Podcast
Questions and Answers
In the synthesis of copper(II) compounds, what is the primary role of ethyl alcohol after the addition of ammonia to the copper sulfate solution?
In the synthesis of copper(II) compounds, what is the primary role of ethyl alcohol after the addition of ammonia to the copper sulfate solution?
- To decrease the solubility of ionic compounds, promoting crystallization. (correct)
- To react with copper ions and form a soluble complex.
- To increase the solubility of ionic compounds.
- To oxidize copper(II) ions to copper(I) ions.
Why is color change considered significant in determining the nature of the product in the synthesis of copper(II) compounds?
Why is color change considered significant in determining the nature of the product in the synthesis of copper(II) compounds?
- Color change reflects changes in the oxidation state of copper ions within the compound. (correct)
- Color change is merely an aesthetic observation and does not affect the product's nature.
- Color change indicates the formation of by-products, affecting the purity of the final compound.
- Color change suggests the presence of impurities in the initial reactants.
In the zinc metal test for copper(II) ions, what observable change indicates the reduction of copper(II) ions?
In the zinc metal test for copper(II) ions, what observable change indicates the reduction of copper(II) ions?
- The solution becomes cloudy with a white precipitate.
- The blue color of the solution fades, and a reddish-brown precipitate forms. (correct)
- The solution turns from colorless to blue.
- A black precipitate forms immediately.
What is the initial product formed when tin(II) chloride ($SnCl_2$) is added to a solution containing copper(II) ions ($Cu^{2+}$)?
What is the initial product formed when tin(II) chloride ($SnCl_2$) is added to a solution containing copper(II) ions ($Cu^{2+}$)?
What observation confirms the presence of copper(II) ions after excess ammonia ($NH_3$) is added to a solution containing $Cu^{2+}$?
What observation confirms the presence of copper(II) ions after excess ammonia ($NH_3$) is added to a solution containing $Cu^{2+}$?
What is the direct product formed when sulfide ions ($S^{2-}$) react with copper(II) ions ($Cu^{2+}$) in the sodium sulfide test?
What is the direct product formed when sulfide ions ($S^{2-}$) react with copper(II) ions ($Cu^{2+}$) in the sodium sulfide test?
If the theoretical yield of a copper(II) complex is 1.97 g, but the actual yield obtained in the experiment is 1.5 g, what is the experimental yield percentage?
If the theoretical yield of a copper(II) complex is 1.97 g, but the actual yield obtained in the experiment is 1.5 g, what is the experimental yield percentage?
What is the purpose of measuring the mass of reactants accurately using an analytical balance in the synthesis of copper(II) compounds?
What is the purpose of measuring the mass of reactants accurately using an analytical balance in the synthesis of copper(II) compounds?
Why is it important to use dry and clean glassware in the synthesis of copper(II) compounds?
Why is it important to use dry and clean glassware in the synthesis of copper(II) compounds?
What potential issue can arise if a precipitate is not completely dry before weighing it in the context of copper(II) compound synthesis?
What potential issue can arise if a precipitate is not completely dry before weighing it in the context of copper(II) compound synthesis?
What are the common oxidation states of copper?
What are the common oxidation states of copper?
What color is typically associated with copper(II) compounds in solution?
What color is typically associated with copper(II) compounds in solution?
Why is the percentage yield in a laboratory synthesis rarely 100%?
Why is the percentage yield in a laboratory synthesis rarely 100%?
What are the four principal species involved in the synthesis process of copper(II) ammine sulfate?
What are the four principal species involved in the synthesis process of copper(II) ammine sulfate?
What indicates the presence of copper(II) ions ($Cu^{2+}$) in a solution during the ammonia test?
What indicates the presence of copper(II) ions ($Cu^{2+}$) in a solution during the ammonia test?
What is the balanced chemical equation for the copper(II) ammine sulfate synthesis reaction?
What is the balanced chemical equation for the copper(II) ammine sulfate synthesis reaction?
In the context of crystallization, what does the term 'kinetic barrier' refer to?
In the context of crystallization, what does the term 'kinetic barrier' refer to?
Why is it important to cool the solution containing the blue crystalline compound slowly?
Why is it important to cool the solution containing the blue crystalline compound slowly?
In determining the limiting reactant, what conversion is essential for comparing the amounts of each reactant?
In determining the limiting reactant, what conversion is essential for comparing the amounts of each reactant?
Which test among the copper(II) ion tests serves as a confirmation test due to the difference in precipitation?
Which test among the copper(II) ion tests serves as a confirmation test due to the difference in precipitation?
Flashcards
What is synthesis?
What is synthesis?
The process where substances combine to form a specific compound.
Copper oxidation states
Copper oxidation states
Copper's common oxidation states are +1 and +2.
Reaction with copper sulfate
Reaction with copper sulfate
Copper sulfate (CuSO4) solution turns deeper blue, and small blue-to-violet crystals form.
What are the main species in the synthesis process?
What are the main species in the synthesis process?
Signup and view all the flashcards
Why is ethanol used?
Why is ethanol used?
Signup and view all the flashcards
How does zinc react with copper (II) ions?
How does zinc react with copper (II) ions?
Signup and view all the flashcards
Tin (II) Chloride Test Result
Tin (II) Chloride Test Result
Signup and view all the flashcards
Ammonia test result
Ammonia test result
Signup and view all the flashcards
Sodium Sulfide Test Result
Sodium Sulfide Test Result
Signup and view all the flashcards
Why use an analytical balance?
Why use an analytical balance?
Signup and view all the flashcards
Why cool the solution to form crystals?
Why cool the solution to form crystals?
Signup and view all the flashcards
Why know reactant masses?
Why know reactant masses?
Signup and view all the flashcards
Study Notes
Experiment Overview
- This experiment focuses on synthesizing a copper (II) compound through chemical reactions
- The experiment quantitatively analyzes copper (II) ion reactions
Synthesis Background
- Synthesis is when substances combine
- Copper has +1 and +2 oxidation states
- Copper (II) compounds are commercially valuable when combined with other substances
- Valuable copper (II) compounds include copper oxide (CuO), copper chloride (CuCl), copper sulfate (CuSO4), and copper carbonate (Cu2(OH)2CO3)
- These compounds are widely used in glass production, pesticides, and as coloring agents
Experiment Procedure
- The first part involves adding NH3 to a concentrated aqueous copper sulfate solution, followed by ethyl alcohol
- This process forms small, deep blue-to-violet crystals, obtained through vacuum filtration and drying
- The second part tests copper (II) ions to observe and record color changes, using zinc metal, tin(II) chloride, ammonia, and sodium sulfide tests
Preparation of Copper Ammine Sulfate - Quantitative Data
- Mass of CuSO4⋅5H2O used: 2.0 g
- Mass of filter paper and watch glass: 0.9 g
- Mass of filter paper, watch glass, and dried complex: 2.4 g
- Mass of dried complex: 1.5 g
- Theoretical weight: 1.97 g
- Experimental yield: 76.1%
Copper (II) Ions Testing - Results
Zinc Metal Test
- The blue color fades as Cu²⁺ ions are reduced
- A reddish-brown Cu metal precipitate forms on the Zn surface
Tin (II) Chloride Test
- A white precipitate of CuCl forms initially
- CuCl can further reduce to Cu metal, turning the precipitate grayish
Ammonia Test
- Initially, a light blue precipitate of Cu(OH)₂ forms
- Adding excess NH₃ dissolves the precipitate, forming a deep blue tetraamminecopper(II) complex
Sodium Sulfide Test
- A black precipitate of CuS forms
- The solution may appear cloudy or dark
Calculations
- Reaction: CuSO4⋅5H2O + 4NH3 → [Cu(NH3)4]SO4⋅H2O + 4H2O
- Mass of CuSO4⋅5H2O: 2.0 g
- Molar mass of CuSO4⋅5H2O: 249.68 g/mol
- Moles of CuSO4⋅5H2O: approximately 0.008 mol
- Mole ratio of CuSO4⋅5H2O to [Cu(NH3)4]SO4⋅H2O is 1:1
- Molar mass of [Cu(NH3)4]SO4⋅H2O: 245.74 g/mol
- Theoretical weight calculation: 0.008 mol × 245.74 g/mol = 1.97 g
- Experimental yield calculation: (1.5 g / 1.97 g) × 100% = 76.1%
Discussion - Theoretical Background
- Copper has +1 and +2 oxidation states
- Copper solutions are colorless when +1, and blue or blue-green when +2, with exceptions like CuI and Cu₂O
- Synthesis involves adding NH3 to copper sulfate, turning the blue solution deeper blue, and forming blue-to-violet crystals with ethyl alcohol addition
- Analyzing for Cu2+, SO42-, and NH3 helps determine the compound formula
- The synthesis involves copper (II) ions (Cu(H2O)62+ ions), ammonia (NH3), sulfate ions (SO42-), and water
- Ethanol decreases ionic compound solubility and the marked color change indicates the product's nature
Discussion - Interpretation of Results
- CuSO4⋅5H2O plus NH3 yields the [Cu(NH₃)₄]²⁺ complex ion
- The experiment obtained a dried complex mass of 1.5 g, with a theoretical weight of 1.97 g
- The experimental yield was 76.1%, within the expected range for lab synthesis
- A 23.9% loss could be due to crystals remaining in the beaker, passing through the filter paper, incomplete reaction, or slight product solubility
- Copper (II) ions were tested using zinc metal, sodium sulfide, ammonia, and tin (II) chloride
Reaction mechanisms for each test
- Zinc reduces Cu²⁺ to Cu⁰, fading the blue color, and creating a reddish-brown copper precipitate
- Tin (II) chloride forms CuCl, a white insoluble solid, with further reduction potentially turning the precipitate gray
- Ammonia forms a light blue Cu(OH)₂ precipitate, dissolving in excess NH₃ to form the deep blue tetraamminecopper (II) ion
- Sodium sulfide forms CuS, a black insoluble substance, confirming the presence of Cu²⁺ ions
- Color changes, precipitate production, and redox activity in each test provide unique and reliable evidence of copper (II) ions
Safety and Suggestions
- Wear gloves and a lab coat for chemical splash protection
- Handle copper (II) sulfate and ammonia carefully due to their irritant or toxic nature
- Follow proper storage and disposal for excess chemicals
- Maintain optimal heating temperatures to prevent overheating of heat-sensitive chemicals
- Use an analytical balance for accurate reactant mass measurements for precise calculations
- Use dry, clean glassware to prevent contamination and side reactions
- Ensure precipitates are completely dry before weighing to avoid inaccurate results from moisture
Conclusion
- The experiment successfully synthesized copper (II) compounds, achieving a 76.1% yield
- This indicates a reasonably efficient conversion, slightly below the theoretical maximum, typical for coordination complex synthesis
Post-Lab Questions
Cooling for Crystal Formation
- Cooling the solution encourages crystal formation due to overcoming kinetic barriers
- Crystallization may need initiation, and warm solutions are preferrable to avoid fast crystallization
Importance of Reactant Masses
- Knowing reactant masses is crucial for determining stoichiometric ratios, which requires converting masses to moles using molar masses
- Reactant masses determine limiting reactants used in the balanced chemical equation to compare mole ratios
- Theoretical yield is then based on mole-to-mass conversion once the limiting reactant and product moles are known
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
