CHEM 1021 Lecture Notes - Lecture 22: Chemical Change, Flowchart, Sulfuric Acid

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16 Oct 2016

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Chemical change: one or more substance is converted to one or more new substances. Rusting iron: change in color and chemical composition. Clues that we have a chemical change: light, color change, heat, absorbed or produced, forming of a solid, precipitate, smoke, solid coating, formation of a gas. Carbon reacts with oxygen to produce carbon dioxide. C(s) + o2(g) co2 (g) (sometimes we can use physical state or phase) Solid carbon (graphite) reacts with oxygen gas producing carbon dioxide gas. H2 + o2 h2o (cid:862)skeleto(cid:374) (cid:272)he(cid:373)i(cid:272)al e(cid:395)uatio(cid:374)(cid:863) Law of conversation of mass must be obeyed balanced chemical equation: Mass is neither created nor destroyed in any ordinary. **things to keep in mind*: consistent with experimental observations, all formulas must be correct, law of conservation of mass is obeyed, balance by writing numbers to the left of symbols/formula. Balancing chemical equations flowchart: translate the statement, make sure the formulas are correct, adjust the coefficients, check atom balance.

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I need help doing my lab homework, I missed lab that day because, I was sick and it's due.

Chemical Reactions and Equations Learning objectives To observe physical and chemical properties associated with chemical changes To be able to give evidence for the occurrence of a chemical reaction To write a balanced chemical equation To identify areaction as a combination, decomposition, precipitation, single or double replacement, or combustion reaction ntroduction When a substance undergoes a physical change, it changes its appearance but not its composition. For example, when ice melts to form water, it undergoes a physical change from solid to liquid. In a chemical change, the composition of a substance is changed to give a new substance with different physical and chemical properties. For example, when silver tarnishes, the shiny silver (Ag) changes to a dull gray silver sulfide (AgaS). Not only has the chemical formula changed from Ag to Agus, but also the physical properties (shininess) of the substance have changed. Some examples of physical and chemical changes are listed in Table 1 below. Table 1. Comparison of Physical and Chemical Changes Examples of Physical changes Examples and Evidence of Chemical Changes Change in state (melting, freezing, evaporating Formation of a gas (bubbles) subliming) Formation of a solid (precipitate) Change in size Tearing Change in Color Heat is given off or absorbed A solid dissolving in a solvent In a chemical reaction, atoms in the reactants are rearranged to produce new combinations of atoms in the products. However, the total number of atoms of each element in the reactants is equal to the total number of atoms in the products. This is true according to the Law of Conservation of Mass, which states that the total mass remains constant during a chemical reaction. In other words, matter cannot be created or destroyed in a chemical reaction. In a chemical equation, the reactants are shown on the left and the products are on the right. An arrow in between indicates that a chemical reaction occurs. Finally, the physical state of each compound is designated in parentheses after the chemical formula. Solid, liquid, gas, and aqueous (dissolved in water) are shown as(s,(n,(g), and (aq), respectively.

7.
Calculate the percentage, by mass, of fluorine in sulfurhexafluoride (SF6), a potent greenhouse gas.
A) 78.0%
B) 59.2%
C) 22.0%
D) 82.1%
E) 85.7%

8.
Octane (C8H18) is one of the principal components of gasoline. Howmany moles of CO2 are produced during the combustion of 3.0 mol ofoctane?
Unbalanced equation: C8H18 + O2 --> CO2 + H2O
A) 3.0
B) 26
C) 24
D) 8.0
E) 4

9.
How many atoms are present in 0.375 mol of palladium (Pd)atoms?
A) 6.23 x 1021
B) 2.26 x 1023
C) 6.02 x 1023
D) 1.61 x 1024
E) 2.12 x 1021

10.
How many molecules are present in 1.0 kg of hydrogen (H2)gas?
A) 6.0 x 1023
B) 3.0 x 1026
C) 6.0 x 1026
D) 3.0 x 1023
E) 1.7 x 1025

11.
What evidence indicates that the rising atmospheric CO2 levels arecaused by the combustion of fossil fuels?
A) Both the average global temperature and the atmospheric CO2level have risen.
B) The 14C/12C ratio in atmospheric CO2 is unusually low.
C) Increased precipitation in most of the NorthernHemisphere.
D) The 18O/16O ratio in atmospheric CO2 is the same as inatmospheric oxygen.
E) The level of atmospheric moisture has increased.

12.
Heat is a form of
A) Energy
B) Pressure
C) Work
D) Volume
E) Temperature

13.
Oxygenated gasolines
A) Are gasolines that have oxygen gas bubbled through them
B) Contain nitrogen containing compounds
C) Are formulated to contain water
D) Have higher activation energies for combustion than regulargasolines.
E) May contain MTBE or ethanol

14.
A chemical reaction accompanied by a release of energy is calleda/an ______ reaction.
A) exothermic
B) fast
C) activated
D) catalyzed
E) endothermic

15.
The diagram below shows a simplified version of a fractionatingcolumn used in the petroleum industry.

The compounds with the lowest boiling points are condensed atposition

A) C.
B) D.
C) B.
D) A.

16.
Where is most of the carbon on earth stored?
A) in the form of fossil fuels
B) in the deep ocean
C) in the atmosphere
D) in surface water
E) in the forests and soil

17.
Find the molar mass of ethanol, C2H6O.
A) 22.1 g/mol
B) 26.0 g/mol
C) 46.07 g/mol
D) 45.06 g/mol
E) 29.02 g/mol

18.
Determine the shape or geometry of PH3. (Hint: Use the PeriodicTable to arrive at the electron configuration forphosphorous.)
A) trigonal planar
B) linear
C) trigonal pyramidal
D) bent
E) tetrahedral

19.
The energy stored in the chemical bonds of fossil fuels is a formof ______ energy.
A) nuclear
B) potential
C) mechanical
D) kinetic
E) electrical

20.
The heat of combustion of methane, CH4, is 50.1 kJ/g. How much heatwould be generated if 1.00 mol of methane undergoes completecombustion?
A) 50.1 kJ
B) 804 kJ
C) 601 kJ
D) 0.32 kJ
E) 3.12 kJ

21.
Methane is approximately 23 times more powerful than carbon dioxideas a greenhouse gas. Which are significant sources of methaneemissions?
I. The digestive systems of ruminants (cows, sheep, etc.)
II. Automobile exhaust
III. Rice cultivation
IV. Decaying wetland vegetation
A) I and II only
B) I only
C) All of these
D) II only
E) I, III, and IV only

22.
Which atmospheric component does not contribute to globalwarming?
A) CH4
B) CO2
C) CFC
D) N2
E) H2O

23.
What is the effect of infrared energy on matter?
A) It breaks chemical bonds.
B) It excites bonding electrons.
C) It increases molecular rotation.
D) It increases the vibration of chemical bonds.
E) It excites non-bonding electrons.

24.
According to current estimates, the fuel in greatest abundance onearth is
A) natural gas.
B) hydrogen
C) uranium.
D) coal.
E) petroleum.

25.
A gasoline's octane rating is a measure of the
A) purity of the gasoline.
B) energy content of the gasoline.
C) percent of gasoline that contains octane
D) pollutants produced by burning the gasoline in a vehicle'sengine.
E) gasoline's resistance to causing knocking in a vehicle'sengine.

26.
Advertising claims sometimes state that adding something mechanicalto a car's engine will allow it to recover 100% of the energy thatcomes from burning gasoline. You should be skeptical of such claimsbecause they are not consistent with the
A) first law of thermodynamics.
B) energy difference between reactants and products
C) second law of thermodynamics.
D) law of conservation of matter.
E) activation energy requirements of all chemical reactions.

27.
In order to make useful predictions, which factors must beaccounted for by climatic models?
I. Cooling effect of atmospheric aerosols
II. Smoke, haze, and cloud cover
III. Change in land use
IV. Combustion of fossil fuels
A) III and IV only
B) II, III, and IV
C) II and III only
D) I, II, III, and IV
E) IV only

28.
Use the equation to help you calculate the heat of combustion ofethylene, C2H4. The bond energies are: C H 416 kJ/mol; C C 598kJ/mol; O O 498 kJ/mol; C O 803 kJ/mol; H O 467 kJ/mol.

The heat of combustion of ethylene is

A) 1216 kJ/mol.
B) 220 kJ/mol.
C) 1324 kJ/mol.
D) 754 kJ/mol.
E) 242 kJ/mol.

29.
Scientists believe they know the average global temperature overthe last 160,000 years. Which property of the ice core samples fromAntarctica provides this information?
A) the 1H/2H ratio
B) the density of the ice
C) the thickness
D) the temperature
E) the carbon dioxide concentration

30.
(Both the Clinton) and the George W. Bush administrations have beenunwilling to sign the Kyoto Protocol. What has been a stated reasonfor their objection to the treaty?
A) Enforcement of the treaty will be impossible.
B) Lack of conclusive evidence that increased atmospheric CO2 leadsto global warming.
C) The target emission levels are not sufficiently low to affectthe greenhouse effect.
D) The treaty does not include a provision for trading emissionallowances.
E) Developing countries are not required to control greenhouse gasemissions.

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Decomposition of Malachite

Here is what Malachite is Made Out Of

Malachite is a famous and very popular semi-precious stone. Its banded light and dark green bands are one-of-a-kind, and give it a unique ornamental quality unlike that of any other stone. The light and dark green bands are so distinctive that malachite may be one of the most easily recognized minerals by the general public. Malachite is popular in jewelry, especially Native American southwestern jewelry. The stones inlayed in silver make a nice alternative to traditional turquoise jewelry.

Malachite is a form of copper carbonate with the molecular formula Cu₂CO₃(OH)₂. When heated to around 200 ï¿½C, malachite decomposes into copper (II) oxide (CuO) and other products.

Reaction Stoichiometry

The Law of Conservation of Mass states that matter can neither be created nor destroyed. Therefore, the number of atoms of each element on the reactants side must be same as the number of atoms on the products side. This quantitative study of chemical reactions is called stoichiometry. The substances in a balanced reaction are related to each other by stoichiometric molar ratios. For example, magnesium reacts with hydrochloric acid in a 1:2 stoichiometric ratio in the balanced equation below.

Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)

The molar ratios can be used as conversion factors to find the amount (in moles) of one substance given the amount of another. For example, given the number of moles of HCl, the amount of MgCl₂ can be determined as shown below.

nMgCl2=nHCl x (1mol MgCl2) / (2mol HCL)

The molar ratios are used to determine the amount in moles. However, the amount of reactant or product is often measured in grams. Mass can be converted to moles and vice versa as shown below.

n = m / (MM)

m = n x MM

where n is the number of moles, m is the mass of the product in g, and MM is its molar mass in g/mol.

To observe the Law of Conservation of Mass, you can perform different types of chemical reactions. For example, you can use a decomposition reaction to observe one compound being broken down into two or more elements or new compounds. For this reaction to take place, you must break existing bonds within the starting compound. Different sources of energy such as heat, light, or electricity may be used. Through a decomposition reaction, you can observe that the atoms in the original compound are not destroyed but are rearranged to form simpler substances, such as elements or compounds.

About This Lab

In this lab, you will test if the relationship between malachite and copper (II) oxide is stoichiometric. To do this, you will heat a known mass of malachite to produce copper (II) oxide. You will then compare the amount of copper (II) oxide obtained experimentally with the amount of copper (II) oxide expected from the balanced equation for the decomposition reaction.

1.Take a crucible from the Containers shelf and place it on the workbench.

2.Take a balance from the Instruments shelf and place it on the workbench.

3.Move the crucible onto the balance. Record the mass of the empty crucible to the nearest 0.001g in your Lab Notes.

4.Move the crucible onto the workbench.

5.Take copper (II) carbonate hydroxide from the Materials shelf and add 10 g to the crucible.

6.Move the crucible onto the balance and record the mass of the crucible containing copper (II) carbonate hydroxide in your Lab Notes.

7.Take a Bunsen burner from the Instruments shelf and place it on the workbench.

8.Move the crucible onto the Bunsen burner.

9.Double-click on the crucible to open its properties. Select Show Contents and click OK. This gives you a cut-away view of the crucible's contents.

10.Turn the Bunsen burner on to low flame by clicking the knob at the bottom once. Clicking multiple times will increase the intensity of the flame until it is turned off.

11.Watch the crucible until the malachite fully decomposes. You will see a distinct color change.

12.Move the crucible onto the workbench to cool.

13.Turn off your Bunsen burner.

14.Weigh the crucible with its contents and record the mass to the nearest 0.001 g in your Lab Notes.

Clear your station.

Lab Notes:

Numbers below refer to numbers in the above âAbout this Labâ

3. Empty crucible = 88 g

5. Added 10 g of Copper (II) carbonate hydroxide to crucible

6. Crucible with Copper (II) carbonate hydroxide = 98 g

11. to Black

14. after heating crucible with its contents = 95.195

Questions I have answered:

How many grams of malachite did you add to the crucible? 10g

How many grams of product were in the crucible after heating? 7.195

By how much did the mass of the crucible's contents change after heating? -2.805

The molar mass of malachite is 221.1 g/mol. How many moles of malachite were present before the reaction? 0.04523 mol

The product remaining in the crucible after heating is copper (II) oxide. The molar mass of copper (II) oxide is 79.55 g/mol. How many moles of copper (II) oxide were produced during the reaction?

0.0945 mol

Please answer the following:

Q1 a. Which of the following represents the balanced chemical equation for this reaction?

Cu2CO3(OH)2=2CuO+H2O

Cu2CO3(OH)2=CuO+CO2

Cu2CO3(OH)2=2CuO+H2O+CO2

Cu2CO3(OH)2=CuO+H2O+CO2

b. Based on the number of moles of malachite that you started with, how many grams of water were produced? The molar mass of water is 18.0153 g/mol. Choose the closest answer.

1.815 g 0.8148 g 1.630 g 1.982 g

c. Based on the number of moles of malachite that you started with, how many moles of CO₂were produced? Choose the closest answer.

1.000 mol 0.04523 mol 0.9000 mol 0.09045 mol

d. Based on the number of moles of malachite that you started with, how many grams of CO₂were produced? The molar mass of CO₂ is 44.01 g/mol. Choose the closest answer.

1.991 g 0.4401 g 0.04523 g 3.981 g

Q2a. Based on the number of grams of CO₂ and H₂O produced during the reaction, does this compensate for the observed loss of mass?

A. No, because this violates the law of conservation of mass

B. yes, this compensates for the mass lost in the reaction

C. No, because more copper oxide was produced

D. No because mass is conserved

b. You observed that the products in the crucible weigh less than the reactants that you added. How is this possible?

A. Mass was lost due to experimental error

B. The Malachite absorbed CO2 from the air

C. CO2 and H2O were released as gases

D. Mass was converted to energy

c. What kind of a reaction took place upon heating?

A. decomposition

B. single displacement

C. synthesis

D. Double displacement

d. Baking soda is used as a leavening agent in baking. When heated, baking soda undergoes a decomposition reaction to form carbon dioxide. Given the data below, which of the following reactions occurs during baking? The molar mass of baking soda is 84.007 g/mol and the molar mass of carbon dioxide is 44.01 g/mol.

Mass of empty crucible (g) = 55.000

mass of crucible with baking soda (g) = 57.000

mass of crucible and contents after the reaction (g) =56.260

A. 2NaHCO3= 2Na+2CO2 +H2O

B. 2NaHCO3 = Na2O + 2CO2 +H2O

C. NaHCO3 = NaOH +CO2

D. 2NaHCO3 = Na2CO3 + CO2 +H2O

CHEM 1021 Lecture Notes - Lecture 22: Chemical Change, Flowchart, Sulfuric Acid

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