CHM 120 Lecture Notes - Lecture 16: Atomic Mass, Molar Mass, Unified Atomic Mass Unit

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4 Oct 2016

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One more of atoms, ions or molecules generally makes up objects of reasonable seize. Example: 22 copper pennies contain approximately 1 mole of copper (cu) atoms. 1mole cu atoms = 6. 022x 10&23 cu atoms. Converting between moles and number of atoms. Solution map: mol atoms number of atoms ( = avogadros number) 1mol atoms = 6. 022 x 10^23 atoms (avogadros number) Example 1: calculate the number of iron atoms in 125 moles of iron atoms. Solution map: mol fe number of fe atoms. 1mol fe atoms= 6. 022 x 10623 fe atoms. 125 mol fe (6. 022 x 10^23 fe atoms) / 1mol fe = 7. 53 x 10^25 fe atoms (3s. f. ) Example 2: convert 1. 1 x 10^22 silver atoms to moles of silver. 1mol ag atoms = 6. 022 x 10^23 ag atoms. 1. 1 x 10^22 ag atoms x 1 mol ag / 6. 022 x 10^23 ag atoms = 1. 8 x 10^-2 mol ag. Converting between grams and moles of an element.

Related Questions

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

1. Consider the unbalanced equation for the reaction of solid lead with a silver nitrate solution.

_____Pb (s) + ______AgNO3 (ac) â ______Pb(NO3)2 (ac) + _______Ag (s)

a. Balance the equation.

b. How many moles of silver nitrate are required to react completely with 9.3 mol of lead?

c. How many moles of silver, Ag, are formed by the complete reaction of 28.4 mol of Pb?

2. For the following reaction: _____CaO (s) + _____CO2 (g) â _____CaCO3 (s), Calculate how many grams of CaCO3, are formed when 2.4 g of CaO Do they react completely with CO2?

3. For the following reaction: 2 Li (s) + F2 (g) â 2 LiF (s), find the reagent limiting with the amounts of 1.0 mol of Li and 1.0 mol of F2.

4. For the next reaction, determine the limiting reagent, calculate the yield Theoretical product in grams with 5.5 g of Al and 19.8 g of Cl2.

2 Al (s) + 3 Cl2 (g) â 2 AlCl3 (s)

5. Consider the reaction between NiS2 and O2:

2 NiS2 (s) + 5 O2 (g) â 2 NiO (s) + 4 SO2 (g)

When 11.2 g of NiS2 react with 5.43 g of O2, 4.86 g of NiO are obtained. Determine the limiting reagent, the theoretical yield of NiO and the% yield for the reaction.

6. How many atoms of mercury are in 5.8 mol of mercury?

7. Complete the following table:

Element Moles Mass Number of molecules

8. How many grams of sodium are there in 1.00 g of each of the following compounds?

a. Na3PO4

b. NaC7H5O2

c. Na2C6H6O7

9. A sample of 4.78 g of aluminum reacts completely with oxygen to form 6.67 g of aluminum oxide. Use the data to calculate the percent of composition by mass.

10. Citric acid, the compound responsible for the bitter taste in lemons, has the following composition: C - 37.51%

H - 4.40%

O - 58.29%

Calculate the empirical formula.

11. A compound containing phosphorus and oxygen has a molar mass of 219.9 g / mol and an empirical formula of P2O3. Find the molecular formula of compound.

12. It is a term used in chemistry, to describe a system in which a

or more substances, are mixed or dissolved homogeneously in another

substance.

a. Mixture

b. Solution

c. Compound

d. None of the above

13. It is the component that is in a solution, in smaller quantity.

a. Solution

b. Solvent

c. Solvent

d. Soluto

14. It is the component that is in a solution in greater quantity.

a. Solution

b. Solvent

c. Solvent

d. The answers b and c are correct.

15. The quantitative expression of the dissolved amount of solute in a quantity determined solvent is known as:

a. Solution

b. Volume

c. Concentration

d. Stoichiometry

16.Express the moles of solute among the liters of solution

a. Molality

b. Molarity

c. % weight by volume

d. % weight by weight

17.Express the moles of solute between kg of solvent

a. Molarity

b. ppm

c. ppt

d. Molality

18. What is the molarity of a solution prepared by dissolving 7.50 g of nitrate of magnesium, Mg (NO3) 2 in enough water to prepare 25.0 mL of solution?

a. 10.3 M

b. 5.6 M

c. 6.5 M

d. 2.03 M

19. How many grams of sodium chloride, NaCl are needed to prepare 125 mL of 0.037 M NaCl solution

a. 1.021 M

b. 0.268 M

c. 0.201 M

d. 0.500 M

20. Calculate the molality of a solution containing 12.5 g of ethylene glycol (C2H6O2) dissolved in 135 g of water.

21. A solution of ethylene glycol contains 21.2 g of ethylene glycol (C2H6O2) in 85.4 mL of water. Calculate the freezing point and the boiling point of the solution. (Assume the water density is 1.00 g / mL)

22. At what volume should you dilute 75 mL of a 10.0 M solution of H2SO4 to obtain a 1.75 M solution of H2SO4.

Having trouble with thse questions. Please answer all questions correctly. Will provide a thumbs up.

1.Which of these equations is the balanced reaction between nitrous acid solution and solidmagnesium hydroxide ?

A.2NH₃(aq) + MgOH (s) Mg(NH₄)₂(aq) + 2 H₂O(l)

B.2HNO₂(aq) + Mg(OH)₂(s) Mg(NO₂)₂(aq) + 2 H₂O(l)

C.2HNO₃(aq) + Mg(OH)₂(s) Mg(NO₃)₂(aq) + 2 H₂O(l)

D.2HNO₂(aq) + MgOH (s) Mg(NO₃)₂(s) + 2H₂O(l)

2.Balance the following chemical equation:

C₃H₇OH(l) + O₂(g)CO₂(g) + H₂O(g)

a. C₃H₇OH(l) + 4 O₂(g)3 CO₂(g) + 4 H₂O(g)

b.2 C₃H₇OH(l) + 9 O₂(g)6 CO₂(g) + 8 H₂O(g)

c.C₃H₇OH(l) + 5 O₂(g)3 CO₂(g) + 4 H₂O(g)

d.C₃H₇OH(l) + O₂(g)CO₂(g) + H₂O(g)

3.Which species would be considered a spectator ion based on the following equation?

Ba²⁺ + 2NO₃^â + 2Na⁺ + SO₄^2- â BaSO₄(s) + 2NO₃^â + 2Na⁺

SO₄^2-

2NO₃^â

Ba²⁺

BaSO₄

4.Barium sulfate is often ingested to aid in the diagnosis of GI tract disorders. The equation for its production is Ba²⁺ + SO₄^2- â BaSO₄(s). What type of equation is this?

A full equation

A net ionic equation

A total ionic equation

An oxidation-reduction equation

5.Which species is being reduced in this reaction?

CuO(s) + H₂(g) Cu(s) + H₂O(g)

H₂O

CuO

H₂

6.Which of the following is an oxidizing agent?

H₂

NH₃

O₂

H₂O

7.The following chemical equation,

HC₂H₃O₂(aq) + KOH(aq) KC₂H₃O₂(aq) + H₂O(l),

is an example of a(n) _______ reaction.

a.oxidation-reduction and acid-base

b.acid-base

c.precipitation

d.oxidation-reduction and precipitation

e.oxidation-reduction

8.What substance is oxidized in the following reaction?

4HCl + MnO₂ â Cl₂ + 2H₂O + MnCl₂

a.Mn in MnO₂

b.O in MnO₂

c.Cl in HCl

d.H in HCl

9.What is the reducing agent in the following reaction?

4HCl + MnO₂ â Cl₂ + 2H₂O + MnCl₂

Cl₂

MnCl₂

HCl

MnO₂

10.All redox reactions involve oxygen.

True

False

11.The term formula weight can be used with respect to which of the following?

A.ionic compounds

B.covalent compounds

C.both a and b

D.neither a nor b

12.What is the molecular weight of ibuprofen, C₁₃H₁₈O₂?

A.206.3 amu

B.377.7 amu

C.29.0 amu

D.289.4 amu

13.The mass of an atom of ¹²C is exactly 12 atomic mass units. Which of the following describes a mole of ¹²C atoms?

A.a sample which weighs exactly 12 atomic mass units

B.a sample which contains 6.02 Ã 10²³ atoms of ¹²C

C.both a and b

D.neither a nor b

14.The mass of an atom of ¹²C is exactly 12 atomic mass units. Which of the following describes a mole of ¹²C atoms?

A.a sample which contains 6.02 Ã 10²³ atoms of ¹²C

B.a sample which weighs exactly 12.011 grams

C.both a and b

D.neither a nor b

15.What is the molar mass of water, H₂O?

A.18.02 g

B.18.02 amu

C.17.01 g

D.17.01 amu

16.What is the molar mass of glucose, C₆H₁₂O₆?

A.180.2 amu

B.180.2 g

C.60.05 amu

D.60.05 g

17.In the reaction 2H₂O â 2H₂ + O₂, 2.0 mol water will produce how many grams of O₂?

18.In the reaction 2CH₄ + O₂ â 2CO + 4H₂, how many molecules of CO will be produced by the complete reaction of 1.60 grams of CH₄?

3.01 Ã 10²²

2.00

12.0 Ã 10²³

6.02 Ã 10²²

19.Suppose 2.43 g of magnesium is reacted with 3.20 g of oxygen: 2Mg + O₂ â 2MgO. How many grams of MgO will be produced?

1.27

4.03

5.63

8.06

20.Which of the following conversion factors would allow one to calculate the amount of PbI₂produced from a given amount of NaI in the following unbalanced reaction?

Pb(NO₃)₂ + Nal â Pbl₂ + NaNO₃

21.The unbalanced equation for the reduction of copper(I) sulfide with oxygen is given below. What mass of copper is produced from the reduction of 7.50 g Cu₂S?

Cu₂S(s) + O₂(g) Cu(s) + SO₂(g)

18.8 g

5.99 g

1.50 g

9.39 g

2.99 g

22.How many grams of aluminum oxide are produced by the complete reaction of 19.8 g aluminum with excess oxygen?

10.5 g aluminum oxide

37.4 g aluminum oxide

49.9 g aluminum oxide

74.8 g aluminum oxide

23.If 5 grams of CO and 5 grams of O₂ are combined according to the reaction, which is the limiting reagent?

2CO + O₂ â 2CO₂

O₂

CO and O₂

CO₂

24.In an industrial process, nitrogen is reacted with hydrogen to produce ammonia. The percent yield of this particular process is 26%. How much hydrogen is needed to produce 4.8 kg ammonia?

1.5 kg

7.0 kg

0.85 kg

3.3 kg

25.A percentage yield greater than 100% has been reported in a scientific paper you are assigned to read. What would be a reasonable explanation for this?

a. The product was measured more than once.

b. It must be a typographical error since yields can't exceed 100%.

c. A lack of training of the professor who published the study.

d. Small measurement errors could have caused this to occur.

26.In an industrial process, nitrogen is reacted with hydrogen to produce ammonia. The percent yield of this particular process is 24.8%. How much hydrogen is needed to produce 3.7 kg ammonia?

1.8 kg

1.2 kg

4.4 kg

12 kg

2.7 kg

27.The following reaction has a percent yield of 90.5%. How many grams of carbon dioxide are produced from 78.5 g calcium carbonate via this reaction?

2 HNO₃(aq) + CaCO₃(aq) Ca(NO₃)₂(aq) + H₂O(l) + CO₂(g)

34.5 g

21.6 g

38.1 g

31.2 g

28.When gas molecules dissolve in liquids to form a saturated system, the process is usually

exothermic.

endothermic.

independent of the nature of the liquid.

temperature independent.

29.The reaction below would be considered.

CaCO₃ + heat â CaO + CO₂

an exothermic combination.

an exothermic decomposition.

an endothermic combination.

an endothermic decomposition.

30.The combustion of one mole of propane, C₃H₈, releases 531 kcal. How much heat is released by the combustion of 1.20 moles of propane?

A.584 kcal

B.690 kcal

C.443 kcal

D.637 kcal

31.The combustion of one mole of propane, C₃H₈, releases 531 kcal. How much heat is released by the combustion of 4.40 g of propane?

A.531 kcal

B.5.31 Ã 10⁴ kcal

C.53.1 kcal

D.5.31 Ã 10³ kcal

32.Metabolism of one mole of glucose, C₆H₁₂O₆, releases 670 kcal. How much heat is released by the combustion of 0.300 moles of glucose?

A.201 kcal

B.2.41 Ã 10³ kcal

C.186 kcal

D.2.23 Ã 10³ kcal

33.Metabolism of one mole of glucose, C₆H₁₂O₆, releases 6.70 Ã 10² kcal. How much heat is released by the combustion of 50.0 g of glucose?

A.201 kcal

B.2.41 Ã 10³ kcal

C.186 kcal

D.2.23 Ã 10³ kcal

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CHM 120 Lecture Notes - Lecture 16: Atomic Mass, Molar Mass, Unified Atomic Mass Unit

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