Strong acids and strong bases react and give salts and water as products. Usually strong acids gave less pH values and strong bases have higher pH values. When a base is added to an acid, pH value of acidic solution is increased.
See below tutorial how pH of strong acid is changed when a base is added to the strong acidic solution.
Strong acid and strong bases titration curveHydrochloric (HCl), sulfuric acid (H2SO4), nitric acid (HNO3 are some examples to strong acids. Also NaOH, KOH are strong bases.
Learn more about strong acids and strong basesIn this lesson, first we discuss about how to calculate pH of acidic solution of strong acids such as HCl, H2SO4. Then, we study reactions of strong acids and strong bases and calculting pH of thise solutions in different situations.
Sometimes, we can represent H3O+(aq) as H+(aq)
Example 1
You are provided 100 cm3 of HCl acid solution. It's concentration is 0.1 mol dm-3.
HCl → H+(aq) + Cl-(aq)
According to the stoichiometry ratio, concentrations of,
[HCl] = [H3O+(aq)], Therefore,
[HCl] = 0.1 mol dm-3
Now, we know the concentration of H+(aq). Let's substitute that value to the pH equation.
pH = -log10[H3O+(aq)]
pH = -log10[0.1]
pH = 1.0
Example 2
You are provided 100 cm3 of H2SO4 acid solution. It's concentration is 0.01 mol dm-3.
H2SO4(aq) → 2H+(aq) + SO42-(aq)
According to the stoichiometry ratio, concentrations of,
2*[H2SO4(aq)] = [H3O+(aq)], Therefore,
[H3O+(aq)] = 2 * 0.01
[H3O+(aq)] = 0.02 mol dm-3
Now, we know the concentration of H+(aq). Let's substitute that value to the pH equation.
pH = -log10[H3O+(aq)]
pH = -log10[0.02]
pH = 1.7
Example 3
An acid and a base(alkali) react and give salt and water as products. pH of acidic solution increases when pouring a base into the acidic solution, and pH of basic solution decreases when pouring an acid into the basic solution. This phenomenon happens due to Neutralization of acid or base.
HCl is a strong acid. NaOH is a strong base.Hence they react until one reactant finishes. Therfore we have to find what reactant will remain.
The relationship of dissolved moles, concentration and volume of solution
NaOH and HCl react and give NaCl and H2O as products. NaOH and HCl reacts 1:1 ratio. Therefore same amount of moles of NaOH and HCl will react. Excess reactant(excess moles) will remain in the solution.
Construct a simple table which includes total initial moles of each reactant, number of moles reacting(reactants) and producing(products). Then you can calculate remaining reactant. In this example 0.0025 moles of HCl remains in the solution and solution becomes acidic. We don't consider about producing water because reaction occurs in aqueous medium and concentration of water is very high and don't change due to reaction(change is negligible).
We know how many moles of HCl remaining in the solution now(0.0025mol) and total volume of
the solution(100ml). So, we can calculate the concentration of HCl from concentration equation.
HCl is a strong acid. Therefore it dissociates completely into H+ (or H3O+) and Cl- in water. When we write the dissociation equation, we can see the concentration of H3O+ receives from HCl dissociation is equal to the concentration of HCl.
Questions
There are 0.05 moles of sulfuric acid 1 dm3 of aqueous solution. To calculate pH, you should know H+ concentration. Sulfuric acid is a strong acid and completely dissociates to H+ ions SO42- ions.
So, if there are 0.05 moles of sulfuric, there are 0.01 moles of H+ ions. Volume of solution is 1 dm3. Then concentration of H+ is 0.1 mol dm-3.
Then pH is 1.