1.When barium nitrate solution is added to sodium sulphate solution, followed by addition of dilute nitric acid, what will you observe??
2.Two vessles x and y of equal volumes contain ammonia and nitrogen under similar conditions of temperature and pressure. If vessel x contains ' a" molecules state the no. of moles of nitrogen in vessel 'y'?
3.When manganese(IV)oxide is heated with concentrated hydrochloric acid?{state the observation)
4.Why ionic compounds exist as hard solids but covalent compounds exist as sof solids liquids or gases?
5. calculate the mass of 40cc of carbon monoxide at stp?
Answers
Answering the given questions :
1. When barium nitrate solution is added to a sodium sulphate solution, followed by addition of dilute nitric acid, a white precipitate of barium sulphate is observed.
• Barium nitrate and sodium sulphate react to give a white precipitate of barium sulphate, which, on the addition of dilute nitric acid, remains insoluble in it.
(BaNO₃)₂ + Na₂SO₄ → BaSO₄ (white) + NaNO₃
BaSO₄ + dil. HNO₃ → no reaction
2. The number of moles of nitrogen in vessel 'y' is {a / ( 6.022 × 10²³ )}.
• According to Avogadro's law, equal volumes of different gases under similar conditions of temperature and pressure contain equal number of molecules.
• Applying this law, since vessel x containing ammonia has 'a' molecules, therefore, vessel 'y' containing nitrogen also has 'a' number of molecules.
• Now, we know that 1 mole of a gas contains 6.022 × 10²³ molecules.
=> 1 molecule has ( 1 / 6.022 × 10²³ ) moles
Therefore, 'a' molecules contain { 1 / ( 6.022 × 10²³ ) } × a moles
Or, the vessel 'y' contains { a / ( 6.022 × 10²³ ) } moles of nitrogen.
3.When manganese (IV) oxide is heated with concentrated hydrochloric acid, the colour of MnO₂ changes from black to light brown, and a greenish-yellow pungent smelling gas is evolved along with.
MnO₂ + 4 conc. HCl + ∆ → MnCl₂ + Cl₂ + 2H₂O
• Black MnO₂ changes into light brown MnCl₂ on reacting with conc. HCl, along with the evolution of chlorine gas recognized by a pungent odour and greenish-yellow colour.
4. Ionic compounds exist as hard solids but covalent compounds exist as soft solids, liquids or gases because of the difference in the type of intermolecular forces acting in them.
• Ionic compounds are formed by strong intermolecular forces of attraction acting between cations and anions.
• Covalent compounds are formed by Vander waals forces of attraction acting between the atoms.
• Electrostatic force of attraction is much stronger than vander waals forces of attraction. This is why ionic compounds are very hard, whereas, covalent compounds are not.
5. The mass of 40cc of carbon monoxide at S.T.P is 0.057 g.
The molecular weight of CO is 12g + 16g = 32 g
According to Avogadro's law, 32 g of CO weighs 22400 cm³ at S.T.P.
=> 1 cc of CO weighs 32 g / 22400 cc
40 cc of CO weighs = (32 g / 22400 cc) × 40 cc = 0.057 g