Which of the following is a single replacement?

Question

a. KOH + HCl ---> KCl + H20
b. 2Na + Zn(NO3)2 ---> 2NaNO3 +Zn
c. 2C2H6 +7)2 ---> 4CO2 +6H2O
d. H2O + CO2 ---> H2CO3

Answer 1

A single replacement reaction is where one element replaces another in a compound. There are two possibilities:

1) A cation replaces another cation - a cation is a positively charged ion with fewer electrons (in the orbital shells) than protons (in the nucleus); and

2) A anion replaces another anion - an anion is a negatively charged ion with more lectrons that protons.

In addition, there are a few simple rules:

1) An anion can only replace an anion, and a cation a cation, but a cation CANNOT replace an anion, or vice versa;

2) The number of components on the LHS must equal the RHS - i.e. two reactants cannot combine to produce just one reactant; and

3) The replacements are always elements - no compounds.

An example is: AX + Y ---> YX + A, where element Y replaced element A

So analyzing the possible answers:

a. NO. Here a Potassium (K) cation replaced Hydrogen (H) (which can be an anion and or cation - i.e proton or Hydride) , and Hydrogen replaced Potassium (K) - this is an example of a "Double Replacement Reaction".

b. YES. This is a classic example where the Sodium(Na) cation replaced the Zinc (Zn) cation.

c. NO. There is a typo here, but this is clearly meant to be the combustion reaction of Ethane:

2 C2H6 + 7 O2 → 4 CO2 + 6 H2O

There are multiple replacements here and this is not a single replacement reaction.

d. NO. Two reactants are combining to form one compound so clearly not a single replacement reaction.

So the answer is B.

Answer 2

b. 2Na + Zn(NO3)2 ---> 2NaNO3 +Zn

The Na replaces the Zn, thus it's a single replacement reaction.

Answer 3

Time to ask you to think about it. Single replacement means ONE of the reactants has an atom switched with another atom. So which one of these DO YOU think it is.

Answer 4

b