Question

1. On page 26 in Chapter 3 Watney thinks “… each liter of hydrazine, N₂H_4, has enough hydrogen for two liters of water.” There is a huge error Watney’s estimation, what is

A. Each gram of hydrazine will produce 2 grams of water

B. 1 liter of hydrazine will only produce 1 liter of water if they are both gases at the same temperature and pressure.

C. 1 liter of hydrazine will produce 1 liter of water since Avagadro's law says that at the same temperature and pressure equal volumes contain equal number of particles (moles.)

D. There is no telling how much water will be produced by 1 L of hydrazine.

2. How much water can 1.0L hydrazine actually yield? (Density of hydrazine is 1.02g/mL and the density of water is 1.00g/mL)

A. 1.1L

B. 2.1L

C. 3.0 L

D. 4.1 L

Answer 1

Q1) The correct answer is B

That is 1 litre of hydrazine will only produce 1 litre of water if they are both gases at the same temperature and pressure. This is in accordance with Avogadro's law i.e.at the same temperature and pressure equal volumes of gases contain an equal number of particles (moles.)

Q2) The step reactions for hydrazine to water are :

N2 H4 + N2 + 2H2 2H2 + O2 + 2H2O

Clearly, 1 mole of hydrazine produces 2 moles of water

So, the mass of 1 L hydrazine = Volume x density = 1000 mL x 1.02 = 1020 g

No. of moles of hydrazine = 1020 / mol wt. = 1020 / 32 = 31.875 moles.

Now, since 1 mole of hydrazine produces 2 moles of water,

$\therefore$ 31.875 moles. of hydrazine will produce 2 x 31.875 moles. of water

Therefore, no .of moles of water formed = 63.75 moles.

Weight of water formed = moles of water x molar weight = 63.75 x 18 = 1147.5 g

Volume of water formed = mass / density= 1147.5 g / 1 (g/ml) = 1147.5 mL = 1.1475 L $\approx$ 1.1 L

$\therefore$ The correct answer is A i.e 1.1 L

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