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

A. Zn metal initial _________ gB. Zn metal final __________ gC. Empty dish __________ gD. 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 exampleZn reacted (g) ZnCl produced

(g)Ratio (Zn reacted/ZnCl

produced

0.43 0.77

0.86 1.11

1.3 2.53

1.71 3.54

1.9 1.48

1.9 3.97

1.88 3.98

1.8 3.71

0.42 0.83

0.87 1.75

Graph

• ZnCl produced vs. Zn reacted.

DependentVariable

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

Zn reacted vs ZnCl produced

0

1

2

3

4

5

0 0.5 1 1.5 2 2.5

Zn reacted (g)

ZnCl

pro

duce

d (g

)

ZnCl produced

Best Fit Line

ConclusionPurpose The purpose of this experiment is to investigate what

happens when a metal is dissolved in an acid.

Hypothesis My hypothesis that the amount of Zinc that reacts with HCl will depend on the amount of Zn was partly supported.

Group Data Our group data revealed that the mass ratio of Zn reacted to ZnCl produced was 0.50. See group data in page 35.

Class Data The class also had an average mass ratio of 0.50. See the group data in page 36.

Summary Zinc and HCl will chemically combine in a constant proportion no matter the amounts of the reactants that is used.

• 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.

Zn

Zn

Zn

Zn

HCl

HCl

HCl

HCl

HCl

HCl Left over HCl

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

HCl

HCl

Left over Zn

Zn

Zn

Zn

Zn

Zn

Groups with greater than 1.9g Zn used up all their HCl and were evaporating water.

The limiting reactant in these groups was HCl.

By Amparo Krug2006

POST LAB

Lab 6.6 Reaction with Copper

This lab will be done as a demo because we are running out of time.

BDQBDQ 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

• CuO will 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.

Mixture

Pure substance Pure substance

Compound Element

Pure substance Element

Compound Element

Concept Map

Separate into

Can beCan be

orBroken into

Concept map

• Mixtures can be separated by physical means into pure substance.

• A pure substance can be a compound or an element

Compounds1. Cannot be separated by physical means, because

they are chemically bonded.2. Have different properties from the elements of

which they are made.3. Are synthesize from other pure substances in

constant ( definite ) proportions.4. 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 the same 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.

ANTOINE LAURENT LAVOISIER, 1743-1794

• 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

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.

Elements Near the Surface of the Earth (top 8)

1. Oxygen2. Silicon3. Hydrogen4. Aluminum5. Iron6. Calcium7. Sodium8. Magnesium

• The first 5 form 92% of the total mass of the elements found near the surface of the earth.

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