Calcs

Question 1

Empirical formula

Answer 1

Simplest whole number ratio of atoms of each element in a compound

Question 2

Atom economy

Answer 2

Molar mass of desired product/ sum of molar masses of all products x100

Question 3

Colour of phenolphthalein in acid

Answer 3

Colourless

Question 4

Colour of phenolphthalein in alkali

Answer 4

Pink

Question 5

Colour of methyl orange in alkali and in acid

Answer 5

Alkali- yellow
Acid- red

Question 6

Calculating percentage error for double measurement apparatus (eg burette)

Answer 6

2 x tolerance/ reading x 100

Question 7

Measuring molar volume of a gas eg between HCl and CaCO3

Answer 7

Add known mass of calcium carbonate to excess acid and measure the total volume of CO2 released on reaction completion
Repeat with different masses of calcium carbonate
Graph of volume of CO2 against mass of calcium carbonate and pick a point on the line of mass
Calculate moles of calcium carbonate then use for moles of CO2
Use graph to find volume of co2 given off at that mass
Molar volume is this volume divided by the mole of co2

Question 8

Making a standard solution of NaOH

Answer 8

Calculate moles and mass of NaOH needed
Weight out this mass using a top pan balance
Dissolve in a minimum volume of distilled water in a (250cm3) beaker using a glass stirring rod
Transfer solution to rinsed (250cm3) volumetric flask using a funnel
Rinse beaker with distilled water and add to the volumetric flask
Make up volumetric flask to the mark with more distilled water
Invert to ensure solution is homogenous

Question 9

Setting up a titration

Answer 9

Rinse burette with distilled water then with solution (acid or alkali) being used (removes excess H2O that would dilute the solution and increase mean titre)
Fill burette, tap to remove air bubbles that would make titration larger than expected
Take meniscus into account
Rinse conical flask with distilled water
Rinse pipette with distilled water then with solution as the water dilutes and decreases mean titre

Question 10

Performing a titration notes

Answer 10

Swirl conical flask- homogenous
Rough titre
Concordat results
Add drop my drop
Read meniscus at eye level
Rinse inside conical flask with distilled water near end point

Question 11

Percentage yield

Answer 11

Actual yield/ theoretical yield x 100

Question 12

Finding XH2O

Answer 12

Find number of moles of salt and number of moles of water
Divide both by the smallest number to give a ratio

Question 13

Molecular formula

Answer 13

Mr molecular/ Mr empirical