OCR A2 Quantitative ocr 2013 [j/500/8555]

OCR A2 Quantitative ocr 2013 [j/500/8555] :

Apparatus

• 6 X 10 cc syringes with Clear Plastic tube at least 10cc long

• 6 X boiling tubes in rack

• 2 X 10 cc syringes

• Glass rod

• Transparent ruler

• Marker pen

• Timer

• Water bath (1 or 2)

• Thermometer

• Paper towel

Materials (Each candidate)

• 100 cc of 7.0% yeast suspension to be prepared about one hour before examination as follows

  • •  7.0 g of dried yeast for baking is added to warm distilled water, stir and made up to 100 cc. this should be kept for about 30mn at a temperature of 35-40 °C .

    • After  about 30mn, 20g of glucose should be sprinkled over the surface of the mixture and stirred. As the mixture will froth, it should be kept in a large container. The suspension should be dispensed to the candidates in 250 beakers labelled yeast.

    • The Glucose MUST be added to the yeast 10 to 15 mn before the candidate start task. Maintain the yeast at 35 °C for as long as possible before it is used by candidates.

• 20 cc of distilled water in a beaker labelled 0%

• 20 cc of the following chloride solution in beaker labelled 30 %-20%-15%-10%-5% in large beaker for candidate to share them

  • • 30% (30g in 100 distilled water)

    • 20% (20g in 100 distilled water)

    • 15% (15g in 100 distilled water)

    • 10% (10g in 100 distilled water)

    • 05% (05g in 100 distilled water)

• Large beaker for waste solution

• Access to warm/hot water at approx. 35°C (Waterbath)