C7 Chemical Calculations With Moles

Question 1

Equation for concentration of a solution and moles

Answer 1

Concentration of solution (mol/dm^3) = number of moles of solute / volume of the solution (dm^3)

Question 2

Equation for percentage yeild

Answer 2

Percentage yield = (actual yield / theoretical yield) x 100

Question 3

Equation for atom economy

Answer 3

Atom economy = (Mr of useful product / Mr of all products) x 100

Question 4

Equation for moles in a gas

Answer 4

Moles of gas = volume (dm^3) / 24dm^3

Question 5

Why do we use titration

Answer 5

Titration is an experimental technique used to work out the concentration of an unknown solution in the reaction between an acid and alkali

Question 6

What indicator do we use in the conical flask at the bottom of the titration

Answer 6

Phenolphthalein or Universal indicator

Question 7

Why should you place the conical flask on a white tile

Answer 7

So you can clearly see change in colour of the indicator used. This increases the accuracy of the titration.

Question 8

Why should you swirl the conical flask during titration

Answer 8

So the acid and alkali neutralise when they should. This increases overall accuracy of your results

Question 9

To increase accuracy of your results, what should you do while taking readings from the Burette during titration.

Answer 9

Take the readings from the bottom of the meniscus (curved line that marks the surface of the solution)

Question 10

When calculating the mean of a titration, what should you do

Answer 10

Only use concordant (within 0.1cm^3 of each other) results to calculate the mean accurately while discarding anomalous results