Semester 1 Exam Review

Transcription

1 Semester 1 Exam Review 1. Compare physical and chemical changes in matter. Physical changes involve changing a substance s shape, texture, or size, not its chemical composition. Chemical changes result in a new substance being formed since the atoms have been rearranged. Some signs a chemical reaction has taken place include formation of a precipitate, formation of a gas, bubbles, change in color, and heat. Example: Chemical: iron rusting Physical: bending or crushing a metal rod 2. State the law on conservation of mass. Matter is neither created nor destroyed. In a chemical equation, the reactants must equal the products in terms of number and type of atoms and mass. 3. Define the following terms and list one example of each. a) heterogeneous mixture- Mixtures made up of distinct parts, like a salad or trail mix. b) homogenous mixture- Mixtures uniform in terms of consistency, like salt water or air. c) solution- A homogenous mixture made up of 2 or more substances with small particles. No Tyndall Effect d) colloid- A homogenous mixture made up of medium-sized particles. Tyndall Effect e) suspension- Mixture that contains large particles that slowly settle out. No Tyndall Effect 4. Define the following terms - see your textbook for definitions and examples. a. Chemical property b. Chemical change c. Physical property d. Physical change 5. Distinguish the symbols of common elements, and match the names of common elements to their symbols a. aluminum Al d. O oxygen b. nitrogen N e. C carbon c. copper Cu f. S sulfur

2 6. Define a neutral atom. An atom where the number of protons and electrons are equal, and therefore does not exhibit a charge. Atoms listed on the periodic table are neutral. 7. What is the name of C 6 14 Carbon-14 C 6 13 would be Carbon Element//Symbol Atomic # # of P + # of E - # of N 0 Mass # Hydrogen//H Carbon//C Neon//Ne Aluminum//Al Chlorine/Cl or or 36 Sodium//Na Potassium//K Given the electron configurations for the following neutral atoms, predict the oxidation number each is most likely to have. Element Configuration Oxidation Number A 1s 2 2s 2 2p 6 3s 2 +2 B 1s 2 2s 2 2p 6 3s 1 +1 C 1s 2 2s 2 2p 6 0 D 1s 2 2s 2 2p 5-1 E 1s 2 2s 2 2p Why do flame tests appear different colors? As the electrons absorb energy from the flame they move from the ground state to a higher energy level further from the nucleus (the excited state). When the return to the ground state they release this energy, often in the form of visible light. Because different atoms have different electron configurations the distance between the ground and excited states are different this leads to different color flames.

3 Different elements give off different light, in a sense providing a unique fingerprint for that element. 11. Write the electron configurations for the following elements. a. Lithium 1s 2 2s 1 b. Nitrogen 1s 2 2s 2 2p 3 c. Zinc 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 d. Bromine 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 e. Barium 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s What is the characteristic set of valence electrons for the following groups on the periodic table? Alkali metals (1 valence electron); alkaline earth metals (2); Halogens (7); Noble Gases (8) 13. Refer to a table of atomic and ionic radii, if necessary, to answer the following questions. a. Within a period, does the size of atoms generally increase or decrease with increasing atomic number? Size (also called atomic radii) increases down groups, decreases across periods. b. Within a family (family is another word for group), does the size of atoms increase or decrease with increasing atomic number? Increases down a group as atomic number increases. c. Within a period, does ionization energy increase or decrease with increasing atomic number? Across a period it increases. (Down a group it decreases.) d. In a group, does ionization energy increase or decrease with increasing atomic number? Down a group it decreases. 14. How is reactivity in metals a trend on the periodic table? Going down groups (especially for the alkali and alkaline earth metals) reactivity increases. Metals are on the left side of the periodic table (non-metals are on the right). The most metallic element is Francium.

4 15. Circle the larger particle in each of the following pairs. Na Li Br I F F- Cs Ba K K What are the characteristics of each of the following reaction types? a. Synthesis/Combination Combination of two molecules into one, A + B C b. Combustion Special double displacement; the products include CO 2 and H 2 O c. Decomposition One molecule separates into two; C A + B d. Double Displacement Two molecules switch their cations; AB + CD AC + BD e. Single Replacement One cation replaces another; AB + C AC + B 17. Complete the word equation, write and balance the equation using symbols and indicate the type of the reaction on the left. a. aluminum sulfate + calcium phosphate aluminum phosphate + calcium sulfate double displacement b. sodium chlorate sodium chloride and oxygen gas decomposition c. hydrogen gas + oxygen gas water vapor synthesis (combination) d. zinc metal + copper(ii) nitrate zinc nitrate + copper metal single replacement 18. Write some of the symbols and charges of the following ions. a) magnesium Mg 2+ d. zinc Zn 2+ b) manganese (II) Mn 2+ e. chromium (III) Cr 3+ c) aluminum Al 3+

5 19. Write formulas for the following compounds. a. zinc chloride ZnCl 2 b. lead (IV) oxide PbO 2 c. silver bromide AgBr d. sodium phosphate Na 3 PO 4 e. magnesium sulfide MgS f. cobalt (II) fluoride CoF 2 g. barium oxide BaO h. calcium phosphide Ca 3 P Name the following compounds. a. Pb 3 (PO 4 ) 2 lead (II) phosphate b. Cu(IO 3 ) 2 copper (II) iodate c. Cr 2 O 3 chromium (III) oxide d. Bi 2 (SO 4 ) 3 bismuth (III) sulfate e. RbNO 3 rubidium nitrate f. CaTe calcium telluride 21. Name the following compounds. a. N 2 O 3 dinitrogen trioxide b. PCl 3 phosphorus tricholride c. SiO 2 silicon dioxide d. P 2 O 5 diphosphorus pentoxide e. CS 2 carbon disulfide f. Al 2 O 3 aluminum oxide 22. Solve the following problems a. Find the mass of 0.89 mol of CaCl 2. GFM for CaCl 2 = g/mol so mass = g Multiply 0.89 mol times the GFM for CaCl 2 to find the mass in grams. b. How many molecules are present in mol of NaCl? Multiply moles by Avogadro s Number to get molecules x or 4.5 x molecules To find grams, divide moles by the GFM of NaCl (58.5 g/mol).

6 c. Determine the number of moles of C 5 H 12 that are in g of the compound. GFM for C 5 H 12 = g/mol moles = 5.03 Divide grams by the GFM for C 5 H 12 to find moles. d. How many moles would you have if you had 1.75 x 1022 molecules of HOH? To find moles, divide molecules Avogadro s number moles 23. Find the percent composition of each element in the following: a. PbCl 2 For Pb, 207.2/278.1 x 100 = 74.4% For Cl, 70.9/278.1 x 100 = 25.5% Remember, find the GFM of the part and then divided it by the GFM for the entire compound. Then multiply by 100 to find the percent. b. Aspirin (C 9 H 8 O 4 ) -- same process as above. Find the GFM for C 9 and then divide by the GFM for the entire molecule. Then multiple by 100 to get a percent. Repeat for each element present. 24. Define limiting reactant (reagent). It is essentially the chemical that is used up first. When we burn a match we run out of wood before we run out of oxygen in the room. We say that the wood is the limiting reagent and that the oxygen is in excess. 25. Using the following balanced equation to answer the following questions. 2Al Cl 2 4AlCl 3 + 3O 2 a. If 4.0 mol of Al 2 O 3 react completely, how many moles of AlCl 3 are formed? 4.0 mol Al 2 O 3 x 4 AlCl 3 2 Al 2 O 3 = 8 mol of AlCl 3

7 b. How many grams of Al 2 O 3 are needed to react with 12.0 mol of Cl 2? First find the number of moles of Al 2 O 3 needed using the same technique as above mol Cl 2 x 2 Al 2 O 3 6 Cl 2 = 4 mol of Al 2 O 3 Convert moles to grams for the final answer grams of Al 2 O 3 c. If 30.5 g of Cl 2 react completely, how many molecules of O 2 are produced? Here change grams to moles for Cl 2, then use the ratio to determine how many moles of O 2 are produced. Convert moles to molecules. d. How many grams of AlCl 3 are produced if 24.2 g of Cl 2 react completely? Here determine how many moles of AlCl 3 are produces and then convert to grams.