CHEM 121 EXAM 1 PRACTICE QUESTIONS EXAM WITH CORRECT QUESTIONS AND ANSWERS 2025

CHEM 121 EXAM 1 PRACTICE
QUESTIONS EXAM WITH CORRECT
QUESTIONS AND ANSWERS 2025

Which one of the following is the largest mass?

a. 2 x 10^-4 kg

b. 2 x 10^3 mg

c. 2 x 10^5 ng

d. 2 x 10^-2 g

e. 2 x 10^4 ug - CORRECT-ANSWERS>>>>>>b. 2.5 g (convert all to same

unit)

How many moles of carbon would be found in 52.4 g C3H8 - CORRECT-

ANSWERS>>>>>>b. First calculate how many moles of C3H8 there are

(1.19 moles). Then multiply by molar ratio (3 mol C/1 mol propane) = 3.57

mol C

Which of the following is a postulate of Dalton's atomic theory?

a. Atoms combine in whole number ratios to form compounds

b. Atoms contain a tiny dense nucleus

c. Protons are found in the nucleus of an atom

d. The number of neutrons in an atom determines the identity of the element

e. Atoms contain electrons. - CORRECT-ANSWERS>>>>>>a. Atoms combine

in whole number ratios to form compounds

,The density of an unknown substance is 8.76 g/cm3. How many cm3 would a

98.3 g sample of this substance occupy? - CORRECT-ANSWERS>>>>>>c.

multiply 98.3 g by (1 cm3/8.76 g) to make 11.2 g/cm3

Which of the following statements is TRUE about these 3 atoms: 43/23 V (this

means Vanadium with a 43 on upper left and 23 on lower left); 40/20

Ca^2+; 37/17 Cl^-

a. All of the atoms are isotopes of one another

b. All of the atoms have the same number of electrons

c. All of the atoms have the same number of protons

d. All of the atoms have the same number of neutrons

e. All of the atoms belong in the fourth period - CORRECT-

ANSWERS>>>>>>d. all of the atoms have the same number of neutrons

How many significant figures are present in the following calculations (SHOW

WORK) (2 pts)

(24.3 - 15.44) / 3.242 - CORRECT-ANSWERS>>>>>>=8.9/3.242 = 2.7. Two

sig figures. The subtraction part gives one decimal place after the decimal,

because that was the level of uncertainty in the subtraction. That number

thus as 2 sig digits.

4 NH3 + 7 O2 --> 4 NO2 + 6 H2O

If 5.82 moles of NH3 are reacted with 9.74 moles of oxygen gas, how many

moles of NO2 will be formed? Which reactant is limiting? (3 pts) - CORRECT-

ANSWERS>>>>>>5.82 mol NH3 ( 4 mol NO2/4 mol NH3) = 5.82;

, 9.74 mol O2 (4/7) = 5.57 mol NO2 so O2 is limiting and can only make 5.57

moles of NO2

Balance, including the states of matter:

The reaction of solid aluminum with liquid bromine to form solid aluminum

bromide (1 pts) - CORRECT-ANSWERS>>>>>>2 Al (s) + 3 Br2 (l) --> 2 AlBr3

(g)

Balance, including the states of matter:

Al(ClO4)3 (aq) + Ba(OH)2 (aq) --> Ba(ClO4)2 (aq) + Al(OH)3 (g) - CORRECT-

ANSWERS>>>>>>3 Al(ClO4)3 (aq) + 3 Ba(OH)2 (aq) --> 3 Ba(ClO4)2 (aq) +

2 AL(OH)3 (s)

Balance, including the states of matter:

The combustion of C5 H10 O in oxygen gas to corm carbon dioxide gas and

water vapor - CORRECT-ANSWERS>>>>>>C5H10O + 7O2 --> 5 CO2 (g) +

5 H2O (g)

Give an example of each of the following: (.5 pts each)

a. Alkaline earth metal

b. noble gas

c. transition metal

d. metalloid - CORRECT-ANSWERS>>>>>>Ca, Ar, Fe, Si

Why does the mass of an element in the periodic table not have whole

numbers (2 pts) - CORRECT-ANSWERS>>>>>>The mass in the periodic

table is a weighted average of

all isotopes of bromine. So no atom has a