Chapter 6 Post Lab 6.4 to the end

Chapter 6Post Lab 6.4 to the end 2009

Synthesis of Zinc Chloride(single-replacement)A + B → ABZn + 2HCl → ZnCl2 + H2 By Amparo Krug 2009

Group Data • Zn metal initial _________ g • Zn metal final __________ g • Empty dish __________ g • Dish with solid (ZnCl) ________ g Total 38 points on grade book divide by 2, 19 points

Calculations • Mass of Zinc Reacted = B – A • Mass of ZnCl produced = D – C • Ratio of mass of Zn reacted = ____ mass of ZnCl produced

Class Data example

Graph • ZnCl produced vs. Zn reacted. Dependent Variable Independent Variable

BDQ1 What is the gas given off in the reaction? The gas is hydrogen • BDQ2 Why should you add the washing water to the evaporating dish? Because it contains some of the dissolved product • BDQ3 How much of the metal reacted with the HCl? Mass Zn initial – mass of Zn remaining.

BDQ4 What is the ratio of the mass of zinc reacted to the mass of zinc chloride formed? 0.48 • BDQ5 Compare your results with those of your classmates. Did an excess of either zinc or hydrochloric acid affect your results? No an excess of either reactant did not affect the final ration. • BDQ6 If the zinc chloride were not completely dry when massed, how would this affect your ratio? The mass of the product would be larger and the final ratio would therefore be smaller.

Graph Best Fit Line

Conclusion

The graph shows a line with a positive slope which flattens at about 4.0 g of ZnCl produced and1.9g Zn reacted. • There was enough HCl to react with 1.9g of ZnCl. Any additional Zn would go un-reacted because there is not enough HCl to react with.

Groups with less than 1.9g of Zn did not have enough Zn to react with the Chlorine The limiting reactant in this part of the graph was Zinc. Zn HCl HCl Zn Zn HCl Zn HCl HCl HCl Left over HCl

Groups with greater than 1.9g Zn used up all their HCl and were evaporating water. The limiting reactant in these groups was HCl. Zn HCl Zn HCl Zn HCl Zn HCl Zn Left over Zn Zn

Lab 6.6 Reaction with Copper This lab will be done as a demo because we are running out of time. By Amparo Krug 2006 POST LAB

BDQ BDQ 6.6.1: Does a reaction take place? Yes, because there was a color change. BDQ 6.6.2: Did the crucible and contents gain or lose mass? Gained mass

BDQ 6.6.3: Is your answer to the previous question evidence that a reaction has taken place? Increase in mass is evidence that something was added to the copper. • BDQ 6.6.4: What do you predict will happen if you continue to heat the crucible for an additional 10-15 minutes? Accept any reasonable response.

BDQ 6.6.5: Do you think that all the copper has reacted? No, because there were flakes of copper in the solid. If not, what fraction do you estimate did not react? about 1/8 (accept any reasonable fraction) • BDQ 6.7.1: What does the remaining solid look like? The solid remaining in test tube A looked like copper. • BDQ 6.7.2: Is the black substance a mixture? Yes, because we were able to separated the unreacted copper by using solubility. • BDQ 6.9.1: Can you identify the solid? It looks like copper.

Conclusion (each purpose is address in one encompassing statement) • The purpose of these labs was to determine if: • 6.6) The reaction of copper with oxygen goes to completion. Our lab group found that the reaction of copper with oxygen is incomplete producing a mixture. • 6.7) Can this mixture be separated and the un-reacted copper collected. Yes, we separated the un-reacted copper in the mixture. • 6.9) Can the Cu in the reacted CuO be isolated from the compound. Definitely, we precipitated the copper that was chemically combined with oxygen to make CuO. • Theoretically, the mass of the copper in the two separations of the product equals the initial mass of the Copper used.

Lab 6.6 • 2Cu (s) + O2 (g) > CuO +Cu • A reaction has taken place because of the mass increase (something is added to the Cu) and color changed. • CuO +Cu was a mixture and mixtures can be separated by physical means. Which method was used? Separation by solubility, dissolving • CuOwill dissolve in HCl and Cu will not

Lab 6.7 • CuO +Cu + 2HCl > 2CuCl + H2O ↓ Un-reacted Copper stays behind in test tube A CuCl (green liquid) is now in test tube B

Even though, copper reacted with air to produce a compound, subjected to heat and acid, we still were able to recover the copper. The properties of the copper had not changed. • A substance that can keep its identity through all these processes can be called an Element.

Lab 6.9 • 2CuCl (green) + Zn + H2O > ZnCl2 (dissolves in water and becomes clear) + 2Cu+ H2O ↓ Copper is filtered out • You know that a reaction has taken place because of the color change, formation of precipitate, and release of energy (exothermic). The product has a different identity than the reactant.

Mixture • Is a combination of different substances that can be separated because they have different physical properties – such as boiling point, melting point, density. • The substances are not chemically bonded.

Concept map Concept Map Separate into Mixture Pure substance Pure substance Compound Element Pure substance Element Compound Element Can be Can be or Broken into

Mixtures can be separated by physical means into pure substance. • A pure substance can be a compound or an element

Compounds • Cannot be separated by physical means, because they are chemically bonded. • Have different properties from the elements of which they are made. • Are synthesize from other pure substances in constant ( definite ) proportions. • Can be written as a chemical formula which shows the proportion of the elements in the compound.

Elements: • Are pure substances made up of atoms of thesame type, all with the same atomic number. • Cannot be broken down by electrolysis, reacting with acid, nor heating to form simpler substances.

In summary • Compounds can be separated into other compounds or elements • But Elements cannot be subdivided.

Famous Scientist who helped separated compounds into elements.

Discovered iron, copper, silver, gold, hydrogen, oxygen, and carbon. Discovered the true nature of burning Chemical addition of oxygen Introduced quantitative analysis Help invent the metric system Father of modern chemistry ANTOINE LAURENT LAVOISIER, 1743-1794

Alessandro Volta • invents the battery, 1800, which helped chemist separate pure substances into other pure substances (elements and compounds)

Sir Humphry Davy, 1778 – 1829 • English chemist using electrolysis decomposes Potash into potassium and sodium in 1807. • Isolates calcium from Lime (as in limestone)in 1808. • Isolates strontium, barium and magnesium in 1808. • Davy isolates the new gas from his experiments with muriatic acid and names it chlorine because of its’ green color. • Discovered the anesthetic action of nitrous oxide.

Oxygen Silicon Hydrogen Aluminum Iron Calcium Sodium Magnesium The first 5 form 92% of the total mass of the elements found near the surface of the earth. Elements Near the Surface of the Earth (top 8)

Silicates • Oxygen and silicon form silicon dioxide. • Silicon dioxide is the compound found in rock forming minerals.

Ores are materials found in the ground from which metals can be profitably extracted. • Iron is produced by mixing iron ore with coal or charcoal and heated strongly • Aluminum comes from Bauxite –aluminum ore

Chapter 6 Post Lab 6.4 to the end