Chem A Final Exam Review In-class problem-solving.

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.

6. What is the difference between:Boiling/condensationSublimation/depositionMelting/freezing

Solid Liquid Gas

deposition

sublimation

condensationfreezing

evaporationmelting

Endothermic processes

Exothermic processes

Heat curve – be able to label!

Solid

Boiling(lg)

Melting (sl)

Liquid

Gas

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

11. What is the empirical formula for C4H10?

Empirical formula = simplest whole-number ratio

C2H5

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

23. Write the Ksp expression for Iron (II) nitrate (s).Ksp = [Fe2+][NO3

-]2

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.

27. Calculate [H3O+] for a substance with a pH of 5.7.

[H3O] = 10-pH

= 2.0 x 10-6

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.

33. Which molecule is nonpolar?a. CO2 b. NaCl c. NH3

Carbon dioxide

34. What particle is omitted when Po-210 changes to Pb-206?alpha

35. How many moles are in 236 g of NaOH?5.90 moles

36. What is the IUPAC name for Ni3(PO4)2?

Nickel (II) phosphate

37. How many grams of Na are in 56 g of NaOH?22.99/40.00 X 56g= 32 g

38. Consider the following reactants:Cu(NO3)2 (aq) + Zn(s) Predict productsBalance equationWhat is the oxidizing agent?

Cu(NO3)2 (aq) + Zn (s) Zn(NO3)2(aq) + Cu(s)

OIL RIGZn must lose electrons to form ion so it is

being oxidized. Cu 2+ is oxidizing agent