reaction types important info

Question 1

What is stoichiometry

Answer 1

Stoichiometry is the study of more relationship involved in chemical reactions

Question 2

What are potential reasons for why percentage yield may be reduced

Answer 2

The percentage yield can be reduced by: mass transfer, and side reactions

Question 3

What is the meaning of ‘weighing by difference approximately’

Answer 3

Means to weigh roughly 5g but know the exact weight

Question 4

What is gravimetric analysis used to determine

Answer 4

Grav analysis is used to determine the mass of an element or a compound in a substance

Question 5

Mixed-melting point

Answer 5

if melting point range is lowered and widened, it means that the two are different compounds
If melting point stays the same it’s likely the two compounds are identical

Question 6

Mixed melting point determination

Answer 6

involves mixing a small quantity of the product with some of the pure compound (50% each) and determining the melting point. If the melting point turns out to be sharp and close to the expected value, then the two substances must be identical. If the two substances are not similar, then the melting point of the mixture will be much lower and the melting range much broader.

Question 7

What is distillation

Answer 7

Its an experimental technique used to separate liquids with different boiling points

Question 8

What is distillation used for

Answer 8

Distillation can be used to purify a compound by separating it from less volatile substances in the mixture

Question 9

How can distillation be used to identify compounds

Answer 9

Distillation is used for identification and purification of organic compounds.
The boiling point of a compound, determined by distillation, is one of the physical properties that can be used to confirm its identity

Question 10

What is heating under reflux

Answer 10

When carrying out heating under reflux, the reaction mixture is placed in a round-bottomed flask with anti-bumping granules and the flask is fitted with a condenser. The flask is then heated using an appropriate source of heat.

Question 11

What is the purpose of heating under reflux

Answer 11

Heating under reflux allows heat energy to be applied to a chemical reaction mixture over an extended period of time without volatile substances escaping.

Question 12

What is the purpose of recrystallisation

Answer 12

Recrystilisation is a tedhnique used to purify an impure solid

Question 13

What is the process of recrystallisation

Answer 13

dissolving an impure solid gently in a minimum volume of a hot solvent
hot filtration of the resulting mixture to remove any insoluble impurities
cooling the filtrate slowly to allow crystals of the pure compound to form, leaving soluble impurities dissolved in the solvent
filtering, washing and drying the pure crystals

Question 14

What is the purpose of solvent extraction

Answer 14

Solvent extraction involves isolating a solute from a liquid mixture or solution by extraction using an immiscible solvent in which the solute is soluble.

Question 15

What is the process of solvent extraction

Answer 15

When carrying out a solvent extraction, the two immiscible solvents form two layers in the separating funnel. The solute dissolves in both solvents and an equilibrium establishes between the two layers. The ratio of solute dissolved in each layer is determined by the equilibrium constant, K . The lower layer is run off into a container and the upper layer is poured into a second container. This process is repeated to maximise the quantity of solute extracted. The quantity of solute extracted is greater if a number of extractions using smaller volumes of solvent are carried out rather than a single extraction using a large volume of solvent.

Question 16

What is the melting point of a substance

Answer 16

The melting point of a substance is the temperature range over which the solid state to melt, to when all of the solid has melted

Question 17

How can the identity of a pure compound be confirmed

Answer 17

To the identity of a pure compound can be confirmed by melting point analysis and a comparison of the experimentally determined melting point with a literature or known melting point value

Question 18

How can melting point give an indication of any impurities

Answer 18

Determination of the melting point of a compound can give an indication of the purity of a compound. A broader lower range suggests impurities

Question 19

What is TLC

Answer 19

Chromatography is a technique used to separate compounds present within a mixture, it separates substances by making use of differences in polarity, or molecular size.

Question 20

What is the retention factor

Answer 20

Rf= distance travelled by the sample/ distance travelled by the solvent. A determining agent or UV light is normally required to visualise the spots in the chromatogram. Under the same conditions (temp, solvent, solution levels) a compound always has the same Rf value

Question 21

What is TLC used to assess

Answer 21

TLC is used to assess the purity os substances. A pure substance, when spotted and developed on a TLC plate, should appear as a single spot, the presence of more than one spot shows that impurities are present

Question 22

A primary standard must:

Answer 22

be available in a high state of purity
 be stable when solid and in solution
 be soluble
 have a reasonably high GFM

Examples of primary standards include:
 sodium carbonate, Na2CO3