Quantitative Analysis (1)

Question 1

Define

titration.

Answer 1

an experiment that lets you see what volume of a reactant is needed to react completely with a certain volume of another reactant

Question 2

Describe how you would carry out an

acid-alkali titration.

(12 steps)

Answer 2

1. Use a pipette with a pipette filler to measure out a set volume of alkali.
2. Put the alkali in a flask with a few drops of indicator.
3. Using a funnel, fill a burette with some acid of a known concentration and measure the starting volume.
4. Put the flask containing the alkali under the burette.
5. First, do a rough titration. Add the acid to the alkali a bit at a time, giving the flask a regular swirl.
6. When the indicator changes colour, calculate the amount of acid that was needed to neutralise the alkali. This is your rought titre.
7. Now, do an accurate titration. Take an initial reading of how much acid is in the burette.
8. Add acid until you are within 2ml of the end point.
9. Continue to add the acid drop by drop until you observe the indicator colour change.
10. Calculate the volume of acid used to neutralised the alkali.
11. Repeat this accurate titration until you have at least three concordant results (within 0.1ml).
12. Calculate the mean volume of acid that was needed to neutralise the alkali using your concordant results.

Question 3

Why isn’t

universal indicator suitable for titrations?

Answer 3

it changes colour too gradually

Question 4

What equation links

concentration, moles and volume?

Answer 4

moles = concentration x volume

n = CV

n: mol
C: mol/dm^3
V: dom^3

Question 5

What equation alolows you to convert concentration from

mol/dm^3 and g/dm^3?

Answer 5

C (g/dm^3) = C(mol/dm^3) x RFM

Question 6

Define

theoretical yield.

Answer 6

the amount you would get if all the reactants formed the desired products and none of the products were lost

Question 7

Define

yield.

Answer 7

the actual amount of product you actually get in reaction

Question 8

What is

percentage yield?

and how is this calculated?

Answer 8

it is a comparison between the yield you actually get and the theoretical yield

it is calculated using the equation:
percentage yield = actual yieldx100 / theoretical yield

Question 9

What are the main reasons why

percentage yields are never 100%?

(3 reasons with a brief explanation)

Answer 9

1. The reaction is incomplete - not all of the reactants are converted to products.
2. Product is lost during practical procedures - when transferring liquids, some of it always gets left behind on the surfce of the old container. Also, when filtering a solid from a liquid you always lose a bit of the liquid or solid.
3. Unexpected reactions may be happening - sometimes, unexpected side-reactions occur.

Question 10

Define

atom economy.

Answer 10

in a reaction, what percentage of the mass of the reactants ends up as a desired product

Question 11

What equation allows you to calculate

atom economy?

Answer 11

atom economy = total RFM of desired productsx100 / total RFM of all products

Question 12

What are the negatives of

reactions with low atom economies?

(3)

Answer 12

• they use up resources very quickly
• they make lots of waste materials that have to be disposed of
• they aren’t very profible as raw materials can be expensive and waste products can be expensive to dispose of properly

Question 13

What are some important factors that need to be taken into account when

choosing reactions in industry?

(3)

Answer 13

• percentage yield
• rate of reaction
• whether or not the reaction is reversible

Question 14

Define

molar volume.

and state what it is measured in.

Answer 14

the volume occupied by one mole of gas

this is measured in dm^3 / mol

Question 15

What equation allows you to calculate the

molar volume of a gas?

Answer 15

molar volume = gas volume / number of moles

Question 16

What equation links

gas volume and moles?

Answer 16

gas volume = moles x 24

V = n x 24

V: dm^3
n: mol