measuring cylinder has been filled to the top with water.
3. record the volume of gas in the measuring cylinder
4. pour 100cm3 of distilled water into the conical flask
5. remove the metal from the oil and shake it so there is as little oil on it as possible. using a filter paper, remove as much oil
6. weigh the metal and take a note of this.
7. add it to the water immediately after, replacing the bung asap
8. hydrogen gas will be produced. Wait until the gas volume stays constant and measure this.

Question 20

what is a hydrated salt

Answer 20

it contains water of crystallisation

Question 21

explain how to find the formula of a hydrated salt

Answer 21

When a hydrated salt is heated, the water evaporates and you are left with the anhydrous salt. By recording the mass of the salt before and after heating, you can find its formula by calculating the moles and the simplest whole number ratio.

Question 22

method for finding the formula of a hydrated salt

Answer 22

1. set up experiment
2. weigh an empty crucible
3. add 2g of the hydrated salt and reweigh
4. heat gently (airhole half open) for 1 minute and then strongly for 5
5. leave to cool for 5 mins
6. heat strongly for 1 min
7. reweigh
   repeat until the mass stays constant
   stop heating if a red coloration appears in the white powder.

Question 23

what is the mass of water removed (PAG)

Answer 23

mass of crucible and hydrated salt - mass of crucible and salt after heating

Question 24

what is the mass of anhydrous salt remaining (PAG)

Answer 24

mass of salt after heating - mass of crucible

Question 25

if the question says :

deduce the simplest whole number ratio of the anhydrous salt: water what do you do

Answer 25

use the empirical formula

1. find moles of water
2. moles of salt
3. divide both by the smallest number of moles
4. deduce a simplest whole number ratio