Bonding: Physical Properties Questions

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  • Created by: chela_123
  • Created on: 06-12-20 18:12
Silicon dioxide (SiO2) has a crystal structure similar to diamond. a) Give the name of the type of crystal structure shown by silicon dioxide.
Macromolecular / Giant covalent
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b) Suggest why silicon dioxide does not conduct electricity when molten.
There are no delocalised electrons. / No free charged electrons
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c) Silicon dioxide reacts with hydrofluoric acid (HF) to produce hexafluorosilicic acid (H2SiF6) and one other substance. Write an equation for this reaction.
SiO2 + 6HF -------> H2SiF6 + 2H2O
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Sodium azide is made by N2O with sodium NaNH2 as shown by the equation. 2NaNH2 + N2O ---> NaN3 + NaOH + NH3 Calculate the mass of NaNH2 needed to obtain 550g of NaN3 assuming there is a 95.0% yield of NaN3. Give your answer to 3 s.f.
100% yield NaN3: 550 x 100/95 = 578.9g Mole NaN3: 578.9 ÷ (23+14x3) = 8.906mol Mole NaNH2: 8.906 x 2/1 = 17.812 Mass NaNH2: 17.812 x (23+14+1x2) = 695 (3s.f.)
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NaN3 decomposes to form Na and N as shown in the equation 2NaN3 ---> 2Na + 3N2. The N produced inflates the airbag to a volume of 7.50 x 10^-2 m^3 at a pressure of 150kPa and temperature of 35ºC. Calculate the minimum mass of NaN3 that must decompose
pV =nRT ==> n = pV/RT . n = ((150x10^3) x (7.5x10^-2)) / (8.31 x 308) = 4.395 Mole NaN3: 4.395 x 2/3 = 2.93 min. mass NaN3: 2.93 x (23+14x3) = 190g
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Sodium azide has a high melting point. Predict the type of bonding in a crystal of sodium azide (NaN3). Suggest why its melting point is high.
Type of bonding: ionic Reason for high melting point: oppositely charged ions Na+ and N3-. Strong attraction between ions/ lots of energy needed to overcome attractions
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Card 2

Front

b) Suggest why silicon dioxide does not conduct electricity when molten.

Back

There are no delocalised electrons. / No free charged electrons

Card 3

Front

c) Silicon dioxide reacts with hydrofluoric acid (HF) to produce hexafluorosilicic acid (H2SiF6) and one other substance. Write an equation for this reaction.

Back

Preview of the front of card 3

Card 4

Front

Sodium azide is made by N2O with sodium NaNH2 as shown by the equation. 2NaNH2 + N2O ---> NaN3 + NaOH + NH3 Calculate the mass of NaNH2 needed to obtain 550g of NaN3 assuming there is a 95.0% yield of NaN3. Give your answer to 3 s.f.

Back

Preview of the front of card 4

Card 5

Front

NaN3 decomposes to form Na and N as shown in the equation 2NaN3 ---> 2Na + 3N2. The N produced inflates the airbag to a volume of 7.50 x 10^-2 m^3 at a pressure of 150kPa and temperature of 35ºC. Calculate the minimum mass of NaN3 that must decompose

Back

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