Acid-Base Reactions with Metals

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Questions and Answers

What is the first step when checking the odour of cloth strips?

Add dilute HCl

Add clove oil

Add vanilla essence

Rinse with water (correct)

What is used to test the change in odour in the experiment?

Dilute HCl and NaOH solutions (correct)

Concentrated salt solution

Pure water

Dilute sugar solution

Which of the following can potentially be used as an olfactory indicator?

Salt

Sugar

Water

Vanilla (correct)

In Activity 2.3, what acid is initially used in the test tube?

Sulfuric acid (B) Signup and view all the answers

What material is added to the acid in the test tube in Activity 2.3?

Zinc granules (A) Signup and view all the answers

In Activity 2.3, the gas evolved is passed through which solution?

Soap solution (C) Signup and view all the answers

What is used to test the gas-filled bubble?

A burning candle (C) Signup and view all the answers

What is the primary caution mentioned at the beginning of Activity 2.3?

Activity needs teacher's assistance (A) Signup and view all the answers

Besides sulfuric acid, which of the following acids is also used in a similar activity?

Hydrochloric acid (C) Signup and view all the answers

What do you observe on the surface of zinc granules when they react with dilute sulfuric acid?

Gas bubbles form (D) Signup and view all the answers

Why is it important to rinse the cloth strips with water before checking their odour again?

To neutralize any remaining chemicals and obtain a more accurate odour assessment. (A) Signup and view all the answers

What is the purpose of using dilute solutions of vanilla essence and clove oil in the experiment with acids and bases?

To observe how acids and bases affect the characteristic odours of these substances, indicating their potential as olfactory indicators. (C) Signup and view all the answers

What does a change in odour of vanilla essence or clove oil when reacted with an acid or a base indicate?

A chemical reaction has occurred, potentially signifying the substance's suitability as an olfactory indicator. (B) Signup and view all the answers

In Activity 2.3, what is the function of passing the evolved gas through a soap solution?

To trap the gas in bubbles, making it easier to test its flammability. (D) Signup and view all the answers

What does the burning of a gas-filled bubble indicate about the gas that was produced in Activity 2.3?

Confirms the presence of hydrogen gas, which is flammable. (B) Signup and view all the answers

What is the expected outcome when a burning candle is brought near a bubble filled with hydrogen gas?

The bubble will burst with a pop, indicating the rapid combustion of hydrogen. (C) Signup and view all the answers

What is the purpose of repeating Activity 2.3 with different acids like HCl, HNO3, and CH3COOH?

To compare the reaction rates and gas evolution with different acids, assessing their relative strengths. (A) Signup and view all the answers

What does it mean if the observations in Activity 2.3 are different when using HCl compared to CH3COOH?

The acids have different strengths, affecting the rate of hydrogen gas production. (C) Signup and view all the answers

If the reaction between an acid and zinc granules produces a gas, what general type of chemical reaction is taking place?

A single displacement reaction where zinc replaces hydrogen from the acid. (A) Signup and view all the answers

Considering the activities performed, what is the most accurate conclusion about olfactory indicators?

Substances whose odour changes distinctly in acidic or basic conditions can be used as olfactory indicators. (C) Signup and view all the answers

If the odour of clove oil completely disappears in a NaOH solution, but remains unchanged in HCl, what can be concluded about clove oil?

It reacts selectively with bases. (C) Signup and view all the answers

Suppose a student performs Activity 2.3 but forgets to use the soap solution. What direct observation would they likely miss?

The ability to test the evolved gas with a burning candle. (B) Signup and view all the answers

In Activity 2.3, if the evolved gas extinguishes a burning candle with a 'pop' sound, which alternative gas could produce a similar result?

Methane (D) Signup and view all the answers

When testing the odours of vanilla essence after reacting with HCl and NaOH, a control sample of vanilla essence is needed. What is the primary purpose of this control?

To compare any changes in the odour. (D) Signup and view all the answers

Why is it essential to use dilute solutions of acids and bases when testing olfactory indicators, rather than concentrated ones?

Concentrated solutions may damage the olfactory receptors or overpower the scent of the indicator. (A) Signup and view all the answers

In Activity 2.3, if copper granules were used instead of zinc, what would be the most likely observation?

No significant reaction. (D) Signup and view all the answers

A student notes that the reaction of zinc with hydrochloric acid (HCl) produces a different rate of bubble formation compared to acetic acid (CH3COOH). What inference can be drawn?

HCl is a stronger acid than CH3COOH under these conditions. (C) Signup and view all the answers

If, after reacting an olfactory indicator with an acid, a base is added and the original odour returns, what does this suggest about the reaction?

The reaction is reversible. (A) Signup and view all the answers

Consider a scenario where a student uses a different soap solution in Activity 2.3, and no bubbles form despite the gas being produced. What is the most likely explanation?

The surface tension of the soap solution is too high to form bubbles. (D) Signup and view all the answers

In a modified Activity 2.3, if a drying tube containing anhydrous calcium chloride ($CaCl_2$) is placed between the reaction vessel and the soap solution, what specific aspect of the evolved gas is being addressed?

Humidity (C) Signup and view all the answers

Consider a scenario where, after reacting vanilla essence with dilute HCl, the resulting solution is meticulously neutralized with $Ca(OH)_2$ until pH 7 is achieved. If the original vanilla scent does not return, which complex phenomenon MOST likely accounts for this observation?

The volatile aromatic compounds in vanilla essence undergo irreversible protonation changes, preventing their reconversion to the original form. (C) Signup and view all the answers

In Activity 2.3, if the evolved gas is passed through a solution of lead(II) acetate instead of soap solution, and a black precipitate forms, which of the following inferences is MOST accurate regarding the composition of the evolved gas?

The evolved gas contains hydrogen sulfide ($H_2S$) due to sulfur impurities in the zinc granules reacting with the acid. (D) Signup and view all the answers

While performing Activity 2.3 with $HNO_3$, a brown gas is observed evolving along with the primary gas. What is the MOST probable explanation for the formation of this brown gas?

The brown gas is nitrogen dioxide ($NO_2$), formed due to the decomposition of nitric acid ($HNO_3$) and its reaction with zinc. (D) Signup and view all the answers

Assume that in a modified Activity 2.3, the evolved gas is collected over water before testing its flammability. If the 'pop' sound upon ignition is significantly diminished compared to the standard procedure, what is the MOST likely reason for this?

The water vapor present in the collected gas reduces the concentration of hydrogen, diluting it below the stoichiometric ratio required for a loud 'pop'. (C) Signup and view all the answers

Suppose a student uses copper turnings instead of zinc granules in Activity 2.3 with dilute sulfuric acid. After a prolonged period, no gas evolution is observed. If a small amount of concentrated nitric acid is then added to the mixture, and gas evolution begins, which species is MOST likely being produced, and why?

Nitrogen dioxide ($NO_2$), because copper reacts with concentrated nitric acid to produce nitrogen dioxide gas. (C) Signup and view all the answers

If during the testing of olfactory indicators, a student observes that both vanilla essence and clove oil exhibit altered odours in acidic conditions (dilute HCl) but no noticeable change in basic conditions (dilute NaOH), what inference can be BEST drawn?

The active odor-causing compounds in vanilla essence and clove oil contain functional groups that undergo acid-catalyzed reactions, but are stable under basic conditions. (B) Signup and view all the answers

In a variation of Activity 2.3, a redox indicator such as methylene blue is added to the sulfuric acid before the addition of zinc granules. If the solution changes from blue to colourless during the reaction, what is this MOST indicative of within the context of the experiment?

The production of hydrogen gas ($H_2$) which contributes to the overall reducing environment, causing the reduction of methylene blue. (D) Signup and view all the answers

Suppose Activity 2.3 is conducted in a closed system, and the pressure is continuously monitored. If the pressure increases initially but then plateaus despite the continued addition of zinc granules, what is the MOST likely explanation for this phenomenon?

The zinc granules have become passivated by a layer of zinc sulfate ($ZnSO_4$), preventing further reaction. (B) Signup and view all the answers

When testing the flammability of the gas evolved in Activity 2.3, a student observes that the 'pop' sound is followed by a faint yellow flame instead of a clean blue flame. What does this MOST likely indicate about the purity of the gas?

The gas is contaminated with carbon monoxide (CO) due to incomplete combustion of hydrocarbons present as impurities. (D) Signup and view all the answers

In a meticulously controlled experiment based on Activity 2.3, the rate of hydrogen gas evolution from the reaction of zinc with various concentrations of dilute $H_2SO_4$ is measured. If the data are plotted according to the Eyring equation, what kinetic parameters can MOST accurately be determined from the slope and intercept of the resulting linear plot?

The activation enthalpy ($\Delta H^\ddagger$) and the activation entropy ($\Delta S^\ddagger$) for the rate-determining step. (A) Signup and view all the answers

What is the immediate next step after rinsing the cloth strips with water in the context of odour testing?

Check their odour again. (B) Signup and view all the answers

What should be done immediately after adding a few drops of dilute vanilla essence to test tubes containing dilute HCl and NaOH solutions?

Shake well. (A) Signup and view all the answers

Which of the following is NOT explicitly mentioned as being tested for its olfactory indicator properties?

Dilute HCl (A) Signup and view all the answers

In Activity 2.3, what is the purpose of passing the evolved gas through a soap solution?

To make the gas visible as bubbles. (C) Signup and view all the answers

What is the expected observation when zinc granules react with dilute sulfuric acid?

Bubbles form on the surface of the zinc granules. (C) Signup and view all the answers

What is the primary reason for repeating Activity 2.3 with different acids, such as HCl, $HNO_3$, and $CH_3COOH$?

To see if the observations are the same or different. (C) Signup and view all the answers

During the reaction of zinc granules with dilute sulfuric acid, what does the formation of bubbles in the soap solution directly indicate?

The evolution of a gas. (D) Signup and view all the answers

If the odour of vanilla essence diminishes in dilute HCl but intensifies in dilute NaOH, what can be inferred?

Vanilla's odour is affected differently by acids and bases. (B) Signup and view all the answers

Suppose that in Activity 2.3, after adding dilute sulfuric acid to zinc granules, no gas is evolved even after several minutes. Which of the following is the MOST probable reason, assuming the reagents are fresh?

The zinc granules are coated with an oxide layer. (A) Signup and view all the answers

In a modified version of Activity 2.3, the evolved gas is collected, and its molar mass is experimentally determined to be approximately 2 g/mol. However, when this gas is mixed with air and ignited, it burns with an orange, sooty flame instead of a clean blue flame, and analysis reveals traces of $SO_2$. What is the MOST likely explanation for the observed discrepancy?

The sulfuric acid was impure, containing organic contaminants. (A) Signup and view all the answers

What is the purpose of shaking the test tubes after adding vanilla essence to dilute HCl and NaOH solutions?

To ensure uniform mixing of the vanilla essence with the acid and base. (D) Signup and view all the answers

In Activity 2.3, what is the immediate observation when dilute sulfuric acid is added to zinc granules?

Bubbles appear on the surface of the zinc granules. (A) Signup and view all the answers

Why is it important to test the evolved gas from the reaction between acids and zinc granules using a burning candle?

To identify the gas by its flammability. (D) Signup and view all the answers

What is the main reason for repeating Activity 2.3 with different acids like HCl, $HNO_3$, and $CH_3COOH$?

To determine if all acids react similarly with metals. (D) Signup and view all the answers

Which of the following is a crucial safety precaution for Activity 2.3?

Having teacher's assistance (C) Signup and view all the answers

What observation would confirm that the gas evolved from the reaction of zinc and sulfuric acid is hydrogen?

The gas puts out a burning splint with a 'pop' sound. (D) Signup and view all the answers

Why are vanilla essence and clove oil useful as olfactory indicators?

Their odours change or disappear in acidic or basic solutions. (B) Signup and view all the answers

If no bubbles form in the soap solution during Activity 2.3, despite adding zinc to sulfuric acid, what is the MOST likely reason?

The zinc granules are coated with an oxide layer. (C) Signup and view all the answers

Suppose you perform Activity 2.3 with zinc and dilute hydrochloric acid (HCl) and the resulting gas is collected in a balloon. If this balloon is then placed near a strong electromagnetic field, what, if anything, would you expect to observe? (Assume ideal conditions).

There would be no observable effect. (A) Signup and view all the answers

A student performs Activity 2.3 using zinc granules and dilute sulfuric acid but finds that the reaction proceeds very slowly, even with freshly prepared acid. Upon adding a few drops of copper sulfate solution ($CuSO_4$) to the reaction mixture, the rate of hydrogen gas evolution significantly increases. Which of the following mechanisms BEST explains this observation?

A galvanic cell is created between the zinc and the copper ions, facilitating electron transfer and accelerating the reaction. (C) Signup and view all the answers

Flashcards

Olfactory Indicators

Substances that change odour in acidic or basic solutions.

Dilute Vanilla Essence

A weaker solution of vanilla used for testing odour changes.