Page 227 - Chemistry ICSE Class X

Study of Compounds – Hydrogen Chloride 213
heat
NaCl(s) + H SO o NaHSO (s) + HCl(g)
2
4
4
<200° C
(conc.)
heat
NaCl(s) + NaHSO o Na SO + HCl(g)
2
4
4
>200° C
heat
ƒ Net reaction. 2NaCl(s) + H SO o Na SO (s) + 2HCl(g)
4
2
4
2
>200° C
(conc.)
ƒ Reactants. Sodium chloride (NaCl) ,LJĚƌŽŐĞŶ ĐŚůŽƌŝĚĞ ĐĂŶŶŽƚ ďĞ
ĐŽůůĞĐƚĞĚ ďLJ ƚŚĞ ĚŽǁŶǁĂƌĚ
Sulphuric acid (conc.) (H SO ) ĚŝƐƉůĂĐĞŵĞŶƚ ŽĨ ǁĂƚĞƌ ďĞĐĂƵƐĞ ŝƚ ŝƐ
4
2
ƒ Products. Sodium sulphate, Hydrogen chloride highly soluble ŝŶ ǁĂƚĞƌ͘
ƒ Conditions. *GCVKPI ſTUV IGPVN[ DGNQY u% CPF VJGP UVTQPIN[ Fountain Experiment
(above 200°C)
ƒ Procedure. 5QFKWO EJNQTKFG KU VCMGP KP C FT[ TQWPF DQVVQO ƀCUM CPF
the apparatus is set up as shown in Fig. 8.1. Conc. sulphuric acid is
CFFGF VQ VJG ƀCUM YKVJ VJG JGNR QH VJKUVNG HWPPGN *GCV VJG TGCEVKQP
OKZVWTG ſTUV QP C NQY ƀCOG CPF VJGP QP JKIJ ƀCOG

Fig. 8.2 Fountain experiment to
illustrate the very high solubility of HCl
gas in water

Procedure:
/Ŷ ƚŚŝƐ ĞdžƉĞƌŝŵĞŶƚ͕ Ă ƌŽƵŶĚͲďŽƩŽŵ
ŇĂƐŬ ŝƐ ĚƌŝĞĚ ĂŶĚ ĮůůĞĚ ǁŝƚŚ , / ŐĂƐ͘
dŚĞ ŇĂƐŬ ŝƐ ƚŚĞŶ ĮƩĞĚ ǁŝƚŚ Ă ĐŽƌŬ
ƐƵƉƉŽƌƟŶŐ Ă ĚƌŽƉƉĞƌ ĐŽŶƚĂŝŶŝŶŐ Ă
Fig. 8.1 Laboratory preparation of hydrogen chloride (HCl) gas
ůŝƩůĞ ĂŵŽƵŶƚ ŽĨ ǁĂƚĞƌ͕ ĂŶĚ ǁŝƚŚ Ă
ƒ Drying of gas. The gas is dried by passing through a U-tube containing ůŽŶŐ ũĞƚ ƌĞĂĐŚŝŶŐ ƚŽ ƚŚĞ ďŽƩŽŵ ŽĨ
anhydrous calcium chloride. ƚŚĞ ŇĂƐŬ͘ dŚĞ ŽƉĞŶ ĞŶĚ ŽĨ ƚŚĞ ũĞƚ
ŝƐ ŝŵŵĞƌƐĞĚ ŝŶƚŽ water ĐŽŶƚĂŝŶŝŶŐ
ƒ Collection of gas. Hydrogen chloride is collected by the upward Ă ƐŵĂůů ĂŵŽƵŶƚ ŽĨ blue litmus͘
displacement of air because it is heavier than air. ůŝƩůĞ ƋƵĂŶƟƚLJ ŽĨ ǁĂƚĞƌ ŝƐ ƚŚĞŶ
ŝŶƚƌŽĚƵĐĞĚ ŝŶƚŽ ŇĂƐŬ ďLJ ƉƌĞƐƐŝŶŐ
What are the physical properties of hydrogen chloride ƚŚĞ ƚĞĂƚ ŽĨ ƚŚĞ ĚƌŽƉƉĞƌ͘ dŚŝƐ ǁĂƚĞƌ
ƒ Colour, odour and taste. Hydrogen chloride is a colourless gas with ƌĞĂĚŝůLJ ĚŝƐƐŽůǀĞƐ , / ŐĂƐ͕ ƚŚĞƌĞďLJ͕
pungent odour and acidic taste. It attacks the mucous membrane of ůŽǁĞƌŝŶŐ ƚŚĞ ƉƌĞƐƐƵƌĞ ŝŶƐŝĚĞ ƚŚĞ
ŇĂƐŬ͘ dŽ ŵĂŬĞ ƵƉ ĨŽƌ ƚŚŝƐ ĚŝīĞƌĞŶĐĞ
nose and throat. Hydrogen chloride fumes in moist air. ŽĨ ƉƌĞƐƐƵƌĞ͕ ǁĂƚĞƌ ĨƌŽŵ ƚŚĞ ďƌĞĂŬĞƌ
ƒ Density. Hydrogen chloride is heavier than air. Its density is ƌƵƐŚĞƐ ŝŶƚŽ ƚŚĞ ŇĂƐŬ ŝŶ ƚŚĞ ĨŽƌŵ ŽĨ
1.64 g/L. Ă ĨŽƵŶƚĂŝŶ ;&ŝŐ͘ ϴ͘ϮͿ͕ ĐŚĂŶŐŝŶŐ ŝƚƐ
ĐŽůŽƵƌ ƚŽ ƌĞĚ͘
ƒ Solubility in water. Hydrogen chloride (HCl) is extremely soluble in ƋƵĞŽƵƐ ƐŽůƵƟŽŶ ŽĨ ŚLJĚƌŽŐĞŶ
water. One volume of water dissolves about 450 volumes of HCl(g) ĐŚůŽƌŝĚĞ ƚƵƌŶƐ
under normal conditions. Such a high solubility of HCl can be ͻഩ ůƵĞ ůŝƚŵƵƐ ZĞĚ
demonstrated by the fountain experiment. ͻഩKƌĂŶŐĞ ŵĞƚŚLJů ŽƌĂŶŐĞ ƚŽ ZĞĚ
ƒ Liquefaction. *[FTQIGP EJNQTKFG IGVU NKSWGſGF YKVJ FKHſEWNV[ VQ C ͻഩ /ƚ ŚĂƐ ŶŽ ĞīĞĐƚ ŽŶ
colourless liquid. (boiling point: –85°C). ƉŚĞŶŽůƉŚƚŚĂůĞŝŶ͘