Which of the following is an oxidation-reduction reaction? A) Mg(s) + 2 HCl(aq)

Question

Which of the following is an oxidation-reduction reaction? A) Mg(s) + 2 HCl(aq) rightarrow MgCl_2 (aq) + H_2(g) B) NaI(aq) + AgNO_3(aq) rightarrow AgI(s) + NaNO_3(aq) C) HCl(aq) + LiOH(aq) rightarrow LiCl(aq) + H_2O(l) D) Pb(C_2H_3O_2)_2(aq) + 2 NaCl(aq) rightarrow PbCl_2(s) + 2 NaC_2H_3O_2(aq) E) All of the above are oxidation-reduction reactions. What is the volume (in cm^3) of a 9.37 g piece of metal with a density of 4.66 g/cm^3? A) 6.65 B) 2.01 C) .425 D) 19.5 E) none of the above What does "X" represent in the following symbol?^14_6X A) carbon B) nitrogen C) oxygen D) beryllium E) boron Identify the crystalline solid. A) plastic B) rubber C) bleach D) diamond E) water The specific heat of copper is 0.385 J/(g middot degree C). If 34.2 g of copper, initially at 25.0 degree C, absorbs 4.689 kJ, what will be the final temperature of the copper? A) 25.4 degree C B) 356 degree C C) 27.8 degree C D) 381 degree C Which of the following is an acid-base reaction? A) Fe(s) + 2 AgNO_3(aq) rightarrow 2 Ag(s) + Fe(NO_3)_2(aq) B) C(s) + O_2(g) rightarrow CO_2(g) C) MgSO_4(aq) + Ba (NO_3)_2(aq) rightarrow Mg(NO_3)_2(aq) + BaSO_4(s) D) 2 HClO_4 (aq) + Ca(OH)_2(aq) rightarrow 2 H_2O(l) + Ca(ClO_4)_2(aq) E) None of the above are acid base reactions. Place the following in order of increasing radius. Mg^2+ O^2- F^- A) Mg^2+

Explanation / Answer

15. Here, in (A) oxidation number of Mg in the reactant side is 0 and product side is +2 which implies that it undergoes oxidation. Also, oxidation number of H in the reactant side is +1 and product side is 0 which implies that it undergoes reduction. So, this reaction is a redox reaction.

In (B) oxidation number of Na in the reactant side is +1 and product side is +1 which implies that there is no change in the oxidation number. Also, oxidation number of Ag in the reactant side is +1 and product side is +1 which implies that there is no change in the oxidation number. So, this reaction is not a redox reaction.

In (C) oxidation number of H in the reactant side is +1 and product side is +1 which implies that there is no change in the oxidation number. Also, oxidation number of Li in the reactant side is +1 and product side is +1 which implies that there is no change in the oxidation number. So, this reaction is not a redox reaction.

In (D) oxidation number of Pb in the reactant side is +2 and product side is +2 which implies that there is no change in the oxidation number. Also, oxidation number of Na in the reactant side is +1 and product side is +1 which implies that there is no change in the oxidation number. So, this reaction is not a redox reaction.

16. We know that the relation of mass, volume and density is given as: Mass=Volume x Density.

Therefore, Volume = Mass / Density

In, this problem, we are given that mass = 9.37 g and density= 4.66 g/cm3. Thus, volume=9.37/4.66 = 2.01 cm3. So, the option (B) is the correct choice.

17. For the given symbol 146X we know that the element X has mass number of 14 and atomic number of 6. The element in the periodic table with atomic number 6 is carbon. Hence, the correct option is (A).

18. A crystalline solid is defined as a material with a perfectly ordered arrangement of atoms in the form of lattice. Here, amongst all the options given we observe that only diamond has a perfect arrangement of atoms in an ordered manner. Hence, the correct option is (D).

19. The expression for specific heat of a reaction is:

Heat change = mass x specific heat of the metal x change in temperature

Here, in the question we are given:

Heat change=4.689kJ= 4689J

mass = 34.2g

Specific heat of copper = 0.385J/g

T1= 25oC

T2= ? oC

Putting the above values in the expression we get:  

4689 = 34.2 x 0.385 x (T2 - 25)

T2 = 381.1 oC

Hence, option (D) is the correct answer.

20) Acid–base reaction, is a type of chemical process which involves the exchange of one or more hydrogen ions, H+, between species that may be neutral or electrically charged resulting in the formation of salt and water. Here, amongst all the given reactions, option (D) is the correct choice.

21) The atomic number of Mg=12, O=8 and F=9.

If we remove two electrons from Mg, its ionic radius becomes smaller. Similarly, if we add 1 and 2 electrons respectively to fluorine and oxygen, the ionic radius becomes bigger. The three elements will have the following set of electrons: Mg2+=10, O2-=10 and F-=10. We know that the effective nuclear charge increases as we move from left to right in the peroiodic table. Hence, although all the three atoms have the same number of electrons, the ionic radii will increase in the order: Mg2+<F-<O2-. Option (A) is the correct choice.

22) We are given q= 125kJ and w=-15kJ

From the first law of thermodynamics we know that: change in energy= q+w

Hence, delta E= 125-15 = 110 kJ.

Also, the change in enthalpy = dE + PdV

From thermodynamics calculations we know that w = -PdV

So, PdV= -w = -(-15) = 15kJ.

Hence, delta H = dE + PdV = 110 + 15 = 125kJ

Now, if we correlate the above calculations, we know that option (B) is the correct choice.

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