Required practical 4: investigate temperature changes in solutions
| English | 中文 | Pinyin |
|---|---|---|
| temperature change | 温度变化 | wēn dù biàn huà |
| best-fit intersection | 最佳拟合线交点 | zuì jiā nǐ hé xiàn jiāo diǎn |
What would explain this observation?
- Adding alkali to acid first raises the temperature, but later additions can make the mixture cooler. A falling part of this graph does not automatically mean neutralisation became endothermic.
- 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 4 investigates variables affecting temperature change 温度变化 in reacting solutions: suitable acid–metal, acid–carbonate, neutralisation or displacement reactions. In the acquired handbook neutralisation activity, a polystyrene cup is supported in a beaker and fitted with a lid and thermometer. Students start with 30 cm³ dilute hydrochloric acid, record its temperature, then add teacher-prepared sodium hydroxide in successive 5 cm³ portions up to 40 cm³.
- temperature change: Final or peak temperature minus the stated initial temperature; best-fit intersection 最佳拟合线交点: Where fitted rising and falling trends meet to estimate a peak.
Why can temperature fall after all the acid has reacted?
After each addition, replace the lid, stir gently and record the highest temperature. Repeat the whole investigation with fresh starting solutions and calculate means at each added volume. Plot mean temperature against total alkali volume added. Draw appropriate best-fit lines through the rising and falling regions and estimate their intersection. It estimates the peak between discrete readings; do not join every noisy point and call the highest measured point exact.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- After each addition, replace the lid, stir gently and record the highest temperature. Repeat the whole investigation with fresh starting solutions and calculate means at each added volume. Plot mean temperature against total alkali volume added. Draw appropriate best-fit lines through the rising and falling regions and estimate their intersection. It estimates the peak between discrete readings; do not join every noisy point and call the highest measured point exact.
- Use the school-approved risk assessment, eye protection and technician-prepared solutions. Sodium hydroxide presents a particular eye hazard. Keep initial acid volume, solution concentrations, starting temperatures, cup, stirring and reading procedure comparable. Record actual observations and an apparatus sketch in the laboratory; this lesson prepares and interprets that work, rather than certifying performance from a written answer. A lid and insulation reduce heat exchange but do not eliminate it.
Which two habits make the investigation or model in this case more defensible?
Use the school-approved risk assessment, eye protection and technician-prepared solutions. Sodium hydroxide presents a particular eye hazard. Keep initial acid volume, solution concentrations, starting temperatures, cup, stirring and reading procedure comparable. Record actual observations and an apparatus sketch in the laboratory; this lesson prepares and interprets that work, rather than certifying performance from a written answer. A lid and insulation reduce heat exchange but do not eliminate it.
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: an original illustrative pair of runs at one volume gives 30.4 °C and 30.8 °C, so mean temperature=(30.4+30.8)/2=30.6 °C. Starting mean temperature is 20.2 °C, giving a rise of 10.4 °C. After acid is exhausted, further cooler alkali adds no comparable neutralisation warming, while mixing and energy transfer to surroundings can lower temperature. This does not establish an endothermic neutralisation.
Two repeat temperatures are 29.2 °C and 29.8 °C. Find their mean. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Two repeat temperatures are 29.2 °C and 29.8 °C. Find their mean.
The result is 29.5 °C. Known: an original illustrative pair of runs at one volume gives 30.4 °C and 30.8 °C, so mean temperature=(30.4+30.8)/2=30.6 °C. Starting mean temperature is 20.2 °C, giving a rise of 10.4 °C. After acid is exhausted, further cooler alkali adds no comparable neutralisation warming, while mixing and energy transfer to surroundings can lower temperature. This does not establish an endothermic neutralisation.
Check the conclusion and its limits
- Do not prepare concentrated stock chemicals independently, heat this mixture to force a peak, or remove inconvenient repeats without recording a reason. A greater added volume changes both reactant amount and total liquid volume, so the graph is not a simple measure of reaction energy per mole. No heat-capacity calculation is required here. Bond-breaking explanations belong to the separate Higher lesson.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A downward part of the alkali-volume graph proves neutralisation has become endothermic. This claim is false: Do not prepare concentrated stock chemicals independently, heat this mixture to force a peak, or remove inconvenient repeats without recording a reason. A greater added volume changes both reactant amount and total liquid volume, so the graph is not a simple measure of reaction energy per mole. No heat-capacity calculation is required here. Bond-breaking explanations belong to the separate Higher lesson.
Required practical 4: investigate temperature changes in solutions: After each addition, replace the lid, stir gently and record the highest temperature. Repeat the whole investigation with fresh starting solutions and calculate means at each added volume. Plot mean temperature against total alkali volume added. Draw appropriate best-fit lines through the rising and falling regions and estimate their intersection. It estimates the peak between discrete readings; do not join every noisy point and call the highest measured point exact.
A downward part of the alkali-volume graph proves neutralisation has become endothermic.
Do not prepare concentrated stock chemicals independently, heat this mixture to force a peak, or remove inconvenient repeats without recording a reason. A greater added volume changes both reactant amount and total liquid volume, so the graph is not a simple measure of reaction energy per mole. No heat-capacity calculation is required here. Bond-breaking explanations belong to the separate Higher lesson.
Final or peak temperature minus the stated initial temperature: write the technical term.
temperature change means Final or peak temperature minus the stated initial temperature.