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A student uses a calibrated pH meter to measure an aqueous ethanoic acid solution. Figure 1 shows the meter reading.
State the pH of the solution shown in Figure 1.
Calculate the hydrogen ion concentration, [H⁺], in the solution. Give your answer in mol dm⁻³ to two significant figures.
An aqueous solution of sodium hydrogencarbonate is at 298 K. For and Which option pairs the predominant hydrolysis of with the expected pH relative to 7?
Answer: D. can act as an acid or a base. Its base strength is which is greater than its acid strength, The predominant hydrolysis produces so the solution is basic.
A: Treats hydrogencarbonate as an acid and predicts the acidic effect of producing although this hydrolysis is weaker.
B: Identifies the predominant hydrolysis but reverses the pH effect of producing
C: Predicts a basic solution but pairs it with acid hydrolysis, which produces
Remember: for an amphiprotic ion, compare its acid strength with its base strength.
At room temperature, of magnesium ribbon is added to excess dilute hydrochloric acid. Figure 1 shows the measured volume of gas collected over time.
Use Figure 1 to state the volume of gas collected after
Write a balanced equation, including state symbols, for the reaction of magnesium with dilute hydrochloric acid.
In a voltaic cell, electrode A undergoes the reaction
Identify electrode A as the anode or cathode and state its sign.
In an electrolytic cell, electrode B undergoes the reaction
Identify electrode B as the anode or cathode and state its sign.
A piece of magnesium is added to dilute hydrochloric acid. Which equation represents the reaction?
Answer: B. Magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen gas. Magnesium chloride has the formula MgCl₂; balancing the atoms gives Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g).
A: identifies the products but leaves chlorine unbalanced by using one HCl.
C: balances the atoms but gives magnesium the wrong charge in the salt formula, writing MgCl instead of MgCl₂.
D: balances the atoms but represents the hydrogen as individual atoms rather than diatomic hydrogen, H₂.
Remember: hydrogen released in these reactions is H₂(g).
Ethane reacts with bromine under ultraviolet light. Bromoethane is one product, and the reaction proceeds by a radical chain mechanism.
Write the two propagation equations for the reaction of ethane with bromine.
Write a termination equation involving two ethyl radicals.
State one reason why a mixture of organic products can form.
State two features of alkanes that contribute to their low reactivity.
Chlorine reacts with propane when irradiated with ultraviolet (UV) light. Figure 1 shows the displayed structural formula of propane.
Determine the number of different monochlorinated structural isomers that can form from propane.
Write the equation for the initiation step, using single-barbed arrows to show the movement of electrons.
For the formation of 2-chloropropane:
Write the first propagation equation, in which a hydrogen atom is transferred from propane to a chlorine radical.
Using the propan-2-yl radical, CH₃CH•CH₃, write the second propagation equation.
Write one equation for a termination step in this chain reaction.
In a reaction mechanism for bromomethane, a curly arrow starts at the C–Br bond and points to Br. Which equation represents the products of this bond cleavage?
Answer: C. The curly arrow from the bond to Br shows the bonding electron pair moving to Br. Carbon loses its share of the pair, giving CH₃⁺; bromine gains both electrons, giving Br⁻.
A: splits the pair between the fragments, producing radicals by homolytic fission.
B: reverses the electron-pair movement, assigning both electrons to carbon.
D: represents cleavage of a C–H bond rather than the specified C–Br bond.
Remember: a curly arrow from a bond to an atom shows that the bonding pair moves to that atom.
Boron trifluoride forms a 1:1 adduct with ammonia:
Reaction I: BF₃ + NH₃ → BF₃·NH₃
A proton reacts with water to form a hydronium ion:
Reaction II: H⁺ + H₂O → H₃O⁺
Identify the electrophile in reaction I and state which reactant supplies both electrons in the new B–N bond.
Identify the electrophile in reaction II and explain the origin of both electrons in the new O–H bond.
A student claims that an electrophile must be positively charged. Assess this claim using both reactions.
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