How to Understand Chemistry

My grandma used to bake cakes.

To bake a cake for five people you have to mix:
1 cup of flour
3 eggs
1/2 cup of sugar
100 gram of butter

There was no such thing as fat free cakes at that time that is why they tasted so good.:)

What if you need to bake a cake for 20 people? She did not know chemistry, but she had common sense to calculate proportions.

20 is 4 times greater than 5. So, you have to take 4 times greater number of cups of flour, 4 times greater number of eggs and so on. As a result, you will get a new receipt.

1 * 4=4 cups of flour
3 * 4=12 eggs
1/2 * 4 = 2 cups of sugar
100 * 4 = 400 grams of butter.

In the same way you can solve a problem with chemical reaction.

All chemical reactions occur in equivalent proportions.

If 10 grams of Na₂CO₃ react with CaCL₂ how many grams of CaCO₃ is produced?

10g ? g
1. Na₂CO₃ + CaCL₂ = CaCO₃ + 2NaCL

All compounds react with each other in certain proportions In given reaction one mole of Na₂CO₃ produces one mole of CaCO₃.

Mole is Molecular Weight (MW) in grams.

Atomic weight of Na=23
Atomic weight of C = 12
Atomic weight of O = 16

For Na₂CO₃ MW is 23 *2 + 12 + 16*3 = 106 g. g - 1 mole

For CaCO₃ MW is 40 + 12 + 48 = 100g. g 1 Mole.

106 g Na₂CO₃ g produces g 100g CaCO₃

10 g Na₂CO₃ g produces g X g CaCO₃ g

To calculate X multiply matched up values on the opposite ends of diagonal and divide the product by unmatched value as shows on the figure below.

106g		100 g

10g		X g

X=10 * 100 / 106 = 9.4 g of CaCO₃

Now you not only solved the chemical equation problem, but also prove to yourself that you can understand chemistry.

General Chemistry (Simplified)

All elements can be divided on metals and not metals

In periodic table metals are on the left. Not metals are on the right.

Group number shows how many electrons are in the most outer orbit. These electrons are called valence electrons. For example, Na (sodium) is in the first group. It has one electron on the most outer orbit Na can easily give this electron to Cl (chlorine). Cl is in the seventh group. It has 7 electrons and it takes one electron from Na. As a result Na becomes a positive ions Na+ and Cl becomes negative ions Cl -. Ions with opposite charge form ionic bond.

Na+ Cl- atoms that form ionic bonds usually form crystal structures. That is why salt is made of crystals.

Carbon C located in 4th group. It has four valence electrons. As a result C forms four covalent bonds with four atoms of Cl. C does not give its electrons to Cl. Carbon and chlorine share electrons. When atoms share electrons they form covalent bonds.

Oxides

Oxides are produced when metals or not metals react with oxygen.

Oxygen located in 6th group and has 6 valence electrons. It tends to gain 2 more electrons to get complete octet and its valence is 2.

2Ca + O₂ = 2CaO

In nature metal oxides exist in clay. Clay is a mixture of the oxides
SiO₂
Al₂O₃
K₂O
Na₂O
MgO
CaO
Fe₂O₃
TiO₂

In reaction with water metals or metal oxides produce bases:

2Na + 2H₂0 = 2NaOH + H₂

CaO + H₂O = Ca(OH)₂

Bases dissociate in water and produce OH - ion.

Non metal oxides are NO₂, SO₃, P₂O₅

In reaction with water non metal oxides produce acids:

H₂O + SO₃ = H₂SO₄ - sulfuric acid

H₂O + NO₂ = HNO₃ - nitric acid

H₂O + CO₂ = H₂CO₃ - Carbonic acid

Acids dissociate in water and produce proton of hydrogen H+

SALTS

When an acid reacts with a base, a salt is produced

NaOH + HNO₃ = NaNO₃ + H₂O

Calculate the percentage composition of NaNO₃?.

First find molecular weight of NaNO₃

23 (Na) + 12 (N) + 16*3 (O₃) = 83

Molecular weigt of NaNO₃ = 83

83 - 100%
23 (Na) - X% X = 23 * 100 /83 = 27.7% of Na

83 - 100%
12 (N) - X % X = 12 * 100/83 = 14.5% of N

83 - 100%
48 (O) - X % X = 48 * 100/83 = 57.8 % of O

Some salts are more soluble in water; some are less soluble or not soluble. When a not soluble salt is produced as a result of acid and base reaction a precipitate is formed.

Ca(OH)₂ + H₂CO₃ = CaCO₃ + 2H₂O

CaCO₃ is not soluble in water. A white precipitate is formed.

Salts may react with each other and new salts are produced:

Equivalent proportions

All chemical reactions occur in equivalent proportions

10g ?g
1. Na₂CO₃ + Ca Cl₂ = CaCO₃ + 2NaCL

All compounds react with each other in certain proportions

In given reaction one mole of Na₂CO₃produces one mole of CaCO₃.

Mole is MW(Molecular Weight) in grams.

For Na₂CO₃ MW is 23 *2 + 12 + 48 = 106 g. = 1 mole

For CaCO₃ MW is 40 + 12 + 48 = 100g. = 1 mole.

106 g produces 100g

10 g produces X g X= 10 * 100 / 106 = 9.4 g

0.5 M
2. Na₂CO₃ + Ca Cl₂ = CaCO₃ + 2 NaCL
100 ml g?

1 liter of I M solution of Na₂CO₃ contains 106 g

How many grams of Na₂CO₃ in 1 liter of 0.5 M solution?

1 M - 106 g
0.5 M - X g X = 0.5 M * 106 g / 1 M = 53 g

I liter of 0.5 M solution contains 53 grams
How many grams are in 100 ml?

1 liter - 53 g
0.1 liter - X g X = 0.1 * 53 /1 = 5.3 g

106 g of Na₂CO₃ produces 100 g of CaCO₃

5.3 g of Na₂CO₃ produces X g of CaCO₃ X= 5.3 * 100 / 106 = 5 g

ACID BASE

Molarity vs. Normality

Let say we have 100 ml of H₂SO₄ solution and it contains 0.49 g of H₂SO₄

What is Molarity?

What is Normality?

1 Molar solution contains number of gram equals to molecular weight per one liter.

MW of H₂SO₄ = 2 + 32 + 4* 16 = 98

I mole = 98g/L

We have to find how many gram of H₂SO₄ given solution contains

100 ml = 0.1 L and contains 0.49 g
1 L contains X g X = 0.49 * 1 / 0.1 = 4.9 g.

98g/L - 1 Mole
4.9 g/L - X Mole X = 4.9 * 1 / 98 = 0.05 Mole

Molarity of 100 ml solution of H₂SO₄, which contains 0.49 g of H₂SO₄ equals 0.05 Mole.

What is normality? An equivalent is the molecular weight or mass of acid or base that produce one mole of protons (H+) or one mole of hydroxyl (OH-) ions.

One mole of H₂SO₄ produces 2 moles of H+ then equivalent of H₂SO₄ = MW/2 = 49g/L

49g/L is 1 N solution
4.9g/L solution is - X N X= 4.9 * 1/ 49 = 0.10 N.

Normality of 100 ml solution of H₂SO₄, which contains 0.49 g of H₂SO₄ equals 0.10 N.

2. We have 10 ml of NaOH unknown concentration. The solution was titrated with 0.10 N solution of H₂SO₄ and 15 ml were required for neutralization. What is concentration of NaOH?

N_b * V_b = N_a * V_a where V is volum, N is Normality, b - base and a - acid

N_b = N_a * V_a / V_b = 0.10 * 15 / 10 = 0.15 N

Concentration of NaOH = 0.15 N.

Weigh and Volume problem:

2H₂0 = 2H₂ + 0₂
1 L ?L

Question: How many liters of Hydrogen are produced from one liter of water?

First, we have to find how many grams of water spent and how many grams of H2 produced?

MW of H₂0 = 2 + 16 = 18 We spent 2 molecules of H₂0 then we spent 18 * 2 =36 g.

MW H₂ = 2 and we got 2 molecules of H₂. 2*2 = 4g

36 g of water produces 4 g of Hydrogen

1000 g of water produces X g of Hydrogen. X = 4 * 100 / 36 = 111.1 g

I mole of Gas under normal conditions occupies 22.4 liters. So we have to know how many mole of H₂ is produced.

1 mole of H₂ equals 2 g

X mole of H₂ equals 111.1g

X = 111.1g / 2g = 50.6 Mole of H2

1 mole of H₂ occupies 22.4 liters

50.6 mole of H₂ occupies X liters

X = 50.6 Mole * 22.4L = 1232 L

Equilibrium Le Chatelier's Principle

Any chemical reaction go both way

According to Le Chatelier, the position of equilibrium will move to counteract the change.
If reaction produces heat then heating the system will move equilibrium to the left
And cooling the system will move equilibrium to the right. If volume of the products is
greater than volume of the reactants then increasing the pressure will move equilibrium to the left. Decreasing pressure will move equilibrium to the right. Increasing concentration of reactants will move equilibrium to the right, increasing concentration of the products will move equilibrium to the left.

Equilibrium constant Keq = [C] * [D] / [A] * [B] where [ ] is concentration in Moles

2H₂S <=> 2H₂ + S₂ concentration of products and reactants is raised to the power of their respective coefficients.

Keq = [H2]² * [S2] / [H2S]²

pH Acidity or Basicity of a solution.

PH = -Log [H+] where [H+] is concentration of H+ ions.

What is log? log is logarithm with base 10. Log 10 = 1 because 10¹ = 10

Log100 = 2 because 10² = 100. Log 1000 = 3 because 10³ = 1000

log1/1000 = -3 because 10^-3 = 1/1000

- log 1/1000 = 3.

pH of water is 7 (neutral)

What is pH of 0.0001 N HCl?

HCl = H+ + Cl-

Concentration of H+ equals concentration of HCl = 0.0001 N

pH = - log [1 * 10^-4] = 4

Liquid Properties

Freezing point constant = degree C per 1M of solute per 1000g of solvent.

For water Fpk = 1.86

Given: 1 M of NaCl solution. What is freezing point?

Pt = Molarity * Fpk = 1 * 1.86 = 1.86 C
Freezing point of water is 0 C then freezing point of solution = 0 C - 1.86 C = -1.86 C

Given: 196 g of H₂SO₄ added to 500 g of water. What is freezing point of the solution?

How many mole of H₂SO₄ is in 196g? MW = 2+32+64=98g

196g/98g = 2 M. is in 500g
X M is in 1000g X = 2 * 1000 / 500 = 4 M

Fr p. depression =4 M * 1.86 C = 7.44 C

Frp = 0 C - 7.44C = -7.44 C Where 0C Freezing point of water.

Boiling Point

Boiling point depends on number of solute particles per number of solvent particles.

For water Kb = 0.52

Given: 106 g Na₂CO₃ in 500 g of water. What is boiling point of the solution?

MW of Na₂CO₃= 23+23+12+48 = 106

106 g in 500 g water
Xg in 1000g water X = 106 * 1000 / 500 = 212 g

106 g/L - 1 M
212 g/L - X M X = 212 / 106 = 2 M.

Bp. raise = 2 M * 0.52 = 1.4 C Bp = 100 C + 1.4 C = 101.4 C

Home

Send message to your friend about this page. Link to the page will be authomatically added to your message. Both emails will not be stored in our database.
Напишите своему другу. Ссылка на эту страницу автоматически будет добавлена к сообщению. Мы не сохраняем ваши емайлы в нашей базе данных. Они используются только для того чтобы послать сообщение.
Your Email:
Friend Email:
Subject:

Home	Copyright 2006 by Sergey Skudaev.All right reserved. Contact us