Purpose:
The purpose of this lab is to complete various chemical reactions to demonstrate the Law of Conservation of Mass.
Qualitative and Quantitative Data:
Qualitative Data
ReactionCu + HNO3
Cu(NO3)2 + NaOH Cu(OH) 2 CuO + H2SO4 CuSO4 + Zn Zn + H2SO4 |
ObservationsBubbles formed in the beaker, and yellow gas escaped the beaker. The solution started turning blue and the outside of the beaker felt warm.
The blue liquid began to make a precipitate, and gas was released. The precipitate looked gooey and stringy. In the beaker there was a black solution. The black precipitate looked like dust pellets. They appeared to be soft, and were a dark black. When the H2SO4 was added, the solution in the beaker began to fizz. The solution started to turn green, and moved towards a teal color. When zinc was added, there was fizz in the beaker. There was also a white gas that was emitted. When H2SO4 was added, the excess zinc began to dissolve. The solution turned a foggy white color, and then cleared up. At the bottom of the beaker, there was a redish precipitate. |
Quantitative Data
Initial mass of copper
Mass of evaporating dish Mass of evaporating dish and copper Mass of recovered copper |
2.0g
54.1g 57.95g 3.84g |
Net Ionic Equations:
Balanced net ionic equations for all major reactions.
(This picture does not show the net ionic equation for the reaction of Zn2+ (s) + H2SO4 (aq) ----> ZnSO4 (aq) + H2 (g). The net ionic equation for this reaction is Zn (s) + 2H+ (aq) ----> Zn2+ (aq) + H2(g). )
Calculations:
Final mass of copper: Final mass of copper in evaporating dish - mass of evaporating dish= final mass of copper
57.95g-54.1g = 3.84g
Final moles of copper: .0604 moles Cu 3.84g Cu / 63.55g (molar mass) x 1 mol= .0604 moles Cu
Initial moles of copper: .0315 moles Cu 2.0g Cu / 63.55g (molar mass) x 1 mole= .0315 moles Cu
Percent yield: 192% actual / theoretical x 100= percent yield
3.84g Cu / 2.0g Cu= 1.92 x 100= 192%
57.95g-54.1g = 3.84g
Final moles of copper: .0604 moles Cu 3.84g Cu / 63.55g (molar mass) x 1 mol= .0604 moles Cu
Initial moles of copper: .0315 moles Cu 2.0g Cu / 63.55g (molar mass) x 1 mole= .0315 moles Cu
Percent yield: 192% actual / theoretical x 100= percent yield
3.84g Cu / 2.0g Cu= 1.92 x 100= 192%
Conclusions:
After the lab was complete, the final mass of copper was 3.84 g. There was an increase in mass of 1.84 g from the initial mass of 2.0 g. During the lab, there were excess substances that were not removed which were reflected in the final mass.
Discussion of theory:
In this lab, chemical reactions were used to demonstrate the Law of Conservation of Mass. This law states that mass is neither created nor destroyed and allows copper to be reacted with other substances, but never removed or loss. The lab that was conducted demonstrates this law because the lab starts off with a mass of copper, and is sopposed to end with the same mass of copper after many reactions. These reactions add substances and take substances away, but copper remains in the reaction the entire time. The Law of Conservation of Mass holds true to many substances other than copper in this lab. Even if a gas, such as NO2 is released, it is not destroyed. The gas remains in the air, but it just changes forms.
Another aspect of this lab is the stoichiometry that is used. Stoichiometry was used to calculate both the initial and final number of moles of copper. This could be done by dividing the mass given by the molar mass from the periodic table and then multiplying it my one mole. These mole ratios could then be used to find amounts of other substances in the reactions using the mole to mole ratios. This lab also incorporated percent yield into its steps. Percent yield is the amount that is acutally yielded over the theoretical amount and multiplied by one hundred. The percent yield shows how much of a substance is made in comparison to how much should have been made. In this lab, chemical reactions also had to be written and balanced.
The states of the substances had to be added in order to help identify what each substance was in the beaker. From the balanced equation, the net ionic equation had to be written. The net ionic equation is the equation that only shows the ions that took place in the reaction and changed. Ions that did not participate in the reaction or change are called spectator ions. It is helpful to write a net ionic equation because it shows which ions were directly involved in the chemical reaction. In this lab, there was a redox reaction, a decomposition reaction, single replacement reactions, and double replacement reactions. A redox reaction is the name for a reaction where electrons are transfered. In an oxidation-reduction reaction, one reactant is oxidized and looses electrons, and the other reactant is reduced and gains electrons. A decomposition reaction is where heat is added to a substance and it is broken down into parts. A single replacement reaction is a reaction where one reactant replaces another in a compound and they switch places. A double replacement reaction is where both compounds switch partners and react with the other oppositely charged reactant. This lab incorporated each of these types of reactions at one time or another during the experimet.
This copper lab required measurements to be made, which tested measuring skills. An electronic scale was used to weigh the initial and final copper. Safety was a large part of this lab as well. Gogles were worn to protect people's eyes from irritating chemicals being released or accidental spills or explosions. It was important to use a hood to remove gases that made breathing uncomfortable as well. During this lab, hot plates were used, and chemicals had to be measured into graduated cylinders. This lab incorporated many aspects of chemistry in a fun way. The lab really showed the importance of being accurate with measurements, observations, and chemical reactions.
Another aspect of this lab is the stoichiometry that is used. Stoichiometry was used to calculate both the initial and final number of moles of copper. This could be done by dividing the mass given by the molar mass from the periodic table and then multiplying it my one mole. These mole ratios could then be used to find amounts of other substances in the reactions using the mole to mole ratios. This lab also incorporated percent yield into its steps. Percent yield is the amount that is acutally yielded over the theoretical amount and multiplied by one hundred. The percent yield shows how much of a substance is made in comparison to how much should have been made. In this lab, chemical reactions also had to be written and balanced.
The states of the substances had to be added in order to help identify what each substance was in the beaker. From the balanced equation, the net ionic equation had to be written. The net ionic equation is the equation that only shows the ions that took place in the reaction and changed. Ions that did not participate in the reaction or change are called spectator ions. It is helpful to write a net ionic equation because it shows which ions were directly involved in the chemical reaction. In this lab, there was a redox reaction, a decomposition reaction, single replacement reactions, and double replacement reactions. A redox reaction is the name for a reaction where electrons are transfered. In an oxidation-reduction reaction, one reactant is oxidized and looses electrons, and the other reactant is reduced and gains electrons. A decomposition reaction is where heat is added to a substance and it is broken down into parts. A single replacement reaction is a reaction where one reactant replaces another in a compound and they switch places. A double replacement reaction is where both compounds switch partners and react with the other oppositely charged reactant. This lab incorporated each of these types of reactions at one time or another during the experimet.
This copper lab required measurements to be made, which tested measuring skills. An electronic scale was used to weigh the initial and final copper. Safety was a large part of this lab as well. Gogles were worn to protect people's eyes from irritating chemicals being released or accidental spills or explosions. It was important to use a hood to remove gases that made breathing uncomfortable as well. During this lab, hot plates were used, and chemicals had to be measured into graduated cylinders. This lab incorporated many aspects of chemistry in a fun way. The lab really showed the importance of being accurate with measurements, observations, and chemical reactions.
Sources of error:
During this lab, the final mass of copper was not equal to the initial mass of copper. The yield of copper was too high. According to the Law of Conservation of Mass, these two masses should have been equal. Since the yield was too high, it means that excess substances were weighed with the copper. A possible source of error could have been during step 5 when the solution was heated on a hot plate. The solution used took a longer period of time on the hot plate, and the solution continued to stay dark blue instead of black. This may have caused the mass to be higher because some of the nitrate ions may have stayed bonded to the copper. Another possible source of error could have been step 9 when the H2SO4 was added to seperate the excess zinc. Not enough of the H2SO4 could have been added, and excess Zn2+ ions could have been weighed with the copper. The balance used to measure the final and initial mass could have made an error due to being caloborated incorrectly. Through all of these reactions, there were many ways cooper could be lost or excess substances could be gained. Each step had to be done carefully and accurately to ensure good results. Just because the two masses did not match does not mean the Law of Conservation of Mass is incorrect, it just means errors were made along the way.
Questions:
1. The product of the reaction between copper and nitric acid in step two was placed on ice to cool the products down so they did not over heat.
2. The reaction in step four was a precipitation reaction that was double replacement. The reaction in step seven was an acid-base reaction, and the reaction in step nine was a reduction reaction that was single replacement.
3. The balanced equation for this reaction is Zn2+ (s) + H2SO4 (aq) ----> ZnSO4 (aq) + H2 (g). Problems that would arise from an incomplete reaction would be that excess zinc would be left in the beaker. This would inflate the final mass of copper and cause the final mass to be too high.
4. When the CuO was washed, the ions that were removed were Na+ ions and NO3- ions that remained in the beaker.
5. The form of copper present in the beaker after the H2SO4 was added the first time was Cu+ ions. These ions were in an aqueous solution. The second time the H2SO4 was added, the copper was in solid form.
6. When the precipitated copper was washed, the Zn 2+ ions and the SO4 2- ions were removed.
2. The reaction in step four was a precipitation reaction that was double replacement. The reaction in step seven was an acid-base reaction, and the reaction in step nine was a reduction reaction that was single replacement.
3. The balanced equation for this reaction is Zn2+ (s) + H2SO4 (aq) ----> ZnSO4 (aq) + H2 (g). Problems that would arise from an incomplete reaction would be that excess zinc would be left in the beaker. This would inflate the final mass of copper and cause the final mass to be too high.
4. When the CuO was washed, the ions that were removed were Na+ ions and NO3- ions that remained in the beaker.
5. The form of copper present in the beaker after the H2SO4 was added the first time was Cu+ ions. These ions were in an aqueous solution. The second time the H2SO4 was added, the copper was in solid form.
6. When the precipitated copper was washed, the Zn 2+ ions and the SO4 2- ions were removed.