Question 1
A student looks at a carton labelled 'pure orange juice' in a supermarket. Which statement best explains why this juice is NOT considered pure in a scientific sense?No clue? Show me the answer
Correct answerCorrect!
IncorrectStep-by-step walkthrough
Choose a solution method
Method #1Direct ApproachStep 1: Recall the scientific definition of a pure substance
In science, a pure substance contains only one type of material. It has a fixed, uniform composition throughout.
Step 2: Analyse what orange juice contains
Orange juice contains water, sugars, acids, and vitamins — these are several different substances combined together, making it a mixture.
Step 3: Choose the correct answer
Because orange juice contains more than one type of substance, it is scientifically a mixture, not a pure substance. The correct answer is that it contains water, sugars, acids, and vitamins mixed together.
Method #2Process of EliminationStep 1: Identify what the question is asking
The question asks why orange juice is not scientifically pure. We need the reason that relates to the definition of a pure substance.
Step 2: Eliminate 'It has been heated during processing'
Heating does not automatically make something impure in a scientific sense. Purity is about composition, not how it was processed. This option is incorrect.
Step 3: Eliminate 'It comes from a natural source'
Coming from a natural source has nothing to do with scientific purity. Many natural substances are mixtures. This option confuses everyday language with scientific definitions.
Step 4: Eliminate 'It has a pH below 7'
While orange juice is acidic, pH alone does not determine purity. Pure substances can have various pH values; this is not the reason it fails the scientific purity test.
Step 5: Select the correct answer
The only answer that correctly explains scientific impurity is that orange juice contains water, sugars, acids, and vitamins mixed together — multiple substances, making it a mixture.
Question 2
Which of the following is the best scientific definition of a pure substance?No clue? Show me the answer
Correct answerCorrect!IncorrectStep-by-step walkthrough
Choose a solution method
Method #1Direct ApproachStep 1: Recall the scientific meaning of 'pure'
In science, pure does not mean clean, safe, or natural. It has a very specific meaning related to composition.
Step 2: Apply the definition
A pure substance contains only one type of material and has fixed, precise physical properties such as a definite melting point and boiling point.
Step 3: Match to the correct option
The option 'A substance that contains only one type of material with fixed physical properties' matches the scientific definition exactly.
Method #2Process of EliminationStep 1: Identify the key concept being tested
This question tests whether students know the scientific definition of 'pure' — which is different from everyday meanings.
Step 2: Eliminate 'A substance that is safe to eat or drink'
Safety is a property of clean substances, not pure ones. Tap water is safe to drink but is not scientifically pure.
Step 3: Eliminate 'A substance that has been cleaned to remove dirt'
This describes cleanliness, not purity. A substance can be clean but still contain dissolved minerals or other materials, making it a mixture.
Step 4: Eliminate 'A substance that comes directly from nature without any processing'
Natural substances are often mixtures — for example, seawater contains salt, minerals, and dissolved gases. Being natural does not make something scientifically pure.
Step 5: Select the correct answer
The only scientifically accurate definition is: a substance that contains only one type of material with fixed physical properties.
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