Preparing Salts- IB Lab Essay
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Calcium chloride (CaCl2) has been manufactured for over 100 years. The salt is used in a variety of industrial and consumer products, and is supplied as flakes, pebbles, pellets, powders and solutions with varying concentrations. Calcium chloride dissociates easily in water to form Ca and Cl ions. Calcium is essential for the formation of skeletons, neural transmission, and muscle contraction, coagulation of the blood, and algae and higher plant growth. Chloride ions are also required for normal cellular operations in animals and humans, and serve as a micronutrient for plants, playing important roles in photosynthesis and osmoregulation.
Calcium chloride is considered to be practically non-toxic to aquatic organisms and bioaccumulation is unlikely. Calcium chloride does not burn and is not flammable. Calcium chloride is corrosive to some metals. Calcium chloride is completely soluble in water. Because calcium chloride is hygroscopic, it should be stored in a dry place and be protected from atmospheric moisture. Heat is produced when calcium chloride is dissolved in water and spattering and boiling can occur. (Calcium Chloride SIDS Initial Assessment Profile, 4, 12-14)
Salts are prepared by five methods. A metal can combine directly with a nonmetal to form a salt. A metal can react with acid to form a salt and release hydrogen gas. A base can react with an acid to form a salt and water. An acid can react with a carbonate and form a salt, carbon dioxide and water. And finally two salts can react to form two other salts.
Our aim was to create 0,124 grams of calcium chloride. In order to prepare the salt, we used a base and an acid. The reason why we chose this method was first, we had the chemicals and second, using two salts was dangerous. So we have decided to use neutralization method.
We predict that we will obtain 0.124 grams of CaCl2, because we used the correct stoichiometric amounts of the reactants HCl and Ca(OH)2 , according to the mole ratio for their reaction.
To prepare the right amount of salt, we had to keep the temperature stable. We used room temperature. Although we heated the beaker, we let it cool down before measuring its mass. Another constant variable was concentration. We had to keep it still so that there wouldn’t be a change in the reaction. Everybody in the class prepared different salt so everybody had different kinds of ions and since the salts were different, their solubility was different too.
MATERIALS AND EQUIPMENT
Beaker 100 ml
0.0815 grams of HCl
0.0828 grams of Ca(OH)2
1) First of all, we decided which acid and base we should use. Since we had HCl and Ca(OH)2 in chemistry lab, we decided to use this acid and base.
2) We wrote the chemical equation of the reaction.
2HCl + Ca(OH)2 –> 2H2O + CaCl2
We used HCl acid and Ca(OH)2 base. When an acid and a base react, they form water and a salt. After writing down the products and reactants, we balanced the equation.
3) In order to make 0.124 grams of salt, we needed to know the amount of reactants we should use. To find out, we used stoichiometry.
2HCl + Ca(OH)2 –> 2H2O + CaCl2
2 moles 1 mole 2 moles 1 mole
H:1.01 Ca:40.08 H2:2.02 Ca:40.08
Cl:35.45 O2: 32.00 O:16.00 Cl2:70.9
(35.45+1.01)ï¿½2 H2: 2.02 (2.02+16.00)ï¿½2
Mr: 72.92 grams Mr: 74.1 grams Mr: 36.04 grams Mr: 110.98 grams
72.92ï¿½0.124ï¿½110.98= 0.0815 grams of HCl (which is 20 drops)
36.04ï¿½0.124ï¿½110.98= 0.0828 grams of Ca(OH)2
4) We measured exactly 0.0828 grams of Ca(OH)2 .
5) We added 20 drops of HCl into the Ca(OH)2.
6) To have only salt as a product, we needed to heat the beaker so that the water would evaporate. After we heated the beaker for several minutes, we let it cool.
7) When the beaker was cool enough, we measured the salt and the beaker’s mass. It was 32,5097 ï¿½0,0005 grams. To make sure that there was no water, we decided to heat and measure it again.
8) The second time we heat and cooled and measured it, we found 32, 4896 ï¿½0,0005 grams.
9) Then we washed the beaker and measured it when it’s empty. We found 32.3551ï¿½0,0005 grams.
10) We subtracted the beaker and the salt’s mass from the empty beaker’s mass to find salt’s mass. The salt’s mass is 0,1345ï¿½ 0,0005 grams. Our aim was to prepare 0.124 grams of CaCl2 salt.
1st Measurement (ï¿½0,00005 g)
2nd Measurement (ï¿½0,00005 g)
32,5097 ï¿½0,0005 g
0.1546 ï¿½0,0005 g
32, 4896 ï¿½0,0005 g
0,1345 ï¿½0,0005 g
Our aim was to create 0,124 grams of calcium chloride. In order to prepare the salt, we used a base and an acid.
To achieve our aim, first we decided which method we should use to prepare this salt. We had two options because we didn’t have other materials. We could have used either two salts or a base and an acid. After deciding to use a base and an acid, we used stoichiometry, which is a quantitative branch of chemistry. “Stoichiometry is the science of measuring the quantitative proportions or mass ratios in which chemical elements stand to one another”(Jeremias Benjaim Richter, 1762-1807). We calculated the amount of chemicals we should use. Then we started preparing our salt and reacted base with the acid. After heating the beaker to eliminate water, we get our salt. We measured it and found out that we prepared 0,1345 ï¿½0,0005 grams of CaCl2 salt.
The reason why we get water and a salt when we react bases and acids is simple. Everything started with Swedish chemist Jons Berzelius, who said that acids and bases have opposite charges. After that the Arrhenius Theory explained that an acid is a compound which produces hydrogen ions and a base is the one that produces hydroxide ions when dissolved in water. Then as the Bronsted-Lowry Theory indicated, when an acid behaves like a donor (an acid as an H+ ion), it means that the hydrogen ion is separating from the acidic compound and when a base behaves like an acceptor (a base as an H+ ion), the hydrogen ion is bonding with the basic compound.
“Because water molecules are polar, the negative charges tend to congregate on one end of the molecule with the oxygen atom, while the positive charges remain on the other end with the hydrogen atoms. The Brï¿½nsted-Lowry model emphasizes the role played by water, which pulls the proton from the acid, resulting in the creation of the hydronium ion” (Zumdahl, Introductory Chemistry: A Foundation). Then finally with the Lewis Theory, which extends Arrhenius and Bronsted-Lowry theories, it was discovered that bases gives electrons and acids accepts them.
So, an acid and a base react, since they attract each other. And when they react, the base generates OH+ and the acid generates H+ which forms water. And the other ions react to form a salt.
With this experiment we not only used what we have learned about preparing salts but we also used stoichiometry, which is a very important topic in chemistry. We did all the calculations and the experiment ourselves and we get to apply our knowledge.
Although the result we get was really close, we didn’t exactly find 0.124 grams of CaCl2. The percentage error of the experiment is %9. We found 0.1345 ï¿½ 0,0005 grams.
To make this experiment better, first of all we could have research our salt and learn more about it. We didn’t know that Ca(OH)2 is hygroscopic in the first time we measured it’s mass. That’s why its mass may have been measured more than it should be. But the second time we measured the beaker, we were more careful however still when we let the beaker to cool, its mass might have increased.
After we heated the beaker, we waited for several minutes and waited it to cool but the beaker and the salt within might have been still warm. If we measured salt’s mass when it was still hot, that means we found the mass more than it should be. If we had more time, maybe we could be sure that it was in the room temperature and then measure it.
Although we cleaned the beaker after the experiment, we might have left salt in it and when we measured empty beaker’s mass, we might have found something wrong. We could have cleaned it more neatly.
Calcium Chloride SIDS Initial Assessment Profile, UNEP Publications, SIAM 15, Boston, October 22-25, 2002, pages 4, 12-14.
Zumdahl, Steven S. Introductory Chemistry: A Foundation, 4th ed. Boston: Houghton Mifflin, 2000.