CLS 231 questions



 

 

1. Both classical and instrumental methods can be used to determine the concentration of a specific element or species in a compound. Which of the following pairs is the WRONG combination of the type of analysis with its characteristic? 

Gravimetric analysis - mass

Potentiometric analysis - voltage

Volumetric analysis - volume

Spectrophotometric analysis – density

 

answer is spectrophotometric analysis

Actually, spectrophotometric exploits the light properties of chemical compounds. In a spectophotometric analysis, one measures how much light is absorbed by a certain solution 

 

 

 

2. The unit molarity (mole per liter) is used to express the concentration of a certain species of chemical element in a concentrated solution. Meanwhile, other more appropriate units are more commonly used to describe the concentration of more diluted solutions. One of these units, which is equivalent to milligram per liter, is? 

Part per million (ppm)

Part per billion (ppb)

Part per thousand (ppt)

Part per trillion (pptr)

answer ppm

For example, a solution with a concentration of 1.5 ppm sodium is interpreted as there is only 1.5 milligram of sodium in 1 liter of solution.
The concentration of salt (sodium chloride) in typical sea water is around 32-35 ppt. 1 ppt (part per thousand) means 1 milligram per 1 liter of solution) 

 

 

 

 

4. In chemical equilibrium, a principle states that if a stress (for example, a change in concentration, pressure, temperature or volume of the vessel) is applied to a system in equilibrium, the equilibrium will shift in such a way to lessen the effect of the stress. This principle is called? 

The Hess Principle

The Aufbau Principle

The Le Chatelier’s Pinciple

The Robert Principle

 answer is chateliers principle

 

 

 

3. Many statistical tests are performed for the data obtained in analytical chemistry. One of the tests decides whether a given datum (either the value is too big or too small compared to the other data) can be rejected or not. This test is? 

F test

Q test

T test

A test

answer is Qtest

The F test is used to test whether the standard deviations for 2 sets of data are significantly different from each other. On the other hand, the T test, also known as the Student T test, is used to compare the obtained value in experiments with the real (actual) value 

 

4. In chemical equilibrium, a principle states that if a stress (for example, a change in concentration, pressure, temperature or volume of the vessel) is applied to a system in equilibrium, the equilibrium will shift in such a way to lessen the effect of the stress. This principle is called? 

The Hess Principle

The Aufbau Principle

The Le Chatelier’s Principle 

The Robert Principle

answer is le chateliers principle

 

 

5. Amphoteric salts, also known as amphiprotic salts, are often used in the preparation of buffer solutions. An amphoteric salt can act as an acid or a base, depending on the values of its dissociation constants. Which of the followings is (are) an amphiprotic molecules(s)? 

 

 

 

 

 

 

6. In acid-base titration in analytical chemistry, the Kjeldahl method involves dissolution of a substance in sulfuric acid, treatment with sodium hydroxide and also back titration using hydrochloric acid. It was developed by Johan Kjeldahl and is used to determine the percentage of a specific element in chemical compounds. Which element is it?

Oxygen, O

Hydrogen, H

Carbon, C

Nitrogen, N

( the answer n nitrogen )

 The nitrogen in a substance will react with sulfuric acid, H2SO4 to produce ammonia, NH3. The ammonia produced will then be neutralized by sodium hydroxide, NaOH. The excess NaOH will be neutralized again with hydrochloric acid, HCl.
Using the backward calculation, we will know the percentage of nitrogen in the given substance.