CHE-1A Practice Midterm #1 Name. 1. (10 pts.) Write chemical formulas for each of the following compounds.

Transcription

1 1. (10 pts.) Write chemical formulas for each of the following compounds. a.) ammonium phosphate b.) aluminum hydrogen sulfite c.) acetic acid d.) sodium bicarbonate e.) mercury (II) chloride 2. (10 pts.) Give the name of each of the following compounds. a.) Fe(MnO 4 ) 3 b.) Sn(NO 3 ) 2 c.) HClO 4 d.) SiCl 4 e.) HI (gas) 3. (2 pts.) Explain what we mean when we say that a particular element has more than one isotope. 1

2 4. You and your lab partner are asked to determine the density of an aluminum bar. The mass is known accurately to 4 significant figures. You use a simple metric ruler to determine its size and calculate the results in column A. Your partner (using a precision micrometer for the first time) obtains the results in column B. (The accepted density of aluminum is g/cm 3.) Method A results (g/cm 3 ) Method B results (g/cm 3 ) a.) (2 pts.) Calculate the average density for each method. b.) (2 pts.) Which method s average value is more precise? Which method s average value is more accurate? 5. (6 pts.) Perform the following calculations to the correct number of significant figures. a.) ( ) / 6.3 = b.) = 6. (2 pts.) Indicate whether the following statement is true or false. Rutherford's bombardment experiments with metal foil suggested that the alpha particles were being deflected by coming near a large, negatively charged atomic nucleus. 2

3 7. (8 pts.) For the following pairs of ions, predict the formula of the simplest compound that the ions are most likely to form. a. As 3+ and Cl - b. Sn 2+ and P 3- c. Zn 2+ and O 2- d. Mn 4+ and S 2-8. A farmer finds a jagged piece of a meteorite in his field that he is sure is pure gold. He weighs it and gets its mass as 350 lbs. and then roughly estimates its dimensions to be 12 inches by 14 inches by 10 inches. Assume that 1 inch = 2.54 cm and 1 lb. = 454 g. (5 pts.) From the above data, calculate the density of the meteorite in g/cm 3. (1 pt.) Given that gold is one of the densest element in the known universe at 19.3 g/cm 3, do you think the farmer's rough estimate of mass and/or size are very accurate? (2 pts.) What would be a better method to determine the density of this irregularly shaped object? 3

4 9. (2 pts.) The following compounds containing only nitrogen and oxygen are all gases in the atmosphere with varying reactivities. Which one of these four has the highest mass percent of N? Defend your choice by calculating the mass percent of N in it. NO NO 2 N 2 O N 2 O (9 pts.) Fill in the blanks to complete the following table. Symbol Common # of protons # of neutrons # of electrons Ion Formed in ion in ion in ion 115 In In Se 36 Be (5 pts.) Three isotopes of silicon are naturally occurring with 28 Si at 92.2% and amu, 29 Si at 4.67% and amu, and 30 Si at 3.10% and amu. What is the atomic mass of silicon? 4

5 12. (6 pts.) Calculate the number of molecules present in each of the following samples. a.) 4.75 g of phosphine, PH 3 b.) 4.75 millimoles of phosphine, PH (6 pts.) Complete the following table. Substance Pure or Mixture Homogeneous or Heterogeneous apple juice (filtered) hydrogen peroxide chicken soup 14. (6 pts.) Balance the following unbalanced chemical equations. a.) As 2 O 3 (s) + KI(aq) + HCl(aq) AsI 3 (s) + KCl(aq) + H 2 O(l) b.) Ca(OH) 2 (s) + H 3 PO 4 (aq) Ca 3 (PO 4 ) 2 (s) + H 2 O(l) 5

6 15. (10 pts.) Select answers to the questions listed below from the following list of elements whose symbols start with the letter C: C Ca Cr Co Cd Cl Cs Give your answer using the name of the element. Expect to use some symbols more than once! a.) which are non-metals? b.) which are main group elements? c.) which are transition elements? d.) which are gases at room temperature? 16. (6 pts.) A compound contains 47.08% carbon, 6.59% hydrogen, and 46.33% chlorine by mass. What is the empirical formula of the compound? If the molar mass of the compound is 153 g/mol, what is the molecular formula? Avogadro's Number 1 mole = x of anything (usually atoms, molecules, ions, or electrons) = N A 6