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PS_11_Group_09

Page history last edited by emanuele rullo 11 years, 7 months ago

 

EXPERIMENTAL PROBLEM n. 11 GROUP 9

By: Julietta, Elina, Emanuele, Ivan, Paola

 

You receive a sample of a salt formed by an "s-block" metal and an halogen. The amount of this sample contains as many halogen ions as there are in 1,00 grams of sodium chloride. You have to recognize the metal and the halogen in that salt.

 

Vi viene assegnato un campione di sale formato da un metallo del "blocco s" e da un alogeno. La quantità di questo campione contene tanti ioni alogenuro quanti ve ne sono in 1,00 g di cloruro di sodio. Dovete riconoscere il metallo e l'alogeno nel sale.

 

Saat suolanäytteen, joka koostuu alkali- tai maa-alkaliryhmän metallista (=s-ryhmä) ja halogeenista. Näyte sisältää yhtä monta halogeeni-ionia kuin 1,00 grammassa natriumkloridia (NACl) on kloridi-ioneita. Tehtävänä on tunnistaa, mistä metalli- ja halogeeni-ioneista suola koostuu.

 

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

1.1 Colours of alkali metals to the bunsen flame:

Lithium  Sodium  Potassium  Calcium  Strontium  Barium 
deep purple  yellow-orange  lilac  orange+red sparkle  scarlet red  green-yellow 

 

1.2 Atomic relative mass of sodium and chlorine: Na=22.99; Cl=35.45.

1.3 Formula Weight of NaCl: 58.44.

1.4 Formula of a salt formed by Me+ and X- ions: MeX

1.5 Formula of a salt formed by Me2+ and X- ions:MeX2

 

2. Main idea

Synthetic description of the strategy to identify the metal ion and halide ion in the salt

To recognize the cation we must do the test flame, while the halogen must make can be found through a calculation based on the weight of the salt.

 

 

3. Planning

1. Weigh the bowl with the salt.

2. Transfer the salt in another bowl.

3. Weigh the empty bowl.

4. Clean wire Ni-Cr with hydrochloric acid 1:1 until the flame is colorless.

5. Soak the line Ni-Cr wire again in the acid and take a grain of salt.

6. See the colour obtained from taken by the flame. 

 

4.  Report

 

Italian  (29.3.2010) Finnish (31.3.2010)

weight of salt + bowl= 3.63 g of empty bowl = 1.82 g

 

flame test colour is lilac.

 

 

 

empty plastic box = 13,5 g

sample = 1,9 g

sample + plastic box = 15,4 g

 

flame test colour is lilac.

 

 

 

5. Elaboration and Interpretation

 

Italian   Finnish 

From the colour we understand the cation is potassium.

3.63-1.82= 1.81

Potassium relative atomic mass = 39,1

 

proportional number of sodium and chlorine in one gram of NaCl = 1,00:58,44 = 0,0171

Potassium mass = 0.0171· 39,1 = 0.669 g

Halogen mass = 1.81 - 0.669 = 1.141 g

halogen atoms number = n. Li atom= n.Na atoms

relative atomic mass of halogen atom = 1.141:0,0171= 66,7 g. This is nearest to bromine (79,9) among the halogens

Metal-ion is potassium, because the colour of the flame was lilac.

Welcome Elina!!!

you may edit the wrong calculation by Emanuele Paola and Ivan (they mistaked the lithium atomic mass from start)

Then you can calculate the same based on your data.

Common conclusions

Our conclusion is that our salt is potassium bromide (KBr).

 

 

Weight of salt+bowl

 

The test flame.

 

Our teachers. Prof.essa Eugeni e Prof. Tifi.

 

This is the group 09. Emanuele, Ivan e Paola.

 

 

 

 

Questions & Answers

 

Please review each other the answers

 

1. Why are atoms emitting light at the flame?

Answer 1

Because the atoms with placed to the heat and stir are continuously getting excited and relaxed emitting light impulses

 

2. How did you recognize the metal element in the salt?

Answer 2

Through the flame test we have seen the color of the flame that was the same of a previous test where we known the metal produced the heat and we put the salt that produced this color.

 

3. What measure permitted you to deduce which halogen was in the salt?

Answer 3

The measure is ph We deduced the halogen mass by the salt mass minus the calculated metal mass. Then we calculated the halogen relative atomic mass by knowing the proportional number of its atoms.) 

 

4. Does your salt contain more cations or anions?  

Answer 4

In this salt, that is KBr,  is the cations there are the same number of anions and cations.

 

5. Does your salt contain more mass as halide ions or as metal ions or the same?

Answer 5

Our salt contains more mass of halide ions because bromine atoms are heavier than potassium atoms.

 

 

 

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