CHEMISTRY 127 EXAM I September 24, Lab (L) Section. Signature: ID #

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1 CHEMISTRY 127 EXAM I Name : Signature: ID # Lab (L) Section TA PLEASE READ THE FOLLOWING INSTRUCTIONS Do NOT begin the exam until asked to do so. There are 11 numbered pages, and a periodic table in this exam. Check to see that they are all here before you begin the exam. Return all these papers when you are finished. Write your name on every page. Use a pen with blue or black ink for the entire exam. Be sure to follow the directions in answering all questions. Write your final answers in the blanks provided. In working problems and the BONUS, you must SHOW ALL WORK. No credit will be given unless all work is clearly shown and the method of solution is logically correct. Use correct units. THE FOLLOWING INFORMATION MAY BE USEFUL Avogadro s number : x moles mass molar mass Density : mass volume m T o 1.8T 32 F o C V Do not write below this line Grader I II III IV BONUS TOTAL

Name I. (25 points) A. (8 points) Answer the questions below, using LT (for is less than), GT (for is greater than), EQ (for is equal to), or MI (for more information required) in the blanks provided.

2 Name I. (25 points) A. (8 points) Answer the questions below, using LT (for is less than), GT (for is greater than), EQ (for is equal to), or MI (for more information required) in the blanks provided. 1. A thermometer registers the following temperature shown below. The number of significant figures in the measurement (1) Consider two liquids A and B. Both have the same volume. Liquid A has a larger mass than liquid B. The density of liquid A (2) the density of liquid B. 3. Butanol is a colorless liquid with a density of 0.81 g/ml. Its solubility in water is 9 g/100 g H 2 O. It boils at 118 o C and when burned in oxygen produces CO 2 and H 2 O. The number of physical properties listed for butanol (3) A beaker has a volume of ml. A rock is placed in the beaker. It takes 38.6 ml to fill the beaker that has the rock. The volume of the rock is _(4)_ 38.6 ml. 1

3 Name B. (10 points) Answer the questions below, using Y if the statement is true and N if the statement is false. Write your answers in the blanks provided m equals 303 x 10 3 km. 2. CuS is a mixture. 3. Considering that at 25 o C, only 1.9 mg of silver chloride dissolves in 1.0 L of water, we will need 1.3 x 10 2 L of water to dissolve 2.5 x 10 2 mg of silver chloride o F is higher than 0 o C. 5. There are 3 significant figures in C. (7 points) The solubility of potassium chloride is 37.0 g /100 g water at 30 o C and 48.3 g/100 g water at 70 o C. A solution is made up containing 200 g of water and 86.4 g of potassium chloride at 70 o C. 1. Is the solution unsaturated, saturated or supersaturated? 2. If the solution is cooled to 30 o C, how many grams of potassium chloride will crystallize out? 2

4 Name II (40 points) A. (10 points) Answer the following questions on the blanks provided. 1. Write the symbol of the alkali metal in period Write the symbol of a metalloid in Group A new element with atomic number larger than 106 is synthesized. It behaves like the halogens. How many protons does the element have? 4. Write the symbol for the transition element with 26 protons and 23 electrons. (Include a charge if one is present) 5. Which of the 2 isotopes of calcium is more abundant: Ca-40 or Ca-41? B. (6 Points) Choose the best answer for the following multiple choice questions. Put the correct answer in the space provided. 1. The element found in Group 4, Period 5 in the periodic table is a) Zn b) V c) Ti d) Zr e) Sn 2. Which of the following is not a transition element? a) Sc b) Ba c) Ag d) Cu e) Zn 3. Which of the following CANNOT be considered a simplest formula? a) K 2 Cr 2 O 7 b) H 3 PO 4 c) N 2 O 5 d) C 2 H 6 e) KMnO 4 3

5 Name C. (10 points) Write the names of the following compounds on the blanks provided. 1. N 2 O 3 2. H 2 O 3. HCl (g) 4. K 2 Cr 2 O 7 5. Na 2 SO 3 D. (10 points) Write the formula for the following compounds on the blanks provided. 1. ammonium sulfide 2. ammonia 3. perchloric acid 4. iodine trichloride 5. potassium phosphate E. (4 Points) Write your answers on the blanks provided. electrons 1. Consider 19-9 F. How many electrons are there in this ion? neutrons 2. Consider F How many neutrons are there in this atom? 4

6 Name III. (60 points) A. (10 points) Answer the questions below, using Y if the statement is true and N if the statement is false. Write your answers in the blanks provided. 1. Suppose that He-4 is taken to be the standard for expressing atomic masses and is assigned an atomic mass of 1.00 amu. The new atomic masses based on the He-4 standard will be approximately 4 times those based on C In SO 2, the mass of oxygen is approximately equal to the mass of sulfur. 3. For the reaction 2N 2 (g) + 5O 2 (g) 2N 2 O 5 (g) When one mole of N 2 is made to react with 2 moles of O 2, all the oxygen is consumed. 4. Consider Box A which contains lead (Pb) and Box B which contains gold (Au). Both boxes have the same number of moles. The mass of Box A equals to the mass of Box B. 5. Consider the same two boxes described in Question (4). Box B will have more atoms than Box A. 5

7 Name B. (15 points) Dimethylhydrazine is made up of carbon, hydrogen and nitrogen atoms. The combustion of g of dimethylhydrazine in excess oxygen yields g of carbon dioxide and g of water. 1. Fill in the table according to the data given in the problem. Grams Moles Ratios C (Carbon) H (hydrogen) N (Nitrogen) 2. What is the simplest formula for dimethylhydrazine? 6

8 Name C. (9 points) Consider the balanced equation given below for the preparation of methanol, CH 3 OH. CO (g) + 2H 2 (g) 3 OH (g) g CO (MM = g/mol) is allowed to react with 10.2 g of H 2 (MM = 2.02 g/mol). What is the limiting reactant? (show by calculation) 2. In another experiment 4 moles of CO react with excess H 2 (g), how many moles of methanol (CH 3 OH) are formed? D. (11 points) A mass of 2.00 g of O 2 (g) reacts with excess of H 2 (g). 2H 2 (g) + O 2 (g) 2 O ( 1. Assuming 100% yield how many grams of H 2 O ( ld be obtained? 2. If 1.94 g of H 2 O ( (based on your answer to 1) 7

9 Name E (15 points) An oxide of a metal, X, has the formula XO 4. The oxide reacts with excess H 2 to yield the free metal and H 2 O according to the following balanced reaction. XO 4 (s) + 4H 2 (g) X (s) + 4H 2 O ( 1. A g sample of XO 4 yields g of H 2 O. How many moles of H 2 O are produced? 2. How many moles of XO 4 are consumed? 3. What is the molecular mass of XO 4? 4. What is the atomic mass of X? 8

10 Name IV. (25 points) A. (16 points) The following data was obtained in an experiment designed to determine the density of an unknown metal: a) mass of flask + stopper g b) mass of flask + stopper + ethanol g c) mass of flask + stopper + metal g d) mass of flask + stopper + metal + ethanol g density of ethanol g/ml Using the data above, calculate: 1. The volume of the flask 2. The mass of the metal 3. The volume of the metal 4. The density of the metal 9

11 Name B. (4 points) The student forgot in the last step (step d) to insert the stopper. This oversight will cause the calculated density for the metal to be: greater than the true value smaller than the true value the same as the true value C. (5 points) A student spotted an ion solution on a chromatography paper at the location labeled 'origin'. He/She then placed the paper into an elution solution. After the solvent front nearly reached the upper edge of the paper, the paper was taken out, dried and stained to develop one black spot. Calculate the R f value for this ion using the numbers provided. 10

12 Name BONUS (15 points) All or nothing An element X forms both a dichloride (XCl 2 ) and a tetrachloride (XCl 4 ). Treatment of g XCl 2 with excess chlorine forms g XCl 4. Calculate the atomic mass of X, and identify X. You must show your work clearly for credit. 11

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