(U3) Practicals

Question 1

Give the colour changes for Phenolphthalein and Methyl Orange

Answer 1

1. phenolphthalein :

• colourless in acid.
• pink in alkaline solutions.
• colourless in neutral solutions

2. methyl orange :

• red in acid.
• yellow in alkaline solutions.
• yellow in neutral solutions

Question 2

During any titrations, how do you ensure all chemicals are transferred between apparatus?

(2)

Answer 2

• Rinse apparatus with deionised water in a wash bottle
• transfer washings into the appropriate container

Question 3

what is a standard solution?

Answer 3

solution of a known concentration

Question 4

Describe how you can use test tube reaction to distinguish between butan-2-ol and 2-methylpropan-2-ol.

Include reagents, conditions, observations & explain chemistry involved.

Answer 4

• add acidified potassium dirchromate —> acidified in H₂SO₄ —> heat with sample
• butan-2-ol is secondary, 2-methylpropan-2-ol is tertiary
• butan-2-ol turns green from orange, 2-methylpropan-2-ol won’t
• 2-methylpropan-2-ol is tertiary and the intermediate carbocation is too stable to react
• butan-2-ol is secondary and is therefore less stable
• further oxides to a ketone

Question 5

How do you release pressure in a separating funnel? (4)

Answer 5

• stopper the funnel and hold it upside down with the tap closed
• point the tap away from yourself and others
• open the tap slowly
• close the tap and turn the funnel upright again, shake gently if needed

Question 6

What 3 essential pieces of apparatus are needed for determining temperature increase of water by burning a fuel?

Answer 6

• thermometer
• spirit burner
• calorimeter / copper can

Question 7

Describe the process used to prepare a halogenoalkane from an alcohol (9)

Answer 7

Reflux:

• sodium halide plus conc sulfuric acid added to reflux condenser w/ anti bumping granules
• heat under reflux with the alcohol

Rearrange for distillation:

• collect distillate around the boiling temp of the halogenoalkane
• add to separating funnel & decant aqueous layer if possible
• add conc HCl
• add NaHCO₃ - invert and open top to release pressure
• add anhydrous sodium sulfate
• filter

Finally:

• Distill - distillate at range of temps of boiling of halogenoalkane - should be pure

Question 8

Describe how 250 cm³ of a solution of acid can be prepared from the solid acid (5)

Answer 8

depending on concentration given in question - work out a mass of solid acid, then:

• dissolve in approximately 100 cm³ of deionised water in a beaker
• transfer to a 250 cm³ volumetric flask
• ensuring all washings go into the flask
• add deionised water until the bottom of the meniscus is at the mark
• stopper and invert to mix