Question
What is the sum of the coefficients when the equation is balanced with the lowest whole number ratio?
__Na2S2O3(aq) + __HCl(aq) → __S(s) + __SO2(g) + __NaCl(aq) + __H2O(l)
A. 6
B. 7
C. 8
D. 9
▶️Answer/Explanation
C
Explanation: Firstly, count the number of Na atoms in reactants and products side. There are 2 Na atoms in the reactants side, then there must be 2 Na atoms in the products side also. Hence, place the coefficient 2 in front of NaCl to balance Na.
Na2S2O3(aq) + HCl(aq) → S(s) + SO2(g) + 2NaCl(aq) + H2O(l)
Similarly for Sulfur atoms, the number of S atoms on both sides is equal i.e. 2.
For Oxygen atoms, there are 3 O atoms on both sides.
There is only 1 H atom in the reactants, but there are two H atoms in products. Hence, place the coefficient 2 in front of HCl. After doing this, Cl atoms also get balanced on both sides.
So, the equation becomes :
1Na2S2O3(aq) + 2HCl(aq) → 1S(s) + 1SO2(g) + 2NaCl(aq) + 1H2O(l)
Now, Sum of the coefficients: 1 + 2 + 1 + 1 + 2 + 1 i.e 8.
Hence, correct answer is C.
Question
Which is a homogeneous mixture?
A. Oil and water
B. Sand and water
C. Ethanol and water
D. Chalk and sand
▶️Answer/Explanation
C
Option A : Oil and water do not mix. They forms two phases as there is a boundary of separation between oil and water, it is a heterogeneous mixture.
Option B: Sand doesn’t dissolve in water, it settles down in it, hence it is a heterogeneous mixture.
Option C: Ethanol combines with water to form a single phase only and there is no boundary of separation between ethanol and water. Hence the mixture is homogeneous in nature.
Option D: Chalk doesn’t mix with sand. it forms a heterogeneous mixture.
Hence correct answer is C.
Question
What is the sum of the coefficients when the following equation is balanced using the smallest whole numbers?
__C6H12O6 (aq) → __C2H5OH (aq) + __CO2 (g)
A. 4
B. 5
C. 9
D. 10
▶️Answer/Explanation
B
Number of H atoms in reactants side is 12 and in products side is 6. Hence, place the coefficient 2 in front of C2H5OH.
C6H12O6 (aq) → 2C2H5OH (aq) + CO2 (g)
Now, There are 6 C atoms in reactants and 5 in products. Place 2 in front of CO2.
C6H12O6 (aq) → 2C2H5OH (aq) + 2CO2 (g)
Now the equation is balanced.
Sum of the coefficients is: 1 + 2 + 2 = 5.
Question
What is the sum of the coefficients when the equation is balanced with whole numbers?
—C8H18(g) + —O2(g) → —CO(g) + —H2O(l)
A. 26.5
B. 30
C. 53
D. 61
▶️Answer/Explanation
C
There are 8 C atoms in reactants and 1 in products. Place 8 in front of CO.
C8H18(g) + O2(g) → 8CO(g) + H2O(l)
Number of H atoms in reactants side is 18 and in products side is 2. Hence, place the coefficient 9 in front of H2O.
C8H18(g) + O2(g) → 8CO(g) + 9H2O(l)
Number of O atoms in reactants side is 2 and in products side is 17.
Place 8.5 in front of O2.
C8H18(g) + 8.5O2(g) → 8CO(g) + 9H2O(l)
Since equation is to be balanced with whole numbers, multiply both sides by 2.
2C8H18(g) + 17O2(g) → 16CO(g) + 18H2O(l)
Now, sum of coefficients : 2 + 17 + 16 + 18 = 53.
Question
What is the sum of the coefficients when the following equation is balanced using the smallest whole numbers?
__C6H12O6 (aq) → __C2H5OH (aq) + __CO2 (g)
A. 4
B. 5
C. 9
D. 10
▶️Answer/Explanation
B
Number of H atoms in reactants side is 12 and in products side is 6. Hence, place the coefficient 2 in front of C2H5OH.
C6H12O6 (aq) → 2C2H5OH (aq) + CO2 (g)
Now, There are 6 C atoms in reactants and 5 in products. Place 2 in front of CO2.
C6H12O6 (aq) → 2C2H5OH (aq) + 2CO2 (g)
Now the equation is balanced.
Sum of the coefficients is: 1 + 2 + 2 = 5.