Chemical Calculations

Question 1

What is an atom

Answer 1

The smallest part of an element

Question 2

What is the molecular formula

Answer 2

A chemical formula that shows the actual numbers of the different types of atom in a molecule

Question 3

What is the empirical formula

Answer 3

A chemical formula to show the simplest ratio of the numbers of atoms in a compound

Question 4

What is the atomic number

Answer 4

The number of protons in a nucleus of an atom or an element

Question 5

What is the mass number

Answer 5

The number of protons + the number of neutrons in an element

Question 6

What does the period show in the periodic table

Answer 6

How many shells there are

Question 7

what does the group show in the periodic table

Answer 7

How many electrons in the last shell

Question 8

Iron has a 26 electrons
30 neutrons
Work out the:
Atomic number =
Mass number = 
Number of protons=

Answer 8

Atomic number = 26
Mass number = 56
Number of protons = 26

Question 9

What is an isotope

Answer 9

Isotopes are atoms of the same element with a different number of protons

Question 10

What is the relative atomic mass

Answer 10

Is the average mass of an atom of an element, compared to 1/12th of the mass of carbon.

Question 11

Work out the relative atomic mass of this:
75% of chlorine atoms are the type 35CI
25% of chlorine atoms are the type 37CI

Answer 11

= 75 x 35 + 25 x 37
————————–
100
= 35.5

Question 12

What is the relative formula mass (Mr)

Answer 12

Add up the relative atomic masses to give you the relative formula mass of the whole compound

Question 13

Find the relative formula mass of MgCO3

Answer 13

Mg = 24
C = 12
O = 16, (16 x 3) = 48
24 + 12 + 48 = 84
Mr = 84

Question 14

How do you find the empirical formula of a magnesium oxide using experiments data.
(Practical we did)

Answer 14

Find the mass of an empty crucible lid

Take a clean piece of magnesium, coil it up and place in crucible

Find the mass of the crucible + lid

Heat the crucible strongly using tongs, occasionally lift the lid to allow oxygen to reach the magnesium.

When the magnesium no longer glows, remove the lid and heat strongly for a minuet.

Allow crucible to cool and re-weigh it

Question 15

Give 3 reasons on why the practical about the empirical formula of magnesium oxide, was not that reliable

Answer 15

By lifting the lid, you are letting some magnesium oxide escape, (smoke).

The magnesium may have been coated in a layer of oxide, affecting the results.

Before the start of the experiment, there was no guaranteeing that there wasn’t some hidden substance in the crucible that could of affected the results in any way

Question 16

Give the word equation for the practical about finding the formula of copper oxide

Answer 16

Copper oxide + methane = water + carbon dioxide + copper

Question 17

Explain the practical with methane and copper oxide

And give 3 possible hazards preventions

Answer 17

Copper oxide is heated in a stream of gas, (methane)

The gas is a reducing agent; it removes the oxygen from the copper to make pure copper and water.

Run gas through first so no chance of an explosion
Burn of excess gas
Flame on a safety flame, coming out of the tube