Required Practical 1: prepare pure, dry soluble salt crystals
| English | Français |
|---|---|
| crystallisation/ˌkrɪstəlaɪˈzeɪʃn/ | crystallisation |
| excess insoluble solid | excess insoluble solid |
What would explain this observation?
- Copper oxide is an insoluble black solid; copper sulfate solution is blue. Adding excess oxide lets the remaining acid react, then filtration removes the unused solid.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Required Practical 1 prepares a pure, dry soluble salt from an insoluble oxide or carbonate. For copper sulfate use dilute sulfuric acid and copper(II) oxide: CuO + H₂SO₄ → CuSO₄ + H₂O. Warm the dilute acid gently under the approved method, then add oxide in small portions with stirring until a little remains unreacted. The excess indicates that acid is used up under the method’s assumptions.
- crystallisation 结晶: Formation of solid crystals from a solution under suitable concentration and cooling conditions; excess insoluble solid 过量不溶固体: Undissolved reagent remaining after the acid has reacted under the preparation method.
Why filter after adding excess copper oxide?
Allow cooling and filter to remove excess insoluble oxide. The filtrate contains dissolved copper sulfate, so it passes through filter paper. Gently concentrate it in an evaporating basin using a water bath or electric heater, then allow cooling to form crystals. Separate the crystals and dry gently as directed. Evaporating completely to dryness is not the crystal-preparation endpoint.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Allow cooling and filter to remove excess insoluble oxide. The filtrate contains dissolved copper sulfate, so it passes through filter paper. Gently concentrate it in an evaporating basin using a water bath or electric heater, then allow cooling to form crystals. Separate the crystals and dry gently as directed. Evaporating completely to dryness is not the crystal-preparation endpoint.
- Carry out the school-supervised task with the specified dilute reagents, eye protection and risk-assessed heat equipment. Record the actual sequence, observations and recovered dry sample. The handbook’s copper sulfate example uses warmed acid, then a water bath for evaporation. Avoid overheating the solution; hot apparatus can look cold. The teacher/technician determines appropriate crystal handling and disposal.
Which two habits make the investigation or model in this case more defensible?
Carry out the school-supervised task with the specified dilute reagents, eye protection and risk-assessed heat equipment. Record the actual sequence, observations and recovered dry sample. The handbook’s copper sulfate example uses warmed acid, then a water bath for evaporation. Avoid overheating the solution; hot apparatus can look cold. The teacher/technician determines appropriate crystal handling and disposal.
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: a supplied preparation records empty collection vessel 18.40 g and vessel plus dry crystals 21.65 g. Crystal mass=21.65−18.40=3.25 g. A wet sample would include retained solution and give an inflated recovered mass. This measured mass is not a theoretical yield unless starting amounts and product form are also specified.
An empty vessel weighs 22.30 g and vessel plus dry crystals weighs 26.85 g. Find crystal mass. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
An empty vessel weighs 22.30 g and vessel plus dry crystals weighs 26.85 g. Find crystal mass.
The result is 4.55 g. Known: a supplied preparation records empty collection vessel 18.40 g and vessel plus dry crystals 21.65 g. Crystal mass=21.65−18.40=3.25 g. A wet sample would include retained solution and give an inflated recovered mass. This measured mass is not a theoretical yield unless starting amounts and product form are also specified.
Check the conclusion and its limits
- Filtration removes excess solid, not the dissolved salt. Heating concentrates the solution; cooling promotes crystals rather than a new neutralisation reaction. A written sequence and fabricated observations do not establish that RP1 was completed: retain the student’s actual supervised work and records.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Filtration alone recovers pure dry salt from its dissolved solution. This claim is false: Filtration removes excess solid, not the dissolved salt. Heating concentrates the solution; cooling promotes crystals rather than a new neutralisation reaction. A written sequence and fabricated observations do not establish that RP1 was completed: retain the student’s actual supervised work and records.
Required Practical 1: prepare pure, dry soluble salt crystals: Allow cooling and filter to remove excess insoluble oxide. The filtrate contains dissolved copper sulfate, so it passes through filter paper. Gently concentrate it in an evaporating basin using a water bath or electric heater, then allow cooling to form crystals. Separate the crystals and dry gently as directed. Evaporating completely to dryness is not the crystal-preparation endpoint.
Filtration alone recovers pure dry salt from its dissolved solution.
Filtration removes excess solid, not the dissolved salt. Heating concentrates the solution; cooling promotes crystals rather than a new neutralisation reaction. A written sequence and fabricated observations do not establish that RP1 was completed: retain the student’s actual supervised work and records.
Formation of solid crystals from a solution under suitable concentration and cooling conditions: write the technical term.
crystallisation means Formation of solid crystals from a solution under suitable concentration and cooling conditions.