module 1: practical skills

Question 1

how do you know the melting point of an impure solid, when given the melting point range of compounds in the mixture

Answer 1

its NOT higher that the range of the pure compound

Question 2

why are anti-bumping granules used

Answer 2

to prevent very large bubbles from forming during the reaction

Question 3

why may a water bath or heating mantle be preferable to a bunsen burner

Answer 3

the temperature can be controlled more easily which is important when chemicals are flammable

Question 4

how is a pH probe calibrated

Answer 4

rinse the probe with distilled water, then shake to remove excess

place the tip in an acidic (pH4) solution and let sit till stabilised to correct pH and then repeat both steps with an alkaline solution (pH9)

Question 5

how does [H+] change with pH

Answer 5

each one unit increase in pH equals a 10x decrease in [H+]

Question 6

what are some safety precautions to take other than using safety glasses and a lab coat and why

Answer 6

using a fume cupboard as compounds may be toxic/poisonous

Question 7

how can you ensure that a reaction goes to completion

Answer 7

• heat until mass is constant
• break up solid reactant
• use an excess

Question 8

how can you find the melting point of a substance

Answer 8

• place a small amount of the solid in a capillary tube
• gently tap to get the solid to fall to the bottom
• place the tube in a beaker of oil with a very sensitive thermometer
• slowly heat and stir constantly until the solid just melts and read the temp

Question 9

how do melting/boiling points differ with pure and impure substances

Answer 9

pure: very specific mp and bp
impure: lower mp and raised bp
very impure: mp and bp will be over a wide range of