Calculations Flashcards
How can you calculate the relative formula mass for calcium chloride
CaCl2
1 x 40 =40 Ca
2 x 35.5 =71 Cl
40 + 71
= 111
Mr = sum of Ar
How can you calculate the number of moles of a substance
Mass/Mr
What is percentage yield
Actual mass/theoretical mass x 100%
Describe how to find empirical formula
Find the mass of a substance
Find the Mr
Find the number of moles
Divide by smallest mole value
Why does the mass of a hydrated substance decrease when it is heated
It is dehydrated, water molecules add mass and the removal of these molecules reduces the mass
How can you find empirical formula through the use of combustion reactions
Heat a crucible to remove contamination
Weight it and the lid
Add a magnesium ribbon and weigh it
Heat the crucible and leave a little gap for oxygen to enter
Leave for 10 minutes
Allow the crucible too cool and reweigh the crucible and its contents
How can you find empirical formula through the use of reduction reactions
Use a balance to measure the weight of a test tube with a rubber bung
Add copper (II) oxide and weight the tube again
Turn on the gas and light the gas by holding a burning splint next to the hole in the test tube
Use a Bunsen burner to heat the test tube for 10 minutes Allow
Leave the tube to cool
Reweigh the tube and its contents
How can you calculate molar enthalpy change
Divide the heat energy transferred by the number of moles
