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CHE 2A Lecture Notes - Lecture 4: Molar Mass, Molecular Mass, Chemical Formula

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UC-Davis
Department
Chemistry
Course
CHE 2A
Professor
toupadakis

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CHE 2A Full Course Notes
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CHE 2A Full Course Notes
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Document Summary

From experimental data, we find the mass % composition of a chemical compound. Mass % composition of a chemical compound: compound. Ex: mass % composition of sodium chloride, nacl. 39. 34% na and 60. 66% From mass % composition of a chemical compound, we find the empirical formula of the compound. Assume 100g of the compound because they gave you a percentage. For hydrogen, divide 11. 19g by 1. 008g (molar mass of hydrogen) to get moles. For oxygen, divide 88. 79g by 16. 00 (molar mass of oxygen) to get moles. Now we have 11. 10 moles of hydrogen and 5. 549 moles of oxygen. Divide both of these numbers by the smallest number of moles, which is. Now we have 2 moles of hydrogen and 1 mole of oxygen. From the empirical formula of a chemical compound, we find the molecular formula of the compound. We need to know the molecular mass. Ex: empirical formula is ch . molecular formula could be n(ch )

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Related Questions

CHM111

Q1. Which of the following contains the MOST atoms? You shouldn't need to do a calculation here.

A) 10.0 g Ne

B) 10.0 g He

C) 10.0 g Ar

D) 10.0 g Kr

E) 10.0 g Mg

Q2. How many atoms are present in 0.23 moles of Calcium?

Q3. How many atoms are present in 5.6 mg of Silicon?

Q4. How many grams of iodine do 5.6 x 1025 atoms of iodine represent?

Q5. Balance the following Chemical Equations:

_____ CaC2(s) + _____H2O(l) ? _____ Ca(OH)2(aq) + _____ C2H2(g)

_____ P4O10 + _____ H2O? ______ H3PO4

___ C3H8O3 + ___ O2 ? ___ CO2 + ___ H2O

_____ C4H10(l) + _____ O2(g) ? _____ CO2(g) + _____ H2O(g)

___ Al + ___ N2 ? ___ Al2N3

___ NaN3 ? ___ Na + ___ N2

___ C3H5N3O9 ? ___ CO2 + ___ N2 + ___ H2O + ___ O2

Q6. Calculate the percent composition of each element in Al(NO3)3

Q7. A 65.0 g sample of a pure compound containing only Nickel, Oxygen and Carbon is found to contain 22.36 g Nickel and 18.27 g Carbon. What is the empirical formula of compound?

Q8. Determine the Empirical formula and Molecular formula of a compound that contains: 65.4% C, 9.15% H and 25.4% N by mass and has a molar mass of 220 g/mol.

Q9. Oxygen gas can be produced by the decomposition of KClO3

2KClO3 (s) ? 2 KCl + 3 O2 (g)

How many grams of O2 can be produced from 1.625 g of KClO3?

Q10. Consider the following balanced reaction: 2 Fe (s) + Al2O3 (s) ® 2 Al (s) + Fe2O3 (s)

If 6.25 moles of Fe react with 2.50 moles of Al2O3

Which reactant is the limiting reagent?

How many grams of Al are produced?

Q11. Consider the reaction for the manufacture of Aluminum sulfate:

2 AlCl3 (aq) + 3 H2SO4 (aq) ? Al2(SO4)3(aq) + 6 HCl (aq)

If 15.0 g of AlCl3was mixed with 25.0 g of H2SO4, which reactant is the limiting reagent?

Calculate the theoretical yield of Al2(SO4)3.

If only 18.63 g of Al2(SO4)3 was produced, what is the percent yield of Al2(SO4)3?

Q13. How many grams of Nickel (II) chloride are needed to prepare 100.0 ml of 0.125 M solution?

Q14. What volume of 0.125 M KMnO4 (aq) solution can be prepared from 12.623 g of KMnO4?


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

_____Pb (s) + ______AgNO3 (ac) → ______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) → _____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) → 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) → 2 AlCl3 (s)

5. Consider the reaction between NiS2 and O2:

2 NiS2 (s) + 5 O2 (g) → 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.