Kafli 4 - Svör við æfingum

Svör við æfingum

4.1 Að skrifa og stilla efnajöfnur

Jafna er stillt þegar sami fjöldi hvers frumefnis er táknaður á hvarfefna- og myndefnahliðinni. Jöfnur verða að vera stilltar til að endurspegla nákvæmlega lögmálið um varðveislu efnisins.

(a) ${{{\text{PCl}}}_{5}(s)+{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, {{\text{POCl}}}_{3}(l)+2\text{HCl}(aq\text{);}}$ (b) ${3\text{Cu}{(s)}+8{{\text{HNO}}}_{3}(aq)\, \longrightarrow \, 3\text{Cu}{{({{\text{NO}}3})}}2(aq)+4{\text{H}}_{2}\text{O}(l)+2\text{NO}(g\text{);}}$ (c) ${{\text{H}}_{2}(g)+{\text{I}}_{2}(s)\, \longrightarrow \, 2\text{HI}(s\text{);}}$ (d) ${4\text{Fe}(s)+3{\text{O}}_{2}(g)\, \longrightarrow \, 2{{\text{Fe}}}_{2}{\text{O}}_{3}(s\text{);}}$ (e) ${2\text{Na}(s)+2{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, 2\text{NaOH}(aq)+{\text{H}}_{2}(g\text{);}}$ (f) ${({{{\text{NH}}}_{4}} {)}_{2}{{\text{Cr}}}_{2}{\text{O}}_{7}(s)\, \longrightarrow \, {{\text{Cr}}}_{2}{\text{O}}_{3}(s)+{\text{N}}_{2}(g)+4{\text{H}}_{2}\text{O}(g\text{);}}$ (g) ${{\text{P}}_{4}(s)+6{{\text{Cl}}}_{2}(g)\, \longrightarrow \, 4{{\text{PCl}}}_{3}(l\text{);}}$ (h) ${{{\text{PtCl}}}_{4}(s)\, \longrightarrow \, \text{Pt}(s)+2{{\text{Cl}}}_{2}(g)}$

(a) ${{{\text{CaCO}}}_{3}(s)\, \longrightarrow \, \text{CaO}(s)+{{\text{CO}}}_{2}(g\text{);}}$ (b) ${2{\text{C}}_{4}{\text{H}}_{{10}}(g)+13{\text{O}}_{2}(g)\, \longrightarrow \, 8{{\text{CO}}}_{2}(g)+10{\text{H}}_{2}\text{O}(g\text{);}}$ (c) ${{{\text{MgC1}}}_{2}(aq)+2\text{NaOH}(aq)\, \longrightarrow \, \text{Mg}{{\text{(OH)}}}_{2}(s)+2\text{NaCl}(aq\text{);}}$ (d) ${2{\text{H}}_{2}\text{O}(g)+2\text{Na}(s)\, \longrightarrow \, 2\text{NaOH}(s)+{\text{H}}_{2}(g)}$

(a) Ba(NO₃)₂, KClO₃; (b) ${2{{\text{KClO}}}_{3}(s)\, \longrightarrow \, 2\text{KCl}(s)+3{\text{O}}_{2}(g\text{);}}$ (c) ${2\text{Ba}{({\text{NO}}3)}2(s)\, \longrightarrow \, 2\text{BaO}(s)+2{\text{N}}_{2}(g)+5{\text{O}}_{2}(g\text{);}}$ (d) $2\text{Mg}(s)+{\text{O}}_{2}(g)\, \longrightarrow \, 2\text{MgO}(s);$ $4\text{Al}(s)+3{\text{O}}_{2}(g)\, \longrightarrow \, 2{\text{Al}}_{2}{\text{O}}_{3}(s);$ $4\text{Fe}(s)+3{\text{O}}_{2}(g)\, \longrightarrow \, 2{\text{Fe}}_{2}{\text{O}}_{3}(s)$

(a) ${4\text{HF}(aq)+{{\text{SiO}}}_{2}(s)\, \longrightarrow \, {{\text{SiF}}}_{4}(g)+2{\text{H}}_{2}\text{O}(l\text{);}}$ (b) heildarjónajafna: ${2{{\text{Na}}}^{\text{+}}(aq)+2{\text{F}}^{\text{−}}(aq)+{{\text{Ca}}}^{{2+}}(aq)+2{{\text{Cl}}}^{\text{−}}(aq)\, \longrightarrow \, \text{Ca}{\text{F}}_{2}(s)+2{{\text{Na}}}^{\text{+}}(aq)+2{{\text{Cl}}}^{\text{−}}(aq\text{),}}$ nettójónajafna: ${2{\text{F}}^{\text{−}}(aq)+{{\text{Ca}}}^{{2+}}(aq)\, \longrightarrow \, {{\text{CaF}}}_{2}(s)}$

(a) $\begin{aligned} 2{\text{K}}^{\text{+}}(aq)+{\text{C}}_{2}{\text{O}}_{4}^{{2−}}(aq)+{\text{Ba}}^{{2+}}(aq)+2{\text{OH}}^{\text{−}}(aq)\, \longrightarrow \, 2{\text{K}}^{\text{+}}(aq)+2{\text{OH}}^{\text{−}}(aq)+{\text{BaC}}_{2}{\text{O}}_{4}(s)\, \text{(complete)} \\ {\text{Ba}}^{{2+}}(aq)+{\text{C}}_{2}{\text{O}}_{4}^{{2−}}(aq)\, \longrightarrow \, {\text{BaC}}_{2}{\text{O}}_{4}(s)\, \text{(net)} \end{aligned}$
(b) $\begin{aligned} {\text{Pb}}^{{2+}}(aq)+2{\text{NO}}_{3}^{\text{−}}(aq)+2{\text{H}}^{\text{+}}(aq)+{\text{SO}}_{4}^{{2−}}(aq)\, \longrightarrow \, {\text{PbSO}}_{4}(s)+2{\text{H}}^{\text{+}}(aq)+2{\text{NO}}_{3}^{\text{−}}(aq)\, \text{(complete)} \\ {\text{Pb}}^{{2+}}(aq)+{\text{SO}}_{4}^{{2−}}(aq)\, \longrightarrow \, {\text{PbSO}}_{4}(s)\, \text{(net)} \end{aligned}$
(c) $\begin{aligned} {\text{CaCO}}_{3}(s)+2{\text{H}}^{\text{+}}(aq)+{\text{SO}}_{4}^{{2−}}(aq)\, \longrightarrow \, {\text{CaSO}}_{4}(s)+{\text{CO}}_{2}(g)+{\text{H}}_{2}\text{O}(l)\, \text{(complete)} \\ {\text{CaCO}}_{3}(s)+2{\text{H}}^{\text{+}}(aq)+{\text{SO}}_{4}^{{2−}}(aq)\, \longrightarrow \, {\text{CaSO}}_{4}(s)+{\text{CO}}_{2}(g)+{\text{H}}_{2}\text{O}(l)\, \text{(net)} \end{aligned}$

4.2 Flokkun efnahvarfa

(a) oxunar-afoxunarhvarf (álagning); (b) sýru-basa hvarf (hlutleysing); (c) oxunar-afoxunarhvarf (bruni)

Það er oxunar-afoxunarhvarf vegna þess að oxunartala silfursins breytist í efnahvarfinu.

(a) H +1, P +5, O −2; (b) Al +3, H +1, O −2; (c) Se +4, O −2; (d) K +1, N +3, O −2; (e) In +3, S −2; (f) P +3, O −2

(a) sýru-basa; (b) oxunar-afoxun: Na er oxað, H⁺ er afoxað; (c) oxunar-afoxun: Mg er oxað, Cl₂ er afoxað; (d) sýru-basa; (e) oxunar-afoxun: P³⁻ er oxað, O₂ er afoxað; (f) sýru-basa

(a) ${2\text{HCl}(g)+\text{Ca}{{\text{(OH)}}}_{2}(s)\, \longrightarrow \, {{\text{CaCl}}}_{2}(s)+2{\text{H}}_{2}\text{O}(l);}$ (b) ${\text{Sr}{{\text{(OH)}}}_{2}(aq)+2{{\text{HNO}}}_{3}(aq)\, \longrightarrow \, \text{Sr}{({\text{NO}}3)}2(aq)+2{\text{H}}_{2}\text{O}(l)}$

(a) ${2\text{Al}(s)+3{\text{F}}_{2}(g)\, \longrightarrow \, 2{{\text{AlF}}}_{3}(s);}$ (b) ${2\text{Al}(s)+3{{\text{CuBr}}}_{2}(aq)\, \longrightarrow \, 3\text{Cu}(s)+2{{\text{AlBr}}}_{3}(aq);}$ (c) ${{\text{P}}_{4}(s)+5{\text{O}}_{2}(g)\, \longrightarrow \, {\text{P}}_{4}{\text{O}}_{{10}}(s);}$ (d) ${\text{Ca}(s)+2{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, \text{Ca}{{\text{(OH)}}}_{2}(aq)+{\text{H}}_{2}(g)}$

(a) ${\text{Mg}{{\text{(OH)}}}_{2}(s)+2{{\text{HClO}}}_{4}(aq)\, \longrightarrow \, {{\text{Mg}}}^{{\text{2+}}}({aq})+2{{\text{ClO}}}_{4}^{\text{−}}(aq)+2{\text{H}}_{2}\text{O}(l);}$ (b) ${{{\text{SO}}}_{3}(g)+2{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, {\text{H}}_{3}{\text{O}}^{\text{+}}(aq)+{{\text{HSO}}}_{4}^{\text{−}}(aq),}$ (lausn af H₂SO₄); (c) ${\text{SrO}(s)+{\text{H}}_{2}{{\text{SO}}}_{4}(l)\, \longrightarrow \, {{\text{SrSO}}}_{4}(s)+{\text{H}}_{2}\text{O}}$

${{\text{H}}_{2}(g)+{\text{F}}_{2}(g)\, \longrightarrow \, \text{2HF}{(g)}}$

${\text{2NaBr}(aq)+{{\text{Cl}}}_{2}(g)\, \longrightarrow \, 2\text{NaCl}(aq)+{{\text{Br}}}_{2}(l)}$

${2\text{LiOH}(aq)+{{\text{CO}}}_{2}(g)\, \longrightarrow \, {{\text{Li}}}_{2}{{\text{CO}}}_{3}(aq)+{\text{H}}_{2}\text{O}(l)}$

(a) ${\text{Ca}{{\text{(OH)}}}_{2}(s)+{\text{H}}_{2}\text{S}(g)\, \longrightarrow \, \text{CaS}(s)+2{\text{H}}_{2}\text{O}(l);}$ (b) ${{{\text{Na}}}_{2}{{\text{CO}}}_{3}(aq)+{\text{H}}_{2}\text{S}(g)\, \longrightarrow \, {{\text{Na}}}_{2}\text{S}(aq)+{{\text{CO}}}_{2}(g)+{\text{H}}_{2}\text{O}(l)}$

(a) þrep 1: ${{\text{N}}_{2}(g)+3{\text{H}}_{2}(g)\, \longrightarrow \, 2{{\text{NH}}}_{3}(g\text{),}}$ þrep 2: ${{{\text{NH}}}_{3}(g)+{{\text{HNO}}}_{3}({aq})\, \longrightarrow \, {{\text{NH}}}_{4}{{\text{NO}}}_{3}(aq)\, \longrightarrow \, {{\text{NH}}}_{4}{{\text{NO}}}_{3}(s)\, \text{(after drying);}}$ (b) ${{\text{H}}_{2}(g)+{{\text{Br}}}_{2}(l)\, \longrightarrow \, 2\text{HBr}(g\text{);}}$ (c) ${\text{Zn}(s)+\text{S}(s)\, \longrightarrow \, \text{ZnS}(s)}$ og ${\text{ZnS}(s)+2\text{HCl}(aq)\, \longrightarrow \, {{\text{ZnCl}}}_{2}(aq)+{\text{H}}_{2}\text{S}(g)}$

(a) ${\text{Sn}}^{{4+}}(aq)+{\text{2e}}^{-}\, \longrightarrow \, {\text{Sn}}^{{2+}}(aq),$ (b) ${{[{\text{Ag}{{({{\text{NH}}3})}}2}]}}^{\text{+}}(aq)+{\text{e}}^{-}\, \longrightarrow \, \text{Ag}(s)+2{\text{NH}}_{3}(aq);$ (c) ${\text{Hg}}_{2}{\text{Cl}}_{2}(s)+2{\text{e}}^{-}\, \longrightarrow \, 2\text{Hg}(l)+2{\text{Cl}}^{\text{−}}(aq);$ (d) $2{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, {\text{O}}_{2}(g)+4{\text{H}}^{\text{+}}(aq)+4{\text{e}}^{-};$ (e) $6{\text{H}}_{2}\text{O}(l)+2{\text{IO}}_{3}^{\text{−}}(aq)+10{\text{e}}^{-}\, \longrightarrow \, {\text{I}}_{2}(s)+12{\text{OH}}^{\text{−}}(aq);$ (f) ${\text{H}}_{2}\text{O}(l)+{\text{SO}}_{3}^{{2−}}(aq)\, \longrightarrow \, {\text{SO}}_{4}^{{2−}}(aq)+2{\text{H}}^{\text{+}}(aq)+2{\text{e}}^{-};$ (g) $8{\text{H}}^{\text{+}}(aq)+{\text{MnO}}_{4}^{\text{−}}(aq)+5{\text{e}}^{-}\, \longrightarrow \, {\text{Mn}}^{{2+}}(aq)+4{\text{H}}_{2}\text{O}(l);$ (h) ${\text{Cl}}^{\text{−}}(aq)+6{\text{OH}}^{\text{−}}(aq)\, \longrightarrow \, \text{Cl}{\text{O}}_{3}^{\text{−}}(aq)+3{\text{H}}_{2}\text{O}(l)+6{\text{e}}^{-}$

(a) ${{{\text{Sn}}}^{{2+}}(aq)+2{{\text{Cu}}}^{{2+}}(aq)\, \longrightarrow \, {{\text{Sn}}}^{{4+}}(aq)+2{{\text{Cu}}}^{\text{+}}(aq);}$ (b) ${{\text{H}}_{2}\text{S}(g)+{{\text{Hg}}}_{2}^{{2+}}(aq)+2{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, 2\text{Hg}(l)+\text{S}(s)+2{\text{H}}_{3}{\text{O}}^{\text{+}}(aq);}$ (c) ${5{{\text{CN}}}^{\text{−}}(aq)+2{{\text{ClO}}}_{2}(aq)+3{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, 5{{\text{CNO}}}^{\text{−}}(aq)+2{{\text{Cl}}}^{\text{−}}(aq)+2{\text{H}}_{3}{\text{O}}^{\text{+}}(aq);}$ (d) ${{{\text{Fe}}}^{{2+}}(aq)+{{\text{Ce}}}^{{4+}}(aq)\, \longrightarrow \, {{\text{Fe}}}^{{3+}}(aq)+{{\text{Ce}}}^{{3+}}(aq);}$ (e) ${2\text{HBrO}(aq)+2{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, 2{\text{H}}_{3}{\text{O}}^{\text{+}}(aq)+2{{\text{Br}}}^{\text{−}}(aq)+{\text{O}}_{2}(g)}$

(a) ${2{{\text{MnO}}}_{4}^{\text{−}}(aq)+{{\text{3NO}}}_{2}^{\text{−}}(aq)+{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, 2{{\text{MnO}}}_{2}(s)+3{{\text{NO}}}_{3}^{\text{−}}(aq)+2{{\text{OH}}}^{\text{−}}(aq);}$ (b) ${3{{\text{MnO}}}_{4}^{{2−}}(aq)+2{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, 2{{\text{MnO}}}_{4}^{\text{−}}(aq)+4{{\text{OH}}}^{\text{−}}(aq)+{{\text{MnO}}}_{2}(s)\, \text{(in basi)};}$ (c) ${{{\text{Br}}}_{2}(l)+{{\text{SO}}}_{2}(g)+2{\text{H}}_{2}\text{O}(l)\, \longrightarrow \, 4{\text{H}}^{\text{+}}(aq)+2{{\text{Br}}}^{\text{−}}(aq)+{{\text{SO}}}_{4}^{{2−}}(aq)}$

4.3 Hlutfallaefnafræði efnahvarfa

(a) 0,435 mól Na, 0,217 mól Cl₂, 15,4 g Cl₂; (b) 0,005780 mól HgO, 2,890 ${\times}$ 10⁻³ mól O₂, 9,248 ${\times}$ 10⁻² g O₂; (c) 8,00 mól NaNO₃, 6,8 ${\times}$ 10² g NaNO₃; (d) 1665 mól CO₂, 73,3 kg CO₂; (e) 18,86 mól CuO, 2,330 kg CuCO₃; (f) 0,4580 mól C₂H₄Br₂, 86,05 g C₂H₄Br₂

(a) 0,0686 mól Mg, 1,67 g Mg; (b) 2,701 ${\times}$ 10⁻³ mól O₂, 0,08644 g O₂; (c) 6,43 mól MgCO₃, 542 g MgCO₃ (d) 768 mól H₂O, 13,8 kg H₂O; (e) 16,31 mól BaO₂, 2762 g BaO₂; (f) 0,207 mól C₂H₄, 5,81 g C₂H₄

(a) ${\text{rúmmál HCl lausn}\, \longrightarrow \, \text{mol HCl}\, \longrightarrow \, {{\text{mol GaCl}}}_{3};}$ (b) 1,25 mól GaCl₃, 2,2 ${\times}$ 10² g GaCl₃

(a) 5,337 ${\times}$ 10²² sameindir; (b) 10,41 g Zn(CN)₂

${{{\text{SiO}}}_{2}+3\text{C}\, \longrightarrow \, \text{SiC}+2\text{CO,}}$ 4,50 kg SiO₂

5,00 ${\times}$ 10³ kg

1,28 ${\times}$ 10⁵ g CO₂

161,4 ml KI lausn

176 g TiO₂

4.4 Heimtur efnahvarfa

Takmarkandi hvarfefnið er Cl2.

${\text{Prósent heimtur}=\text{31%}}$

${\text{g}\, {{\text{CCl}}}_{4}\, \longrightarrow \, \text{mol}\, {{\text{CCl}}}_{4}\, \longrightarrow \, \text{mol}\, {{\text{CCl}}}_{2}{\text{F}}_{2}\, \longrightarrow \, \text{g}\, {{\text{CCl}}}_{2}{\text{F}}_{2},}$ ${\text{Prósent heimtur}=\text{48,3%}}$

${\text{Prósent heimtur}=\text{91,3%}}$

Breytið massa etanóls í mól af etanóli; tengið mól etanóls við mól eters sem myndast með því að nota hlutfallaefnafræði stilltrar jöfnu. Breytið mólum eters í grömm; deilið raunverulegum grömmum af eter (ákvarðað með eðlismassa) með fræðilegum massa til að ákvarða prósentuheimtur; 87,6%

Umreikningurinn sem þarf er ${\text{mol Cr}\, \longrightarrow \, \text{mol}\, {\text{H}}_{3}{{\text{PO}}}_{4}.}$ Berðu síðan saman magn Cr við magn sýrunnar sem er til staðar. Cr er takmarkandi hvarfefnið.

Na₂C₂O₄ er takmarkandi hvarfefnið. Prósentuheimtur = 86,56%

Aðeins er hægt að búa til fjórar sameindir.

Þetta magn er ekki hægt að vega á venjulegum vogum og er verðlaust.

4.5 Magnbundin efnagreining

3,4 ${\times}$ 10⁻³ M H₂SO₄

9,6 ${\times}$ 10⁻³ M Cl⁻

22,4%

Reynsluformúlan er BH₃. Sameindaformúlan er B₂H₆.

49,6 ml

13,64 ml

0,0122 M

34,99 ml KOH

Reynsluformúlan er WCl₄.