Reactivity 3. What are the mechanisms of chemical change?

Which species is produced when a Brønsted-Lowry acid loses a proton?

In the titration of a strong acid with a strong base, the $pH$ at the equivalence point is:

What is the $pH$ of a $0.01\text{ mol dm}^{-3}$ solution of $NaOH$ at $298\text{ K}$?

Which is a characteristic property of bases?

A $0.10\text{ mol dm}^{-3}$ solution of a weak monoprotic acid, $HA$, has a $pH$ of 4.0 at 298 K. Which of the following statements is correct regarding this solution?

Consider the following two-step ionization process for carbonic acid in aqueous solution:

Reaction 1: $H_{2}CO_{3}(aq) + H_{2}O(l) \rightleftharpoons HCO_{3}^{-}(aq) + H_{3}O^{+}(aq)$ Reaction 2: $HCO_{3}^{-}(aq) + OH^{-}(aq) \rightleftharpoons CO_{3}^{2-}(aq) + H_{2}O(l)$

Which statement correctly describes the species in these reactions?

A student mixes $20.0\text{ cm}^{3}$ of $0.10\text{ mol dm}^{-3}\text{ HCl}(aq)$ with $10.0\text{ cm}^{3}$ of $0.10\text{ mol dm}^{-3}\text{ NaOH}(aq)$. What is the hydrogen ion concentration, $[H^{+}]$, in the resulting solution at 298 K?

The diagram illustrates the relationships between chemical species based on the Brønsted–Lowry theory. Each arrow represents the loss of a single proton ($H^+$) from the preceding species.

Species 1: $H_2CO_3$ Species 2: $HCO_3^-$ Species 3: $CO_3^{2-}$ Species 4: $H_3O^+$ Species 5: $H_2O$ Species 6: $OH^-$

Which statement correctly identifies the Brønsted–Lowry relationships?

In the auto-ionization of water, $H_2O + H_2O \rightleftharpoons H_3O^+ + OH^-$, what is the role of the water molecules?

Which statement is true for a titration between a strong acid and a weak base?

In the reaction $Mg + 2HCl \rightarrow MgCl_{2} + H_{2}$, what happens to the hydrogen ions?

What is the oxidation state of fluorine in all its compounds?

Which of these is a typical observation at the cathode during the electrolysis of molten $PbBr_{2}$?

What is the oxidation state of Iron in $FeCl_{2}$?

A voltaic cell is constructed using a nickel electrode in a $1.0\ mol\ dm^{-3}\ NiSO_4(aq)$ solution and an iron electrode in a $1.0\ mol\ dm^{-3}\ FeSO_4(aq)$ solution. The following standard reduction potentials are provided:

$Ni^{2+}(aq) + 2e^- \rightleftharpoons Ni(s) \quad E^\ominus = -0.26\ V$ $Fe^{2+}(aq) + 2e^- \rightleftharpoons Fe(s) \quad E^\ominus = -0.45\ V$

Which statement correctly describes the spontaneous operation of this cell?

Which of the following is required for a reaction to be spontaneous in a voltaic cell?

What is the oxidation number of carbon in $CH_4$ and $CO_2$ respectively?

A student investigates the reactivity of three metals $X, Y,$ and $Z$ by placing them into aqueous solutions of their $2+$ ions. The following observations are made:

• Metal $X$ reacts when placed in an aqueous solution of $Y^{2+}(aq)$.
• No reaction occurs when metal $X$ is placed in an aqueous solution of $Z^{2+}(aq)$.

A voltaic cell is then constructed using half-cells of $Y$ in $Y^{2+}(aq)$ and $Z$ in $Z^{2+}(aq)$ connected by a $KNO_3$ salt bridge as shown in the diagram.

Which of the following correctly describes the direction of electron flow in the external circuit and the movement of $K^+$ ions from the salt bridge as the cell operates?

Which change represents an oxidation?

What is the oxidation state of hydrogen in $NaH$?

Which type of species is attracted to a positive center in a molecule?

Which of the following describes a lone pair of electrons?

What does the '2' in $S_N2$ represent?

Which molecule is most likely to undergo homolytic fission when exposed to sunlight?

Which type of reaction occurs when 1-chloropropane is treated with warm aqueous potassium hydroxide?

Which of the following is an electrophile in the reaction of alkenes?

What is the role of the ultraviolet light in the chlorination of methane?

In the electrophilic addition of $HBr$ to an alkene, what is the role of the $Br^-$ ion in the second step?

Which of the following best defines a 'leaving group' in a nucleophilic substitution reaction?

When chlorine reacts with excess methane, the main organic product is $CH_3Cl$. If chlorine is in excess, what happens?

Which reagent would react with ethene via electrophilic addition?

What is the electronic state of the Boron atom in $BF_3$?

Which bond is formed in the reaction $NH_3 + H^+ \rightarrow NH_4^+$?

In a nucleophilic substitution reaction, what does 'nucleophile' mean?

In the reaction of ammonia with water ($NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$), water acts as a Bronsted-Lowry acid. What is the role of $NH_3$ in terms of Lewis theory?

Which of the following is a neutral electrophile?

Which property of a halogenoalkane bond determines the site of nucleophilic attack?

For the reaction $R-Br + OH^- \rightarrow R-OH + Br^-$, the rate is found to be $Rate = k[R-Br]$. What does this imply about the mechanism?

In the hydration of $ethene$ to $ethanol$, what is the role of $H_2O$?

Which of the following contains a carbon atom with a partial positive charge ($δ+$) that is most susceptible to nucleophilic attack?