Empirical formulae

Question 1

a molecule is

Answer 1

a group of two or more atoms joined together by covalent bonds

Question 2

a molecule of water can be represented by the formula

Answer 2

H2O

Question 3

the term ‘empirical’ indicates that some information has been found

Answer 3

by experiment

Question 4

an empirical formula

Answer 4

shows the smallest whole-number ration of atoms of each element in a compound

Question 5

an oxide of copper is

Answer 5

a black solid

Question 6

copper oxide can be converted into copper by

Answer 6

removing the oxygen

Question 7

the stages of the experiment for converting copper oxide into copper are:

Answer 7

placing a known mass of copper in a tube and heating it in a stream of hydrogen gas, and the oxygen is removed. The copper is then reweighed.

Question 8

the colour change from copper oxide to copper is

Answer 8

black to orange-brown

Question 9

when heating copper oxide to convert to copper, and reweighing the copper, it is good practise to

Answer 9

heat the copper again to check if the mass changes. A constant mass when heated should indicate that the conversion is complete

Question 10

the first step for calculating empirical formula is

Answer 10

divide the mass, or percentage composition by mass, of each element by its relative atomic mass

Question 11

relative atomic mass is

Answer 11

the number pf protons and neutron in the atom of an element

Question 12

the second step in calculating empirical formula is

Answer 12

dividing the answers to step 1 by the smallest answer if necessary

Question 13

when calculating empirical formula from combustion analysis, you need to

Answer 13

calculate the masses of carbon and hydrogen in the products as they come from the organic compound being burned and not the combustion

Question 14

you can calculate the mass of carbon from carbon dioxide in combustion analysis by

Answer 14

dividing the relative formula mass of the product (carbon dioxide, 44.0) by the relative atomic mass of carbon (12.0) and then multiply this answer by the mass of CO2 obtained in the experiment

Question 15

you can calculate the mass of hydrogen from the water produced in combustion analysis by

Answer 15

dividing the relative formula mass of the product containing hydrogen (water, 18.0) by the relative formula mass of hydrogen (2 x 1.0= 2.0) and multiply this answer by the actual mass of H2O obtained in the experiment

Question 16

if the subscripts in a formula will reduce, such as C6H12O6, then it is

Answer 16

not an empirical formula