Chemistry Mid Exam – Debre Berhan

Part I: Write true for the correct statement and false for the wrong statement

1. Cooking red meat is an example of physical change

2. Temperature is one example of extensive property of matter

3. An atom becomes a cation when the number of protons is more than the number of electrons

4. During dilution, the number of moles of the solute remains unchanged

5. Change the volume of sample of oxygen gas from 10 ml to 11 ml as the temperature changed is a chemical change

6. Molecular formula represents absolute numbers of atoms that compose a compound

7. A mass-mass percent is a ratio of a solute’s mass to the solutions volume expressed as a percentage

8. Plasma is the gaseous state of matter that contain free electrons that conduct electricity

9. The relative number of reactant and product species in chemical reactions is represented by coefficients

10. A mole is the amount of a substance

Part II: chooses the best answer from the given alternative and write the answer on the space provided

1. Which one represents the macroscopic domain of chemistry?

A. A bottle with a label that AI contains aluminum metal
B. The mass of a certain chlorine atom is 35 amu
C. A certain molecule contains one H atom and one CI atom
D. Copper wire has a density of about 8 g/cm3
E. A Sulphur molecule is composed of eight Sulphur atoms

2. Among the following measurements. Which one has four significant figures

A. 1.04150 *10-4  j    
B. 0.0613 cm3
C. 0.01400 g/MI
D. 0.0038661 kg

3. The accepted value is 1.43. Which correctly describes this student’s experimental data?

Measurement-l= 1.19               Measurement-2= 1.93                Measurement-3=0.88

A. Accurate but not precise         
B. Precise but not accurate
C. Both accurate and precise
D. Neither accurate nor precise

4. Which one of the following pairs of elements is most likely to form an ionic compound?

A. B and I2
B. K and O2
C. O2 and CI2
D. Al and CI
E. B and D

5. The Number of Oxygen Atoms in 50 g of CaCO3 is?

A. 6.033 x 1023 atoms
B. 9.033 x 1023 atoms
C. 8.033 x 1023 atoms
D. 3.033 x 1023 atoms

6. Which one will have maximum numbers of water molecules?

A. 18 molecules of water 
B. 18 grams of water
C. 1.8 grams of water
D. 18 moles of water

7. Calculate 923 g ÷ 20312 cm3 and give your answer with the correct number of significant figures

A. 0.04 g/cm3
B. 0.045 g/cm3
C. 0.0454 g/cm3
D. 0.05 g/cm3

8. Different isotopes of an element have the same number of ____

A. Atomic mass
B. Proton
C. Proton and neutron
D. Neutrons

9. Which one of the following elements is most likely to form a 2- ion?

A. scandium (atomic number = 21 )  
B. silicon (atomic number = 14)
C. selenium (atomic number = 34)
D. strontium (atomic number = 34)
E. iodine (atomic number 53)

10. A phosphide ion (3115P-3) has: ____ proton, ____ neutron, and ____ electrons respectively

A. 15, 16, and13
B. 15, 16 and 18
C. 15, 18 and 15
D. 15, 19 and 15
E. 15, 20 and 15

11. A modem periodic table arranges the elements in increasing order of:

A. Atomic mass.
B. Molecular mass
C. Atomic weigh
D. Atomic number

12. The formula mass of ammonium biphosphate (NH4)2HPO4

A. 132g/mol
B. 114g/mol
C. 113g/mol
D. none

13. A compound contains by mass 40.0% carbon, 6.71% hydrogen and 53.3% oxygen a 0.1mol sample of this compound weighs 9 grams. The molecular formula of this compound is

A. C2H4O2
B. C3H603
C. C2H4o
E. C4H7O2

14. If 20 mL of 2M NaOH is diluted to 60 mL, then the concentration of the resulting solution will be

A. 0.67M
B. 0.33M
C. 0.50M
D. None

15. The nomenclature of the compound Cr2 (SO4)3 is

A. chromium (I) sulphate
B. chromium (II) sulphate
C. chromium (III) sulphate
D. None

Part III: Write your answer accordingly

1. The element copper is composed of two isotopes: About 69.17% of all copper atoms have a mass of 62.930 amu, and the remaining 30.83% are with a mass of 64.928 amu. Calculate the average atomic mass of copper.

2. An aqueous solution of H2SO4 is 98% by mass and its density is 1.84g/ml. calculate the morality of the solution.

3. Calculate the molar concentration of a solute of vinegar is a solution of acetic acid, CH3CO2H in water. A 0.10 L vinegar solution contains 25.2 g of acetic acid. What is the molar concentration of acetic acid solution? Given its molar mass = 60.052 g/mol

4. Round the numbers in the following calculations, assuming that the numbers are all measurements?    

A. 420 + 38.34        

B. 35.346 — 14.20

5. Explain the following pairs with example: Chemical formula and molecular formula

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