Required Practical 3: test an electrolysis-product hypothesis
Введено| English | Значение |
|---|---|
| hypothesis/haɪˈpɒθəsɪs/ | гипотеза |
| electrode observation/ɪˈlektrəʊd ɒbzəˈveɪʃn/ | наблюдение на электроде |
What would explain this observation?
- Comparing copper chloride with sodium chloride lets a student test a prediction about cathode products while keeping chloride as the common anion.
Build the model
- Required Practical 3 is an actual investigation of aqueous electrolysis using inert electrodes and a developed hypothesis 假设.
- A suitable prediction is that copper chloride will give a copper deposit at the cathode, while sodium chloride will give hydrogen under the approved conditions; both will show chlorine at the anode.
- State the reason using metal reactivity and the specified aqueous product rules before observing.
- hypothesis: A testable prediction with a stated reason.
- electrode observation 电极观察: A recorded change identified with its electrode sign and conditions.
Which observation most directly supports copper at the cathode?
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
Copper is a brown-red metal, so a brown-red coating on the negative electrode (cathode) - backed by the predicted reaction and a suitable check - is direct evidence for copper. Random bubbles or a bottle cap identify nothing.
Match each technical term to its precise meaning.
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- The handbook uses carbon rods, low-voltage direct current and approved CuCl₂/NaCl solutions.
- A brown/red deposit supports copper at the negative electrode; gas at the positive electrode bleaches damp blue litmus under the approved test.
- A bubble observation alone does not identify a gas.
- Label each observation with electrode sign and keep the products separate.
In the lab: The teacher/technician approves concentrations, small quantities, voltage, duration, ventilation and disposal. Keep the carbon rods apart and fixed to avoid a short circuit. Use the prescribed contained small-scale gas test and never inhale chlorine. Record matched solution volumes, electrode spacing, supply setting and elapsed time. Retain actual results, labelled apparatus and a conclusion comparing them with the hypothesis.
Which two habits make the investigation or model in this case more defensible?
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a supplied model comparison records gas collection 12 cm³ after 4 min and 18 cm³ after 6 min under stated equal conditions.
- Both mean collection rates are 3 $\dfrac{\text{cm}^3}{\text{min}}$.
- Equal rates do not establish gas identity; the electrode location, predicted reaction and appropriate product test provide that evidence.
Your turn: A supplied model records 21 cm³ gas in 7 min. Find mean collection rate.
A supplied model records 21 cm³ gas in 7 min. Find mean collection rate.
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
The result is 3 cm³ per min. Known: 21 cm^3 in 7 min. Use mean rate = volume / time. Rate = 21/7 = 3 cm^3 per minute. Equal rates in two trials do not prove the gas is the same without a product test.
Check the conclusion and its limits
- Do not label invented measurements as a completed practical.
- Inert-electrode predictions need review if the electrode material reacts.
- Changes in concentration, spacing or supply can alter the comparison.
- The handbook notes chlorine production and short controlled operation; follow the current school risk assessment rather than treating a written lesson as full practical permission.
Not true: Bubbles alone prove that an electrode is producing chlorine. Hydrogen, oxygen and chlorine are all gases that bubble off electrodes. Bubbles alone cannot distinguish them - identity needs the electrode position plus a specific test such as bleaching damp litmus paper for chlorine.
- Required Practical 3 is an actual investigation of aqueous electrolysis using inert electrodes and a developed hypothesis.
- The handbook uses carbon rods, low-voltage direct current and approved CuCl₂/NaCl solutions.
- Watch for: do not label invented measurements as a completed practical.
Bubbles alone prove that an electrode is producing chlorine.
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
Hydrogen, oxygen and chlorine are all gases that bubble off electrodes. Bubbles alone cannot distinguish them - identity needs the electrode position plus a specific test such as bleaching damp litmus paper for chlorine.
A testable prediction with a stated reason: write the technical term.
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
hypothesis means A testable prediction with a stated reason.