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Page history last edited by alfredo 14 years, 4 months ago




You have a given amount of sodium chloride (3,0 grams) in a small test tube. Your task is to put, in a second empty test tube, as many ions of lithium and chloride as they are in the 3,0 grams of NaCl, and then to compare the actual volumes of the two amounts of solids. You have also alcohol, cylinder and pipette.

Ricevete 3,0 g di cloruro di sodio in una piccola provetta. L'obiettivo del gruppo è di introdurre in un'altra provetta tanti ioni litio e cloruro quanti ve ne sono nella provetta con l'NaCl, quindi comparare i volumi effettivi delle due quantità di solidi. Avete a disposizione anche alcool, cilindro e pipetta graduati.




1. Useful knowledge (reference data, concepts and principles)

First:           The  formula mass of NaCl is 58,44.

Second:          Salt doesn't dissolve in alcool.

Third:         The formula mass of KCl is 74,55 

Fourth:       Formulas and ions in 3 grams of NaCl = 3,0 : 58,44 = 0,05133

Fifth:          Mass of the same number of formulas - ions of KCl = 0,05133 · 74,55 = 3,83 g


2. Main idea

We put in a test tube the sodium chloride and in another test tube the 3,8 grams of potassium chloride. We fill a cylinder up to 5 ml of alcohol and add the sodium chloride in this cylinder. Thanks to this metod we find the volume of sodium chloride. We do the same thing with potassium chloride. At the end we compare the two volumes. 


3. Planning

1) Put in a test tube 3.0 g of sodium chloride;

2) Put in a second test tube 3.8 g of potassium chloride;

3) Fill a graduated cylinder up to 5ml of alcohol;

4) Add the sodium chloride and find the volume;

5) Fill in other graduated cylinder 5ml of alcohol;

6) Add the potassium chloride and find the volume;

7) Compare the two volumes.


4.  Report

We should have had to calculate the volume of lithium chloride, but we were wrong and we have used the potassium chloride.

- Mass of sodium chloride = 3.0 g;

- Mass of potassium chloride = 3.8 g;

- Volume of graduated cylinder with alcohol = 5 mL;

- Graduated cylinder with alcohol and sodium chloride = 6.62 g;

- Volume of sodium chloride = 1.6 mL 

- Volume of graduated cylinder with alcohol = 5 mL;

- Volume of graduated cylinder with alcohol and potassium chloride = 6.8 g;

- Volume of potassium chloride = 1.8 mL


5. Elaborazione e Interpretazione

We have seen that the volume of potassium is slightly higher that the sodium's chloride volume.


Questions & Answers


1. Question 1

Why is the amount of KCl more than three grams?

Because the atomic mass of potassium atom are different is higher than sodium atom mass. 


2. Question 2

What data do you need to calculate volumes from masses, without measuring?

We need the density to calculate the volume.


3. Question 3

Why are the volumes of the two salts so different?

Because the salts have different density.

No. You should take in account that you have different volumes of the same number of ions in the two amounts of substances.

Therefore your explanation should rely on the difference in some property of single potassum and sodium ions.


4. Question 4

Why is a lithium ion smaller than a sodium ion?


5. Question 5

Which is the largest between:

a) a bromide ion and a chloride ion

b) a cesium ion and a cesium atom

c) a sodium ion and a magnesium ion

d) a iodine atom and a iodide ion

e) an oxygen atom and a sulphur atom 


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