Chemistry-only: percentage yield compares recovered and possible product
| English | 中文 | Pinyin |
|---|---|---|
| actual yield | 实际产量 | shí jì chǎn liàng |
| percentage yield/pəˈsentɪdʒ jiːld/ | 百分产率 | bǎi fēn chǎn lǜ |
What would explain this observation?
- A calculation predicts 10 g product, but only 8 g dry product is recovered. The missing recovered mass does not establish that atoms were destroyed.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Actual yield 实际产量 is the amount of desired product obtained. Theoretical yield is the maximum predicted by the reaction calculation under its stated conditions. Percentage yield 百分产率 equals actual product mass divided by theoretical product mass, multiplied by 100. When the theoretical mass is supplied, this calculation is both-tier Chemistry-only content; deriving that theoretical mass from reactants and an equation is separately Higher-only.
- actual yield: The amount of desired product obtained; percentage yield: Actual yield divided by theoretical yield, multiplied by 100.
Which can lower recovered yield without destroying atoms?
Recovery may be below the maximum because a reversible reaction does not go to completion, product is lost during separation, or reactants undergo side reactions. Some atoms can remain in reactants or enter unwanted products; some desired product can remain dissolved or on apparatus. Conservation concerns all atoms and substances, while yield concerns the recovered desired product.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Recovery may be below the maximum because a reversible reaction does not go to completion, product is lost during separation, or reactants undergo side reactions. Some atoms can remain in reactants or enter unwanted products; some desired product can remain dissolved or on apparatus. Conservation concerns all atoms and substances, while yield concerns the recovered desired product.
- Record a dry product mass rather than including retained solvent or unrelated material. Write actual and theoretical values in the same unit before dividing. Inspect a proposed explanation against the method: transfer loss, incomplete crystallisation or reversible conversion are different causes and need different evidence. School-supervised separations remain actual tasks; this written evaluation supports them rather than replacing them.
Which two habits make the investigation or model in this case more defensible?
Record a dry product mass rather than including retained solvent or unrelated material. Write actual and theoretical values in the same unit before dividing. Inspect a proposed explanation against the method: transfer loss, incomplete crystallisation or reversible conversion are different causes and need different evidence. School-supervised separations remain actual tasks; this written evaluation supports them rather than replacing them.
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 theoretical product mass is 12.0 g and dry recovered mass is 9.0 g. Percentage yield=9.0/12.0×100=75%. The shortfall is 3.0 g desired product relative to the maximum, not necessarily 3.0 g spilled solid. The cause cannot be assigned uniquely from these two mass values alone.
Theoretical yield is supplied as 20 g; actual dry product is 16 g. Calculate percentage yield. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Theoretical yield is supplied as 20 g; actual dry product is 16 g. Calculate percentage yield.
The result is 80 %. Known: a supplied theoretical product mass is 12.0 g and dry recovered mass is 9.0 g. Percentage yield=9.0/12.0×100=75%. The shortfall is 3.0 g desired product relative to the maximum, not necessarily 3.0 g spilled solid. The cause cannot be assigned uniquely from these two mass values alone.
Check the conclusion and its limits
- Divide actual by theoretical, not the reverse. A yield above 100% prompts a check for wet/impure product, incorrect mass data or assumptions; it does not prove extra atoms were created. A catalyst can speed reaching a result without changing the stoichiometric maximum from fixed limiting reactants.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A 75% yield means 25% of the original atoms were destroyed. This claim is false: Divide actual by theoretical, not the reverse. A yield above 100% prompts a check for wet/impure product, incorrect mass data or assumptions; it does not prove extra atoms were created. A catalyst can speed reaching a result without changing the stoichiometric maximum from fixed limiting reactants.
Chemistry-only: percentage yield compares recovered and possible product: Recovery may be below the maximum because a reversible reaction does not go to completion, product is lost during separation, or reactants undergo side reactions. Some atoms can remain in reactants or enter unwanted products; some desired product can remain dissolved or on apparatus. Conservation concerns all atoms and substances, while yield concerns the recovered desired product.
A 75% yield means 25% of the original atoms were destroyed.
Divide actual by theoretical, not the reverse. A yield above 100% prompts a check for wet/impure product, incorrect mass data or assumptions; it does not prove extra atoms were created. A catalyst can speed reaching a result without changing the stoichiometric maximum from fixed limiting reactants.
The amount of desired product obtained: write the technical term.
actual yield means The amount of desired product obtained.