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PS_09_D

Page history last edited by mikibomber_95@... 11 years, 6 months ago

EXPERIMENTAL PROBLEM n. 09 GROUP D

 

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 potassium 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 potassio 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

 

 take the two salts,  put each of them in a test tube with alcohol and then see

the difference between the volumes of alcohol and of the mixture, and so we find the volume of the two salts.

 

3. Planning

 

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

2. Put in a second test tube the calculated mass of potassium chloride;

3. Fill a graduated cylinder up to 5 mL of alcohol;

4. Add the sodium chloride in it and find the new volume;

5. Fill in the other graduated cylinder with 5 mL of alcohol;

6. Add the potassium chloride in it and find the new volume;

7. (Compare the two volumes of the two solid salts.)

(Last point, 7, is unimportant because is not an operative step)

 

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 chloride is slightly higher that the sodium's volume.

 

Questions & Answers

 

1. Question 1

Why is the amount of KCl more than three grams?

 

because the atoms of K are  bigger heavier than the atoms of sodium OK

 

2. Question 2

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

We need the density to calculate the volume. OK

 

3. Question 3

 

Why are the volumes of the two salts so different?

 

Because their molecular mass is  different. NO. You should relate volumes of solids to the volume of their atoms or ions.

 

4. Question 4

Why is a lithium ion smaller than a sodium ion?

Answer 4

Because have a number of different atoms. No! a single ion is a single atom See pag 214 of your textbook (also to answer next question)

 

 

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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