Chemical reactions are a fundamental aspect of technology, society, and even existence. A chemical reaction occurs when one or more compounds, known as reactants, are changed into one or more distinct substances, known as products. Chemical elements or compounds are examples of substances. A chemical reaction rearranges the constituent atoms of the reactants to produce various products.
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Definition: A neutralisation reaction occurs when an acid and a base react to produce salt and water. |
Neutralisation Reaction Chemistry Questions with Solutions
Q-1: Write the net ionic equation for the neutralisation reaction between calcium hydroxide and hydrobromic acid solution?
Answer: Write the molecular equation first.
Ca(OH)2 (aq) + 2HBr(aq) → CaBr2(aq) + 2H2O(l)
Dissociate the ionic compounds in the aqueous phase into ions
Ca2+(aq) + 2OH–(aq) +2H+(aq) +2Br–(aq) → Ca2+(aq) + 2Br–(aq)+ 2H2O(l)
Remove the spectator ions from the above equation to get the net ionic equation.
2OH–(aq) +2H+(aq) → 2H2O(l)
Or
OH–(aq) +H+(aq) → H2O(l)
Q-2: In comparison to acetic acid, formic acid is a stronger acid. Formate ion or acetate ion: which is the stronger base?
Answer: Acetate ion is a stronger base.
Explanation: A conjugate base is formed when an acid releases protons. A strong acid has a weak conjugate base and a weak acid always has a strong conjugate base.
Q-3: Make a list of the several uses for neutralisation reactions.
Answer: The various applications of neutralisation reactions are:
1. Titration methods: Chemical titration is used to determine unknown acid or base concentrations by determining their neutralisation point. A pH indicator or pH metre is used to locate the point where neutralisation occurs. The molarity of the unknown particle can be determined using simple stoichiometric calculations and knowledge of the volume and molarity of the known quantity.
2. Toothpaste: Toothpaste is used not only to keep our mouths clean, but it also acts as a neutralizer for the effects of the foods we eat. The majority of the food we eat is acidic, and the acidic action of the food reacts with the enamel or calcium phosphate layer of our teeth, causing a cavity to form. It is toothpaste’s basic quality that prevents cavities by neutralising the reaction.
3. Digestive systems: Food must be neutralised as it travels from our stomach to our intestines. However, an alkaline environment is essential for nutrients to be absorbed via the intestinal walls. To achieve this favourable state, antacid bicarbonate is created.
4. Controlling soil pH: Plants cannot grow in very acidic or excessively basic soil, neutralisation is frequently used to adjust the pH of the soil. Adding bases such as CaCO3, CaO, or burnt wood ash to the soil is a safe way to regulate its acidity.
5.Wastewater treatment: The majority of trash that comes in the form of industrial effluents contains toxins that are damaging to our ecosystem. As a result, we must first neutralise their toxicity before discarding them. Different chemicals are utilised depending on the application. Sodium bicarbonate, magnesium hydroxide, and calcium carbonate are among examples.
Q-4: Is it possible to have a neutralisation reaction when one of the reactant phases is solid?
Answer: Yes, it is possible to conduct a neutralisation reaction with one reactant in solid phase.
The following is an example:
Cr(OH)2 (s) + 2HCl(aq) → CrCl2(aq) + 2H2O(l)
Q-5: Which of the following statements about spectator ions is incorrect?
- They are a part of the net ionic equation.
- Their elimination leads to a net ionic equation.
- No reaction takes place if there are only spectator ions
- They are present only at the reactant side.
Answer: a) and d)
Explanation: Chemical reactions are not affected by spectator ions. It can be found in both the reactant and the product. We cancel the spectator ions from both sides of the equation when creating a net ionic equation.If all of the ions are spectators, no reaction occurs.
Q-6: When phosphoric acid combines with calcium hydroxide, the pH of the salt formed is
- Greater than 7
- Less than 7
- Slightly less than 7
- Exact;y 7
Answer: a) Greater than 7
Explanation: The following reaction takes place when phosphoric acid (H3PO4) combines with calcium hydroxide(Ca(OH)2):
2H3PO4(aq)+ 3Ca(OH)2(aq) → 6H2O(l) + Ca3(PO4)2(s)
Because phosphoric acid is a weak acid and calcium hydroxide is a little stronger base, a basic salt with a pH higher than 7 is produced.
Q-7: What happens if you write a neutralisation reaction with a hydronium ion instead of a proton? Explain your answer with a suitable example.
Answer:
Let us consider a neutralisation reaction between KOH and HCl
KOH(aq) + HCl(aq) → KCl(aq) + H2O(l)
Dissociate the aqueous solution of ionic compounds into ions
K+(aq)+ OH–(aq)+ H+(aq)+ Cl–(aq)→K+(aq)+ Cl–(aq) + H2O(l) ……….1)
The net ionic equation (when proton is used) is:
OH–(aq)+ H+(aq) →H2O(l)
Replace H+ ion with H3O+ ion in equation 1
K+(aq)+ OH–(aq)+H3O+(aq)+ Cl–(aq)→K+(aq)+ Cl–(aq) + 2H2O(l)
The net ionic equation (when H3O+ ion is used) is:
OH–(aq)+H3O+ (aq) →2H2O(l)
As a result, the only difference is the presence of an additional water molecule as a product.
Q-8: A 250 mL aqueous solution of 6.3 g oxalic acid dihydrate is prepared. The volume of 0.1N NaOH necessary to neutralise 20mL of this solution is
- 80 mL
- 40 mL
- 8 mL
- 4 mL
Answer: a) 80 mL
Explanation:
Step-1 Calculate the number of moles of oxalic acid dihydrate
Moles = Weight of oxalic acid dihydrate/Molar mass of oxalic acid dihydrate
=(6.3g)/(126g/mol)
= 0.05 mol
Step-2 Calculate the molarity of oxalic acid dihydrate.
Molarity = Number of moles of oxalic acid dihydrate/Volume ( in L)
= 0.05 mol/0.25 L
= 0.2 M
Step-3 Calculate the normality of oxalic acid dihydrate
Normality = Molarity × n-factor
= 0.2 × 2
= 0.4 N
Use the equation,
N1V1 ( oxalic acid ) = N2V2 ( NaOH)
0.4 N× 20 mL = 0.1N × V2
V2 = 80 mL
Note: n-factor of an acid is equal to the number of replaceable H-atoms present in it.
Q-9: If the products of neutralisation are HOH and SrSO4, what are the acid and base?
- H2SO4 + SrOH
- H2SO4 + Sr(OH)2
- HSO4 + Sr(OH)2
- Acid + base
Answer: b) H2SO4 + Sr(OH)2
Explanation: The neutralisation reaction takes place as:
H2SO4 (aq) + Sr(OH)2(aq) → SrSO4(aq) + 2H2O(l)
Q-10: Which of the following statements is an example of a neutralisation reaction?
- Addition of litmus solution to sulphuric acid
- Addition of litmus solution to baking soda
- Applying of quick lime to basic soil
- Applying magnesium hydroxide on ant bite
Answer: d) Applying magnesium hydroxide on ant bite
Explanation: When an ant bites, formic acid is released, causing irritation. Thus, a basic substance such as magnesium hydroxide can be used to neutralise its effects.
Since, it involves a reaction between an acid and base, therefore a perfect example of neutralisation reaction.
Q-11: In a calorimeter, equal amounts of 50 mL, 3M HCl and 3M NaOH react at a temperature of 20.0°C. The temperature of the resulting solution is 40.0°C.Calculate
- qreaction
- Enthalpy change for the reaction
Assume that the densities and specific heat capacity of the solutions(C) are approximately 1.0 g/ml and 4.18 J/g°C, respectively,
Answer:
- Mass of solution, m = Density of solution × Volume of total solution
= 1.0 g/ml × (50mL +50 mL)
= 100 g
qsolution = mCΔt
= 100g × 4.18 J/g°C × (40-20)°C
= 8360 J
The energy released by the reaction is qreaction,
qreaction + qsolution = 0
qreaction = – qsolution = – 8,360 J
- The limiting reactant is either the HCl or the NaOH since there are equimolar amounts present, therefore we can consider moles of any substance.
Moles of the limiting reactant,HCl = (M×V(L))
= (0.050L×3M)
= 0.15 mol
∆H rxn = qreaction / moles of limiting reactant
=( -8,360 J)/ (0.15 mol)
= -55733.3 J/mol
Q-12: Neutralisation reaction is a
- Physical and reversible change
- Physical and irreversible change
- Chemical and reversible change
- Chemical and irreversible change
Answer: d) Chemical and irreversible change
Explanation: A neutralisation reaction is always a chemical and irreversible change since new products are generated as a result of chemical reaction and products cannot be changed back to reactants.
Q-13: a) How many moles of Ca(OH)2 will it take to completely neutralise 4 moles of H3PO4?
b) How many litres of 1.4 M H3PO4 will it take to neutralise 500mL of 0.80 M Ca(OH)2?
Answer: The neutralisation reaction takes place as:
2H3PO4(aq)+ 3Ca(OH)2(aq) → 6H2O(l) + Ca3(PO4)2(s)
a) According to the reaction,
3 moles of Ca(OH)2 neutralises 2 moles of H3PO4
4 moles of Ca(OH)2 neutralise 8/3 moles of H3PO4
b) Moles of Ca(OH)2 = Molarity of Ca(OH)2- × Volume of Ca(OH)2(in L)
= 0.80 M × 0.5 L = 0.4 moles
3 moles of Ca(OH)2 neutralises 2 moles of H3PO4
0.4 moles of Ca(OH)2 neutralises (2×0.4)/3 moles of H3PO4 = 0.27 moles of H3PO4
Volume of H3PO4 required to neutralise 500mL of 0.80 M Ca(OH)2 = Moles of H3PO4 used for neutralisation/ Molarity of H3PO4
Volume of H3PO4 = 0.27 moles/1.4 M
= 0.2 L
Q-14: Which of these acid-base neutralisation processes might be titrated to a sharp end point using the apparatus shown below?
- Sulphuric acid + aluminium oxide
- Sulphuric acid + Magnesium hydroxide
- Sulphuric acid + sodium hydroxide
- Sulphuric acid + magnesium oxide
Answer: c) Sulphuric acid + sodium hydroxide
Explanation: Since, both sulphuric acid and sodium hydroxide split up completely and instantly in the reaction hence giving a sharp end point.
Q-15: Which indicator is preferred in a strong acid and weak base titration?
- Phenolphthalein
- Methyl orange
- Malachite green
- None of the above
Answer: b) Methyl orange
Explanation: Methyl orange will change sharply at the equivalence point. Hence a good choice of indicator in this case.
Practise Questions on Neutralisation Reaction
Q-1: Write the oxalic acid and calcium hydroxide neutralisation reaction. How are you going to handle a net ionic equation? Is the reaction slow or fast?
Q-2: Consider the reaction between a strong acid and strong base
OH– +H+ → H2O(l)
The reaction is
- Endothermic and qreaction is positive
- Exothermic and qreaction is positive
- Endothermic and qreaction is negative
- Exothermic and qreaction is negative
Q-3: Calculate the pH of the resultant solution after mixing 200 mL of a 0.15 M hydrobromic acid solution(HBr) with 100 mL of a 0.2M KOH solution.
Q-4: Is it possible to classify a neutralisation reaction as a salt metathesis reaction?
Q-5: In a neutralisation reaction between HCl(aq) and Fe(OH)3(s), what is/are spectator ions?
- Cl–
- Fe3+
- H+
- OH–
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