Chapter 4, Problem 110GQ

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# A solution of hydrochloric acid has a volume of 125 mL and a pH of 2.56. What mass of NaHCO3 must be added to completely consume the HCl?

Interpretation Introduction

Interpretation:

The mass of NaHCO3 required to consume given volume of HCl completely in the given has to be determined.

Concept introduction:

• Strong acids dissociates completely into ions in solution but weak acids not.
• pH of a solution is the negative of the base -10 logarithm of the hydronium ion concentration.

pH=-log[H3O+]

• Concentration of hydronium ion [H3O+]=10-pH
• Amountofsubstance=Concnetrationofthesubstance×Volume
• Numberofmole=GivenmassofthesubstanceMolarmass
• Stoichiometric factor is a relationship between reactant and product which is obtained from the balanced chemical equation for a particular reaction.
•  For chemical reaction balanced chemical reaction equation written in accordance with the Law of conservation of mass.
• Law of conservation of mass states that for a reaction total mass of the reactant and product must be equal.
Explanation

The balanced equation for the reaction involving NaHCO3 and HCl is,

â€‚Â HCl(aq)â€‰+NaHCO3(s)â€‰â†’â€‰NaCl(aq)â€‰+â€‰H2O(l)â€‰+â€‰CO2(g)

NaHCO3 and HCl reacts in 1:1 ratio.Â  Therefore from the amount of NaHCO3, amount of HCl can be calculated.

Here pH of the HCl solution is given and its value is 2.56.

Concentration of hydronium ion can be determined using the formula,

â€‚Â Concentration of hydronium ion [H3O+]â€‰â€‰=â€‰10-pH

The pH of the given solution is 2.56. Â Substituting this value in the above equation,

Then, concentration of hydronium ion is,

â€‚Â [H3O+]â€‰=â€‰10-â€‰2.56â€‰ â€‰=â€‰2.8â€‰Ã—10-03â€‰Mâ€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰=â€‰â€‰0.0028â€‰â€‰M

From the concentration of hydronium ion amount of HCl involved in the above reaction can be calculated as follows,

Amountâ€‰â€‰ofâ€‰â€‰HCl =â€‰â€‰Concentrationâ€‰HClâ€‰Ã—â€‰Volumeâ€‰HCl =â€‰0

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