Purpose
A solid copper metal of known mass is performed with a series of reactions, eventually recovering the copper at the end and testing the Law of Conservation of Mass.
Quantitative Data
Initial mass of copper………………………...... 2.03 grams
Mass of evaporating dish……………………... 54.142 grams
Mass of evaporating dish and copper……….. 67.245 grams
Mass of recovered copper…………………….. 13.103 grams
Mass of evaporating dish……………………... 54.142 grams
Mass of evaporating dish and copper……….. 67.245 grams
Mass of recovered copper…………………….. 13.103 grams
Qualitative Data
Reactions |
Observations |
Cu + HNO3
|
bubbling, sizzling and foaming, solution turned blue, released a yellow gas, beaker is hot -exothermic, copper dissolves and leaves a dark blue solution.
|
Cu(NO3)2 + NaOH
Cu(OH)2 CuO + H2SO4 CuSO4 + Zn
Zn + H2SO4 |
blue precipitate-shade lighter than earlier solution, pH 13, had to transfer to 250mL beaker and was not able to get all the blue precipitate out
tiny dark blue/navy particles in peacockish blue solution, solution gets darker and eventually becomes completely black, clear-gray solution on top, black precipitate on bottom, bubbles formed and popped (so stir), decant and repeat
black->dark green ->teal ->fluorescent blue change of colors in solution, precipitate dissolved
light blue, sizzling bubbles, red precipitate on bottom, smell-copper
white, sizzling, bubbling, clearer on bottom, sizzling white on top half, red/brown copper precipitate floating, zinc particles on bottom float up, smells bad
|
Net Ionic Equations
Calculations
Conclusion
A solid copper metal is reacted through a series of reactions. During these reactions, a precipitate or gas will form, or a significant temperature change, or a color change will occur. The goal of the lab is to recover the copper precipitated and compare it to the initial copper mass to verify the Law of Conservation of Mass. The final mass of copper is 13.103 grams, clarifying there was an 11.073 grams increase in mass from the initial.
Discussion of Theory
The objective of this lab was to achieve 100% yield of copper. The Law of Conservation of Mass states that matter cannot be created nor destroyed. This lab helped try to prove this theory by starting with an initial mass of 2 grams (more like 2.03 grams), reacting it in multiple reactions, precipitating the copper out, and comparing the initial and final masses. In other words, this lab starts off with a mass of copper and is suppose to end with the same mass of copper after several reactions have taken place. The reactions involve taking substances away and adding substances, but the copper is suppose to remain throughout the reactions.
Stoichiometry was used in this lab to calculate the initial and final number of moles of copper. This is done by taking the given mass, multiplying by one mole, and then dividing it by the molar mass of the element(s) located on the periodic table.
The percent yield was also used in calculations in the lab. It was usd as a comparison to how much copper should’ve been made. Percent yield is the amount actually yielded (recovered mass) over the theoretical amount (initial mass) multiplied by 100.
In addition, the lab required balanced net ionic equations stated with the state of the substances (solid, aqueous, liquid, gas). This was to identify what each substance was in the beaker and what substances were added and removed. The net ionic equation shows the ions that do work (participated) in the reaction. The ions that didn’t do work or participated are the spectator ions. When writing the net ionic equations, there came across a single replacement reaction, a double replacement reaction, a redox reaction, and a decomposition reaction. In a single replacement reaction, one substance replaces another in a compound. In a double replacement reaction, both compounds switch partners. In a redox reaction, electrons are transferred. In a decomposition reaction, the substance is broken down due to heat.
Loads of measurements were to be made. Safety precautions were highly enforced. Gloves, goggles, tongs, hot plates and hoods were used. It was important to keep an eye out for forming bubbles (one must continuously stir) in case it made an explosion.
Stoichiometry was used in this lab to calculate the initial and final number of moles of copper. This is done by taking the given mass, multiplying by one mole, and then dividing it by the molar mass of the element(s) located on the periodic table.
The percent yield was also used in calculations in the lab. It was usd as a comparison to how much copper should’ve been made. Percent yield is the amount actually yielded (recovered mass) over the theoretical amount (initial mass) multiplied by 100.
In addition, the lab required balanced net ionic equations stated with the state of the substances (solid, aqueous, liquid, gas). This was to identify what each substance was in the beaker and what substances were added and removed. The net ionic equation shows the ions that do work (participated) in the reaction. The ions that didn’t do work or participated are the spectator ions. When writing the net ionic equations, there came across a single replacement reaction, a double replacement reaction, a redox reaction, and a decomposition reaction. In a single replacement reaction, one substance replaces another in a compound. In a double replacement reaction, both compounds switch partners. In a redox reaction, electrons are transferred. In a decomposition reaction, the substance is broken down due to heat.
Loads of measurements were to be made. Safety precautions were highly enforced. Gloves, goggles, tongs, hot plates and hoods were used. It was important to keep an eye out for forming bubbles (one must continuously stir) in case it made an explosion.
Sources of Error
The yield of copper recovered is too high. The percent yield is 645% which is incredibly high compared to the usual percentages around 100%. The difference in mass between the initial amount of copper used and the amount of copper reclaimed is 11.073 grams. This was not expected considering that during the transferring of beakers, not all of the blue precipitate was able to transfer. It was thought that the recovered copper would weigh much less than the initial copper mass. Throughout this lab, there were several possible random errors. For example, pouring too much water, decanting and accidentally spilling tiny bits of copper, having the copper sit out for a day with water (in which the copper could have absorbed water, making its mass more dense), or not really evaporating all the water out as the scientists thought they did. The systematical errors were most likely from the digital scale. The scale would not be exactly precise and stay still on a digit. It would keep bouncing back and forth in the tenths and hundredths decimal place.
Questions
1. The product reaction of the reaction between copper and the nitric acid in step two was placed on ice in order to cool the products and not over heat.
2. The reaction in step four was a double replacement reaction. The reaction in step seven was an acid-base reaction. The reaction in step nine was a single replacement reaction.
3. The balanced equation for this reaction is Zn+2(s) + H2SO4 (aq) -> H2(g) + ZnSO4 (aq). A problem that would arise of this reaction was incomplete is that excess zinc would remain in the beaker. This would cause the final mass of copper to be too high.
4. The ions that were removed when washing the CuO were the Na+ ions and NO3 ions left in the beaker.
5. The form of copper present in the beaker the first time H2SO4 was added was in aqueous solution. The second time H2SO4 was added, the copper was in solid form.
6. The ions removed when the precipitated copper was washed were the Zn +2 ions and the SO4 -2 ions.
2. The reaction in step four was a double replacement reaction. The reaction in step seven was an acid-base reaction. The reaction in step nine was a single replacement reaction.
3. The balanced equation for this reaction is Zn+2(s) + H2SO4 (aq) -> H2(g) + ZnSO4 (aq). A problem that would arise of this reaction was incomplete is that excess zinc would remain in the beaker. This would cause the final mass of copper to be too high.
4. The ions that were removed when washing the CuO were the Na+ ions and NO3 ions left in the beaker.
5. The form of copper present in the beaker the first time H2SO4 was added was in aqueous solution. The second time H2SO4 was added, the copper was in solid form.
6. The ions removed when the precipitated copper was washed were the Zn +2 ions and the SO4 -2 ions.