Chem -Equations, calculations and electrolysis

Question 1

Relative atomic mass

Answer 1

Relative atomic mass

Relative atomic mass = total atomic mass of all the atoms added together

Question 2

Moles formula

Answer 2

Moles

Moles = mass/relative atomic mass

Question 3

Percentage yield formula

Answer 3

Actual yield/theoretical yield x 100 = percentage yield

Question 4

Water of crystallisation

Answer 4

Salts are made of positive ions and negative ions
Salts can either be hydrous or anhydrous
Hydrous = containing a water of crystallization
Anhydrous (after heated) = no water of crystallization
Eg: Heating hydrated magnesium sulfate, MgSO4.xH2O in a crucible forms anhydrous magnesium sulfate. MgSO4, use the experimental data below to find the value of X and write the formula of the hydrated salt.
Mass of empty crucible = 42g
Mass of crucible + MgSO4.xH2O = 45.210 g
Mass of crucible + MgSO4 = 43.567
Calculate moles of anhydrous magnesium sulfate and water.
Anhydrous magnesium sulfate: (43.567-42)/120 = 0.0131
Water: 1.643/18 = 0.0913 moles
Divide both molar values by the smallest between the 2:
1 mole of salt = 7 moles of water
therefore MgSO4.7H2O

Question 5

Concentration

Answer 5

Concentration (mol/dm^3) = moles/volume (dm^3)

1g = 1000 dm^3

Question 6

Calculating volume

Answer 6

Each mole of gas occupies 24 dm^3 (volume)

So volume = no. moles x 24