Indicators, Mass Spectrometry, Reacting Masses

Question 1

Methyl orange, 3.1 - 4.4 - red to yellow RTY

Phenolphthalein, 8.3 - 10.0 - colourless to pink CTP

1. strong
2. weak

Answer 1

1. Strong acid and strong alkali

The colour change for both indicators takes place at a pH range that falls within the vertical region of the curve

Therefore, either indicator can be used

2. Strong acid and weak alkali

Only methyl orange will change colour at a pH close to the equivalence point and within the vertical region of the curve

3. Weak acid and strong alkali

Now, only phenolphthalein will change colour at a pH close to the equivalence point and within the vertical region of the curve

The pH range at which methyl orange changes colour falls below the curve

4. Weak acid and weak alkali

Neither indicator is useful, and a different method should be considered

Question 2

MASS SPECTROMETRY

1. molecules in the small sample are bombarded with high energy electrons which can cause the molecule to lose an electron

This results in the formation of a positively charged molecular ion with one unpaired electron

One of the electrons in the pair has been removed by the beam of electrons

2. EQN. MOLECULE => MOLECULE+ + e-
3. molecular ion can further fragment to form new ions, molecules, and radicals

WHICH DEFLECTED FIRST?

Answer 2

4. fragmentation ions are accelerated by an electric field

Based on their mass (m) to charge (e) ratio, the fragments of ions are then separated by deflecting them into the detector

For example, an ion with mass 16 and charge 2+ will have a m/e value of 8

5. SMALLER AND MORE POSITIVELY CHARGED FRAGMENT IONS DETECTED FIRST
   DEFLECTED MOST; more attracted to neg pole of magnet

-Each fragment corresponds to a specific peak with a particular m/e value in the mass spectrum

The base peak is the peak corresponding to the most abundant ion

-the heights of the peaks in mass spectroscopy show the proportion of each isotope present

Question 3

Mass spectroscopy can be used to find the relative abundance of the isotopes experimentally

The relative abundance of an isotope is the proportion of one particular isotope in a mixture of isotopes found in nature

For example, the relative abundance of Cl-35 and Cl-37 is 75% and 25% respectively

This means that in nature, 75% of the chlorine atoms is the Cl-35 isotope and 25% is the Cl-37 isotope

3:1 ratio of M+:M+1 peak is Chlorine Cl
1:1 is Bromine Br

1:2:1 Br2
9:6:1 Cl2

Question 4

M+1 peak

Answer 4

caused by the Carbon 13 isotope
-a very small peak to the right of the M peak

-larger M+1 peak => MORE CARBONS

-multiple peaks present: The molecular ion can further fragment to form new ions, molecules, and radicals

Smaller, more positive => deflected MOST.

TALLEST PEAK => base peak; most abundant ion.

+Fe3 has a smaller m/z ratio and will be deflected more
SMALLER M/E => DEFLECT MORE.

Question 5

calc

1. Ar

Answer 5

1. The relative atomic mass of an element can be calculated by using the relative abundance values. Relative abundance of an isotope is either given or can be read off the mass spectrum
2. RELATIVE atomic mass = (ABUNDANCE X MASS + ABUNDANCE X MASS) DIVIDED BY overall ABUNDANCE or 100.