Chemical Calculations

Question 1

Word equation of mass

Answer 1

mass = number of moles x Ar

Question 2

Percentage yield = ?

Answer 2

percentage yield = actual mass /theoretical mass x100%

Question 3

What is yield

Answer 3

The yield of a chemical reaction describes how much product is made

Question 4

Percentage atom economy

Answer 4

relative formula mass of the desires product from equation/sum of the relative formula masses of the reactants from equation x100%

Question 5

Maximise atom economy

Answer 5

Less waste
Little energy
Little raw materials
Reduces pollution
Conserves limited resources
Better for environment

Question 6

Concentration = ?

Answer 6

Concentration = amount of solute (g)/volume of solution (dm3)

Question 7

Titration

Answer 7

1) Measure 25cm3 of solution of known concentration using a pipette
2) Add to conical flask with few drops of indicator and place on white tile
3) Fill burette using unknown solution
4) Read initial volume, open tap adding solution to flask while swirling flask
5) When colour changes turn off tap and read volume burette, from the bottom of the meniscus to the nearest 0.05 cm3
6) Repeat again, adding solution drop by drop near end point
7) Keep repeating until 2 results are within 0.1cm3
8) Calculate mean of the 2 results

Question 8

Why it is not always possible to obtain the calculated amount of product from a reaction

Answer 8

Reaction may not go to completion because its reversible
Some of the product may be lost when it is separated from the reaction mixture
Some of the reactants may react in ways different to the expected reaction
The product being in multiple states and difficult to measure