Intro: Math and Measurement
Which measurement contains a total of two significant figures?
(1) 51.0 (3) 0.051
(2) 0.510 (4) 50
(3) 0.051
The average kinetic energy of water molecules decreases when
1) H2O(l) at 337 K changes to H2O(l) at 300. K
Which subatomic particle(s) are found in regions called orbitals?
electrons
The chemical properties of calcium are most similar to the chemical properties of
1) Ar 3) Mg
2) K 4) Sc
3) Mg
Explain, in terms of element classification, why H2O is a molecular substance.
Because it involves two nonmetals bonded
In an experiment, a student found that the percent of oxygen in a sample of KClO3 was 62%. If the accepted value was 39.3%, the experimental percent error is
57.8%
A sample of lead at 10K is placed in contact with a sample of iron at 25K. State the direction of heat transfer.
Heat transfers from the iron to the lead.
How many electrons are in an S-2 ion?
18
An atom of which element has the strongest attraction for electrons in a chemical bond?
1) chlorine
2) nitrogen
3) oxygen
4) selenium
3) oxygen
Which compound has both ionic and covalent bonds?
4. Na2CO3
A student calculates the density of an unknown solid. The mass is 10.04 grams, and the volume is 8.21 cubic centimeters. How many significant figures should appear in the final answer?
3
Which substance cannot be broken down by chemical means?
1. aluminum
Explain, in terms of electrons, the change in radius when a calcium atom becomes a calcium ion
The radius of a calcium ion is smaller because the calcium atom lost one electron.
A Ca ion is smaller because it has one less occupied electron shell.
State the general trend in atomic radius as the elements in Period 2 are considered in order of increasing atomic number
It decreases
Explain, in terms of charge distribution, why water is a polar molecule
It has an asymmetrical distribution of charge OR an uneven/unequal charge distribution
Convert 102 pm to m
1.02x10-10
or
0.000000000102 (9 zeros)
How much heat energy is required to change 10 grams of water from 20K to 90K?
2926 J
What were Rutherford's two conclusions from his gold foil experiment?
1. the atom is mostly empty space
2. there is a small, dense, positively, charged center = aka the nucleus
In the ground state, which noble gas has atoms with the same electron configuration as a magnesium ion?
Neon
Determine the total number of electrons in the bonds between the phosphorous atom and the three chlorine atoms in PCl3. Hint - draw the Lewis electron-dot diagram
6 electrons or 3 pairs
A student measures the mass and volume of a piece of aluminum. The measurements are 25.6 grams and 9.1 cubic centimeters. The student calculates the density of the aluminum. What is the percent error of the student’s calculated density of aluminum?
4%
A sample of helium gas has a volume of 900. milliliters and a pressure of 2.50 atm at 298 K. What is the new pressure when the temperature is changed to 336 K and the volume is decreased to 450. milliliters?
5.64 atm
Describe, in terms of both electrons and energy states, how light is produced.
Light is produced when electrons fall from higher energy states to lower energy states (from excited to ground)
Explain, in terms of atomic structure, why the noble gas neon is an unreactive element.
Neon's valence electron shell is full
Neon's outermost occupied electron shell is full
If an unknown forms the following compound with oxygen, X2O, write a chemical formula for the compound formed between X and Cl.
XCl