Solving Questions on Some Chemistry Concepts

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        Welcome back to my blog. I know it's been a while since I posted anything on my blog. Today, I'll be posting some questions and solutions about some familiar chemistry concepts. I took most of these questions from the *P.UTME CHAMPIONS GROUP; although, I edited somethings in the questions. These questions are multiple-choice questions, so we'll be able to do some guesses and eliminations to derive our answers. That's because some options are meant to divert your focus from the real question  for you to get the question wrong. I call them distractions. I'll also be explaining why an option is right or wrong in my solutions below. Note that the correct answers will be boldened alongside its option (letter).

        Now, let's take a look at these questions and see their respective solutions:


 

1. In principles that govern electron filing into orbitals, which of the following rules states that in the building up of atoms, electrons enter into orbitals in order of increasing energy?

A. Pauli rule 

B. Hund's rule 

C. Aufbau rule 

D. Milikan rule 

    The answer is option C. It's Aufbau's rule that "states that, in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. For example, the 1s subshell is filled before the 2s subshell is occupied."

     Pauli rule has to do with the nature of electrons and quantum numbers, Hund's rule has to do with the placement of electrons into orbitals.

     Millikan's rule has nothing to do with this question at all, plus I don't think there's any rule like Milikan's rule. Not that I know of.

 


2. Which of the following metallic ions shows deep blue precipitate when reacted with potassium hexacyanoferrate (II) solution?

A. Pb²+ 

B. Fe²+ 

C. Fe³+ 

D. Ca²+ 

         The correct option is C. This has to do with transition metal complex ions. So if you have no idea of what that is, you might not fully grasp the solution to this question. First and foremost, options A and D are wrong because the solution of potassium hexacyanoferrate (II) is mostly used to detect the presence of either Fe2+ or Fe3+ ions in solutions or tissues (as in biology). Also from the word. "ferrate", you would know that the solution is an iron complex. 

       Now, we are left with option B and C. To know which metallic ion that shows deep blue color, we will have to consider the behavior of potassium hexacyanoferrate in compounds containing iron with different ion charges.

        Suppose we have a compound that has Fe2+, let's say (FeS2), then if we mix it with potassium hexacyanoferrate (II), the reaction would just result in a light blue precipitate which would not really form. This is because both compounds have Fe2+ in them. So option B is not correct also.

        So, if we have a compound containing Fe3+, let's say (FeCl3), then mix it with potassium hexacyanoferrate (II), the resulting reaction would be a deep blue solution. That's because the iron(II) in the potassium hexacyanoferrate (II) is slowly changing to iron (III) due to the presence of atmospheric oxygen. That makes option C very correct.



3. Which of the following separation techniques is used to recover a solid from its saturated solution?

A. Distillation 

B. Chromatography 

C. Crystallization 

D. Precipitation 

     The correct option is C. Crystallization is a process in which "a hot, concentrated solution of a substance is allowed to cool slowly, which forms crystals of pure solid. The crystals can be separated by filtration."  This process is used to extract the solid from its solution.

    Chromatography is "the separation of a mixture by passing it in solution or suspension or as a vapor (as in gas chromatography) through a medium in which the components move at different rates." So, option B is not correct

    Precipitation is the emergence of an insoluble solid from a solution by adding a precipitant to the solution. Option D is not close to the question because you have to mix two different solutions to get an insoluble solid.

    Distillation can be used to recover a solid from its saturated solution by apply heat to the solution. This process removes water from the saturated solution which increases the concentration of the solid in its solution. However, this process doesn't separate the solid from its solution. So option A is close but not correct. Distillation extracts *liquid* from a solution while crystallization extracts *solids* from a solution. Keep that in mind.

    


4. The hydrogen ion concentration in 0.02M of tetraoxosulphate VI acid solution is_____ mol/dm^3

A. 2.5 × 10^(-12)

B. 2.5 × 10^(-13)

C. 4 × 10^(-2)

D. 2 × 10^(-2)

    Before solving the question, I'll like to establish one thing. The unit M (which is the molarity) is the same as mol/dm^3.  You'll have to write a balanced ionic equation to see the stoichiometric ratio of each constituent of the chemical equation. Something like this:

                            H2SO4 (aq)  ====>  2H+ (aq) + SO42- (aq)

Now that we know the ratios between these constituents, we can try to find some relations between them to solve for the concentration of hydrogen ion.

    Since 1 mole of  H2SO4 yields 2moles of  H+, then 0.02M of  H2SO4 would yield:

                        2* 0.02M = 0.04M or 0.04mol/dm^3

    This could also be rewritten in scientific notation as: 4 X 10^(-2) mol/dm^3. So the correct option is C.



5. Double salts are salts which ionize to produce how many different types of ions in solution 

A. 4 

B. 3 

C. 2 

D. 1 

         The correct option is B. By definition, "Double salts are salts containing more than one cation or anion. Double salt is a salt that ionizes to produce three different types of ions in solution, two of these are usually positively charged and the other negatively charged." 

        Although C is kinda close because double salts form two forms of ions (cations and anion), however, that's not what the question is asking. So, option A, C, and D are wrong. 


         

6. RNH2 is the functional group of:

A. Nitrile 

B. Amides 

C. Amino acid

D. Amines 

         The correct answer is option D. According to the FSU chemistry website, "primary amines have an alkyl or aromatic group and two hydrogens attached to a nitrogen atom." That's why it is represented as RNH2.  

        Option A is wrong because Nitriles (or organic cyanides) have an alkyl (or aromatic) group attached to a carbon-triple-bond-nitrogen function which is represented as RCN. 

        Option B is wrong because Primary amides have an alkyl or aromatic group attached to an amino-carbonyl function denoted by RCONH2. 

        And option C is wrong because Amino acids, strictly alpha-amino acids, have carboxylic acid, amino function, and a hydrogen attached to the same carbon atom denoted by R-CH(NH2)COOH.



7. Which of the following metals are *not true transition elements*? 

I. Scandium 

II. Chromium 

III. Zinc 

IV. Copper 

V. Nickel 

 

A..I, II, and V 

B..III IV, and V

C. I and III 

D.IV and V

 

        The correct option is C. The reason is that these transition metals (Scandium, Zinc, and Nickel) only have one charge most of the time. For instance, Scandium is one of the two elements in the first transition metal period which has only one oxidation state. Also, Zinc always forms a 2+ ion with almost all the compounds. That's why they may not be true transition metals because by definition, exhibits two or more oxidation states. 




      



     

        Alright, that's the end of solving questions on some chemical concepts. I know some of my explanations are a bit lengthy, but the importance of this blog is to make you understand these solutions to these questions conceptually and not just by making guesses or cramming. I hope you enjoy reading this blog.

        Feel free to like and comment on this blog on any of these questions. Thank you very much for your time.😊🙏🙏

 


Sources

1. (n.d.). Retrieved September 16, 2020, from https://www.chem.fsu.edu/chemlab/chm1046course/functional.html

2.  Periodic Table of Elements. (n.d.). Retrieved September 16, 2020, from https://coolperiodictable.com/resources/acids-and-bases/salts.php

3. (General Science) CHEMISTRY - Solubility & Separation of Mixtures. (n.d.). Retrieved September 16, 2020, from https://www.iasplanner.com/civilservices/general-science/chemistry-solubility-separation-of-mixtures

4. Periodic Table of Elements. (n.d.). Retrieved September 16, 2020, from https://coolperiodictable.com/resources/acids-and-bases/salts.php









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All the contents on this blog including the text, layout, designs are owned by the google blogger app. All the images are from the Brainly website. All questions are from the *P.UTME CHAMPIONS GROUP* Facebook group. Contents may not be copied, reproduced, transmitted, distributed, downloaded, or transferred in any form or by any means without my permission. (For permission to reprint, please contact via Gmail at ibraheemrahman2001@gmail.com

Location: Miami, FL, USA

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