Measurement and Data Processing
A student repeats measurements to reduce the effect of unpredictable fluctuations. Which type of error is the student trying to reduce?
Random Error
A substance takes the shape of its container, maintains a fixed volume, and is difficult to compress. Identify its state.
Liquid
Unit of Ar
None
How many electrons can a 4f sub-level accommodate at maximum?
14
True or False: Molar mass has a unit of g mol.
False
The accepted mass of a sample is 50.0 g. A student records 49.9 g, 50.0 g, and 50.1 g. Comment on the precision and accuracy.
accurate and precise
Convert 250.0 K to degrees Celsius.
-23.15°C.
An atom forms a 2- ion. Which of the following quantities changes: its atomic number, its mass number, both, or neither?
Neither. It involves the loss of two electrons, which does not change the number of protons or neutrons.
An electron moves from n=2 to n=5. Does it absorb or emit energy?
It absorbs energy.
One mole of nitrogen molecules and one mole of copper atoms are placed in separate containers. Which contains more particles?
They have the same number of particles.
Two lengths are measured as (8.6 ± 0.1) cm and (5.4 ± 0.1) cm. Find their sum.
14.0 ± 0.2 cm
A pure substance melts at −12 °C and boils at 78 °C. What is its state at −5 °C?
Liquid
Why is the relative atomic mass of a naturally occurring element not usually a whole number?
It is a weighted average of the masses of its naturally occurring isotopes.
A student claims that a 3s orbital has a different shape from a 1s orbital because it belongs to a higher principal energy level. Evaluate the claim.
Incorrect. They have the same spherical shape, but 3s is larger than 1s orbital.
A student has 18.0 g of water and 18.0 g of glucose (C6H12O6). Which sample contains fewer moles?
The glucose sample contains fewer moles because of larger molar mass.
Calculate (15 - 8.67) × 1.00 and report the answer using the correct number of decimal places.
A particle diagram shows two different types of molecules, each containing atoms of two different elements. The particles are unevenly distributed, with one type concentrated in one region. What kind of sample is represented?
Heterogeneous mixture
Why can two isotopes of the same element have different physical properties but nearly identical chemical properties?
Their different numbers of neutrons result in different masses, which can affect physical properties. However, they have the same electron arrangement, so they exhibit nearly identical chemical behavior.
Which electron is expected to be, on average, closer to the nucleus: one with n=2, l=1, or one with n=3, l=1? Explain.
The first electron, in the 2p sub-level, is closer to the nucleus.
You have 15 g of boron and 15 g of calcium. Which sample contains more atoms? Explain.
Boron. Its molar mass is much lower, so 15 g of boron represents more moles—and therefore more atoms—than 15 g of calcium.
A volume is measured as 60 ± 0.2 mL. State the percentage uncertainty.
0.3%
As a pure solid melts, energy is continuously supplied, yet the average kinetic energy of its particles remains constant. Explain why.
Energy is used to overcome intermolecular attractions rather than increase average kinetic energy.
An element has two isotopes with mass numbers 70 and 72 and a relative atomic mass of 70.6. Is the isotope with mass number 70 more or less than 50% abundant? Explain your answer.
More than 50% abundant. The relative atomic mass (70.6) is closer to 70 than to 72.
An electron has n=2, l=3, ml=0, and ms=-1/2. Which value is invalid, and why?
l=3 is invalid, as l values can only go from 0 to n-1.
A student claims, “If two samples have the same mass, they must contain the same number of particles.” Is the claim correct? Explain.
No. Equal masses of different substances can contain different numbers of particles because their molar masses differ.