Chem A Final Exam Review In-class problem-solving.
Transcript of Chem A Final Exam Review In-class problem-solving.
1. Determine the oxidation state of S in HSO3
-.Set your equation equal to -1 since this is
a -1 ion.Assign the most electronegative atom
first. In this problem it is O. O usually has an oxidation state of -2. Since there are 3, total = -6.
Assign H next. H usually has an oxidation state of +1.
S must be +4. (+1) + (+4) + (-6) = -1
2. What are the products of the reaction between LiOH and HF? What type of reaction is this?
Neutralization reaction.Water and salt (LiF)LiOH + HF H2O+ LiF
3. How many grams of NaOH should be added to 225g of water to produce a 0.10m solution?
m = mol of solute/kg of water0.1 = x/.225X = .0225 mol.0225 mol X 40.00 g/mol = .90g
4. How many unpaired electrons are in the ground state of oxygen?= 2 unpaired electronsElectron configuration = 1s22s22p4
Electron dot = O
5. Which demonstrates the trend for increasing atomic radius?a. Li; Na; K or b. Ba; Sr; Ca
a. Atomic radius increases as you move down a family.
Solid Liquid Gas
deposition
sublimation
condensationfreezing
evaporationmelting
Endothermic processes
Exothermic processes
7. Add 5.47 g, 4.2 cg and 5.39g
1. Be sure to convert so all units are the same.
2. This is a significant figure problem. When adding or subtracting look at places past decimal.
5.47g + .042g + 5.39g=10.90g
8. What is the total number of ions in 2.0 mol Cu(NO3)2?
2 mol X (3 ions/1 mol) x (Avogadro’s #/1 mol)
= 3.6 x 1024ions
9. What is the correct formula for magnesium sulfate?Reminders:Write the charges of ionsThe sum of the charges must equal 0 for a
neutral compoundMagnesium cation = 2+ sulfate anion= 2-Need one of eachORWrite charges and use criss-cross rule. Like
charges cancel out. Remember to reduce if able
Answer = MgSO4
10. Write a balanced equation of the reaction between aluminum sulfate and calcium hydroxide.
Al2(SO4)3 + 3Ca(OH)2 2Al(OH)3 + 3 CaSO4
12. A 5.0 L of krypton gas is at a pressure of 765 mmHg. At constant temperature what volume will the gas occupy if the pressure decreases to 700. mmHg?
Boyle’s Law = P1V1 = P2V2; (765)(5.) = (700.) (x) = 5.5 L
13. Use the following equation: Fe2O3 + CO Fe + CO2
What mass of Fe is formed from 1800g of Fe2O3?
Answer = 1300g Fe (sig figs)1. Balance equation.2. Must have a mole:mole ratio3. In order to achieve this you must use
molar masses to convert to moles4. Fe2O3 + 3CO 2 Fe + 3CO2
14. How many oxygen atoms are present in iron (II) sulfate octahydrate
FeSO4 .8H2O 4 O in iron (II) sulfate8 O in waterAdd! = 12 OThe dot just means water can be removed
– do not multiply!
15. How many liters of H2O (g) at STP will react with one mole of H2S?
H2S + O2 H2O + SO2
Balance equation!2H2S + 3O2 2H2O + 2SO2
Use 22.4 L = 1 molAnswer = 22.4 L
16. A sample of ethanol required 25 kJ of energy to be heated from 20.°C to 28°C . How many grams of ethanol were heated? Ethanol Cp = 3.42 J/g .°C.Q = (m)(∆T)(Cp )25000J = (m)(8)(3.42)m = 914g
17. A weak base is titrated with a known concentration of a strong acid. Sketch the titration curve.
Based on equivalence point.Above 7 = strong base/weak acid
At 7 = strong base/strong acidBelow 7 = weak base/strong acid
Graph on next slide
Titration curve weak base/strong acid
Starting Solution: weak baseAdded Standard: strong acid14 7 equivalence point (below 7) 1 10 20 30 40
18. Choose the series of elements that increases in electronegativity.a. Rb, Cs, Fr b. N, O, F
B. Remember atomic radius! Decreases as you go left to right, increases as you go down. All other trends are opposite!!!
19. Calculate p+, n0, and e- in S 2-.
SulfurAtomic # = 16Atomic mass = 32 proton # = Atomic # =16Neutron# = Mass # - Atomic # = 16Electrons = protons in a neutral atom.
Add 2 electrons to make this ion = 18 electrons
20. Is HSO4- acting as an
acid or a base in this equation?
HSO4- + H2O ↔ SO4
-2 + H3O+
HSO4- is the acid because it
donates a hydrogen ion (H+)
21. What is the atomic average atomic mass of the following isotope?Atomic Mass % Abundance26 66.628 15.730 17.7
Multiply each mass by abundance (move decimal 2 places to left)
Add your product – do NOT divide by 3!Answer = 27
22. The half-life for candium = 100 years. If 12.5% of a sample remains, how old is the candium sample?
3 half-lives go bySample is 300 years old
24. What is the H for the reaction A B? (see diagram on board)Reminders:Products – ReactantsIf products have more energy than the
reactants, the value is positive and the reaction is endothermic.
If the products have less energy than the reactants, the value is negative and the reaction is exothermic.
25. A compound is 36.5% sodium, 25.4% sulfur, and 38.1% oxygen. What is the empirical formula? If the molecular mass is 252, what is the molecular formula?
% to massMass to molesDivide by smallestMultiply until whole= Na2SO3
26. Describe how you would determine the density of cube of copper 1.0 cm on each side? How would determining density of an irregular object differ?D = mass/volume
L x w x h = volume; then mass object
Mass the object and then use a graduated cylinder to determine water displacement.
28. What is the pH and pOH of a solution if the [H3O+] is 3.4 x 10 -5M?
pH = -log[H3O+]pH = 4.5pH + pOH = 14pOH = 9.5
29. Mineral oil dissolves in canola oil but does not dissolve in water. What is the reason for this?
“like dissolves like”Polar solutes dissolve in polar solvents and
nonpolar solutes dissolve in nonpolar solvents
Water is a known polar compoundThe oils must be non-polar.
30. Name the following: H H H H H H H-C - C - C-H H-C = C -C-H H H H H
Propane – 3 carbons, all single bondsPropene – 3 carbons, 1 double bond
31 What is the molecular geometry of the following?
a. BF3 b. CH4 c. NH3a. = trigonal planarb.= tetrahedralc. = trigonal pyramidal
F B F H F H C H N H H H H
32. Which has a greater effect on the melting point of ice?
a. MgBr2 b. CH2H5OH c.KCl
a. Dissociation factor is 3. the d.f. in b is one and the d.f. in c is 2. in equal amounts, magnesium bromide will have the greater effect.