Required Practical 3: test an electrolysis-product hypothesis
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| hypothesis/haɪˈpɒθəsɪs/ | 假设 | jiǎ shè |
| electrode observation | 电极观察 | diàn jí guān chá |
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.
- 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 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?
The acquired 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.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- The acquired 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.
- 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?
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.
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 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.
A supplied model records 21 cm³ gas in 7 min. Find mean collection rate. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A supplied model records 21 cm³ gas in 7 min. Find mean collection rate.
The result is 3 cm³ per min. 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 cm³ per minute. Equal rates do not establish gas identity; the electrode location, predicted reaction and appropriate product test provide that evidence.
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.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Bubbles alone prove that an electrode is producing chlorine. This claim is false: 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.
Required Practical 3: test an electrolysis-product hypothesis: The acquired 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.
Bubbles alone prove that an electrode is producing chlorine.
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.
A testable prediction with a stated reason: write the technical term.
hypothesis means A testable prediction with a stated reason.