CHM151 MIDTERM QUESTIONS AND VERIFIED
ANSWERS
Which of the following series is only made up of elements? - Answers - Oxygen,
Sodium, Xenon
Which of the following is a pure substance? - Answers - Table salt
10.0 g of water freezing at 0 °C is an example of an intrinsic or extensive property? -
Answers - Intensive property
10.0 g of water that can occupy a 10.0 cm3 of volume is an example of an intrinsic or
extensive property? - Answers - Extensive property
Discuss why the scientific community chose the metric system compared to the English
units such gallons and feet. - Answers - The scientific community chose the metric
system for measurement compared to the English system because the English system
was just too difficult. The conversions between units were difficult and not uniform so
they decided to create the metric system to quickly and uniformly convert between units.
An example of this is that 100 centimeters is equal to 1 meter, you simply change the
base unit with a prefix. Base units like mass, length, time, quantity, temperature can all
be made larger or smaller with the use of prefixes. That is why the scientific community
chose the metric system for measurement over the English system.
determine the density of a metal with a mass of 22 g and a volume of 20 mL - Answers -
Density = mass/volume (g/mL)
22 g / 20 mL = 1.1 = 1 g/mL
What is the answer to the following equation with proper significant figures?
(12.1 - 3.25) / 125 = - Answers - 0.071
What is the SI unit for mass - Answers - kg
how many cm are in 15 m - Answers - 1500 cm
convert 150 mL to L - Answers - 0.15 L
convert 350 mg to kg - Answers - 0.00035 kg
If room temperature is usually defined as 25°, what is room temperature in Kelvin (k)? -
Answers - 298 K
how many cm are in 12 inches - Answers - 30.48 cm
, how to convert kg to g - Answers - 1 kg = 1000 g
If the density of iron is 7.9 g/cm3, how much volume would 5.00 kg of iron occupy? -
Answers - Density = M/V
V= M/Density
= 633 mL
If the density of mercury is 13.6 g/cm3, how much mass would be needed to fill a 3 L
vessel? - Answers - 3 L = 3000 mL
D = M/V
M = (D)(V)
= 40,8000 g
Accuracy is defined as how close a measured value comes to a _____. - Answers - true
value
Precision is defined as how _____ the measured values are to one another. - Answers -
reproducible
Variations in average atomic mass may be observed for elements obtained from
different sources. Lithium provides an example of this. The isotopic composition of
lithium from naturally occurring minerals is 7.5% 6Li and 92.5% 7Li, which have masses
of 6.01512 amu and 7.01600 amu, respectively. A commercial source of lithium,
recycled from a military source, was 3.75%6Li (and the rest 7Li). Calculate the average
atomic mass values for each of these two sources. Show your work for partial credit. -
Answers - Fractional abundance = 0.01% X Abundance (%)
Average mass = the sum of (fractional abundance X isotopic mass)
(0.01% X 7.5) = 0.075
(0.01% X 92.5) = 0.925
(0.075 X 6.01512 amu) + (0.925 X 7.01600 amu) = (0.451 + 6.49) amu = 6.941 amu
the average atomic mass is 6.94 amu
(0.01% X 3.75) = 0.0375
(0.01% X 96.25) = 0.9625
(0.0375 X 6.01512 amu) + (0.9625 X 7.01600 amu) = 6.979 amu
The average atomic mass is 6.979 amu
Discuss why technetium and promethium have whole number atomic masses and have
a bracket symbol on the periodic table - Answers - These elements have whole number
ANSWERS
Which of the following series is only made up of elements? - Answers - Oxygen,
Sodium, Xenon
Which of the following is a pure substance? - Answers - Table salt
10.0 g of water freezing at 0 °C is an example of an intrinsic or extensive property? -
Answers - Intensive property
10.0 g of water that can occupy a 10.0 cm3 of volume is an example of an intrinsic or
extensive property? - Answers - Extensive property
Discuss why the scientific community chose the metric system compared to the English
units such gallons and feet. - Answers - The scientific community chose the metric
system for measurement compared to the English system because the English system
was just too difficult. The conversions between units were difficult and not uniform so
they decided to create the metric system to quickly and uniformly convert between units.
An example of this is that 100 centimeters is equal to 1 meter, you simply change the
base unit with a prefix. Base units like mass, length, time, quantity, temperature can all
be made larger or smaller with the use of prefixes. That is why the scientific community
chose the metric system for measurement over the English system.
determine the density of a metal with a mass of 22 g and a volume of 20 mL - Answers -
Density = mass/volume (g/mL)
22 g / 20 mL = 1.1 = 1 g/mL
What is the answer to the following equation with proper significant figures?
(12.1 - 3.25) / 125 = - Answers - 0.071
What is the SI unit for mass - Answers - kg
how many cm are in 15 m - Answers - 1500 cm
convert 150 mL to L - Answers - 0.15 L
convert 350 mg to kg - Answers - 0.00035 kg
If room temperature is usually defined as 25°, what is room temperature in Kelvin (k)? -
Answers - 298 K
how many cm are in 12 inches - Answers - 30.48 cm
, how to convert kg to g - Answers - 1 kg = 1000 g
If the density of iron is 7.9 g/cm3, how much volume would 5.00 kg of iron occupy? -
Answers - Density = M/V
V= M/Density
= 633 mL
If the density of mercury is 13.6 g/cm3, how much mass would be needed to fill a 3 L
vessel? - Answers - 3 L = 3000 mL
D = M/V
M = (D)(V)
= 40,8000 g
Accuracy is defined as how close a measured value comes to a _____. - Answers - true
value
Precision is defined as how _____ the measured values are to one another. - Answers -
reproducible
Variations in average atomic mass may be observed for elements obtained from
different sources. Lithium provides an example of this. The isotopic composition of
lithium from naturally occurring minerals is 7.5% 6Li and 92.5% 7Li, which have masses
of 6.01512 amu and 7.01600 amu, respectively. A commercial source of lithium,
recycled from a military source, was 3.75%6Li (and the rest 7Li). Calculate the average
atomic mass values for each of these two sources. Show your work for partial credit. -
Answers - Fractional abundance = 0.01% X Abundance (%)
Average mass = the sum of (fractional abundance X isotopic mass)
(0.01% X 7.5) = 0.075
(0.01% X 92.5) = 0.925
(0.075 X 6.01512 amu) + (0.925 X 7.01600 amu) = (0.451 + 6.49) amu = 6.941 amu
the average atomic mass is 6.94 amu
(0.01% X 3.75) = 0.0375
(0.01% X 96.25) = 0.9625
(0.0375 X 6.01512 amu) + (0.9625 X 7.01600 amu) = 6.979 amu
The average atomic mass is 6.979 amu
Discuss why technetium and promethium have whole number atomic masses and have
a bracket symbol on the periodic table - Answers - These elements have whole number
