Stoichiometry
Complete the following sentences by filling in the appropriate word or phrase from the list below. Each word or phase may be used once, more than once, or not at all.
reactants actual coefficients molar ratio particles subscripts quantitative conservation of matter mass
1. Stoichiometry is the study of the ______relationships that exist in chemical reactions.
2. Stoichiometry can be used to determine how much product will form from a given amount of ______.
3. The ______in a balanced equation indicate(s) the number of particles of each substance taking place in the reaction.
4. It is possible to interpret the coefficients in a balanced chemical equation as either the number of moles or the number of ______involved in the reaction.
5. The coefficients in an equation do not show the ______number of moles, only the relative number involved.
6. You must determine the ______in a balanced equation before solving any stoichiometry problem.
7. A balanced equation verifies the law of ______.
True or False
9. You can determine the number of moles of any substance produced in a reaction if you know the number of moles of at least one of the reactants. ______
10. The molar ratio of hydrogen to oxygen in the equation 2H2 + O2 yields 2H2O is 1:2 .______
11. The total mass of the reactants is equal to the total mass of the products in a chemical reaction. ______
12. It is possible to change grams of an element directly into atoms by not including the mole step in the solution. ______
Show all work for solutions to the following problems:
13. How many moles of magnesium are required to react with 2.0 mol of hydrochloric
acid? The equation for this reaction is Mg + 2HCl yields MgCl2 + H2.
14. Aluminum reacts with HCl to produce aluminum chloride (AlCl3) and hydrogen gas.Write a balanced equation for the reaction and calculate the number of moles of HCl required to react with 0.87 mol of Al.
15. Glucose (C6H12O6) combines with O2 in the body to produce carbon dioxide and water. Write a balanced equation for this reaction. How many moles of O2 are required to combine with 0.25 mole of glucose? How many moles of CO2and H2O would be produced in this reaction?
16. Calcium carbonate (CaCO3) combines with HCl to produce calcium chloride (CaCl2), water, and carbon dioxide gas. Write a balaced equation for this reaction. How many moles of HCl are required to react with 2.5 mol of CaCO3? How many moles of CO2 would be produced?
17. Zinc reacts with H2SO4 to yield ZnSO4 and hydrogen gas. How many moles of hydrogen will be produced if 0.36 mol of zinc react with an equal amount of H2SO4?
18. For the following reactions identify which reactant is in excess and by how much? (Hint write balanced equations first.)
ReactionNo. / Reactant A / Reactant B / Excess reactant / Amount in excess
1 / 5 g H2 / 22.8 dm3 of O2 at STP
2 / 15 g Zn / 150 ml of 0.1 mol dm-3 HCl
3 / 150 g Fe / 63 g Oxygen
4 / 15 ml 0.5 mol dm-3 AgNO3 / 12 ml 04 mol dm-3 KI
5 / 25 g ethane / 40 g oxygen
6 / 8 g carbon / 2 g hydrogen
19. A certain antacid tablet contains 750 mg of calcium CaCO3. The volume of gastric juice in our stomach is about 2.5 L and the hydrochloric acid is present at a concetnration of about 0.15 mol dm-3 . How many moles of acid is present if no food has been eaten? Write a balanced equation for the reaction. If a student mixes 6 of these tablets with 2.5 L of 0.15 M HCl in the laboratory, which would be in excess the acid or the calcium carbonate? Justify your answer. The CO2 produced was collected in a rubber balloon. What volume would the balloon have at SLC (Vm = 24.5 ), assuming it does not burst or leak?
Atomic Structure Exam Questions
1) The first ionisation energies of the elements Lithium to Neonare given below.
LiBeB CNO F Ne
51990079910901400 1310 16802080
a) Define the term first ionisation of an element, and give an equation illustratingyour answer with oxygen.
b) Explain why the ionisation energies show an overall tendency to increaseacross the period.
c) Explain the irregularities in this trend for
i) Boron
ii) Oxygen
d) Explain the trend in the ionisation energies with increasing atomic number inGroup 1 of the periodic table.
e) An element X has the following successive ionisation energies as follows:
786: 1580: 3230: 4360: 16000: 20000: 23600: 29100 KJ/mol
i) To which group in the periodic table does element X belong?
ii) Write down the outer electronic configuration of an atom of X.
iii) Suggest formulae for TWO chlorides of X.
Part B
1. An element Z has three peaks in its mass spectrum.
a. Explain why an element could show more than one peak in its mass spectrum. (2)
b. Use the following information to calculate the relative atomic mass of element Z. (2)
Mass of Peak % Abundance
71 34
72 55
73 11
c. Chlorine has two isotopes of mass 37 and 35, these have a relative abundance of 25% and 75% respectively. Assuming that the main peaks in mass spectrum of chlorine are due to ionised chlorine molecules (Cl2+)
i.State and briefly explain how many peaks will be observed (2)
ii.Calculate the atomic mass of chlorine. (2)
iii.Bromine has two isotopes of mass 79 and 81. The two isotopes both have approximate relative abundances of 50%. Sketch the mass spectrum of bromine.
d. i. Name the parts A to E in the following diagram of a mass spectrometer:
ii. State the functions of the accelerating electrode and the magnetic field.
2. Calculate the relative atomic mass of molybdenum from the mass spectrum below.
3. Write the complete electronic configuration for Carbon (C)
4. Write the complete electronic configuration for Iron (Fe)
5. Write the complete electronic configuration for Bismuth (Bi)
6. Write the complete electronic configuration for the cation of Zirconium: Zr+1
7. Write the complete electronic configuration for the anion of Antimony: Sb-2
8. Write the complete electronic configuration for Tungston (W)
17. Which of the following represents the proper order of atomic radius increasing from smallest to largest?
A. Si < Si+1 < Si+2
B. Si+2 < Si < Si+1
C. Si+1 < Si+2 < Si
D. Si+2 < Si+1 < Si
E. Si < Si+2 < Si+1
18. Which of the following represents the proper order of atomic radius increasing from smallest to largest?
A. As < As-1 < As-2
B. As-2 < As < As-1
C. As-1 < As-2 < As
D. As-2 < As-1 < As
E. As < As-2 < As-1
19. Which of the following represents the proper order of atomic radius increasing from smallest to largest?
A. Cu < Au < Ag
B. Cu < Ag < Au
C. Au < Cu < Ag
D. Au < Ag < Cu
E. Ag < Au < Cu
F. Ag < Cu < Au
20. Which of the following represents the proper order of atomic radius increasing from smallest to largest?
A. In < Sn < Sb
B. Sn < Sb < In
C. Sb < In < Sn
D. Sb < Sn < In
E. Sn < In < Sb
F. In < Sb < Sn
21. Which of the following represents the proper order of ionization energy increasing from smallest to largest?
A. Na < Rb < K
B. Rb < K < Na
C. K < Na < Rb
D. Rb < Na < K
E. K < Rb < Na
F. Na < K < Rb
22. Which of the following represents the proper order of ionization energy increasing from smallest to largest?
A. Co < Ni < Fe
B. Fe < Ni < Co
C. Ni < Co < Fe
D. Fe < Co < Ni
E. Co < Fe < Ni
F. Ni < Fe < Co
23. Which of the following represents the proper order of electron affinity increasing from smallest to largest?
A. C < N < O
B. O < N < C
C. N < O < C
D. O < C < N
E. C < O < N
F. N < C < O
24. Which of the following represents the proper order of electron affinity increasing from smallest to largest?
A. Al < Ga < B
B. B < Al < Ga
C. Ga < Al < B
D. Ga < B < Al
E. Al < B < Ga
F. B < Ga < Al
25. Complete the table below – remember A = P = E and M = A + N
Species / Atomicnumber / Mass Number / No. protons / No. electrons / No. neutrons / Electronic configuration
25 / 23 / 30
17 / 35 / 18
35 / 35 / 45
26. Explain how an emission spectrum for hydrogen is formed. How does the spectrum vary when the electrons return to n = 1 compared to n = 2?