Q.Take two test tubes and label them as A and B. Add Zinc filings in both the test tubes. In the test tube labelled A add 5 mL of 1M HCl and in test B 5 mL of acetic acid. Keep the test tubes on the stand. Note down your observations. a. Do you see any effervescence coming from the two test tubes ?
b. Which gas is evolved ?
c. How do you identify the gas ?
d. What is the relative rate at which the gas is evolved in the two test tubes
e. Based on your observations comment on the strength of acids used.

Step 1. Zinc reacts with a dilute acid to liberate hydrogen gas: $Zn(s)+2H^+(aq)\rightarrow Zn^{2+}(aq)+H_2(g)$. Both HCl (tube A) and acetic acid (tube B) supply H+, so both tubes are expected to show effervescence (bubbling) as this reaction proceeds.

Step 2. (b) The gas evolved in both cases is hydrogen, H2. (c) Hydrogen is identified by holding a burning splint at the mouth of the test tube -- it burns with a characteristic squeaky 'pop' sound (distinct from, e.g., a glowing splint relighting, which would indicate oxygen).

Step 3. (d) The RATE of gas evolution differs sharply between the two tubes. HCl is a strong acid (section 3.4) -- it is almost completely dissociated, so a 1M HCl solution has [H+] very close to 1 M. Acetic acid is a weak acid -- at a comparable concentration it is only partially dissociated (a few percent, per the degree-of-dissociation calculations elsewhere in this chapter), so its actual [H+] is far lower than its nominal molar concentration. Since the rate of the zinc-acid reaction depends on [H+], not on the nominal acid concentration, tube A (HCl) evolves gas visibly faster and more vigorously than tube B (acetic acid). …

Recognize the zinc-acid reaction produces H2 (identified by the pop test), then explain the differing bubbling rate using the strong-vs-weak acid ionization distinc …

• Assuming both acids react at the same rate because 'both are acids' -- rate depends on actual [H+], which differs hugely between a strong and a weak acid at the same nominal concentration. …