January 22, 2020

Lewis Dot structure is a representation of how electrons are arranged in a molecule.

To correctly draw lewis dot structures we need to follow the following six steps.

1. Calculate the total number of valence electrons

2. Connect atoms in a molecule using bonds

3. Subtract electrons used in bonds from the total electrons calculated in part 1

4. Use remaining electrons to make outer atoms happy (octet, 8 electrons) but rem...

January 21, 2020

The only two elements in alkenes and alkynes are

(1) carbon and nitrogen

(2) carbon and hydrogen

(3) oxygen and nitrogen

(4) oxygen and hydrogen

Answer: (2) carbon and hydrogen


If we look at the Chemistry Regent Reference table, we will see on Table Q, that alkenes and alkynes belong to the Homologous Series of Hydrocarbons. Hydrocarbons are organic molecules that contain carbon and hydrogen. Therefore, they mu...

December 27, 2019

Intermolecular forces are forces of attraction between molecules. These forces influence properties of substances such as boiling and melting points, phases at room temperature, viscosity and many more.

Intermolecular forces can be divided into 4 major categories:


This is the strongest intermolecular force. It is present in all ionic compounds. To recognize it, look at the formula and see if it has metal with a...

November 17, 2019

What is the chemical name of the compound NH4SCN?

(1) ammonium thiocyanate

(2) ammonium cyanide
(3) nitrogen hydrogen cyanide

(4) nitrogen hydrogen sulfate

Answer: (1) ammonium thiocyanate

Explanation: In order to name a compound, we must first figure out whether it is ionic or covalent. Ionic compounds can be divided into three categories: metal + nonmetal, meta+ polyatomic ion, polyatomic ion+ polyatomic ion, polyatomic io...

November 13, 2019

 Which electron configuration represents the electrons in an atom of sulfur in an excited state?

(1) 2 – 8 – 6

(2) 2 – 7 – 7

(3) 2–8– 7

 (4) 2–7– 8

Answer : 2) 2-7-7

Explanation: We must first look at the Periodic Table at the Reference Table, and find Sulfur. Sulfur's electron configuration is 2-8-6 according to the Reference Table. An excited state is a state in which an electron jumps to a higher energy level, while the g...

November 11, 2019

What is the color of bromcresol green indicator in a solution with a pH value of 2.0?

(1) blue

(2) green

(3) red

(4) yellow

Answer: Choice 4

Solution: An indicator allows us to figure out the pH range of the solution and whether it is acidic or basic. To do this problem, we need to look at Table M of the Regent Reference Table, Common Acid–Base Indicators. 

According to the table, bromcresol green, has a pH range for co...

October 23, 2019

To convert grams to moles and vice versa, we must always use Molar Mass.

Molar Mass can be calculated using the Periodic Table.

To calculate the molar mass, we multiply each atom in the molecule by its atomic mass found in the Periodic Table and multiply by the number of atoms.

For example, to calculate the molar mass of CO2

C= 1*12.011 = 12.011

O= 2*15.999 = 31.998

12.011 + 31.998 = 44.009 g/mol

To convert grams to moles, we...

October 21, 2019

Lactic acid has one acidic hydrogen. A 0.1 M solution of lactic acid has a pH of 2.44. Calculate Ka for lactic acid? When we do acid/base questions, we always need to ask ourselves 2 questions.

Question1 Do we have an acid or a base?

In this case the question itself, told us that we are dealing with an acid.

Question 2 Is this a weak or a strong acid?

Strong acids are: HCl - hydrochloric acid HNO3 - nitric acid H2SO4 - sulf...

October 8, 2019

Which notations represent atoms that have the same number of protons but a different number of neutrons?


(1) H-3 and He-3

(2) S-32 and S-32

(3) Cl-3...

September 30, 2019

A sample of the male sex hormone testosterone,C19H28O2, contains 3.88 * 10^21 hydrogen atoms.

(a) How many atoms of carbon does it contain?

(b) How many molecules of testosterone does it contain?

(c) How many moles of testosterone does it contain?

(d) What is the mass of this sample in grams?


To find atoms of carbon, we take the number of hydrogen atoms and multiply the number by 19/28 (ratio of carbon to hydrogen...

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