Обязательный практический 6: разделение и идентификация реальных пищевых красителей
Введено| English | Значение |
|---|---|
| origin line/ˈɒrɪdʒɪn laɪn/ | линия старта |
| solvent front/ˈsɒlvənt frʌnt/ | фронт растворителя |
What would explain this observation?
- An unknown food colouring can contain two known dyes and another dye absent from the reference set. A good result must allow an unmatched spot to remain unmatched.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- RP6 investigates separation and comparison of coloured substances and requires Rf calculation. The acquired handbook uses four known food colourings A–D, an unknown U, chromatography paper, water and separate capillary tubes. Its teacher notes suggest U contain two known dyes and a third not in A–D. Known single dyes are preferable references; a commercial colouring may itself be a mixture. Written predictions do not certify that the practical has been performed.
- origin line 起始线: The marked starting line from which chromatographic distances are measured; solvent front 溶剂前沿: The farthest position reached by the moving solvent in the stated chromatogram.
Почему линия нанесения (начало) должна оставаться выше начального уровня воды?
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Если исходные пятна находились ниже уровня воды, красители растворились бы напрямую в резервуаре, вместо того чтобы подниматься по бумаге. Растворитель должен проходить ЧЕРЕЗ пятна, чтобы переносить красители вверх.
Сопоставьте каждый технический термин с его точным определением.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
Используйте определения для различения смежных величин и процессов.
Choose evidence that can test it
- Draw a horizontal pencil origin 2 cm above the lower paper edge. Mark positions away from the edges, place small concentrated spots using separate clean tubes and label in pencil. The handbook aims for 2–3 mm spots and no more than 1 cm water depth, keeping the origin above the water while the paper bottom dips into it. Support the paper without touching the beaker walls and avoid moving the vessel during the run.
- Stop before the solvent reaches the paper top, remove the paper and mark the solvent front immediately in pencil. Let the paper dry before measuring from the origin to each spot centre and front. Preserve the actual chromatogram, measurements, solvent identity and calculated Rf. Compare U with references in the same run; record an additional spot as unidentified rather than inventing a name. The school method and risk assessment govern capillary handling and any drying equipment.
Какие две привычки делают расследование или модель в данном случае более обоснованными?
Difficulty 2/5 · 140 coins + a small bonus on first completion today
Указание условий и допущений позволяет другим точно воспроизвести работу, а фиксация подтверждающих данных даёт возможность проверить вывод. Сокрытие противоречащих результатов устраняет доказательства, способные оспорить ошибочный вывод, а одно измерение никогда не может обосновать более широкий claim.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: in an original model run the front travels 50 mm. A, B and an unmatched U spot travel 10, 30 and 40 mm respectively. Their Rf values are 0.20, 0.60 and 0.80. If U also has spots at 10 and 30 mm, it supports A and B plus another detectable component. These model readings are practice data; the practical record must contain the student’s real observations.
In an actual run a spot centre travels 33 mm and the front 60 mm from the origin. Calculate Rf. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
В реальном опыте пятно в центре перемещается на 33 мм, а фронт — на 60 мм от исходной точки. Вычислите Rf.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
Результат составляет 0.55. Известно: центр пятна 33 мм; фронт 60 мм от начальной линии. Rf = 33/60 = 0.55. Сравнение с эталонными красителями из ТОГО ЖЕ эксперимента подтверждает идентификацию.
Check the conclusion and its limits
- Ink can move and interfere, so the baseline and labels use pencil. An origin submerged in solvent lets samples dissolve into the reservoir. Large spots can overlap; touching walls can distort the front. No spot matching A–D does not mean the unknown contains no dye. RP6 applies on both tiers and assesses actual separation skills alongside written interpretation.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A written chromatography calculation alone proves RP6 was completed. This claim is false: The practical assesses real observations - an actual chromatogram with measured distances. A written Rf calculation from invented numbers demonstrates arithmetic, not that the practical was performed.
Required practical 6: separate and identify actual food dyes: Draw a horizontal pencil origin 2 cm above the lower paper edge. Mark positions away from the edges, place small concentrated spots using separate clean tubes and label in pencil. The handbook aims for 2–3 mm spots and no more than 1 cm water depth, keeping the origin above the water while the paper bottom dips into it. Support the paper without touching the beaker walls and avoid moving the vessel during the run.
Один только письменный расчет хроматографии не доказывает, что RP6 был выполнен.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Практическая работа оценивает реальные наблюдения — фактическую хроматограмму с измеренными расстояниями. Написанный расчет Rf на основе вымышленных чисел демонстрирует арифметику, но не факт выполнения практической работы.
Отмеченная начальная линия, от которой измеряются хроматографические расстояния: запишите технический термин.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
линия начала означает Отмеченная начальная линия, от которой измеряются хроматографические расстояния.