
Concept explainers
Alka-Seltzer® tablets contain aspirin, sodium bicarbonate, and citric acid. When they come into contact with water, the sodium bicarbonate (NaHCO3) and citric acid (H3C6H5O7) react to form carbon dioxide gas, among other products.
The formation of CO2 causes the trademark fizzing when the tablets are dropped into a glass of water. An Alka-Seltzer tablet contains 1.700 g of sodium bicarbonate and 1.000 g of citric acid. Determine, for a single tablet dissolved in water, (a) which ingredient is the limiting reactant, (b) what mass of the excess reactant is left over when the reaction is complete, and (c) what mass of CO2 forms.
(a)

Interpretation:
For the given reaction, the limiting reactant, the number of moles of excess reactant and the mass of product
Concept introduction:
- Limiting reactant: limiting reactant is a reactant, which consumes completely in the chemical reaction. The quantity of the product depends on this limiting reactant, it can be determined with the help of balanced chemical equation for the reaction.
- Excess reactant: is the reactant, which remains unreacted after the completion of a reaction.
- Balanced chemical equation of a reaction is written according to law of conservation of mass.
- Mole ratios between the reactants of a reaction are depends upon the coefficients of respective reactant in a balanced chemical equation.
- Equation for Number of moles of a substance, from its given mass is,
To find: the limiting reactant for the given reaction.
Explanation of Solution
The mass of
The mass of
Number of moles of a substance, from its given mass is,
Therefore,
The number of moles of
The number of moles of
To find: the limiting reactant for the given reaction.
The liming reactant of the reaction is
Explanation:
The balanced equation of the reaction is given as,
The mole ratio between reactants
That is,
Three moles of
The number of moles of
The number of moles of
Therefore,
The number of moles of
But there are only
Hence,
The liming reactant of the reaction is
(b)

Interpretation:
For the given reaction, the limiting reactant, the number of moles of excess reactant and the mass of product
Concept introduction:
- Limiting reactant: limiting reactant is a reactant, which consumes completely in the chemical reaction. The quantity of the product depends on this limiting reactant, it can be determined with the help of balanced chemical equation for the reaction.
- Excess reactant: is the reactant, which remains unreacted after the completion of a reaction.
- Balanced chemical equation of a reaction is written according to law of conservation of mass.
- Mole ratios between the reactants of a reaction are depends upon the coefficients of respective reactant in a balanced chemical equation.
- Equation for Number of moles of a substance, from its given mass is,
To determine: the mass of excess reactant in the given reaction.
Explanation of Solution
The balanced equation of the reaction is given as,
The mole ratio between reactants
That is,
Three moles of
The liming reactant of the reaction is found as
The number of moles of
The number of moles of
Therefore,
The number of mole of
The number of moles of
So, the number of moles unreacted or the excess reactant
Equation for Number of grams of a substance from its number of moles is,
Then,
The mass of
(c)

Interpretation:
For the given reaction, the limiting reactant, the number of moles of excess reactant and the mass of product
Concept introduction:
- Limiting reactant: limiting reactant is a reactant, which consumes completely in the chemical reaction. The quantity of the product depends on this limiting reactant, it can be determined with the help of balanced chemical equation for the reaction.
- Excess reactant: is the reactant, which remains unreacted after the completion of a reaction.
- Balanced chemical equation of a reaction is written according to law of conservation of mass.
- Mole ratios between the reactants of a reaction are depends upon the coefficients of respective reactant in a balanced chemical equation.
- Equation for Number of moles of a substance, from its given mass is,
To determine: the mass of product
The mass of product
Explanation of Solution
The balanced equation of the reaction is given as,
The mole ratio between reactant
That is,
One mole of
The liming reactant of the reaction is found as
The number of moles of
Therefore,
The number of moles of product
Equation for Number of grams of a substance from its number of moles is,
Then,
The mass of
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