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Grade 11 Chemistry Effective Homework 4: Ionization Equilibrium of Weak Electrolytes | Brief Solutions
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1 Classify electrolytes, nonelectrolytes and sparingly soluble salts. Show answer
2 Choose incorrect ionization equations. Show answer
3 What change occurs both on diluting acetic acid and on adding sodium acetate? Show answer
4 Which ratio increases as acetic acid is diluted? Show answer
5 Ratio of unionized molecules to total ionized ions is $49.5:1$. Find the ionization degree. Show answer
6 $0.1$ mol/L monoprotic HA ionizes by $0.1\%$. Choose the correct statement. Show answer
7 Use formic acid, HCN and carbonic-acid constants to choose the incorrect statement. Show answer
8 Compare ionization, reactions and dilution of HA and H2B. Choose correct statements. Show answer
9.1 Write HCN ionization. Show answer
$\mathrm{HCN\rightleftharpoons H^++CN^-}$
9.2 Which dilution curve belongs to HF rather than equimolar HCN? Show answer
9.3 Find initial pH of $0.2$ mol/L HCN, labeled $x$ on the graph. Show answer
9.4 Find the equilibrium constant for aqueous ammonia reacting with HF to form ammonium, fluoride and water. Show answer
10.1 $6$ g acetic acid in $1$ L gives acetate concentration $1.4\times10^{-3}$ mol/L. Find concentration, $K_a$ and its heating trend. Show answer
$0.10\ \mathrm{mol\,L^{-1}}$; $K_a\approx1.99\times10^{-5}$; increases.
10.2 Acetic acid and HCl initially at pH $2$ are each diluted $100$-fold. Compare final pH and water ionization. Show answer
B, B (acetic acid is lower in both comparisons).
10.3 Equal volumes of $a$ mol/L acetic acid and $b$ mol/L NaOH give neutrality. Find $K_a$. Show answer
$K_a=\dfrac{b\times10^{-7}}{a-b}$
10.4 At pH $7$, find the HClO-to-hypochlorite ratio. Show answer
10.5 Write the ionic equation for a small amount of CO2 added to NaClO. Show answer
$\mathrm{CO_2+H_2O+ClO^-\to HCO_3^-+HClO}$
10.6 Hydroxide concentration in $2.0$ mol/L ammonia; compare hydrogen carbonate and carbonate after CO2 addition to neutrality. Show answer
$6.0\times10^{-3}\ \mathrm{mol\,L^{-1}}$; A ($>$).
11.1 Which species corresponds to the middle curve $\delta_2$ in the phosphorous-acid distribution? Show answer
11.2 Add excess barium hydroxide to NaH2PO3: write the ionic equation. Show answer
$\mathrm{Ba^{2+}+H_2PO_3^-+OH^-\to BaHPO_3\downarrow+H_2O}$
11.3 Given second pKa $6.54$, find $c(\mathrm{HPO_3^{2-}})/c(\mathrm{H_2PO_3^-})$ when hydroxide is $10^{-5}$ mol/L. Show answer
12.1 Write the first arsenic-acid ionization and its equilibrium expression. Show answer
$\mathrm{H_3AsO_4\rightleftharpoons H^++H_2AsO_4^-}$;$K_{a1}=\dfrac{c(\mathrm H^+)c(\mathrm{H_2AsO_4^-})}{c(\mathrm{H_3AsO_4})}$
12.2 Estimate the first ionization constant of arsenous acid from its distribution graph. Show answer
12.3 Titrate arsenous acid with NaOH to faint pink phenolphthalein: write the main ionic reaction and compare Na+ with H2AsO3- at pH $8$. Show answer
$\mathrm{H_3AsO_3+OH^-\to H_2AsO_3^-+H_2O}$;$c(\mathrm{Na^+})>c(\mathrm{H_2AsO_3^-})$.
13.1 Two acids start at pH $2$; after dilution A has higher pH than B. Choose the incorrect strength statement. Show answer
13.2 After $1000$-fold dilution, A has pH $a$. Find its range and explain. Show answer
$2<a\le5$. Dilution raises pH; a fully ionized acid gains $3$ pH units, while further weak-acid ionization makes the increase smaller.
13.3 Compare water-derived hydrogen ions in A and B after dilution. Show answer
13.4 Compare volumes of the same NaOH solution needed to neutralize the two acids. Show answer
13.5 Compare initial hydrogen-generation rates with excess zinc before and after dilution. Show answer
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