PRACTICALS

Question 1

Suggest how the anti-bumping granules prevent bumping during reflux.

Answer 1

allows smaller bubbles to form / prevents the formation of (very) large bubbles
ALLOW provides large surface area for bubbles to form on

Question 2

Dimethylglyoxime is a colourless solid often used in the analysis of nickel in ores.
Dimethylglyoxime reacts with nickel ions and forms a bright red complex. This complex is very insoluble in water and so precipitates out of solution easily.

A scientist was provided with a 5.0 g sample of a nickel-containing ore. The sample was ground into a powder and made into an aqueous solution. The solution was then added to an excess of dimethylglyoxime dissolved in ethanol. This was stirred until all of the ore had dissolved and all of the nickel ions had reacted to form a solid, red complex.
(a) Describe, with practical details, how an accurate value for the mass of the dimethylglyoxime-nickel complex could be obtained.
You should not include details of any calculations.

Answer 2

Filter the solution (under vacuum)
If filtration is not the first step max. 2/4
1
Wash with a (cold) solvent / water / ethanol
Steps must be in a logical sequence
1
Dry the solid by a suitable method
Dessicator / oven / leaving out on the side overnight / washing with propanone
1
Heat the dry product to constant mass to make sure it is dry

Question 3

An incomplete method for recrystallisation of the nickel complex is outlined below.
Step 1: The sample is dissolved in a minimum volume of hot ethanol.
Step 2: The solution is filtered hot.
Step 3: The filtrate is cooled in ice to form crystals.
Explain the importance of each underlined point.

Minimum volume of hot ethanol

Filtered hot

Answer 3

To form a saturated / highly-concentrated solution
So a saturated solution forms on cooling

To prevent crystals forming during filtration process