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Page history last edited by alfredo 14 years, 3 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 potassium and chloride as they are in the 3,0 grams of NaCl, and then to compare the volumes of the two amounts of solids. You have also alcohol, cylinder and pipette.



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

first: Na relative atomic mass = 22,99 a.m.u.

second: Cl relative atomic mass Cl 35.45 a.m.u.

third: Salts don't dissolve in alcohol

fourth K relative atomic mass = 39,10 a.m.u.

fifth: 3.0 g of sodium chloride contain 3,0 : (22,99 + 35,45) = 0,05133;

sixth. Mass of potassium chloride with the same number of ions: 0,05133 ยท (39,10 + 35,45) = 3,83 g.



2. Main idea

  Weigh the calculated mass of potassium   chloride (containing the same number of ions of sodium chloride) in the empty tests tube.  

Then add each of the two salts in a given amount of alcohol in a cylinder and see their volume from the alcohol upraising. 


3. Planning


1. weigh the calculated mass of potassium chloride in the empty test tube

2. put in two  cylinders some alcohol

3. put the  content of the tests tube in the   cylinders

4. mix to eliminate air bubbles then read the volume of the two compounds in alcohol


INSTRUMENTS: -test tube;- beker 10 mL graduated cylinders;- alcohol;- balance


4.  Report

1. NaCl = 3,00 g

2.KCl = 3.80g

3. alcohol volumes = 5 ml

4. alcohol and NaCl volumes = 6.2 mL

5.alcohol and KCl volumes= 6.6 mL


5. Elaborazione e Interpretazione

We have seen that the volume of potassium 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 atoms of sodium


2. Question 2

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

to calculate volumes from masses without measuring

 you need weight and density


3. Question 3


Why are the volumes of the two salts so different?



4. Question 4

Why is a potassium ion bigger than a sodium ion?

Answer 4


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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