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Acid-Bases and Combustion Analysis

Group 3 Steven Syahdiva Zaki Moesbar Johannes Salikin Zakharia Jaka



When an acid and a base are placed together, they react to neutralize the acid and base properties, producing a salt. The H(+) cation of the acid combines with the OH(-) anion of the base to form water. The compound formed by the cation of the base and the anion of the acid is called a salt. The combination of hydrochloric acid and sodium hydroxide produces common table salt, NaCl

Combustion of any organic acid consist of C, H, and O will produce :

CxHyOz + O2 CO2 + H2O

Gastritis Gastritis is an inflammation, irritation, or erosion of the lining of the stomach. It can occur suddenly (acute) or gradually (chronic). It is caused by many factors such as : Helicobacter pylori (H. pylori): A bacteria that lives in the mucous lining of the stomach. Without treatment the infection can lead to ulcers, and in some people would be stomach cancer 2. Pernicious anemia: A form of anemia that occurs when the stomach lacks a naturally occurring substance needed to properly absorb and digest vitamin B12. 3. Bile reflux: A backflow of bile into the stomach from the bile tract (that connects to the liver and gallbladder). 4. Infections caused by bacteria and viruses.

Theory or Fundamental Principles

Such disease could be detected by many symptom such as vomiting, nausea, abdominal disease, headache and many more. There are also some methods on detecting gastritis in some ways : Upper endoscopy. An endoscope, a thin tube containing a tiny camera, is inserted through your mouth and down into your stomach to look at the stomach lining. The doctor will check for inflammation and may perform a biopsy, a procedure in which a tiny sample of tissue is removed and then sent to a laboratory for analysis. 2. Blood tests. The doctor may perform various blood tests such as checking your red blood cell count to determine whether you have anemia, which means that you

do not have enough red blood cells. He or she can also screen for H. pylori infection and pernicious anemia with blood tests. 3. Fecal occult blood test (stool test). This test checks for the presence of blood in your stool, a possible sign of gastritis. pH of Stomach Your stomach secretes hydrochloric acid, but the pH of your stomach isn't necessarily the same as the pH of the acid! The pH of your stomach varies, from 1-2 up to 4-5. When you eat, the stomach releases proteases and hydrochloric acid to aid in digestion. By itself, the acid doesn't really do much for digestion, but the proteases that cleave proteins work best in an acidic environment or low pH, so after a high-protein meal, your stomach pH may drop to as low as 1 or 2. However, buffers quickly raise the pH back to 3 or 4. After the meal has been digested, your stomach pH returns to a resting level of about 4 or 5. Your stomach secretes acid in response to food, so first thing in the morning you can expect a slightly acidic stomach pH, but not an acidic level representative of pure hydrochloric acid. Antacid Antacids are a type of medication that can control the acid levels in your stomach. They are available over the counter from pharmacies and are commonly used to treat the symptoms of heartburn and indigestion. It works by neutralizing the acid in the stomach to aid digestion. Some antacids also coat the surface of the oesophagus (gullet) with a protective barrier against stomach acid or produce a gel on the stomachs surface which helps stop acid leaking into the oesophagus. There are some types of antacids that are sold commercially in drug store :




Antacids react with hydrochloric acid inside the stomach. Below is the reaction between the antacid compounds with the acid : Compound Aluminum hydroxide Calcium carbonate Magnesium carbonate Magnesium hydroxide Sodium bicarbonate Chemical Formula Al(OH)3 CaCO3 MgCO3 Mg(OH)2 NaHCO3 Chemical Reaction Al(OH)3(s) + 3 HCl(aq) -----> AlCl3(aq) + 3 H2O(l) CaCO3(s) + 2 HCl(aq) -----> CaCl2(aq) + H2O(l) + CO2(g) MgCO3(s) + 2 HCl(aq) -----> MgCl2(aq) + H2O(l) + CO2(g) Mg(OH)2(s) + 2 HCl(aq) -----> MgCl2(aq) + 2 H2O(l) NaHCO3(aq) + HCl(aq) -----> NaCl(aq) + H2O(l) + CO2(g)

Acid-Bases Reaction and Properties Substances have long been classified as acids or bases according to some general properties which are summarized below. Their reactions with each other produce salts

Acid Properties: Base Properties:

When dissolved in water, acids When dissolved in water, bases 1. Conduct electricity 2. Change blue litmus to red 3. Have a sour taste 4. React with bases to neutralize their properties 5. React with active metals to liberate hydrogen. 1. Conduct electricity 2. Change red litmus to blue 3. Have a slippery feeling 4. React with acids to neutralize their properties.

Acid-bases reactions combine could neutralize either acid or bases. In case of strong acid, it should be reacted with the strong bases and vice versa. So, the reaction called as a neutralization reaction.

Besides, acid is a compound that dissolve in water water to produce solutions containing hydronium ions, H3O+ (aq), and bases dissolve in water to produce hydroxide ions, HO(aq). When an acidic solution and a basic solution are mixed, hydroxide ions react with hydronium ions to produce water molecules: H3O+ (aq) + HO- (aq)

2 H2O H2O


H+ (aq) + HO (aq)

Abbreviating the hydronium ion as H+ (aq) makes it easier to count the water molecules produced. Below are the reaction between Hydrochloric acid and sodium hydroxide : HCl (g) NaOH (s) H+ (aq) + Cl(aq) + Na+ (aq) + OH(aq) H+ (aq) + OH- (aq) HCl (aq) + NaOH (aq) H+ (aq) + Cl- (aq) Na+ (aq) + OH(aq) Na+ (aq) + Cl(aq) + H2O H2O NaCl (aq) + H2O

But, neutralization sometimes could left some residue which is known as salts. In general, the term salt refers to any ionic compound that could be produced by a neutralization reaction. Salts contain metal cations, and anions that may be monatomic (like chloride) or polyatomic anions derived from oxyacids. The formula of a salt can be predicted from the known charges of the cation and anion as we have seen previously for binary ionic compounds. Sodium sulfate, for example, has the formula Na2SO4. When a formula includes more than one polyatomic ion, it is enclosed in parentheses with a subscript to indicate the relative number of ions. Magnesium nitrate is Mg(NO3)2. There are two nitrate ions (charge 1each) for every Mg2+ ion. When necessary, we include the charge on the cation as part of the name. Mercury(II) acetate is Hg(C2H3O2)2. Some salts form crystalline solids which include some water molecules as part of the structure. Such salts are called hydrates, and we include the water molecules in the formula using a dot and a coefficient. For example, copper(II) sulfate forms blue crystals with five water molecules per formula unit, so the formula is CuSO4.5H2O. Hydrates can be dried by strong heating, which drives the water molecules out of the crystal. Below is the example of equation :

HBr + NaOH NaBr + H2O ( salt : NaBr) HCl + NaOH NaCl + H2O ( salt : NaCl) Strong Acid

Using the formula above, it is very easy to calculate the pH of a strong acid. Virtually because 100% is ionized with the solution, each mole of the strong acids reacts with the solution. For example 0.1 M of Hydrochloric Acid will be dissolved in water. HCl reacts with water to give 1 mole of hydrogen ions and 1 mole of chloride ions. Which means, if the concentration of acid is 0.1 M then the concentration of hydrogen ions is also 0.1 M. Therefore,

log [0.1] = -1 pH HCl = -log [0.1] -(-1) = 1

Then, the pH of the acid is 1. Examples of Strong Acids: HCl - hydrochloric acid HNO3 - nitric acid H2SO4 - sulfuric acid HBr - hydrobromic acid HI - hydroiodic acid HClO4 - perchloric acid Weak Acid A weak acid is an acid which doesn't ionize fully with the solution. For example ethanoic acid is an example of weak acid. It reacts with water to produce hydroxonium ions and ethanoate ions, but the reverse reaction is more successful than the forward one.

At times, only 1% of the ethanoic acid molecules have converted into ions and the rest of it will remain as ethanoic acid. To calculate the pH of a weak acids, is to calculate the dissociation of an acid in the reaction and could be expressed as the equilibrium constant, Ka. For example,

The Ka of this reaction is as follows,

Here are the list of Ka of some basic acids. Note that the smaller the Ka, the weaker the And he higher the Ka the acid will be stronger.
acid hydrofluoric acid methanoic acid ethanoic acid hydrogen sulphide Ka (mol dm ) 5.6 x 10 1.6 x 10 1.7 x 10 8.9 x 10
-4 -3





After finding the Ka of the solution, we are ought to find the pKa of the solution. And unlike Ka who has units (mol dm-3), pKa doesn't. pKa bears exactly the same relationship to Ka as pH with Hydrogen ion, it's formula is : pKa = -log [Ka]
-4 -3

pKa 3.3 3.8 4.8 7.1




By calculating the pKa of the Ka given above, we can see the trends of the pKa. As the pKa get lower, the acid will be stronger, and if the pKa gets higher, the acid will be weaker. Below are some examples of weak acids :

Common Weak Acids Acid Formula Formic HCOOH Acetic CH3COOH Trichloroacetic CCl3COOH Hydrofluoric HF Hydrocyanic HCN Hydrogen HS sulfide 2

Organic Acid Organic acid is an organic compound with acidic properties and the most common organic acid is carboxylic acids which is associated with their carboxyl group -COOH. Sulfonic acids containing the group SO2OH which is relatively a stronger acid. A few common examples of organic acids are lactic acid, acetic acid, formic acid, citric acid, oxalic acid, and uric acid. In general, organic acids are weak acids and do not ionize completely in a solution unlike strong acids do. On the other hand, organic acids are very soluble in organic solvents. Here are the molecular structure of organic acid :

Combustion Analysis The combustion includes a sample of unknown substance which is burn in a large excess of oxygen gas. The combustion products will be trapped separately from each other and the weight of each combustion product will be determined. From this, you will be able to calculate the empirical formula of the substance. This technique has been most often applied to organic compounds.

Here are some points to make combustion analysis :

1) The elements making up the unknown substance almost always include carbon and hydrogen.
Oxygen is often involved and nitrogen is involved sometimes. Other elements can be involved, but problems with C and H tend to predominate followed by C, H and O and then by C, H, O and N. 2) We must know the mass of the unknown substance before burning it. 3) All the carbon in the sample winds up as CO2 and all the hydrogen in the sample winds up as H2O. 4) If oxygen is part of the unknown compound, then its oxygen winds up incorporated into the oxides. The mass of oxygen in the sample will almost always be determined by subtraction. 5) Often the N is determined via a second experiment and this introduces a bit of complexity to the problem. Nitrogen dioxide is the usual product when nitrogen is involved. Sometimes the nitrogen product is N2, sometimes NH3. This is the example of explaining the example of combustion analysis : Dianabol is one of the anabolic steroids that has been used by some athletes to increase the size and strength of their muscles. It is similar to the male hormone testosterone. Some studies indicate that the desired effects of the drug are minimal, and the side effects, which include sterility and increased risk of liver cancer and heart disease, keep most people from using it. The molecular formula of Dianabol, which consists of carbon, hydrogen, and oxygen, can be determined using the data from two different experiments. In the first experiment, 14.765 g of Dianabol is burned, and 43.257 g CO2 and 12.395 g H2O are formed. In the second experiment, the molecular mass of Dianabol is found to be 300.44. What is the molecular formula for Dianabol? SOLUTION

( The solution would be on the next page)

Oxalic Acid Oxalic acid is an organic acid. Despite its toxic nature, oxalic acid enjoys a variety of uses in industry, primarily as a purifying agent in the pharmaceutical industry, a precipitating agent in rare-earth metal processing, a bleaching agent in various industries, a grinding agent and a rust-removal chemical. It is found mostly in the rhubarbs area of the plants or in the dark green leaves that is harmless. Its structure formula is C2H2O4 and at the ends of the structure has a COOH bonds. Because it has 2 carboxylic bonds, so it could be defined that the oxalic acid is one of the strongest organic acid. Below is the diagram of C2H2O4 structure :

Physically, Oxalic acid is a white and crystalline substance. For every molecule of oxalic acid, two more molecules of water are present in the crystal lattice. Solid oxalic acid melts at 101-102 degrees Celsius and boils at 149-160 degrees Celsius. It is 1.6 - 1.7 times as dense as water at room temperature and highly water-soluble; roughly 1 gram can dissolve in 7 mL of water.

Although it is very pure and white physically, but chemically oxalic acid is highly known as dangerous and strong acid. Oxalic acid in solution is highly corrosive. The oxalate ions, when divested of their hydrogen ions, can act as what are called bidentate ligands, meaning they bind to a metal ion in two places, so they can form complexes with metal ions. Many of the salts they form with metals are insoluble. Kidney stones, for example, are often composed of calcium oxalate. Oxalic acid can react violently with strong oxidizing agents and silver compounds, so it should not be used in conjunction with these chemicals.



1. If you are Sari and Dini, what information will you get about this matter? They will find out that gastritis symptoms are causing nausea and abdominal pain for the sufferer and antacid is one of the cure for gastritis usually packed in a tablet and sold commercially in the drug store. The antacid cure gastritis by neutralizing the enzyme, Hydrochloric acid, inside the stomach which causing infection. Gastritis would be occurred also from too much medication using pain killer. At this case, Sari, who had gotten motor accident, using the pain killer three times a day to cure her pain ankle and cold be indicated to trigger the gastritis disease. 2. Do you know about the pH condition of a stomach? Normally, the pH condition of a stomach should be between 3-5 but some people says around 2 too. It is affected by the amount of food go through the digestion system. When more food store inside, the stomach will automatically set the best environment to help the digestion system to its optimum work rate. 3. How antacids could help gastritis sufferer?

As it has been stated above, the antacids will neutralize too acid environment inside the stomach which is caused by Hydrochloric acid. So, the substance inside the antacids are bases in many types such as Aluminium and Potassium which bond with Hydroxide. Below are some reaction between the antacids and Hydrochloric acid : Al(OH)3(s) + 3 HCl(aq) -----> AlCl3(aq) + 3 H2O(l) Mg(OH)2(s) + 2 HCl(aq) -----> MgCl2(aq) + 2 H2O(l) 4. You read from the label on the bottle of mylanta, it contains Aluminum hydroxide 1000 mg and Magnesium hydroxide 1000 mg for each 5 ml solutions. Can you make a prediction of what chemical reactions occur in Sari's stomach? Reaction of Magnesium hydroxide with hydrochloric acid: Mg(OH)2 + 2HCl -> MgCl2 + 2H2O Reaction of Aluminum hydroxide with hydrochloric acid: Al(OH)2 + 2HCl -> AlCl2 + 2H2O 5. You have HCl and CH3COOH 0.05 M and 50 ml each mixed with KOH 0.1 M 20 ml. Calculate the reaction and its pH. HCl (aq) + KOH (aq) KCl (s) + H2O (l) (1) CH3COOH (aq) + KOH (aq) KCH3COO (s) + H2O (l) (2) For (1), it is a neutralizing reaction because HCl is a strong acid and KOH also a strong bases. So, the pH of KCl should be around 7 ( neutral condition) For (2), we will find out that Ka of KCH3COO is 1.8 x 10-5 and therefore lets count out with limiting reaction CH3COOH (aq) + KOH (aq) KCH3COO (s) + H2O (l) 2.5 mmol 2 mmol 2 mmol 2 mmol 2 mmol 2 mmol 0.5 mmol 2 mmol 2 mmol Then by using the formula (CH3COOH is a base salt) we would find the pOH OH- = Ka x CH3COOH/ CH3COOH = 1.8 x 10-5 x 0.25 = 4.5 x 10-6 So pOH = 6 log 4.5 And the pH would be 8 + log 4.5 or around 8.653

6. How do you explain the differences between weak acids and strong acids? And how to calculate it's pH?
Strong acid is an acid whose atoms ionized completely into the solution, while weak acid doesn't ionize completely. The lower the pH of an acid will show that the acid is stronger and the higher the pH it will become weaker and weaker. To calculate the pH of a strong acid, we can use this formula:

And to calculate the pH of a weak acid, we could calculate the pKa of the acid by the acid constant (Ka) which should be already known. We can find the pKa by using: pKa = -log [Ka] We can identify that the lower the pKa, the stronger the acid, and vice versa. 7. Do you think Sari could calculate the minimum of sodium carbonate she could spill to neutralize the sulfuric acid?

Sodium bicarbonate = NaHCO3 Sulfuric acid = H2SO4 50ml 0.5M =0.025 mol NaHCO3 + H2SO4 2NaHCO3 + H2SO4
M R S 0,05 mol 0,025 mol 0,05 mol 0,025 mol -

Na2SO4 + CO2 + H2O Na2SO4 + 2CO2 + 2H2O

0,025 mol 0,025 mol 0,05 mol 0,05 mol 0,05 mol 0,05 mol

m NaHCO3 = 0,05 . (23+1+12+16.3) = 4,2 g 8. Determining the molecular formula

Using mass ratio,

Ar C = 12 ; O = 16 ; H = 1 CxHyOz + O2 M 1,35 g (Mr=90) 0,015 mol R 0,015 mol S Product CO2 C=12/44 .1,32= 0.36 g O=32/44 .1,32= 0,96 g H2O H=2/18 .0,27 = 0,03 g O=16/18 . 0,27 = 0,24 g CxHyOz = 1,35 g 0,36 g + 0,03 g + mO = 1,35 g mO = 0,96 g mole ratio x= 0,36/12 = 0,03 mol 1 y= 0,03/1 = 0,03 mol 1 z= 0,96/16 = 0,06 mol 2 CxHyOz (CHO2)n=90 (12+1+32)n= 90 (45)n= 90 n=2 organic acid formula is C2H2O4 Using mole ratio : Ar C = 12 ; O = 16 ; H = 1 aCxHyOz + bO2 M 1,35 g (Mr=90) 0,015 mol R 0,015 mol 1 S CxHyOz x=2 y=2 z-2b=5 + bO2 2CO2 CO2 + H2O

0,03 mol 1,32 g (0,03 mol)

0,015 mol 0,27 g (0,015 mol)



0,03 mol 2 1,32 g (0,03 mol) + H2O

0,015 mol 1 0,27 g (0,015 mol)

C2H2Oz = 90 12.2+1.2+16.z = 90 24 + 2 + 16z = 90 16z = 64 z=4 the organic acid formula is C2H2O4

9. The structure of carboxylic group acid in molecule

Carboxyl group is symbolized by COOH, carboxyl group has both hydroxyl and carbonyl group attached to one atom. Carboxyl groups frequently ionized, releasing Hydrogen atom from the carboxyl groups as a free proton and the proton will switch back and forth on both negatively charged oxygen atom.

10.Properties of oxalic acid and the reaction

Physically, Oxalic acid is a white and crystalline substance. For every molecule of oxalic acid, two more molecules of water are present in the crystal lattice. Solid oxalic acid melts at 101-102 degrees Celsius and boils at 149-160 degrees Celsius. It is 1.6 - 1.7 times as dense as water at room temperature and highly water-soluble; roughly 1 gram can dissolve in 7 mL of water. C2O4H2 C2O4H + H+; pKa = 1.27 C2O4H C2O42 + H+; pKa = 4.27

References Brown, Theodore. L, Chemistry the Central Science 12th edition, Pearson Prentice Hall\